EVALUATION AND DEVELOPMENT OF A TEST METHOD FOR DELAYED ETTRINGITE FORMATION IN MASS CONCRETE

By

DANIELLE E. KENNEDY

A THESIS PRESENTED TO THE GRADUATE SCHOOL

OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF

MASTER OF ENGINEERING

UNIVERSITY OF FLORIDA

2017

© 2017 Danielle E. Kennedy

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ACKNOWLEDGMENTS

I would first like to thank my family for being so understanding about my

complaining and lack of home visits over the last two years. Both of my sisters, as well

as my mom, dad, and step dad have been so supportive of my entire school career. I

would also like to thank my best friend, Bea, for always being proud and supporting all

of my civil engineering endeavors. Thank you to my boyfriend, Kyle, for being a shining

light during the last year of my master’s degree and being so supportive while job

hunting. Next, I would like to thank my Concrete Canoe, American Society of Civil

Engineers, and Engineering Ambassadors friends for keeping me balanced and sticking

with me through my time at UF. ForeverGlades Forever! Without my involvement

working in the Pit and being on the Concrete Canoe team, I would have never been

given this research opportunity.

I would like to thank my advisor, Dr. Christopher Ferraro, for giving me this

opportunity. I would also like to thank Dr. Riding. I am grateful that he joined our

research group last year and agreed to be on my committee. He has brought so much

to the concrete materials group and I am grateful to have had him as a professor. I

thank our materials research group, Dr. Jerry Paris, and future PhDs - Benjamin Watts

and Caitlin Tibbetts, for the laughs, lunches, and office companionship. Working in this

concrete materials group has helped me become a better and more thorough

researcher, and I have appreciated all of the guidance provided by Dr. Ferraro, Dr.

Riding, Jerry, Ben, and Caitlin during this stressful time in my life. Dr. Paris trusted me

as a research assistant when I first started working in the lab and he has been a mentor

and a friend.

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Without help in the laboratory, this research would have been much less

manageable. I would like to especially thank Philippe Holas for his hard work,

dedication, and willingness to chat and keep me sane over the course of the entire

laboratory portion of the project. I would also like to thank everyone else who dedicated

time and sweat to help me in the lab: Caroline Armstrong, Patrick Bollinger, Kevin

Carabeo, Alejandra Corona, Luisa Chen, Taylor Humbarger, Tyler Mokris, Nathan

O’Donnell, Jason McAllister Pringle, and Neal Turner.

I would also like to thank Dr. Rawlinson for his assistance during the end of my

laboratory work, he has been a wonderful laboratory manager. This research required

some collaboration with the environmental engineering department, so I would like to

thank the whole crew over there, especially Linda Monroy Sarmiento and Kyle Clavier

for their environmental chemistry expertise.

I would also like to thank the Electric Power Research Institute (EPRI) for the

opportunity to work on an interesting project and for sponsoring this research. Dr.

Anthony Bentivegna with CTL Group was also a great help when I was first starting

through his extensive knowledge and research already completed on the project and I

am grateful for all of the resources and help with experimentation that he offered.

I would also like to thank all of the companies who donated materials for

research, Argos, Titan America, Lehigh, and Edgar Minerals for the generous donations

of cement and aggregate.

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TABLE OF CONTENTS page

ACKNOWLEDGMENTS .................................................................................................. 3

LIST OF TABLES ............................................................................................................ 8

LIST OF FIGURES .......................................................................................................... 9

ABSTRACT ................................................................................................................... 11

CHAPTER

1 INTRODUCTION .................................................................................................... 13

Background ............................................................................................................. 13

Research Needs ..................................................................................................... 14

Objectives of Research ........................................................................................... 14

Hypotheses ............................................................................................................. 14

Research Approach ................................................................................................ 15

Significance of Research ........................................................................................ 15

Outline of Thesis ..................................................................................................... 16

2 LITERATURE REVIEW .......................................................................................... 17

Temperature Considerations for Mass Concrete .................................................... 17

Delayed Ettringite Formation .................................................................................. 17

Alkali-Silica Reaction and Secondary Ettringite Formation ..................................... 22

Case Studies .......................................................................................................... 23

Friday Ties ........................................................................................................ 24

Southern USA Case Studies ............................................................................ 24

European Cases ............................................................................................... 26

Testing Methods ..................................................................................................... 27

Kelham ............................................................................................................. 27

Fu ..................................................................................................................... 29

Duggan Test ..................................................................................................... 30

Mitigation and Prevention ....................................................................................... 32

Concluding Remarks .............................................................................................. 34

3 EXPERIMENTAL PROGRAM ................................................................................. 39

Background ............................................................................................................. 39

Materials and Methods ............................................................................................ 39

Materials and Characterization ......................................................................... 39

Methods ............................................................................................................ 42

Alkali-silica reaction ................................................................................... 42

Delayed ettringite formation ....................................................................... 43

Kelham method .......................................................................................... 43

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Revised Kelham method ............................................................................ 44

Fu method .................................................................................................. 44

Revised Fu method .................................................................................... 46

Ferraro method .......................................................................................... 46

Miniature bar method ................................................................................. 46

Long Term Storage and Measuring .................................................................. 48

Full sized bars ............................................................................................ 48

Miniature sized bars ................................................................................... 48

Concluding Remarks .............................................................................................. 49

4 RESULTS AND DISCUSSION OF ORDINARY PORTLAND CEMENT ................. 56

Mortar Bar Results .................................................................................................. 56

ASR .................................................................................................................. 56

DEF Heat Curing .............................................................................................. 56

Kelham method .......................................................................................... 57

Fu method .................................................................................................. 57

Revised Kelham method ............................................................................ 58

Ferraro method .......................................................................................... 58

Miniature Bar Results .............................................................................................. 59

Concluding Remarks .............................................................................................. 59

5 RESULTS AND DISCUSSIONS OF SUPPLEMENTARY CEMENTITIOUS MATERIALS ........................................................................................................... 69

Mitigation ................................................................................................................ 69

Class F Fly Ash ................................................................................................ 69

Class C Fly Ash ................................................................................................ 69

Metakaolin ........................................................................................................ 70

Silica Fume ....................................................................................................... 70

Slag Cement ..................................................................................................... 71

Concluding Remarks .............................................................................................. 71

6 INVESTIGATION OF ACI 201 GUIDE TO DURABLE CONCRETE ....................... 77

Guide to Durable Concrete ..................................................................................... 77

DEF Prevention Recommendations ................................................................. 77

Cement Requirements...................................................................................... 78

Mortar Strength ................................................................................................ 79

Introduction of SCM .......................................................................................... 80

Concluding Remarks .............................................................................................. 80

7 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK ................... 86

Conclusions ............................................................................................................ 86

Recommendations .................................................................................................. 86

LIST OF REFERENCES ............................................................................................... 88

7

BIOGRAPHICAL SKETCH ............................................................................................ 92

8

LIST OF TABLES

Table page 2-1 Cement chemical compounds and abbreviations ............................................... 36

2-2 Hydration products and roles .............................................................................. 36

2-3 Cement types and general contributions ............................................................ 37

3-1 Chemical compositions of cementitious materials .............................................. 50

3-2 ASTM C1260 sand requirements ....................................................................... 51

3-3 Mass fractions of Retveld analysis of XRD patterns ........................................... 51

3-4 Cementitious material particle size ..................................................................... 51

3-5 Sulfate content determined from XRF analysis of fused, pressed pellets, and ASTM C114 ........................................................................................................ 52

3-6 Abbreviations of curing methods ........................................................................ 52

3-7 Mix designs for full-sized mortar bars ................................................................. 53

4-1 Kelham 95°C, 85°C, 70°C expansion % and ages ............................................. 63

4-2 Fu expansion values ........................................................................................... 64

6-1 ACI 201.2R-16 Guide to Durable Concrete ........................................................ 83

6-2 ASTM C150 Standard composition requirements ............................................... 84

6-3 Comparison of cement compositions to ASTM C150 ......................................... 84

6-4 Results of ASTM C109 for cements ................................................................... 84

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LIST OF FIGURES

Figure page 2-1 Kelham method heat curing cycle. ...................................................................... 37

2-2 Fu method heat curing cycle. ............................................................................. 38

2-3 Duggan method heat curing cycle. ..................................................................... 38

3-1 Heat curing profile for K70, K85, and K95. ......................................................... 54

3-2 Heat curing profile for KR70, KR85, and KR95................................................... 54

3-3 Heat curing profile for F70, F85, and F95. .......................................................... 55

3-4 Setup of miniature mortar bar mold. ................................................................... 55

4-1 ASR results and expansion thresholds. .............................................................. 62

4-2 All cements when cured following K70. .............................................................. 62

4-3 All cements when cured following K85. .............................................................. 63

4-4 All cements when cured following K95. .............................................................. 63

4-5 All cements when cured following Fu. ................................................................ 64

4-6 All cements when cured following KR95. ............................................................ 64

4-7 All cements when cured following KR85. ............................................................ 65

4-8 All cements when cured following KR70. ............................................................ 65

4-9 All five cements when cured following F95. ........................................................ 66

4-10 All five cements when cured following F85. ........................................................ 66

4-11 All five cements when cured following F70. ........................................................ 67

4-12 Cement TI-2 miniature and full-sized bars cured following F95. ......................... 67

4-13 Cement TIII-2 miniature and full-sized bars cured following F95. ....................... 68

4-14 Cement TV miniature and full-sized bars cured following F95. ........................... 68

5-1 Class F fly ash in combination with Cement TI-1 cured following F95. ............... 73

5-2 Class C fly ash in combination with Cement TI-1 cured following F95. .............. 73

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5-3 Class C fly ash in combination with Cement TV cured following F95. ................ 74

5-4 Metakaolin and silica fume with Cement TI-1 cured following F95. .................... 74

5-5 Metakaolin with Cement TV cured following F95. ............................................... 75

5-6 Slag cement combinations with Cement TI-1 cured following F95. .................... 75

5-7 Cement TV cured following F95. ........................................................................ 76

6-1 Expansion after curing at 90°C plotted against 2-day mortar strength. ............... 85

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Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the

Requirements for the Degree of Master of Engineering

EVALUATION AND DEVELOPMENT OF A TEST METHOD FOR DELAYED ETTRINGITE FORMATION IN MASS CONCRETE

By

Danielle E. Kennedy

December 2017

Chair: Christopher C. Ferraro Major: Civil Engineering

Internal sulfate attack is a phenomenon that is detrimental and can lead to

deterioration of concrete products. Delayed ettringite formation (DEF) is a form of

internal sulfate attack that is caused by heat curing, moisture, and cement composition.

There currently is no standard test method for the determination of the potential for

concrete to experience delayed ettringite formation. There have been a number of case

studies documenting the presence of and deterioration from DEF, which can manifest in

concrete exposed to relatively high internal temperatures at early ages. Experimental

methods have been developed to mimic the curing conditions of concrete in the precast

industry, but do not capture the time-temperature profile(s) that occur in massive

concrete structures at early ages. Furthermore, there is a deficiency in the state of the

art with respect to the prerequisite conditions which result in the formation of DEF. The

contributions to DEF formation and mitigation with respect to variables such as peak

temperature, temperature duration / curing history, cement chemistry, mixture design

and incorporation of supplementary cementitious materials are not well understood.

Measures can be taken to mitigate sulfate attack through temperature moderation,

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moisture control, and incorporating supplementary cementitious materials (SCM) into

the mix design. Concrete mixtures which incorporate SCMs may be used to lower the

cement content and temperature of portland cement products as well as mitigate the

effects of chemical components known to contribute to the formation of DEF.

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CHAPTER 1 INTRODUCTION

Background

Mass concrete is defined by the American Concrete Institute (ACI) as “any

volume of concrete in which a combination of dimensions of the member being cast, the

boundary conditions, the characteristics of the concrete mixture, and the ambient

conditions can lead to undesirable thermal stresses, cracking, deleterious chemical

reactions, or reduction in the long-term strength as a result of elevated concrete

temperature due to heat from hydration” (ACI, 2016). Due to the exothermic nature of

portland cement hydration, massive concrete elements experience elevated

temperatures and tend to stay at these raised temperatures for an extended period

(Ferraro, 2009). This heat rise, in combination with moisture, and the composition of

cement can have deleterious effects caused by sulfate attack.

There are two types of sulfate attack: internal and external. External sulfate

attack is much more common and occurs when solution containing dissolved sulfates

from the environment penetrates into the concrete. Internal sulfate attack, which is less

common, but also destructive, is caused when there is a source of sulfate within the

aggregates or concrete mixture, which eventually leads to expansion of the concrete.

Either form of sulfate attack can be detrimental to concrete and can cause cracking, and

eventually degradation.

Delayed ettringite formation (DEF), a form of internal sulfate attack, occurs when

ettringite, which forms naturally during the hydration process, goes into solution in a

moist, heated environment, and reappears later. This formation of the ettringite needles

after the plastic stage of concrete causes expansion and cracking in the concrete. DEF

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oftentimes occurs in conjunction with alkali-silica reaction (ASR) and the visual damage

of each manifestation is similar.

Research Needs

There are a number of standardized tests, both short and long-term to determine

if alkali-silica reaction will occur in a concrete mixture; however, there are no developed

standards to determine if delayed ettringite formation will or is able to occur in a

concrete mixture. Several researchers have developed testing methods that include a

ramp to peak temperature but lack sufficient variety of temperatures or peak

temperature soak times.

Objectives of Research

The specific objectives of this research are:

Investigate differences between varying DEF temperature profiles

Develop test method to closely simulate hydration and early age temperature of mass concrete

Develop test method(s) to identify DEF in a rapid, effective way

Hypotheses

Three hypotheses were developed for the investigation of DEF testing methods

for use on mortar.

The incorporation of a time / temperature profile which represents the behavior of mass concrete will cause delayed ettringite formation in a faster rate than the Kelham and Fu methods

The use of pozzolans mitigates the expansion of portland cement based mortar caused by DEF

The development of shorter bars with a high solid to curing solution ratio will expand more rapidly than the “standard” test method

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Research Approach

Testing was completed on both the individual materials and the mortar bar

mixtures in order to determine susceptibility to alkali-silica reaction and delayed

ettringite formation.

The physical testing completed on the raw materials consisted of the following:

ASTM C1365 Standard Test Method for Determination of the Proportion of Phases in Portland Cement and Portland-Cement Clinker Using X-Ray Powder Diffraction Analysis (ASTM C1365, 2011)

X-Ray Fluorescence according to ASTM C114 Standard Test Methods for Chemical Analysis of Hydraulic Cement (ASTM C114, 2015)

ASTM C114, Section 17 Standard Test Method for Chemical Analysis of Hydraulic Cement: Sulfur Trioxide (ASTM C114, 2015)

ASTM C128, Standard Test Method for Relative Density (Specific Gravity) and Absorption of Fine Aggregate (ASTM C128, 2015)

Particle Size Distribution

The testing completed on mortar bars consisted of the following:

ASTM C1260, Standard Test Method for Potential Alkali Reactivity of Aggregates (ASTM C1260, 2014.)

Kelham Mortar Bar Expansion, length change test

Fu Mortar Bar Expansion, length change test

Ferraro Mortar Bar Expansion, length change test

Ferraro Miniature Mortar Bar Expansion, length change test

Significance of Research

Currently, there are no consistent and effective standards for determining if

delayed ettringite formation will occur in concrete. A standard test method should be

developed to test concrete mixtures cured at specific temperatures in a timely manner

for this damage-inducing phenomenon. This creation of a test method will be able to

determine if a concrete mixture and curing regimen combination will be prone to

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destruction caused by DEF. In doing so, this will save time and money on repairs or

reconstruction due to DEF.

Outline of Thesis

Chapter 2 is a review of the literature of delayed ettringite formation in relation to

mass concrete. Chapter 3 addresses current, generally accepted testing methods used

to determine the potential of delayed ettringite formation as well as proposed testing

procedures. Chapter 4 discusses the results of mortar bar testing with ordinary portland

cement and Chapter 5 includes results of mortar bar length change testing with the

introduction of SCM. Chapter 6 goes into detail of the guidance provided by the recently

published ACI’s Guide to Durable Concrete with respect to DEF. Overall conclusions of

the research as well as recommendations drawn are discussed in Chapter 7.

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CHAPTER 2 LITERATURE REVIEW

Temperature Considerations for Mass Concrete

Massive concrete elements are placed daily for a variety of construction projects.

These elements can reach temperatures in excess of 70°C and take days to cool down

to ambient temperatures. Some states implement fresh temperature limits in order to

enhance the life of the concrete, but this does not consider the temperature rise that

happens after placement. Because of this heat rise, delayed ettringite formation can be

a problem for newly constructed structures.

Delayed Ettringite Formation

Delayed Ettringite Formation (DEF) is a form of internal sulfate attack that is

dependent on a combination of high curing temperature, moisture, and cement

composition. This literature review will include a brief overview of cement chemistry

before examining causes of DEF, case studies, common test methods, and mitigation

techniques. DEF is not fully understood and there are currently no standardized test

methods to detect DEF or predict if delayed formation is going to occur in a concrete

mixture for a given curing history.

Hydration is the chemical process of the setting and hardening of concrete that

begins when portland cement and water are combined. The heat generated by the

cement hydration is the cause of temperature rise in concrete (Ingham, 2012). Calcium

silicate hydrate (C-S-H) is the main product of cement hydration and the major source of

concrete strength. It makes up over half of the volume of solids in hydrated portland

cement and is produced in two forms. The outer product, created earlier in the hydration

process, forms away from the cement particle surface to fill water-filled space. The inner

18

product is formed later in the hydration process and occupies the original boundaries of

the cement grains before hydration (Taylor, 2004). The chemical reaction of the

formation of C-S-H is shown in Equation 2-1. Abbreviations for chemical compounds are

shown in Table 2-1 and will be used throughout the document. Four main hydration

products created during the hydration reaction at ambient temperature curing and their

contributions are shown in Table 2-2.

2𝐶2𝑆 + 4𝐻 → 𝐶3𝑆2𝐻4 + 𝐶𝑎(𝑂𝐻)2 (C-S-H) (2-1)

The four main compounds in cement, tricalcium silicate (C3S) which comprises

approximately 50-70%, dicalcium silicate (C2S), 10-30%, tricalcium aluminate (C3A), 3-

13%, and tetracalcium aluminoferritte (C4AF), 5-15%, typically accounts for

approximately 93-97% of the cement content. The remaining 3-7% is composed of

gypsum and impurities (Van Oss, 2005). Gypsum makes up approximately 4.5% by

mass of the cement and of the remaining impurities, alkali and sulfate compounds make

up about 0.3-1.5% (Mehta, 2014). Without the addition of gypsum, C3A would react

immediately, resulting in flash set, making it difficult to transport of finish the concrete

before hardening. The addition of gypsum, (CS̅H2), allows the formation of ettringite and

monosulfates, shown in Equations 2-2 and 2-3.

𝐶3𝐴 + 3𝐶S̅𝐻2 + 26𝐻 → 𝐶3𝐴 𝑥 3𝐶S̅𝐻32 (Ettringite) (Mehta, 2014) (2-2)

𝐶3𝐴 + 𝐶S̅𝐻2 + (10 − 16)𝐻 → 𝐶3𝐴 𝑥 𝐶S̅𝐻12−18 (Monosulfate) (Mehta, 2014) (2-3)

Ettringite is a needle-like crystal that develops during the early stages of

hydration under normal conditions while the concrete is still in the plastic state and, in

most cases, the formation of ettringite is harmless. In the event that the C3A content is

too high, ettringite reacts with the excess C3A to form calcium monosulfoaluminates, or

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monosulfates. Monosulfates are more susceptible to sulfate attack because, in

combination with calcium hydroxide, ettringite reforms in the pores and cracks of the

hardened cement paste and causes damage to the concrete (Mehta, 2014). The type

and composition of cement is an important factor in regards to expansion. Research

shows that type III cements show the largest ultimate expansions while type V cements

typically show little to no expansion during experimentation (Drimalas, 2004). Table 2-3

shows the different cement types and general characteristics (Mehta, 2014).

Hydration, like most chemical reactions, is accelerated under higher

temperatures. However, if the maximum temperature is too high, the results can be

detrimental to the durability of the concrete. Maximum temperatures during curing

exceeding 70°C will cause the dissolution of ettringite and the sulfate and aluminate to

be encapsulated by the formation of the inner C-S-H. In combination with elevated

temperatures during the curing process, sulfates released by the cement will not fully

react with the C3A. Exposure of the concrete to water at ambient temperatures after this

raised curing temperature allows the sulfate and alumina in the inner C-S-H to release

slowly into the pore solution (Ramlochan et al., 2003). The ettringite then forms in the

pores of the outer C-S-H. This phenomenon can lead to expansion and cracking of the

cement paste.

The term “delayed ettringite formation”, first used by Heinz and Ludwig, suggests

that the ettringite does not form naturally during the early hydration periods as it should,

but later due to some constraint (Ceesay, 2004; Heinz and Ludwig, 1986). Delayed

ettringite formation is best known to occur where a high sulfate cement and high

temperatures or steam-curing is involved (Mehta, 2014). DEF is also common in the

20

precast concrete industry as well as in environments that exceed threshold

temperatures, such as during massive concrete pours.

DEF is attributed mostly to curing temperature, but the phenomenon also

requires the presence of moisture and the requisite chemical composition to occur

(Kelham, 1996; Famy et al. 2000). The removal of moisture or lowering the abundance

of sulfate in the portland cement composition reduces the potential for DEF. Curing at

temperatures below 60°C (140°F) mitigates the potential for delayed ettringite formation

(Ramlochan et al., 2003). The exact temperature required for the formation of DEF has

been heavily debated within the research community, though the general consensus

has established a minimum threshold temperature of 70°C (158°F) for DEF to occur.

(Taylor, 2004; Thomas, 2007; Ramlochan et al., 2003; ACI, 2016). Formation

temperatures vary based on cement composition, mixing factors and curing conditions,

but as the curing temperature increases, the risk of DEF is also increased (Shimada,

2005). Curing temperatures above 70°C increase expansion drastically up to at least

95°C (Ramlochan, 2003).

The contributions to DEF by the cement composition, especially sulfate and

aluminate content, is not fully understood. Higher alkali cements will typically deliver

higher expansion than lower alkali cements (Drimalas, 2004). Kelham suggested the

threshold for sulfate content to be ~4%, but higher content does not always contribute to

more expansion (Kelham, 1996). The relationship between sulfate and aluminate in the

reaction plays a major role in the delayed formation of ettringite (Heinz et al., 1989;

Heinz et al., 1999; Day, 1992; Zhang et al, 2002; Shimada, 2005). Researchers have

21

published a number of sulfate to aluminate ratios as well as S̅2 / A and S̅ / A in terms of

molar ratio and mass ratio. Indicated threshold values for the ratio are shown:

S̅ / A < 0.55 (Molar Ratio) (Heinz and Ludwig, 1987)

S̅2 / A < 2.0 (Heinz et al.,1989)

S̅ / A < 0.45 (Heinz et al., 1999)

S̅ / A = 1 (Molar Ratio) (Grabowski, 1992)

S̅ / A < 0.67 (Day, 1992)

S̅ / A < 0.80 (Mass Ratio) (Zhang et al., 2002)

S̅ / A = 1 (Molar Ratio) (Zhang et al., 2002)

S̅ / A < 0.91 (Molar Ratio) (Shimada, 2005)

These ratios show threshold limits in order to avoid creating mortar or concrete

susceptible to DEF. Examination of these values indicates that a molar ratio of S̅ / A of

0.80 is equivalent to a mass ratio of 0.63. Therefore, the ratio proposed by Day is

equivalent to the molar ratio value proposed by Zhang (Day, 1992; Zhang et al., 2002).

Furthermore, the relationships developed by Heinz are the same when at values of

approximately 0.7 (Heinz et al., 1989; Heinz et al., 1999; Day, 1992). The molar ratio is

also discussed and is a concern when approximately 0.80 according to Zhang (Zhang et

al., 2002). While researchers debate values for sulfate and aluminate content and

ratios, they agree that this ratio is significant in delayed ettringite formation and

expansion in concrete specimen. Research has shown correlations between expansion

caused by DEF and varying cement components. However, there is no single

constituent that will reliably predict performance of a mortar or concrete mixture.

The final component of delayed ettringite formation is the concrete must be in an

environment where the presence of moisture is available (Dayarathrne et al., 2013;

Graf, 2007). High temperature curing of concrete in a moist environment is common in

the concrete industry due to steam curing of precast elements and in massive concrete

elements.

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Alkali-Silica Reaction and Secondary Ettringite Formation

Alkali-silica reaction is found when the alkalis in cement and the reactive silica in

the system form to create a gel product around the aggregate. The gel is expansive in

the presence of moisture and causes internal stresses which ultimately result in

cracking within the aggregate and concrete. Both DEF and ASR cause expansion and

are initially identified by map cracking, so there is disagreement over the influence of

each (Shaikh, 2007).

ASR causes cracking to both the hardened cement paste as well as the

aggregates leading to separation and voids in the structure, which can later be filled by

ettringite. This ettringite formation, after deterioration has already occurred due to a

previous source, is considered “secondary ettringite formation” (SEF) and is not the

initial cause of deterioration; researchers have incorrectly used the terms “Secondary

Ettringite Formation” and “Delayed Ettringite Formation” interchangeably (Day, 2002;

Matthews, 2009). The formation of DEF does not occur during the initial hydration

process. At elevated temperatures, ettringite enters into solution, and re-solidifies. This

formation is the result of uninterrupted precipitation and growth of ettringite in the cracks

and voids of the concrete (Thomas et al., 2008). This is problematic when there is no

more allowable void room for the ettringite to fill (Ramlochan, 2003)

ASR commonly causes cracks and the ettringite is able to form within them. This

joint effect of ASR and ettringite formation causes a more severe deterioration

(Ramlochan et al., 2003). While ettringite forming in the cracks can lead to expansion,

more destruction is seen when the ettringite forms in the small pores and causes

internal stresses, leading to cracking and expansion. While DEF is commonly

associated with destruction after ASR has already occurred, DEF does not require ASR

23

in order to occur (Ormsby et al., 2011; Tracy et al., 2004). However, the presence of

microcracking due to other damage processes such as ASR, chloride attack, or freeze-

thaw will introduce delayed ettringite formation earlier and lead to a higher ultimate

expansion (Ekolu, 2004).

Portland cements containing at least 0.6% equivalent alkalis (Na2O + 0.658K2O)

in combination with an alkali-reactive aggregate have shown to cause significant

expansion due to ASR. As a result, ASTM C150 designates low-alkali cements to have

limits of equivalent alkalis with less than 0.6% (ASTM C150, 2015). Limits on total

alkalis in cement are to mitigate the deleterious effects of reactive aggregates, due to

ASR (Mehta, 2014). Accelerated testing for ASR is outlined in the ASTM C1260 test

method in which the presence of ASR potentially be discovered in mortar bars within

sixteen days (ASTM C1260, 2014). Aggregates indicate innocuous behavior with

expansion below 0.10% while expansion measurements between 0.10% and 0.20% are

both inconclusive and further testing is required. Expansion greater than 0.20% are

indicative of deleterious behavior (ASTM C1260, 2014). The use of another test

method, ASTM C1293, should be used to confirm the reactivity of aggregates that fail

ASTM C1260 (ASTM C1293, 2008).

Case Studies

In many cases, ASR is misdiagnosed as DEF or cracking caused by ASR causes

the initiation of DEF. The first reported case of DEF in precast concrete occurred in the

1980’s with railway ties in Europe. This case, documented by Heinz et al. is one of the

only cases in which DEF is the sole cause of destruction (Heinz et al., 1989). In most

other cases, ASR and DEF were found to occur together.

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Friday Ties

Conceivably the most notable case study concerning DEF and ASR is that of the

“Friday ties”. This U.S. railway tie case introduced the possibility of ambient-temperature

DEF. Most of the railway ties were constructed in the project through steam curing,

however, ties poured on Fridays were kept in the formwork over the weekend,

eliminating the need for steam curing. The ties began to deteriorate due to DEF

symptoms, which led to the belief that elevated temperature curing was not required in

order for the phenomenon to occur. It was later discovered that the ambient

temperature cured railway ties had various “hot spots” where the DEF related damage

had occurred and that the entire tie was not impaired. In addition, ASR was found to

occur within the ties. This further proved research that elevated temperatures are

required for the delayed formation of ettringite (Thomas and Ramlochan, 2002).

Southern USA Case Studies

Another important case to note in regards to DEF forming without ASR occurred

in the San Antonio Y located in southern, central Texas, USA. Early analysis using

scanning electron microscopy (SEM) appeared as though DEF was the predominant

cause of distress in the columns of the structure. Researchers selected several

segments of the structure to further investigate by way of core samples. The cores were

tested by soaking in a NaOH solution at 80°C (176°F) and gage studs were added in

order to take length change measurements. This test method was created to determine

the potential of ASR, given that an unlimited amount of alkalis was supplied to the

specimen. The presence of ASR gel was confirmed, even though the aggregate was

previously vetted. In addition to testing cores for ASR, others were tested for DEF, in

which they were stored in water at 23°C (73°F), leaching out alkalis, which causes the

25

pH to drop. This prevents ASR from occurring and promotes DEF. This research

showed that ASR was present in nearly all of the concrete and that three of the samples

showed potential for DEF. Forensic investigation of the samples showed DEF was the

crucial deterioration component. The work developed during this research was

important due to the development of potential future tests (Folliard et al., 2006).

The first experience of delayed ettringite formation was found in Texas and

involves a case of precast concrete box bridge beams. The case involves sixty-nine

beams, which were fabricated in mid-1991 and stored in a precast plant in central Texas

over the years until the investigation in 1995. During the study, fifty-six of the distressed

beams were deemed inoperative and only thirteen were left that met specifications. A

significant amount of ettringite was found in the paste expansion during petrographic

examinations. Following this investigation, at least twelve more structures that were

fabricated using precast and cast-in-place concrete elements were also found with signs

of DEF (Lawrence et al., 1999).

Another case study involves bridge columns constructed in the southern United

States in the late 1980’s which was found to exhibit significant cracking after just 15

years in service. These columns constructed with a high content of type III cement and

a minimum dimension of approximately 6 feet. There is no documentation of internal

temperatures, but researchers estimate that the in-situ temperature exceeded the

threshold value to initiate DEF of 70°C and possibly even 80°C. During the construction

of the columns, the contractor’s documents state that the formwork was deforming due

to the high temperatures and all additional columns incorporated fly ash in order to

lower the heat and temperature rise of the concrete, resulting in undamaged columns

26

(Thomas et al., 2008). Four columns were investigated and core samples were taken

from each. Two columns suffered from extensive damage and cracking, one had

significantly less, but still visible damage, and the final column showed no damage.

After alkali content testing and scanning electron microscopy (SEM) investigation of the

core samples from the three damaged columns, two showed signs of both DEF and

ASR and the final core samples showed damage caused only by DEF. The discovery of

a damaged specimen showing signs of deterioration from only DEF and no other

causes is significant because the column was constructed with no external heating and

was cast in place. This is one of the only cases in history where DEF was found in a

structure in place in the absence of ASR.

Two adjacent bridges constructed in Atascosa County, Texas show significant

distress caused by both DEF and ASR. Another consisted of pre-stressed concrete

beams in Houston, Texas. This structure, built in 1988 began showing distress in 1996

with more than 30% of the I-beams having longitudinal cracking near the base and

throughout the entire beams (Lawrence et al., 1999). In order to identify and ensure

DEF as the cause of the distress in these concrete structures, Texas Department of

Transportation assembled a round-robin investigation with five participants. The beams

from the precast concrete box beam case contained DEF and ASR damage.

European Cases

A similar case to the columns observed in the southern US, consists of cracking

observed within structures in England. In the smaller structures, ASR caused damage,

while in the larger structures, the cracking formed due to ASR and DEF. Ettringite filled

in the gaps around the aggregates and caused 0.3 - 1.3% expansion. In these

structures, the internal temperature was assumed to reach higher than 80°C. The high

27

temperature is said to have occurred because of the large minimum dimension of the

structures as well as the high cement content. (Thomas, 2007; Hobbs, 2001)

In another case, forty-year-old concrete bridge piers in Spain observed a form of

internal sulfate attack. The environmental conditions of the area hold temperatures

between 2°C and 35°C with relative humidity of 80-90%. There was no evidence of

alkali-silica reaction, while there were numerous ettringite deposits in the cracks,

aggregate interfaces, inside and around un-hydrated cement grains (Mendenez, 2002).

Testing Methods

Kelham

Kelham studied the effects of fineness and cement composition on the initiation

of expansion caused by DEF. Throughout the experiment, Kelham used ten cements

with varied cement fineness, C3A, C3S, SO3, and MgO contents. Cement content was

varied using five different clinkers, two variations of limestone, and three sulfate

sources. The clinkers had varying compound amounts: Clinker A high in C3A, Clinker B

high in K2O, Clinker C high in MgO and low in Na2O equivalent, Clinker D low in SO3,

and Clinker E which was low in C3A and suitable for sulfate resistance. The sulfate

content was varied by using three different sources: a natural gypsum, a natural

anhydrite, and a flue gas desulfurization gypsum. The cements were all ground to 250-

450 m2/kg and contained 4-5% SO3.

Kelham developed a curing method representative of conditions used in the

precast concrete industry in order to predict expansion under high temperature

conditions. The curing regimen included a pre-storage moist cabinet for mortar bar

specimens for four hours at an ambient temperature of 20°C and 100% relative humidity

prior to subjecting them to 20°C per hour temperature rise. Following this, a twelve-

28

hour hold at maximum temperature, then followed by a four-hour ramp down to 20°C;

the specimens were then demolded and placed in a limewater solution at ambient

temperature. Kelham worked with over 70 mix designs with varying cement

compositions for peak temperatures of 20°C, 70°C, 80°C, and 90°C (Kelham, 1996).

The specimens that were heated to 70°C and 80°C were cured in environmental

chambers while the experiments for the specimen that were heated to 90°C were

carried out in an accelerated curing tank. After a four-hour pre-curing time, the curing

tank water was heated to 95°C in one hour and the 90°C specimen were held above the

surface of the water for twelve hours. Heating the water to 95°C allowed the specimen

to remain at 90°C for Kelham’s experiment. Samples cooled for approximately six hours

until they reached 20°C. Of the four temperature curing cycles, only curing the

specimen at 90°C showed consistent expansions. Figure 2-1 shows the typical curing

temperature regimen used by Kelham (Kelham, 1996).

Kelham concluded that many of the factors that lead to expansion caused by

delayed ettringite can be the same factors related to high early strength on concrete.

However, the dominating factor was found to be curing temperature. Expansions of

each specimen were measured and considered to be significant at 0.1%. No significant

expansions were measured for the mortar bars cured at 20°C or 70°C. Expansions

began at 80°C and continued to increase with highest expansions of ~1% at curing

temperatures of 90°C. The research showed that 0% of specimens expanded at 20°C

and 70°C while 14% expanded at 80°C and 64% expanded at 90°C (Thomas and

Ramlochan, 2002). Using a known cement composition, Kelham suggested Equation 2-

4 to predict expansion for mortar bars cured at 90°C:

29

Δ𝐿90𝑜𝐶 = 0.00474 × 𝐹𝑖𝑛𝑒𝑛𝑒𝑠𝑠 + 0.0768 × 𝑀𝑔𝑂 + 0.217 × 𝐶3𝐴 + 0.0942

× 𝐶3𝑆 + 1.267 × 𝑁𝑎2𝑂𝑒𝑞 − 0.737 × |S̅ − 3.7 − 1.02 × 𝑁𝑎2𝑂𝑒𝑞|

− 10.1

(2-4)

It was determined that a cement SO3 threshold of approximately 4% indicated

that the material was likely to cause deleterious expansion when cured at 90°C

(Kelham, 1996). The research determined that there is an association between C3A and

ettringite formation since C3A is the main source of alumina and contributes to the

formation of ettringite (Kelham, 1996). Further related research showed that C3S

content has an influence on ettringite formation during the hydration process while

curing at high temperatures (Brown and Bothe, 1993).

Fu

The Fu curing method, though severe, was developed in 1996 to be useful in

evaluating a cement’s use in the typical precast concrete curing procedure. The

purpose of the method is to determine if cements would cause DEF when exposed to

outdoor weathering. Through experimentation, this method has proven to show a

quicker start of expansion while the Kelham procedure generally produced higher

ultimate expansions (Drimalas, 2004). The Fu curing regime can be seen in Figure 2-2.

Initial length measurements were taken upon demolding with subsequent

measurements taken at 7-day increments. Failure was determined to occur at 0.04%

expansion. The shortened pre-storage time and aggressive drying cycle result in the Fu

method being a more severe test and cause micro-cracking in the mortar bars in order

to accelerate the time before expansion (Drimalas, 2004). Fu ran several cement and

supplementary cementitious material ratios at 80°C and 90°C for both 1” x 1” x 6” (25.4

mm x 25.4 mm x 152.4 mm) and 3” x 3” x 11” (76.2 mm x 76.2 mm x 279.4 mm)

30

specimens. Experimentation showed that the larger specimens followed the same

general trends of expansion as the 1” x 1” x 6” (25.4 mm x 25.4 mm x 152.4 mm) mortar

bars. However, the expansion for the large specimens was delayed for the first several

weeks and showed values about 50% higher after 6 months. Additionally, Fu performed

experiments on both 80°C and 90°C to discover that both temperatures resulted in

expansion although the 10°C increase to 90°C significantly increased the expansion

over a course of 42 days (Fu, 1996).

Fu experimented with replacing sand with microfibers in order to reduce micro

cracking. Once a crack is formed in a specimen, ettringite is able to grow into the void.

Sand type has an effect on expansion values, with more rapid expansion linked to

coarse sand versus fine sand. Varying the sand to cement ratio from 1.00 to 2.00 to

2.75 to 3.00 showed similar expansions and research concluded that the effect of the

ratio on expansion was significantly less significant than other parameters such as

cement chemistry, curing temperature, exposure to a moisture, and drying elements

(Fu, 1996). Fu experimented with cement replacements of class F fly ash, class C fly

ash, silica fume, slag, and zeolite. When curing the mortars at 90°C, specimen created

with class F fly ash or slag mitigated DEF and kept expansions below 0.04% while class

C fly ash, silica fume, and zeolite all expanded within 42 days.

Duggan Test

Prior to the development of the Kelham or Fu methods, the Duggan test was

created in order to determine if cement and aggregate combinations showed potential

for alkali-aggregate reactivity. The research conducted by Duggan showed that both the

aggregate and cement type will play a role in determining expansion and that pass or

fail should be considered based on the entire concrete mixture, not just each individual

31

aggregate or pozzolans (Day, 2002). The experiment established a rough correlation

between results of the test and observed behavior in the field. Concrete cores were

taken from both sound and deteriorated sites in order to create a test that could classify

laboratory created specimen and evaluate existing structures (Day, 2002).

The procedure for this test involves concrete cores taken from a structure or

laboratory-cast prisms or cylinders. The specimen were cut and ground to be 1”

diameter and 2” in length (25.4 mm x 50.8 mm). Initial lengths were measured before

any heat treatment and the cores were followed by a three-day soak in distilled water at

21°C (70°F). The cores are then placed in a dry-air oven at 82°C (180°F) for twenty-four

hours, cooled for one hour, and then replaced in the distilled water for 24 hours. The

heating cycle is repeated once, removed and soaked for twenty-four hours. The

specimens then underwent a third heat cycle which lasted for three days followed by

cooling the specimen for one hour, measuring them, and placed back in distilled water

at room temperature. The lengths were measured every 3-5 days (Day, 2002).

Further research of this Duggan test was conducted by Gillott et al. with cements

of varying alkali content, and three varying aggregates: two known for alkali reactivity

and one inert (Gillot et al., 1989). Specimens were exposed to the Duggan test as well

as the standard concrete prism test for Potential Expansivity of Cement/Aggregate

Combinations (CAN/CSA, 2014). Gillott’s research concluded that concretes exposed to

the Duggan test resulted in DEF being the major cause of expansion. The heat

treatment of this test, as well as that of the Fu method, causes microcracking in the

concrete, which then allows ettringite to form faster with the penetration of water.

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Mitigation and Prevention

Once cracking and expansion begin to occur in massive concrete structures, the

only remedial measure is to repair or replace the affected concrete, which can be

potentially costly (Ramlochan, 2003). The American Concrete Institute durability

committee (201) recently revised the Guide to Durable Concrete, which discusses

durability problems in concrete and provides guidance on mitigation and minimization of

damage to concrete (ACI 201, 2016). The document recommends that the maximum

internal temperature of concrete should be controlled and not exceed 70°C. However, if

temperatures do exceed 70°C but do not exceed 85°C, preventative measures can be

taken to mitigate ACI. Under no circumstances should internal concrete temperatures

exceed of 85°C (ACI 201, 2016).

Regulating the temperature can prove to be difficult in cases of massive

structures, but steps can be taken in order to reduce the temperature rise for these

large concrete placements. These consist of introducing supplementary cementitious

materials, reducing the cementitious content of the concrete mixture, precooling

aggregates and mix water, and post cooling circulating cool water through embedded

piping (ACI 207, 2005) Expansion will drastically increase if cured at temperatures of at

least 95°C (Ramlochan, 2003).

Supplementary cementitious materials (SCM) are those that, when in

combination with portland cement will contribute to the properties of hardened concrete.

Slag cement and pozzolans fall under the category of SCM and are typically used to

replace portland cement in concrete mixture to improve desired properties of the

concrete. SCMs have proven to be a useful replacement for portland cement to reduce

or mitigate DEF and produce durable concrete. These mineral additions such as slag

33

cement and fly ash reduce peak temperatures of massive concrete pours (Ingham,

2012). ACI suggests the following minimum cement replacements in concrete mixtures

with internal temperatures of 70°C to 85°C: 25% class F fly ash, 35% class C fly ash,

35% slag cement, 5% silica fume with 25% slag cement, 5% silica fume with 20% class

F fly ash, or 10% metakaolin (ACI 201, 2016).

Research has shown that cement replacement of 30% fly ash or 50% slag

cement completely eliminated expansion while 15% fly ash or 25% slag cement

reduced the ultimate expansion (Ramlochan, 2003). This reduction in expansion is

attributed to the active alumina present in the materials as well as the effective

reduction in S̅ / A (Heinz, Ludwig, Rudiger, 1989). Drimalas conducted research using

two different curing methods with fly ash and metakaolin in which the introduction of

SCMs decreased calcium hydroxide and increased C-S-H, discouraging the formation

of ettringite (Drimalas, 2004). Fu’s research shows that a 30% replacement of class C

fly ash and 15% silica fume failed to mitigate and exceeded 0.04% expansion in 28

days (Fu, 1996). Famy’s research conducted a replacement of 25% class F fly ash,

which showed low amounts of ettringite at 150 days, but no expansion at 200 days

(Famy, 1999). There are disputes between researchers of whether silica fume actively

mitigates expansion of DEF, with Heinz supporting its use and Lagerblad and Utkin

reporting that it does not necessarily mitigate (Ramlochan, 2003). Zacarias’s research

shows that incorporating class F and C fly ashes into the mix design at 15% and 25%

were effective in suppressing expansion (Ramlochan, 2003).

There are no strong correlations between any cement parameters and definite

expansion caused by DEF. However, research conducted by Kelham shows a

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relationship between expansive cements and 2-day mortar strengths. Mixtures that are

more expansive generally showed higher early strengths (Kelham, 1996). ACI includes

1-day mortar cube strengths in the Guide to Durable Concrete as a preventative

measure. Cube strengths of 1-day specimen greater than 2850 psi (19.7 MPa) are

expected to be capable of causing DEF (ACI 201, 2016).

Concluding Remarks

In summary, the studies completed by these researchers have contributed to the

body of knowledge with respect to formation of DEF in concrete, but more and different

curing regimens should be researched to capture the potential for delayed ettringite

formation in massive concrete elements, which undergo elevated temperatures for

longer durations. Currently, there is no standard test method for determining if a

concrete element will exhibit delayed ettringite formation. There is no specific equation,

curing timeframe, or cement composition that will determine if expansion will occur, nor

when. Important factors included in a testing regimen include pre-curing time,

temperature, time at peak temperature, ramp rate, and humidity.

The Kelham, Fu, and Duggan methods are over twenty years old and do not

consider high temperature moist curing times of more than twelve hours. There is a

need for a test method that considers longer curing times because the temperature rise

of the hydration reaction in a massive concrete specimen often peaks subsequent to 1-3

days after placement. A test that can evaluate specimen at heated curing times of

longer than twenty-four hours must be introduced in order to create a more realistic

comparison between laboratory and field exposure conditions. Another variable that is

not widely tested in regards to the three common curing methods is the solubility and

long-term storage of the mortar bar specimen. After the curing cycle, specimens are

35

stored in a large limewater tank at room temperature. This procedure eliminates the

ability to allow experimentation on comparison of composition of the cure water for each

set of samples. Curing the specimen in a controlled amount of water in separate

containers would allow for this.

In addition, further research must be done with the use of SCMs and pozzolans

in regards to mitigation of delayed ettringite formation. Class F fly ash and slag are

common replacements that allow for a reduction in heat produced, but replacements

involving metakaolin, silica fume, class C fly ash, as well as multiple types of cement,

have not been used in combination extensively. Various cementitious mixtures in

combination with more time-temperature profiles will provide a more comprehensive

look into mitigation of deleterious expansion caused by DEF. It typically takes a

minimum of weeks and up to years for the initiation of expansion in mortar bars.

Specimen size should be taken into account to help develop a faster and more accurate

method for determining if expansion due to DEF will occur. This will require extensive

research with varying sized specimen, time-temperature profiles, and mix designs.

36

Table 2-1. Cement chemical compounds and abbreviations

Shorthand Compound Chemical Formula

C Calcium Oxide (Lime) CaO S Silicon Dioxide (Silica) SiO2 F Ferric Oxide (Iron) Fe2O3 A Aluminum Oxide (Alumina) Al2O3 S̅ Sulfur Trioxide (Sulfate) SO3 H (Water) H2O

Table 2-2. Hydration products and roles

Shorthand Compound Role

C3S Tricalcium Silicate Hydrates and hardens rapidly. Largely responsible for initial set and early strength.

C2S Dicalcium Silicate Hydrates and hardens slowly. Contributes largely to strength increase beyond one week.

C3A Tricalcium Aluminate Hydrates rapidly and liberates a large amount of heat. Contributes slightly to early strength. High content will make concrete more susceptible to sulfate attack.

C4AF Tetracalcium Aluminoferritte Contributes little to strength. Reduces clinkering temperature to reduce cost.

37

Table 2-3. Cement types and general contributions

Type Classification Characteristics

I/II General purpose/Moderate sulfate resistance

High C3S and low C3A content. Good early strength development with sulfate resistance. Used for structures exposed to soil or water containing sulfate ions.

III High early strength Ground more finely and higher C3S content. Used for rapid construction in cold weather climates.

IV Low heat of hydration Low C3S and C3A content. Used in massive structures.

V High sulfate resistance Very low C3A content. Used for structures exposed to high levels of sulfate ions.

Figure 2-1. Kelham method heat curing cycle (Reproduced from Kelham, 1996).

38

Figure 2-2. Fu method heat curing cycle (Reproduced from Fu, 1996).

Figure 2-3. Duggan method heat curing cycle (Reproduced from Day, 2002).

39

CHAPTER 3 EXPERIMENTAL PROGRAM

Background

Delayed ettringite formation requires moisture and high temperature at early

ages / during curing in order to occur, though the cement composition does play a large

role in the formation as well. The most prevalent tests used within the concrete industry

to determine potential for DEF were developed by two researchers to mimic the curing

conditions typically used within the precast concrete curing process (Kelham, 1996; Fu,

1996). Further investigation was completed through this research, on the testing

methods established by Kelham and Fu. Additional profiles were developed in order to

create a testing regimen that will show early signs of potential delayed formation of

ettringite and mimic not just the precast, but also the mass concrete curing process.

Although the Fu and Kelham methods are acknowledged in the field of DEF research,

there are currently no standard methods developed for determining expansion caused

by DEF.

Materials and Methods

Materials and Characterization

Five different cements were used for this research; Cement TI-1 is a type I/II

cement from North Central Florida, USA. Cement TI-2 is a type I/II cement from North

East Florida, USA. Cement TIII-1 is a type III Cement from the same plant as Cement

TI-1, Cement TIII-2 is a type III cement from the same location as Cement TI-2, and

Cement TV was ordered and intended to be a Type V cement from North Texas, USA.

Further evaluation was performed on Cement TV determined that it was a low C3A type

I/II cement, not a type V cement, as the sulfate content exceeded 2.3% as per ASTM

40

C150 (ASTM C150, 2015). The chemical oxide composition of each cement used is

shown in Table 3-1. Additionally, supplementary cementitious materials (SCM) were

used to create binary mortar mixtures. The SCM used consist of: class F fly ash, class

C fly ash, slag cement, metakaolin, and silica fume. Chemical compositions of each

SCM are shown alongside the cements in Table 3-1.

The fine aggregate used for mortar bars is from North Central Florida, USA and

was a quartzite sand. The aggregate gradation for the mortar bar mixes followed the

requirements prescribed in ASTM C1260, shown in Table 3-2. This sand had a specific

gravity of 2.64. The fine aggregate used for the mortar cubes discussed in Chapter 6

was shipped in from North Central Illinois, USA. This sand is known as graded standard

or Ottawa sand, required according to ASTM C109, and has a specific gravity of 2.65

(ASTM C109, 2016).

Cementitious materials were characterized using x-ray diffraction, x-ray

fluorescence, and particle size distribution. Quantitative x-ray diffraction (XRD) was

performed with a PANalytical empirical diffractometer and Rietveld analysis was

performed. The mass fractions obtained by Rietveld analysis of XRD patterns of each of

the five cements are shown in Table 3-3. Particle size distribution was determined for

the cementitious materials by way of a laser light particle analyzer with the samples

dispersed in lab grade 200 proof ethanol. Mean particle size was determined for the five

cements and five SCM used in this research, shown in Table 3-4. Cement oxide

analysis was completed by x-ray fluorescence (XRF) spectrometry using PANalytical

IQ+ Quantification program for both fused and pressed pellet samples. The values

41

estimated through this experimentation are shown in Table 3-1 for all cementitious

materials.

An important factor of expansion caused by DEF is sulfate (SO3) content and the

sulfate to aluminate ratio (S̅ / A). Sulfate content was estimated initially by testing XRF

of fused samples. These values are shown in Table 3-1 for all five cements. Due to

excessive expansion in three of the cements at certain curing profiles of mortar bars,

XRF analysis was completed again using pressed pellets to obtain a more accurate

sulfate content. The oxide analysis for the cements created as pressed pellets is shown

is Table 3-5. The second round of XRF analysis showed sulfate contents exceeding the

limits of ASTM C150 for all three cements.

As a further testing method on the chemistry of the given cements, analysis on

sulfur trioxide was completed following Section 17 of ASTM C114 (ASTM C114, 2015).

This test method was performed for the same three cements in order to determine

sulfate content. This standard allows the cements to be analyzed by way of precipitating

sulfate through an acid solution of the cement with barium chloride. Sulfate contents

tested using ASTM C114, these values are shown as a comparison in Table 3-5.

The ASTM C114 test method requires one gram of material to be mixed with cold

water and hydrochloric acid. The solution is then diluted with more water before being

heated the just below boiling. The solution is then filtered through a medium-textured

paper, diluted again, and heated to boiling. Barium chloride is then added slowly and

the beaker containing the solution is placed in an ultrasonic bath for five minutes. The

solution and precipitate was then filtered through a retentive paper and washed with hot

water. The paper was placed in a crucible, charred in a muffle furnace, and then placed

42

into a furnace and ramped to 800°C (1475°F) at 5°C per minute for a total of two hours.

The samples were then cooled in a desiccator and weighed to determine sulfate

content.

Methods

Mortar bar specimens were created to evaluate potential for alkali-silica reactivity

(ASTM C1260) and delayed ettringite formation (Kelham, Fu, and Ferraro Method). The

specimens were batched and created in accordance with ASTM C1260. Due to the

amount of experiments completed and different temperatures for each, a set of

abbreviations have been created, shown in Table 3-6. These abbreviations are used in

Table 3-7, which shows the entire list of mix designs constructed using each cement

and SCM. Full-sized mortar bars created for this experiment were 1” x 1” x 11.25”.

Alkali-silica reaction

Alkali-silica reaction testing was performed to evaluate the potential for the

combinations of cementitious materials and aggregates for deleterious reactivity per

ASTM C1260. Case studies have shown that ASR is commonly found alongside and

oftentimes initially confused with DEF when deleterious expansion is involved (Thomas

and Ramlochan, 2002; Lawrence et al., 1999). The purpose of completing this

experiment is to determine which mixes will have expansion caused by ASR and

differentiate the mixes that have expansion that is caused by DEF, without ASR.

ASTM C 1260, a 16-day test, was completed to prove validity of chosen cements

and aggregates for future mix designs. If there is not expansion found during this

experiment, expansion caused by heat curing is expected to be caused by DEF, not

ASR. The specimens were stored vertically in polyethylene containers. In order to keep

the specimens from resting on the gage studs integrated into the bars, they were stored

43

on metal grates with holes drilled out for the gage studs. Bars were fully submerged and

kept in an oven at 80°C for the duration of the test.

Delayed ettringite formation

Mortar bar specimens were created following ASTM C1260 and cured in an

environmental chamber, which regulated temperature as well as humidity. The mortar-

filled molds were placed in aluminum containers with an inch of tap water in the bottom

of the pan. Paper towels were draped over the molds to enable wicking of the water

onto the specimens to keep them moist during the entire heat curing period. The pans

were then covered with a sheet of foil to help create a sealed environment for the

specimens; additionally the internal humidity of the chambers was maintained at 95%.

Actual time-temperature profile data was exported from the chambers and compared to

desired profiles in order to ensure accuracy.

Kelham method

Kelham’s research presented a heat curing profile that followed the standard

temperature rise applied during the precasting operation. The experiments were

performed on 16 mm x 16 m x 160 mm (0.63 in x 0.63 in x 6.23 in) prisms following the

time temperature profile shown in Figure 2-1. Revisiting, Figure 2-1 the test was

conducted with four different peak temperatures of 20°C, 70°C, 80°C, and 90°C. Mortar

bar specimen were mixed and prepared according to EN 196-1 (EN 196-1, 2016). This

method calls for an initial curing time of four hours from the mixing time at ambient

conditions (the “pre-curing” period), then ramping to the peak temperature at a rate of

20°C per hour. The specimens stayed at the peak temperature for twelve hours and

ramped down at a rate of 20°C per hour to ambient conditions. The bars were then

demolded, measured, and kept in ambient limewater conditions for the lifetime of the

44

test. Kelham’s experiment varied cements in order to determine the effects of cement

composition and fineness on DEF related expansion.

The Kelham profile discussed was performed for this experiment with peak

temperatures of 70°C, 85°C, and 95°C and modifications were made for this research to

have a controlled ramp of four hours to maximum temperature and four hours the cool

back to room temperature. The time-temperature profile for this experiment is shown in

Figure 3-1.

Revised Kelham method

In order to accelerate the Kelham method further, adjustments were made to the

curing regimen. For this version of the Kelham method, specimens were subjected to

the 24 hour Kelham procedure outlined above, followed by storage in ambient

temperature limewater for six hours, and then placed into a dry oven for 24 hours before

storing in ambient temperature limewater. Specimens exposed to the 70°C Kelham

method were placed in an oven at 70°C for 24 hours, and specimens exposed to 85°C

or °95°C Kelham profiles were placed in an 85°C oven for 24 hrs. This method will be

referred to as the “Revised Kelham” profile, shown in Figure 3-2.

Fu method

The heat curing profile developed by Fu also simulates the curing conditions

typically applied within the precast concrete industry, and is more aggressive than the

Kelham method. Two specimen sizes were created: 25.4 mm x 25.4 mm x 152.4 mm

(1” x 1” x 6”) and 76.2 mm x 76.2 mm x 279.4 mm (3” x 3” x 11”). The experimental

curing method developed by Fu has a duration of 48 hours compared to 24-hour during

the Kelham curing cycle. The first portion of the method lasts for eighteen hours and is

comparable to the Kelham profile described previously. This heat curing cycle requires

45

a one hour pre-curing period before subjecting the specimens to a one hour ramp to

maximum temperature. The specimens soak at the peak temperature of 80°C or 90°C

for twelve hours before ramping down to ambient temperature over the course of four

hours. During Fu’s experiments, the ramp down to ambient temperature was not

controlled and consisted of turning off the oven and opening the door before demolding

the specimens four hours later.

After the initial eighteen-hour curing sequence, specimens were demolded and

placed in ambient temperature limewater for six hours before taking initial

measurements. After measuring, the specimens were put into an oven to dry for 24

hours at 85°C to conclude the 48-hour cycle. The dry oven segment of the Fu method is

used to introduce microcracks into the specimens. After removal from the oven, the

specimens are placed back into a lime water tank in a moist room, held at ambient

temperature. Subsequent measurements were taken every seven days. Fu states that

an increase of curing temperature accelerates the expansion rate and suggests a curing

temperature of 95°C. While the test method developed by Fu is severe, his research

suggests that it is necessary for the evaluation of cementitious materials and concrete

mixtures subjected to curing conditions typically used in the precast industry (Fu, 1996).

The Kelham and Fu heat curing profiles were developed around the same time to

simulate the precast concrete industry. The goal of this research is to use curing profiles

developed by Kelham and Fu to create a curing method that can simulate the expansion

of a massive concrete element, not a precast element. Massive concrete structures,

when constructed, can produce excessive amounts of heat for multiple days. The

46

twelve-hour soak at peak temperatures that the Kelham and Fu profiles is not long

enough to simulate the temperature profile of a massive concrete placement.

Revised Fu method

A revised version of the Fu method was conducted for this research, with the

only modifications being that the maximum temperature the specimens were exposed to

is 95°C, as suggested, and the ramp down is a controlled four-hour ramp from 95°C to

ambient temperature. The time-temperature profile which was shown in Figure 2-2 will

be referred to as the “Fu” profile for the remainder of this document.

Ferraro method

A fourth curing method was developed, based upon the Kelham method, to more

accurately represent the heat developed in a massive concrete placement. This method

extends the time period of the peak temperature in the Kelham profile to replicate the

extended elevated temperature profile typically observed during mass concrete

placements. This profile extended the twelve-hour peak time to 36 hours, making the

entire profile 48 hours versus the 24 hours of the baseline Kelham profile. Similar to the

Kelham method, the pre-curing time remained at four hours and the ramp to and from

the maximum temperature remained at four hours. This method will be referred to as

the “Ferraro Method” for the remainder of this document. This profile was executed for

the three maximum temperatures of 70°C, 85°C, and 95°C, shown in Figure 3-3.

Miniature bar method

Standard mortar bar procedures require mortar bars to be 11.25” (285.75 mm) in

length, with ASTM C 1260 and ASTM C1567, the bars have a cross sectional area of 1”

x 1” (25.4 mm x 25.4 mm). For ASTM C1296, the cross sectional area of the concrete

bars is 3” x 3” (76.2 mm x 76.2 mm). These bars can take months, and up to as long as

47

years to show expansion that leads to failure. To expedite the expansion process,

smaller bars were created for this research and a modified length change test was

developed.

Kelham’s research also included smaller bars than the standard size. These bars

were 0.63” x 0.63” x 6.3” (16 mm x 16 mm x 160 mm), this is not a standard size in

America or Europe and did not correspond with the 1.57” x 1.57” x 6.3” (40 mm x 40

mm x 160 mm) size specified in the European standard used (EN 196-1, 2016). The

research does not explain the use of the smaller bars, only that they were made

according to the standard except for the change in specimen size.

The mortar bars for this research were created to have 4.635” (117.73 mm)

length and kept a cross sectional area of 1” x 1”. The miniature bars were created using

three different cements: Cement TI-2, Cement TIII-2, and Cement TV. These bars were

created following the same standard as the full sized bars and have all of the same

characteristics, excluding length.

Bars were created using standard two gang 1” x 1” x 11.25” prism molds, with

modifications to shorten the bar length to 4.635”. This length was chosen in order to

create two miniature bars in the space of each single, full-length mortar bar mold. The

setup of the bar molds is shown in Figure 3-4. This modification, made in the center of

the mold, allowed four miniature bars to be made in one standard mortar bar mold and

have gage studs on both ends. Using the standard prism mold allowed the specimen to

keep the same cross sectional area as the full sized mortar bars, as to reduce the

number of variables in the experiment.

48

This experimentation was started upon the completion of standard length mortar

bars, in order to decide which curing method(s) to follow. Miniature and full-sized mortar

bars were created together and cured following the Ferraro curing method. Specimens

were cured with this time-temperature profile with a peak temperature of 95°C, in order

to determine if expansion rates to failure would be faster for shorter specimens.

Long Term Storage and Measuring

Full sized bars

Initial measurements were taken upon removing the specimens from the molds

for the Kelham, Ferraro, and ambient temperature methods. Initial measurements were

taken after a six hour limewater soak before the oven portion of the Fu and Revised

Kelham methods. All measurements were taken in an ambient room while the

specimens were at a controlled, ambient temperature.

After taking initial measurements, specimens were placed in a limewater solution

for long-term storage. Specimens were measured each week for four weeks, biweekly

for two measurements, and then measured monthly for the extent of the evaluation.

Measurements were taken using a comparator according to ASTM C490 (ASTM C490,

2015).

Miniature sized bars

In addition to changing the length of the mortar bars, long-term storage for the

miniature bars was modified in order to experiment with solubility. Miniature mortar bars

were stored in two ways: upright in a polyethylene plastic container and lying flat in a

larger plastic storage container. In both storage conditions, specimens were rested on

3/8-in. polystyrene plastic crates. The specimen in the upright container, called

“controlled”, were stored in a curing solution with 100 mL of limewater, made of 3 grams

49

of calcium hydroxide per liter of tap water. These containers were made to fit four

miniature bars with only enough excess room to saturate and cover the bars with the

100 mL of limewater. When water level dropped, replacement water was the same

solution stirred vigorously and added dropwise. In the storage containers where

specimens laid flat, approximately 3 liters of limewater was added, these specimens will

be referred to as “uncontrolled”. Full-length bars were also stored in an “uncontrolled”

curing solution using the same plastic storage containers as the miniature bars.

Comparisons were made between specimens with a controlled curing solution,

uncontrolled curing solution, and full-length bars. Measurements were taken using a

comparator with an extension and 4.635” reference bar.

Concluding Remarks

Mortar bars were made for all testing profiles in order to easily compare them.

The Kelham and Fu profiles have been used in research for over twenty years, but

since they do not contain a long enough timeframe at peak temperature to accurately

represent the temperature profile of a massive concrete placement, further curing cycles

were developed for this research. The purpose of this research is to develop a useful

standard to determine if DEF will occur in concrete which requires adjustments in ramp

rates, peak temperatures, as well as the overall timeframe of heat curing to the methods

most commonly used by the industry.

50

Table 3-1. Chemical compositions of cementitious materials

Chemical Oxide Cement

TI-1 Cement

TI-2 Cement

TIII-1 Cement

TIII-2 Cement

TV Metakaolin

Class F Fly Ash

Class C Fly Ash

Slag Cement

Silica Fume

SiO2 19.49 19.81 19.86 20.05 20.46 51.5 57.8 34.7 33.6 90.9 Al2O3 5.04 4.79 5.05 4.91 4.22 43.7 21.4 18.5 14.4 0.39 Fe2O3 3.72 3.86 3.54 3.87 4.02 0.47 11.8 5.66 0.61 2.14 CaO 63.63 64.1 64.17 62.68 64.81 <.01 1.29 26.4 41.1 0.85 MgO 0.83 1.02 0.81 1 2.18 0.14 1.32 6.36 5.88 0.78 SO3 3.07 2.66 3.29 2.67 2.23 0.01 0.24 1.84 2.56 <.01

Na2O 0.15 0.16 0.13 0.17 0.06 0.28 0.9 1.88 0.19 0.2 K2O 0.38 0.3 0.36 0.28 0.63 0.25 2.52 0.43 0.34 1.07 TiO2 0.25 0.22 0.26 0.23 0.23 1.35 0.99 1.45 0.53 <.01 P2O5 0.46 0.13 0.47 0.11 0.07 0.08 0.19 0.86 0.02 0.1

Mn2O3 0.02 0.06 0.02 0.07 0.02 <.01 0.04 0.04 0.35 0.19 SrO 0.07 0.13 0.07 0.13 0.06 0.02 0.05 0.43 0.07 0.01

Cr2O3 0.01 0.02 0.01 0.02 0.01 0.01 0.02 0.01 <.01 <.01 ZnO 0.05 0.11 0.05 0.09 0.01 <.01 30.02 0.01 <.01 0.07 BaO - - - - - 0.2 0.07 0.83 0.06 <.01 L.O.I. 2.61 2.59 1.78 3.08 1.05 1.75 0.9 0.23 - 3.76 Total 99.78 99.95 99.87 99.36 100.06 99.6 99.7 99.5 99.6 100.4

SO3 / Al2O3 (Molar) 0.776 0.707 0.830 0.693 0.673 - - - - - SO3 / Al2O3 (Mass) 0.609 0.555 0.651 0.544 0.528 - - - - - SiO2+Al2O3+Fe2O3 28.25 28.46 28.45 28.83 28.7 95.7 - 58.8 - 93.4 Na2O + 0.658 K2O 0.40 0.36 0.37 0.35 0.47 0.44 0.41 2.17 0.41 0.9

51

Table 3-2. ASTM C1260 sand requirements

Sieve Size Mass %

Passing Retained On

4.75 mm (No. 4) 2.36 mm (No. 8) 10

2.36 mm (No. 8) 1.18 mm (No. 16) 25

1.18 mm (No. 16) 600 µm (No. 30) 25

600 µm (No. 30) 300 µm (No. 50) 25

300 µm (No. 50) 150 µm (No. 100) 15

Table 3-3. Mass fractions of Retveld analysis of XRD patterns

Parameter/Goal Cement TI-1

Cement TI-2

Cement TIII-1

Cement TIII-2

Cement TV

Alite 51.2% 58.7% 54.6% 55.2% 66.9%

Belite 19.1% 12.4% 18.4% 18.7% 8.4%

Tricalcium Aluminate Cubic

3.0% 2.3% 4.0% 1.4% 1.2%

Tricalcium Aluminate orthorhombic

6.1% 4.6% 5.3% 2.0% 0.5%

Ferrite 10.4% 12.9% 10.5% 13.4% 14.1%

Gypsum 1.6% 3.9% 1.8% 3.0% 1.2%

Bassanite 2.4% 0.4% 2.7% 1.0% 2.5%

Anhydrite 0.9% 0.1% 0.2% 0.2% 0.1%

Periclase 0.4% 0.1% 0.2% 0.2% 2.0%

Calcite 2.9% 2.6% 0.2% 3.6% 0.0%

Sodium Sulfate 0.5% 0.8% 0.4% 0.6% 2.2%

Portlandite 1.6% 1.4% 1.9% 0.6% 1.1%

Table 3-4. Cementitious material particle size

Material Mean Size (µm)

Cement TI-1 11.44

Cement TI-2 10.99

Cement TIII-1 7.90

Cement TIII-2 10.77

Cement TV 9.45

C Ash 10.79

Slag 12.72

F Ash 11.00

Silica Fume 30.60

Metakaolin 4.43

52

Table 3-5. Sulfate content determined from XRF analysis of fused, pressed pellets, and ASTM C114

Cement SO3 Content (%)

Fused Pressed Pellets ASTM C114

TI-1 3.07 3.58 - TI-2 3.29 4.36 - TV 2.23 3.12 3.08

Table 3-6. Abbreviations of curing methods

Curing Method Peak Temperature Abbreviation

Ambient 23°C A Kelham Method 70°C, 85°C, 95°C K70, K85, K95 Kelham Revised 70°C, 85°C, 95°C KR70, KR85, KR95 Fu Method 95°C Fu Ferraro Method 70°C, 85°C, 95°C F70, F85, F95

53

Table 3-7. Mix designs for full-sized mortar bars %

SCM

Cement

lb/yd3 Curing Profiles

Water SCM Cement K KR Fu F

Cement TI-1 483 1028 70, 85, 95 70, 85, 95 95 70, 85, 95 Cement TI-2 483 1028 70, 85, 95 70, 85, 95 95 70, 85, 95 Cement TIII-1 483 1028 70, 85, 95 70, 85, 95 95 70, 85, 95 Cement TIII-2 483 1028 70, 85, 95 70, 85, 95 95 70, 85, 95 Cement TV 483 1028 70, 85, 95 70, 85, 95 95 70, 85, 95 10 Class F Fly Ash Cement TI-1 479 102 918 70, 85, 95 70, 85, 95 95 70, 85, 95 20 Class F Fly Ash Cement TI-1 476 202 810 70, 85, 95 70, 85, 95 95 70, 85, 95 35 Class F Fly Ash Cement TI-1 470 350 650 70, 85, 95 70, 85, 95 95 70, 85, 95 50 Class F Fly Ash Cement TI-1 470 500 500 70, 85, 95 70, 85, 95 95 70, 85, 95 10 Class C Fly Ash Cement TI-1 482 102 922 70, 85, 95 70, 85, 95 95 70, 85, 95 20 Class C Fly Ash Cement TI-1 480 204 817 70, 85, 95 70, 85, 95 95 70, 85, 95 35 Class C Fly Ash Cement TI-1 477 355 660 70, 85, 95 70, 85, 95 95 70, 85, 95 50 Class C Fly Ash Cement TI-1 474 505 505 70, 85, 95 70, 85, 95 95 70, 85, 95 10 Slag Cement Cement TI-1 483 103 924 70, 85, 95 70, 85, 95 95 70, 85, 95 20 Slag Cement Cement TI-1 482 205 821 70, 85, 95 70, 85, 95 95 70, 85, 95 30 Slag Cement Cement TI-1 482 307 717 70, 85, 95 70, 85, 95 95 70, 85, 95 50 Slag Cement Cement TI-1 481 511 511 70, 85, 95 70, 85, 95 95 70, 85, 95 70 Slag Cement Cement TI-1 480 714 306 70, 85, 95 70, 85, 95 95 70, 85, 95 5 Metakaolin Cement TI-1 481 51 973 70, 85, 95 70, 85, 95 95 70, 85, 95 10 Metakaolin Cement TI-1 479 102 918 70, 85, 95 70, 85, 95 95 70, 85, 95 5 Silica Fume Cement TI-1 481 51 973 70, 85, 95 70, 85, 95 95 70, 85, 95 10 Class F Fly Ash Cement TI-2 479 102 918 - - - 95 20 Class F Fly Ash Cement TI-2 476 202 810 - - - 95 10 Class C Fly Ash Cement TI-2 482 102 922 - - - 95 20 Class C Fly Ash Cement TI-2 480 204 817 - - - 95 10 Class F Fly Ash Cement TIII-1 479 102 918 - - - 70, 85, 95

10 Class F Fly Ash Cement TV 480 102 920 70, 85, 95 95 - 85, 95

20 Class F Fly Ash Cement TV 477 203 812 70, 85, 95 95 - 85, 95 10 Class C Fly Ash Cement TV 482 922 102 - 95 - 85, 95 20 Class C Fly Ash Cement TV 480 817 204 - 95 - 85, 95 5 Metakaolin Cement TV 481 51 973 - 95 - 85, 95 10 Metakaolin Cement TV 480 102 919 - 95 - 85, 95

54

Figure 3-1. Heat curing profile for K70, K85, and K95.

Figure 3-2. Heat curing profile for KR70, KR85, and KR95.

55

Figure 3-3. Heat curing profile for F70, F85, and F95.

Figure 3-4. Setup of miniature mortar bar mold. Photo courtesy of author.

56

CHAPTER 4 RESULTS AND DISCUSSION OF ORDINARY PORTLAND CEMENT

Mortar Bar Results

ASR

The ASTM C1260 standard was followed to affirm the use of the chosen

aggregate to not expand. The results of expansion below 0.10% after the experiment for

each cement were found to be innocuous to ASR. The bars were measured upon

demolding and at ages of 2, 4, 7, 10, 14, and 16 days after mixing. Expansions of each

cement and limits of the test are shown in Figure 4-1. Values below the yellow line are

indicative of innocuous behavior, in most cases, while cases between the yellow and

red lines are both innocuous and deleterious and typically require further investigation,

and above the red line is indicative of potentially deleterious expansion. With no

expansion during this test, ASR is not considered the cause of expansion through other

heat curing methods discussed further in this document.

DEF Heat Curing

Currently, there is no consensus on the definition of failure for concrete that is

experiencing DEF. Therefore, the term “failure” used from this point forward is defined

as expansion is greater than or equal to 0.10%. This value was chosen based on the

dimensional stability requirements of accelerated mortar bar methods, ASTM C1260

and ASTM C1567 (ASTM C1260, 2014; ASTM C1567, 2013). For these specifications,

a threshold of at least 0.10% expansion in mortar bars indicates a potential risk of

deleterious expansion in concrete under field conditions.

Overall, eleven time-temperature heat curing cycles were developed and

performed throughout this research project, including a control which was held at

57

ambient temperature for all mix designs. Maximum curing temperatures for each mix

design as well as the weight of each constituent was shown in Table 3-7.

Kelham method

The Kelham profile was completed at three temperatures, 70°C, 85°C, and 95°C

for all five cements and all SCM combinations with Cement TI-1, shown in Table 3-7.

Expansion has been shown using this method in research between 56 and 200 days

(Kelham, 1996; Drimalas, 2004). Figures 4-2, Figure 4-3, and Figure 4-4 show the

expansions of the cements at 70°C, 85°C, and 95°C, respectively. Throughout

investigating the research findings, the Kelham profile was the only curing regimen to

produce failure at 70°C. Failure for these specimens was reached at approximately 473

days. No failure has occurred at 85°C at the time of submission, nor does it appear to

reach 0.1% in the near future. When cured at 95°C, only one cement, Cement TV,

reached failure at approximately 438 days, although Cement TIII-1 appears as though it

will also reach failure in the near future. The peak expansion and age for each is shown

in Table 4-1. As shown, the expansion values are far below the threshold failure value

of 0.10% expansion. As of the completion of this document, the Kelham procedure

produced less than 0.05% expansion for all 23 mix designs for all three peak

temperatures at ages of up to 500 days.

Fu method

The Fu profile was performed at 95°C for the mix designs shown in Table 3-7.

This is the most severe time-temperature profile due to the accelerated one hour pre-

cure period and one hour ramp to peak temperature. In addition, the dry oven portion at

the end of the 48 hour test introduces microcracking, facilitating the rate and onset of

expansion. These microcracks increase void space and can give the ettringite a space

58

to form (Ramlochan, 2003; Drimalas, 2004). This can also allow the ettringite to form

faster due to more accessible water penetration (Day, 2002). All five cements were

subjected to the Fu profile; expansions are shown in Figure 4-5. The most expansive

cement for this curing profile at the completion of this document was Cement TV. This

trend of Cement TV being the most expansive is consistent for the other time-

temperature curing profiles completed for this research. The values of peak expansion

and age are shown in Table 4-2.

Revised Kelham method

This method, a combination of the Kelham and Fu baselines, was created to

compare the two methods and to accelerate the Kelham method by adding a 24-hour

oven portion to the end of the Kelham profile. The time-temperature profile for all

temperatures was shown in Figure 3-2. As expected, the most severe expansions

occurred when the specimens were initially cured at 95°C through the Kelham profile

and subjected to an 85°C dry oven period. All cements except Cement TI-1 showed

failure after 300 days when cured in this manner, as shown in Figure 4-6. At over 400

days, no expansion is seen in the mortar bars that are cured at 85°C or 70°C and then

placed in the dry oven for 24 hours. Rates of expansion with respect to time are shown

in Figures 4-7 and 4-8, respectively, for peak temperatures of 85°C and 70°C.

Ferraro method

The Ferraro method proved to show the most expansion, despite the absence of

oven drying to induce microcracking. This method, showed the greatest expansion at

95°C; some expansion was observed when specimens were cured at 85°C, and no

expansion was observed for specimens cured at 70°C after over 300 days, which is at

the time of publication of this thesis. After 200 days of ambient storage, all cements

59

exhibited expansion greater than 0.20% when exposed to 95°C curing as shown in

Figure 4-9. At the time of completion of this thesis, two cements failed when exposed to

the Ferraro method at 85°C. Cement TV failed at 85°C at approximately 64 days and

Cement TIII-1 reached failure after 270 days as shown in Figure 4-10. No mixtures

showed signs of expansion when heat cured with the Ferraro method at 70°C, as shown

in Figure 4-11.

Miniature Bar Results

The age of failure for the miniature bars was determined through linear

interpolation between the measured age just before failure and the measured age just

after failure of 0.1% expansion was recorded. In comparing miniature bars cured in

controlled and uncontrolled limewater solutions, there was a very small amount of

difference between expansion of the two sets of bars.

The uncontrolled miniature bars, which were stored flat and with about 3 liters of

water, from the Cement TI-2 mixture failed at 87 days while the controlled miniature bar

failed at approximately 80 days, shown in Figure 4-12. Both sets of bars expanded to

failure before the full-sized bars, which failed at approximately 96 days. The miniature

bars from the Cement TIII-2 mixture failed at approximately 83 days while the full-sized

bars failed at approximately 99 days, which is shown in Figure 4-13. The miniature bars

from the Cement TV mixture failed at approximately 35 days while the full-length bars

took approximately 51 days to fail, this is shown in Figure 4-14.

Concluding Remarks

When completing experimentation for DEF analysis, it is important to rule out

ASR as a cause for destruction, since they appear very similar. Distinguishing between

these two phenomenon is important, because ASR is easily diminished with the use of

60

non-reactive aggregates. Multiple American standard testing procedures are already

developed to determine if ASR will occur in a concrete or mortar mixture: ASTM C1260,

ASTM C1293, and ASTM C1567 (ASTM C1260, 2014; ASTM C1293, 2008; ASTM

C1567, 2013). ASTM C1260 and ASTM C1567 are short, sixteen day, tests and have

the possibility of providing a false negative result. For this reason, a more extensive test

that runs for at least twelve months is in place with ASTM C1293.

Since ASR and DEF are commonly mistaken for each other, it makes sense to

develop a testing standard for DEF to determine if it will occur instead of or after ASR

damage. This testing program should include initial ASR testing to prove that any

deterioration or destruction caused in the specimens is due to DEF, and not ASR.

Creation of a testing standard will prove to be more difficult, because the causes of DEF

cannot be simply pinpointed. The causes of DEF are high curing temperatures (in

excess of 70°C), moisture, and a focus on sulfate within the cement chemistry. This

occurrence is not caused by the aggregates, but by a formation within the pores of the

cement matrix.

The most effective testing profile when examining DEF for this experimentation

was the Ferraro method at 95°C. All five of the control mixtures exposed to these curing

conditions eventually failed. In order to more certainly prove the efficiency of this test,

further experimentation was completed with the use of SCM to prove that this test would

not relay false positives. If a testing method is too extreme and causes failure for every

mix design, it will not show those specimens that would truly fail when heated with this

curing regimen in the field.

61

In addition to the Ferraro method, experimentation was completed following the

original Kelham profile and three different peak temperatures, the Fu Profile at one peak

temperature, and a modification of the Kelham and Fu profiles, which started with the

Kelham temperature ramp and included the dry oven portion from the Fu design. In

addition, all mix designs created also had a controlled ambient temperature set of

specimens as well. Since DEF is temperature dependent, none of these specimens

were expected to or did expand.

Since results of these mortar bar tests take an excessive amount of time to prove

that mixtures can be deleterious, a change in specimen size is suggested. The

hypothesis of this experiment is that shorter bars will relate to full-length mortar bars

and show expansion at a faster rate. Using smaller bars allows for less material, more

efficient mold use, and faster results.

All miniature bars expanded to failure faster than their full-sized counterparts by

about fifteen days. In all cases, the controlled miniature bars reached failure the fastest.

This is believed to occur because solubility is a factor in the delayed formation of

ettringite, but it is not fully understood. The controlled miniature bars only have 100mL

of limewater, while the uncontrolled and full sized bars have nearly three liters. In

addition, expanding earlier by approximately fifteen days is not a drastic amount in the

grand scale of expansion. Further experimentation should be done with miniature bars

while varying the cross sectional area as well as the curing solution to determine the

root cause of the expedited expansion.

62

Figure 4-1. ASR results and expansion thresholds.

Figure 4-2. All cements when cured following K70.

63

Figure 4-3. All cements when cured following K85.

Figure 4-4. All cements when cured following K95.

Table 4-1. Kelham 95°C, 85°C, 70°C expansion % and ages

Cement 95 Kelham 85 Kelham 70 Kelham

Expansion (%) Age (Days) Expansion (%) Age (Days) Expansion (%) Age (Days)

TI-1 0.02 485 0.01 485 0.003 434

TI-2 0.02 428 0.02 428 0.02 428

TIII-1 0.06 485 0.00 432 0.11 485

TIII-2 0.01 429 0.03 429 0.01 429

TV 0.12 485 0.02 433 0.00 434

64

Figure 4-5. All cements when cured following Fu.

Table 4-2. Fu expansion values

Cement Expansion (%) Age (Days)

TI-1 0.00 338

TI-2 0.05 302

TIII-1 0.16 339

TIII-2 0.05 302

TV 0.70 338

Figure 4-6. All cements when cured following KR95.

65

Figure 4-7. All cements when cured following KR85.

Figure 4-8. All cements when cured following KR70.

66

Figure 4-9. All five cements when cured following F95.

Figure 4-10. All five cements when cured following F85.

67

Figure 4-11. All five cements when cured following F70.

Figure 4-12. Cement TI-2 miniature and full-sized bars cured following F95.

68

Figure 4-13. Cement TIII-2 miniature and full-sized bars cured following F95.

Figure 4-14. Cement TV miniature and full-sized bars cured following F95.

69

CHAPTER 5 RESULTS AND DISCUSSIONS OF SUPPLEMENTARY CEMENTITIOUS MATERIALS

Although the Ferraro method is newly developed, it proved to be the most

reliable to induce early age expansion in materials, especially when heat cured at 95°C.

Therefore, it was deemed most appropriate for fast determination of mitigation by the

addition of supplementary cementitious materials. As the most rigorous test method,

95°C Ferraro method was performed for mix design combinations using SCM to test for

mitigation. All five SCM used for the project were used in various combinations with the

cements to test for minimum contents and variability between materials.

Mitigation

Class F Fly Ash

Class F fly ash was used at cement replacement levels of 10%, 20%, 35%, and

50% for Cement TI-1. Figure 5-1 shows the results of class F fly ash used to mitigate

expansion in Cement TI-1 when heat cured with the Ferraro method at 95°C. At

approximately 360 days, at the time of publication, 10% class F fly ash replacement

showed an expansion of 0.02%. Increasing to 50% class F fly ash, at approximately 370

days, observed expansions were below 0.01%, showing little to no expansion for the

Cement TI-1 specimens. This mitigation of expansion is expected with the use of class

F fly ash due to the lowered sulfate to aluminate ratio and densified microstructure of

the concrete. Having a more dense microstructure will retard the ingress of water to

hydrate the sulfate compounds.

Class C Fly Ash

Class C fly ash was next incorporated in the mix designs. Proportions of 10%,

20%, 35%, and 50% were used in combination with Cement TI-1 and quantities of 10%

70

and 20% were used in mix designs including Cement TV. Cement TI-1 with C ash

replacement of 10% at 360 days, and over 400 days for all other replacements had not

exhibited failure; compared to under 200 days for the Cement TI-1, as shown in Figure

5-2.

When in combination with Cement TV, class C fly ash did not prove to be as

effective in mitigating expansion. As shown in Figure 5-3, Cement TV with 10% class C

fly ash showed signs of expansion and then eventual failure at approximately 100 days.

In addition to a high CaO content, this class C fly ash also contains a high SO3 content

of 1.84%. The excessive expansion caused by Cement TV alone was unable to be

completely stopped, only slowed, by a 10% inclusion of class C fly ash. With an addition

of 20% class C fly ash, specimens at the age of over 210 days exhibited effectively no

expansion.

Metakaolin

Metakaolin was implemented in proportions of 5% and 10% for Cement TI-1 and

Cement TV. Manufacturers recommend a use of 10% to 15% replacement of cement for

optimal performance. This level of replacement improved the mitigation potential as an

inclusion of 5% metakaolin for Cement TI-1 showed a failure at approximately 162 days

and a failure for Cement TV at approximately 80 days, as shown in Figure 5-4 and

Figure 5-5, respectively. While mix designs incorporating 10% metakaolin for both

cements showed no failure at the time of publication, over 400 days with Cement TI-1

and over 240 days with Cement TV.

Silica Fume

Silica fume’s high surface area dictated lower replacement than most SCMs due

to concerns of workability. After over 400 days, 5% silica fume replacement of Cement

71

TI-1 had not exhibited noticeable expansion. This result is included with the plot of

metakaolin mixtures shown in Figure 5-4.

Slag Cement

Slag cement was incorporated into this research project to investigate the

benefits and verify use to mitigate DEF. At proportions of 10%, 20%, 30%, 50%, and

70%, expansion was examined in combination with Cement TI-1. The expansions of

each are shown in Figure 5-6. As shown, 10% slag with Cement TI-1 produces

expansion of 0.089% after 360 days. This mixture is expected to fail in the near future.

With a 70% cement replacement using slag cement, expansion was a mere 0.01%

expansion at over 400 days.

Concluding Remarks

During initial testing, Cement TI-1 had the highest sulfate content and was

expected to contribute to the greatest expansions. After further examination, Cement TV

proved to have the greatest expansions for the bulk of the tests. The most initially

expansive cement was Cement TV, which was marketed as a type V, typically known

for high sulfate resistance. This material showed expansion for the Ferraro method at

95°C and 85°C, the Fu method at 95°C, as well as the Revised Kelham and baseline

Kelham methods at 95°C. Because of this, later in the project, mitigation measures were

included with Cement TV, which have been discussed previously and are shown in

Figure 5-7.

In creating a new method of testing for DEF, it is significant to have long term

results from specimens. Throughout this experimentation, expansion has been shown

to, if not be mitigated, at least delay deleterious expansion with the use of lower

temperatures and the addition of supplementary cementitious materials. In most mortar

72

mix combinations, incorporation of an SCM proved to slow down the expansion process

to show no failure. However, in three cases, 10% class C fly ash as well as 5%

metakaolin in combination with Cement TI-1 or Cement TV, expansion to failure still

occurred. However, the expansion took more than twice as long to occur than in the

control specimens, so the inevitable failure was at least delayed.

73

Figure 5-1. Class F fly ash in combination with Cement TI-1 cured following F95.

Figure 5-2. Class C fly ash in combination with Cement TI-1 cured following F95.

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0 100 200 300 400 500

Exp

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%)

Age (Days)

Cement TI-1

10% Class C Fly Ash

20% Class C Fly Ash

35% Class C Fly Ash

50% Class C Fly Ash

74

Figure 5-3. Class C fly ash in combination with Cement TV cured following F95.

Figure 5-4. Metakaolin and silica fume with Cement TI-1 cured following F95.

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Cement TV

10% Class C FlyAsh20% Class C FlyAsh

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%)

Time (Days)

Cement TI-1

5% Metakaolin

10% Metakaolin

5% Silica Fume

75

Figure 5-5. Metakaolin with Cement TV cured following F95.

Figure 5-6. Slag cement combinations with Cement TI-1 cured following F95.

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Cement TV

5% Metakaolin

10% Metakaolin

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10% Slag-TI-1

20% Slag-TI-1

30% Slag-TI-1

50% Slag-TI-1

70% Slag-TI-1

76

Figure 5-7. Cement TV cured following F95.

77

CHAPTER 6 INVESTIGATION OF ACI 201 GUIDE TO DURABLE CONCRETE

Guide to Durable Concrete

The American Concrete Institute, Committee 201, developed the Guide to

Durable Concrete, which provides a chapter on internal sulfate attack and table

(6.2.2.2), titled “Recommended measures for reducing potential for DEF in concrete

exposed to elevated temperatures at early ages” (ACI 201, 2016). The table, which is

shown in Table 6-1, gives recommendations with respect to the curing temperature and

potential for DEF. Material properties and SCM replacements for concrete exposed to

temperature within the range of 70°C to 85°C are provided to minimize the risk of

expansion. For concrete in which temperatures do not exceed 70°C during the curing

period, no prevention is required; additionally, it is recommended that temperatures

never exceed 85°C. As discussed previously, temperatures in massive concrete

elements rise excessively during the hydration and curing processes.

DEF Prevention Recommendations

The following recommendations were provided by the document in order to

minimize the risk of expansion if temperatures are greater than 70°C up to 85°C:

Portland cement meeting requirements of ASTM C150/C150M moderate or high sulfate-resisting and low-alkali cement with a fineness value less than or equal to 430m2/kg

Portland cement with a 1-day mortar strength (ASTM C109/C109M) less than or equal to 2850 psi (20 MPa)

Any ASTM C150/C150M portland cement in combination with the following proportions of pozzolan or slag cement: a) Greater than or equal to 25 percent fly ash meeting the requirements of ASTM C618 for Class F fly ash

b) Greater than or equal to 35 percent fly ash meeting the requirements of ASTM C618 for Class C fly ash

78

c) Greater than or equal to 35 percent slag cement meeting the requirements of ASTM C989/C989M

d) Greater than or equal to 5 percent silica fume (meeting ASTM C1240) in combination with at least 25 percent slag cement

e) Greater than or equal to 5 percent silica fume (meeting ASTM C1240) in combination with at least 20 percent Class F fly ash

f) Greater than or equal to 10 percent metakaolin meeting ASTM C618

An ASTM C595/C595M or ASTM C1157/C1157M blended hydraulic cement with the same pozzolan or slag cement content as listed in Item 3

Overall, the recommendations for the table state that temperatures less than or equal to

70°C require no prevention and that temperatures should never exceed 85°C.

Cement Requirements

The first of four approaches suggests the use of a moderate or high sulfate-

resisting and low-alkali cement following the requirements of ASTM C150, shown in

Table 6-2. The cements for this research were compared with ASTM C150 to assess

their validity. As shown in Table 6-3, two cements exceeded the limits given in ASTM

C150. Due to the higher sulfate content in Cement TI-1, it was assumed to be the worst

case scenario cement for the research. After further investigation, the two cements that

showed values higher than the standard, as highlighted in Table 6-3 (Cement TI-1 and

Cement TIII-2), proved to be the least expansive of all five cements. Based on the

results obtained in this research, the prevention required per the table is not

conservative as the cements examined throughout this research study exhibited

expansion, and eventual failure, when cured at 70°C and 85°C.

79

Mortar Strength

The second approach calls for the creation of mortar cubes according to ASTM

C109 and requiring a strength of lower than 2850 psi (20 MPa) (ASTM C109, 2016).

Although the text states a limit of 20 MPa, 2850 psi is actually equal to 19.7 MPa, so

this limit will be used throughout. The document bases the threshold strength on

Kelham’s research which found a correlation between 2-day compressive strength of

mortar and expansion to heat curing at 90°C (Kelham, 1996). The age of mortar and

concrete is directly related to the strength and ages of 1 and 2 days are not equivalent.

Compressive strength of mortar cubes tested 1 day will have increase in strength of

approximately 60% by day 2 (Mindess et al., 2003; Ferraro, 2009). Furthermore, the

threshold value, which was derived from Kelham’s research shows failure of 0.1%

expansion at and before 20 MPa, as shown in Figure 6-1. This value of 20 MPa,

recommended by ACI, is not conservative and not resolved in the literature. The

appropriate 1-day compressive strength limit based on Kelham’s research using 2-day

strength of approximately 1800 psi (12.4 MPa).

Experimentation was completed throughout this project in order to test this

suggestion. Mortar cubes were made in accordance with ASTM C109 and tested at one

day for compressive strength. These cubes were made using each of the five cements

and the results are shown in Table 6-4. The most expansive cement from this research

is Cement TV, in which the average strength of the cubes tested was 2890 psi, (19.9

MPa) which is below the given strength threshold of 20MPa. The value of 2890 psi is

value is within 1.4% of the threshold of 2850 psi (19.7 MPa), and well within the

permissible range between specimens in the same batch, which is 8.7%.

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This value of 2850 psi (19.7 MPa) for 1-day strength of mortar cubes is not based

on relatable research and is generally not conservative enough. As shown from the

mortar cubes created for this experiment, mortar bars made with type TV cement,

expanded well beyond the established failure threshold of 0.1% yet were within the

margin of error for the test and under 2% from the threshold value. Further investigation

and testing must be completed to develop an accurate correlation between mortar cube

strength and DEF susceptibility.

Introduction of SCM

The third and fourth recommendations can be combined as an addition of

pozzolans, slag cement, or blended hydraulic cement. The proportions of pozzolans or

slag cement recommended are shown in the Table 6-1. Introducing SCM is a common

and widely accepted technique to mitigate or at least slow the rate of DEF. Mortar bars

were created for this experiment with class F fly ash, class C fly ash, and slag cement in

proportions recommended in the table. Currently, the mortar bars created with these, or

higher, proportions have shown no sign of failure after up to 130 days of curing.

Concluding Remarks

This published table (6.2.2.2) from the ACI 201 Guide to Durable Concrete does

not provide conservative guidance with respect to the mitigation and prevention of DEF

for concrete exposed to temperatures near 85°C. In addition, One limitation of the

guidance provided by ACI 201.2 is the absence of timeframes with respect to peak

temperature. This research has proven that keeping specimens at a high temperature

for longer periods will cause expansion at a faster rate. There are a number of research

gaps with respect to threshold conditions for DEF and the omission of guidance with

81

respect to limits length of time at peak temperature, only that the temperature of the

concrete should never exceed 85°C.

Furthermore, the first suggestion of using a cement that follows ASTM C150 is

not specific enough. All of the cements used on this research project were ASTM C150

approved, but still expanded to failure eventually. All cements reached failure when

cured at 95°C, but Cement TIII-1 also failed when cured at 70°C and 85°C, as well as

Cement TV, which failed at 85°C.

The second suggestion, which includes testing mortar cube strength, does not

give a verifiable strength threshold. The theory behind this is that high early strength

leads to DEF. Type III cement is generally known for high early strength, as shown in

Table 2-3. However, the type V cement proved to expand much faster. Proving that

suggestion one and two from this table require revision.

Finally, the third and fourth suggestions prove to be the most helpful and

accurate of the entire table. The proportions provided have been proven to delay or

mitigate DEF in previous and current research (Ramlochan et al., 2003). This delay or

mitigation is expected because of the characteristics of SCM.

Overall, this list of suggestions supplied by ACI 201 committee are not in depth

enough to provide valid guidance for preventing DEF. Improvements should be made to

add prevention techniques proven to work for temperatures over 85°C in case lowering

the temperature is not a viable option. In addition, more stringent requirements should

be added or modified to the ASTM C150 requirements and threshold strength of 2850

psi (19.7 MPa) for ASTM C109. An overwhelming amount of this table was derived from

one study conducted by Ramlochan et al. and threshold values for the mortar cubes

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were derived from research Kelham completed following a non ASTM standard and for

a curing length twice as long as what is suggested in the recommendation (Ramlochan

et al., 2003; Kelham 1996).

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Table 6-1. ACI 201.2R-16 Guide to Durable Concrete

Maximum concrete temperature Prevention required

T ≤ 158°F (70°C) No prevention required

158°F (70°C) < T ≤ 185°F (85°C) Use one of the following approaches to minimize the risk of expansion:

1. Portland cement meeting requirements of ASTM C150/C150M moderate or high sulfate-resisting and low-alkali cement with a fineness value less than or equal to 430m2/kg

2. Portland cement with a 1-day mortar strength (ASTM C109/C109M) less than or equal to 2850 psi (20 MPa)

3. Any ASTM C150/C150M portland cement in combination with the following proportions of pozzolan or slag cement: a) Greater than or equal to 25 percent fly ash meeting the requirements of ASTM C618 for Class F fly ash b) Greater than or equal to 35 percent fly ash meeting the requirements of ASTM C618 for Class C fly ash c) Greater than or equal to 35 percent slag cement meeting the requirements of ASTM C989/C989M d) Greater than or equal to 5 percent silica fume (meeting ASTM C1240) in combination with at least 25 percent slag cement e) Greater than or equal to 5 percent silica fume (meeting ASTM C1240) in combination with at least 20 percent Class F fly ash f) Greater than or equal to 10 percent metakaolin meeting ASTM C618

4. An ASTM C595/C595M or ASTM C1157/C1157M blended hydraulic cement with the same pozzolan or slag cement content as listed in Item 3

T > 185°F (85°C) The internal concrete temperature should not exceed 185°F (85°C) under any circumstances.

84

Table 6-2. ASTM C150 Standard composition requirements

Cement Type Applicable

Test Method

I and IA

II and IIA

II(MH) and

II(MH)A

III and IIIA

IV V

Aluminum oxide (Al2O3), max, % C114 - 6.0 6.0 - - -

Ferric oxide (Fe2O3), max, % C114 - 6.0 6.0 - 6.5 -

Magnesium oxide (MgO), max, % C114 6.0 6.0 6.0 6.0 6.0 6.0

Sulfur trioxide (SO3),D max, %

When (C3A) is 8% or less C114 3.0 3.0 3.0 3.5 2.3 2.3

When (C3A)E is more than 8 % C114 3.5 4.5 2.5

Loss on ignition, max, % C114 3.0 3.0 3.0 3.0 3.0

Table 6-3. Comparison of cement compositions to ASTM C150

Cement Component Cement

TI-1 TI-2 TIII-1 TIII-2 TV

Al2O3 5.04 4.79 5.05 4.91 4.22

Fe2O3 3.72 3.86 3.54 3.87 4.02

MgO 0.83 1.02 0.81 1.00 2.18

SO3 3.07 2.66 3.29 2.67 2.23

C3A 7.00 6.00 7.00 6.00 4.00

L.O.I. 2.61 2.59 1.78 3.08 1.05

Table 6-4. Results of ASTM C109 for cements

Cement

TI-1 TI-2 TIII-1 TIII-2 TV

Average Strength psi (MPa)

2370 (16.3) 2500 (17.2) 3185 (22.0) 3080 (21.2) 2890 (19.9)

85

Figure 6-1. Expansion after curing at 90°C plotted against 2-day mortar strength (Reproduced from Kelham, 1996).

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Exp

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86

CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS FOR FUTURE WORK

Conclusions

The conclusions drawn from this experiment are based on the relatively short

“exposure” period of < 18 months. The research will continue to draw more conclusions

in the future. The first conclusion drawn from this research is that the length of time

curing at maximum temperature plays an important role in DEF. This was tested with

the development of the Ferraro curing method, with a time at peak temperature of 36

hours, in comparison to the Kelham and Fu methods with only twelve hours at peak

curing temperatures. Next, the miniature bar experiment concluded that the mortar to

curing solution (solid to liquid) ratio is important to the rate of expansion. All miniature

bars expanded to failure faster than their full sized counterparts. Finally, investigation of

the ACI 201 Guide to Durable Concrete section on DEF (Section 6.2.2.3) showed that

the recommendations are not conservative with respect to the use of ordinary portland

cement (in the absence of a pozzolan) in regards to suggestion 1, the use of moderate

or high sulfate resisting cement or suggestion 2, the use of cement with a 1-day mortar

strength of less than 2850 psi (20 MPa).

Recommendations

Recommendations were developed through the experimentation process based

on the findings and conclusions of the research. The first is that the creation of a mortar

bar length change standard curing method that includes a 36-hour time at peak

temperature should be created and put in place to more closely represent the heat

curve of massive concrete pours. Second, further research must be completed on

investigation of the miniature bar solids to curing liquid ratio in order to determine the

87

cause for more rapid expansion. Finally, section 6.2.2.3 of ACI 201 Guide to Durable

Concrete should be revised to remove suggestion 1 and suggestion 2, which are not

conservative enough. Suggestion 1, which states that if a cement qualifies based on

ASTM C150, it is adequate for DEF resistance, requires further specifications. In

addition, suggestion 2, which states that if the 1-day mortar cube strength is at or below

2850 psi (20MPa), it is sufficient for DEF resistance. First, 2850 psi is not equivalent to

exactly 20 MPa. Second, this research showed that values below or on the borderline of

the threshold still expanded to failure. In addition, this value is based on research

completed with 2-day strengths of mortar, which is not adequate for comparison. As

stated before, neither suggestion 1 or 2 are conservative enough and require

adjustment or removal.

88

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BIOGRAPHICAL SKETCH

Danielle Kennedy was born to Dianne and Edwin Kennedy in 1992 in Midland,

Michigan. She graduated from A. Crawford Mosley High School in Panama City, Florida

and attended college at Gulf Coast State College until receiving her Associate of Arts

degree in 2012. Danielle transferred to the University of Florida where she received a

Bachelor of Science degree in Civil Engineering in 2015. Danielle was heavily involved

in the American Society of Civil Engineers and especially the Concrete Canoe team.

She served as the captain of the team when they won a national championship in 2015.

After graduation in 2015, Danielle worked on research projects at UF before starting a

master’s degree and working on her own project in 2016. After graduation, she will

pursue a research engineering position with the Army Corps of Engineers at the Cold

Regions Research and Engineering Laboratory.