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Rheologicalpropertiesofcementpastescontainingamine-andglycol-basedgrindingaids

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Advances in Cement Research, 2015, 27(1), 28–41

http://dx.doi.org/10.1680/adcr.13.00066

Paper 1300066

Received 20/09/2013; revised 23/10/2013; accepted 24/10/2013

Published online ahead of print 25/01/2014

ICE Publishing: All rights reserved

Advances in Cement ResearchVolume 27 Issue 1

Rheological properties of cement pastescontaining amine- and glycol-based grindingaidsAssaad and Issa

Rheological properties of cementpastes containing amine- andglycol-based grinding aidsJoseph J. AssaadProfessor of Civil Engineering, Notre Dame University, Louaize, Lebanon;R&D Manager, Holderchem Building Chemicals, Baabda, Lebanon

Camille A. IssaProfessor of Civil Engineering, Lebanese American University, Byblos,Lebanon

After the clinker grinding process, grinding aids (GAs) remain adsorbed onto cement particles, altering rheological

properties and mechanical performance. The aim of this study was to assess the effect of commercially available

amine-based and glycol-based GAs on variations in rheological properties including static yield stress (�0) and

viscosity (�) of cement pastes over time. Special emphasis is placed on the compliance of ground cement with ASTM

C465 requirements. Compared with control mixtures, the test results showed that the addition of increased GA

concentrations leads to improved flowability immediately after mixing, together with reduced �0 and � values. This is

related to a combination of factors, including the amount of water required to achieve normal consistency and the

creation of repulsive forces between neighbouring cement particles. At longer elapsed times from mixing, however,

the mixtures containing amine-based GA exhibited increased �0 and � values, mostly due to chemical interactions

between these molecules and the cement hydrating compounds. The efficiency of GA molecules to alter the

rheological properties of cement pastes was found to be slightly affected by the increase in temperature that is

normally encountered in real grinding mills.

IntroductionIn the cement industry, it is now accepted that the energy

consumption required during comminution of clinker can be

substantially reduced by adding small quantities of grinding aids

(GAs), generally of the order of 0.01–0.15% of the produced

cement mass (Assaad et al., 2009; Teoreanu and Guslicov, 1999).

Because of their organic polar nature, GAs are preferentially

adsorbed on surfaces formed by the fracture of electrovalent

bonds (Ca–O and Si–O), thus reducing surface energy forces that

cause attraction and agglomeration of the newly ground cement

particles.

The chemical basis of GAs mostly includes ethanolamines (such

as triethanolamine (TEA) and triisopropanolamine (TIPA)) and

glycols (such as monoethylene glycol (MEG), diethylene glycol

(DEG) and propylene glycol (PG)) (Engelsen, 2008). After

grinding, GAs may not preserve their original molecule struc-

tures, given the rise of temperature in the mill coupled with the

high impact and attrition encountered during comminution of

clinker. However, it has been demonstrated that these com-

pounds remain sufficiently active to alter hydration processes

and mechanical properties upon mixing of the cement with

water. For example, Ramachandran (1976) reported that TEA

retards the hydration of C3S and �-C2S and produces some

changes in the morphology and microstructure of the hydration

products. The hydration of C3A was found to be accelerated in

the presence of TEA, due to the accelerated formation of

hexagonal aluminate hydrate and its transformation to a cubic

form. TIPA, on the other hand, was found to remain in the

interstitial paste solution (not adsorbed onto the cement surface,

as is TEA) and form iron complexes to accelerate the hydration

of C3S and C4AF (Perez et al., 2003; Sandberg and Doncaster,

2004). This was reported to yield significant reductions in setting

times and increases in strength development at early and late

ages, regardless of the cement type and chemical composition.

Limited studies have been undertaken to assess the impact of

different types and concentrations of GAs on variations in the

rheological properties of freshly mixed cementitious materials.

Aiad et al. (2003) are among the few researchers to study the

direct effect of GAs on the rheology of Portland cement pastes.

They found that viscosity is highly dependent on the type and

dosage of ethanolamine used, whereby a decrease in viscosity

was noted following the sequence of TEA . poly-TEA . mono-

ethanolamine. This was related to the number of O–H groups in

the ethanolamine molecules that are adsorbed on the surface of

cement grains, causing different repulsive forces and leading to

variations in fluidity levels. It is to be noted, however, that the

tests carried out by Aiad et al. (2003) cannot be considered

conclusive as the ethanolamines were added as post-additions to

the cement (i.e. not during the grinding process) and at concen-

trations varying from 0.1% to 2% of cement weight (i.e.

substantially higher than in real situations). Anna et al. (2008)

reported that the effect of alkanolamines and glycols on clinker

28

grinding does not only result from electrostatic screening, but

also from steric and chemical interactions with the cement

particles. They concluded that the TEA fluidifying mechanism

lies between the steric hindrance associated with polycarboxylate-

based polymers and electrostatic interaction between poly-

naphthalene sulfonated groups with the positive charges of

cement grains. Katsioti et al. (2009) attributed the increase in

workability in the presence of TIPA to the breaking down of

cement agglomerates and balance modification between inter-

particle forces.

The variations in rheological properties of cementitious materials

due to the addition of GAs are not covered by any standard

specification or testing protocol. For example, a series of

chemical and physical tests (i.e. no rheological tests are specified)

is recommended in ASTM C465 (ASTM, 2010) to determine

whether GAs dramatically affect Portland cement properties

prescribed in ASTM C150 (ASTM, 2012a). The most relevant

physical requirement of ASTM C465 includes the water demand

needed to achieve normal consistency for cement containing GA,

which should not increase by more than 1% from that required by

the corresponding control cement. The setting times of cement

ground with GAs should not vary by more than 1 h or 50%,

whichever is the lesser, from those obtained by the control

cement. ASTM C465 (ASTM, 2010) specifies that the mortar

compressive strength should not decrease by more than 5% from

the value resulting from a similar mortar made with the

corresponding control cement.

The work described in this paper is the second part of a

comprehensive research project undertaken to assess the effect of

GAs on the variations in rheological properties (static yield stress

�0 and viscosity �) of cement pastes over various elapsed times

from initial mixing (research submitted for publication). Two

commercially available GAs based on amine and glycol molecules

were tested at various concentrations. This paper also seeks to

quantify the effect of increased temperatures encountered in real

grinding mills on the performance of GA molecules and resulting

variations in cement properties. Special emphasis is placed on the

effect of GAs on ASTM C465 requirements and corresponding

changes in �0 and � values. Relevant properties, including water

demand, setting time and compressive strength, were evaluated.

Research significanceGrinding aids are increasingly used during comminution of

clinker to prevent cement particle attraction and re-agglomeration,

thus resulting in clinker and energy savings that can both lead to

reduced carbon dioxide (CO2) emissions. Nevertheless, the

impact of such additions on flow and rheological properties of

cement pastes is not well understood or considered by any

standard specification or testing protocol. The data presented in

this paper could be of particular interest to Portland cement

manufacturers and concrete technologists as well as standardising

committees dealing with specifications for GAs.

Experimental investigation

Materials

The study employed industrial clinker used for the production of

ASTM C150 type I Portland cement, ground granulated blast-

furnace slag meeting the requirements of ASTM C989 grade 80

and gypsum materials; their chemical compositions are presented

in Table 1. The (C3S + C2S)/(C3A + C4AF) ratio of clinker used

is equal to 3.14, indicating high grindability and requiring a

relatively small amount of energy for a given cement fineness

(Tokyay, 1999). The relative hardness values of the clinker, slag

and gypsum, determined according to the Mohs hardness scale,

were around 5.5, 6.0 and 2.0 respectively.

Two commercially available GAs were tested, amine based and

glycol based. Amine-based GAs are commonly used as both a

GA and strength enhancer in the cement industry. The GA used

Silicon dioxide: % Aluminium oxide: % Iron (III) oxide: % Calcium oxide: % Magnesium oxide: % Sulfur trioxide: %

Clinker 20.6 6.35 4.5 64.1 1.86 0.22

C3S ¼ 54.6%, C2S ¼ 17.4%, C3A ¼ 9.2%, C4AF ¼ 13.7%, LOI ¼ 1.15%, Na2Oeq ¼ 0.39%, free lime ¼ 0.26%,

specific gravity ¼ 3.14

Slag 34.5 12.1 0.75 41.2 9.05 2.4

LOI ¼ 0.21%, moisture content ¼ 0.04%, Na2Oeq ¼ 0.66%, slag activity index with Portland cement at

28 d ¼ 86.4%, specific gravity ¼ 2.94

Gypsum 2.7 0.55 0.4 31.5 1.5 43.2

Free water (T , 458C) ¼ 0.03%, combined water (T , 2308C) ¼ 15.6%, carbon dioxide ¼ 3.7%

Table 1. Chemical compositions of clinker, slag and gypsum

29

Advances in Cement ResearchVolume 27 Issue 1

Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution

in this work had 68% active chemicals when determined by the

Karl Fischer method, and specific gravity and pH values of 1.09

and 7.2 respectively. This GA contained combinations of TIPA

and TEA, having the chemical formulae C3H9NO and C6H15NO3

respectively. The second GA used in this study was glycol based,

containing 72% of DEG (C4H10O3) and MEG (C2H6O2) active

chemicals. It is referred to as a grinding aid and pack-set

inhibitor in the cement industry. Its pH and specific gravity were

7.8 and 1.107 respectively.

Production of cement used for testing

A 50 l laboratory grinding mill connected to an electric counter for

monitoring the specific energy consumption (Ec) was used (Figure

1). Its drum diameter, width and rotational speed were 400 mm,

400 mm and 50 r/min respectively. A total of 80 kg steel balls

(36 kg of 20 mm diameter and 44 kg of 30 mm diameter) were

used for grinding. Prior to grinding, the clinker, gypsum and slag

materials were crushed and sieved so that all particles were smaller

than 10 mm. Prior to use, the gypsum and slag were dried to

constant weight at temperatures of 458C and 1058C respectively.

All tests were conducted using 7 kg of a mix composed of 90%

clinker, 5% gypsum and 5% slag. First, a mix ground without

GAs at 42 kWh/t was tested and considered in this project as

being the reference or control cement; its Blaine fineness was

3460 cm2/g. GAs were then introduced at pre-selected concentra-

tions varying from low to high levels, while the Ec was adjusted

to maintain a Blaine value of 3460 � 100 cm2/g (i.e. similar to

the control cement). As will be discussed later, high levels were

considered as being reached when the water demand, setting time

and/or compressive strength of cement ground with GAs ex-

ceeded the ASTM C465 (ASTM, 2010) limitations.

Immediately after a grinding test in the 50 l laboratory mill, the

temperature of the ground materials generally increased from

ambient to around 35 � 38C, that is, well below the temperature

rise in real grinding mills, which can easily exceed 1108C.

Cement manufacturers pay special attention to limit the tempera-

ture rise to a maximum of 1058C to minimise false set situations

by cooling down the exterior of the mill with water or fresh air,

and sometimes by pulverising water inside the mill (Assaad and

Asseily, 2011). Therefore, to evaluate the effect of increased

temperature on the alteration of rheological properties due to

GAs, five additional cement mixes were ground to the same

Blaine value but heated to a temperature of 105 � 58C prior to

testing. The mixes included a control cement ground without GA,

two mixes containing 0.06% and 0.11% amine-based GA and two

others containing similar concentrations of glycol-based GA. The

procedure for heating the 7 kg samples obtained following

grinding consisted of placing the powder cement mixes in a

preheated oven at a temperature of 105 � 58C for a period of

2.5 h. This duration generally corresponds to that normally

needed for grinding clinker in a real ball mill to a Blaine fineness

of around 3500 cm2/g (Assaad and Asseily, 2011). Regular

temperature checks were conducted to ensure that the powder

cement reached the specified temperature. Prior to testing, all

samples were allowed to cool, for a period of 24 h, to an ambient

temperature of 23 � 28C.

Testing equipment and procedures

Tests on powder cement

Following grinding, chemical tests were performed using the

cement sample ground with or without GAs. The chemical tests,

including magnesium oxide (MgO) and sulfur trioxide (SiO3)

contents, were determined according to the ASTM C114 (ASTM,

2013) test method, and were found to be fairly close to those of

an ASTM C150 (ASTM, 2012a) type I control cement prepared

without GAs.

Cement fineness was determined using the Blaine apparatus as

per ASTM C204 (ASTM, 2011a) and by mechanical sieving on

106, 90 and 38 �m mesh openings. The R90 and R38 values given

in this paper refer to the percentages retained on the 90 �m and

38 �m sieves respectively. Although the Blaine values and sieve

residues reflect the fineness of cement, it is important to note that

these properties are affected by different phenomena. The Blaine

value is mostly affected by the packing density of the cement,

whereas sieve residues are functions of the maximum particleFigure 1. The grinding mill used for testing

30

Advances in Cement ResearchVolume 27 Issue 1

Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution

size (Assaad et al., 2009). The residues on the 106 �m sieve were

in the range 0.2–3.5%, depending mostly on the Ec used (note

that all particles retained on this sieve were not included in the

cement mix used for testing).

The heat of hydration H was determined according to ASTM

C186 (ASTM, 2005) by measuring the difference between the

heat of solution of dry cement and that of hydrated cement in a

mixture of nitric and hydrofluoric acids. The paste was prepared

by mixing 150 g of ground cement with 60 ml of distilled water.

The H values were determined after hydration periods of 3, 7 and

28 d; however, given that similar trends were obtained, only the

7 d results are reported here.

Tests on cement pastes

All pastes were batched with a laboratory mixer using water

cooled to constant temperature of 20 � 38C. Water was first

introduced to the mixer, followed gradually by the ground cement

over 2 min. After a rest period of 30 s, mixing was resumed for a

further 60 s. The ambient temperature and relative humidity

during testing were maintained at 23 � 38C and 55 � 5% respec-

tively. The water demand required to achieve normal consistency

was determined by mixing 650 g of ground cement with a

measured quantity of water, as per ASTM C187 (ASTM, 2011b).

Using the same cement paste produced for normal consistency,

the Vicat initial and final setting times were then determined as

per ASTM C191 (ASTM, 2008) (for clarity, only the final setting

values are reported here).

The effects of GA type and concentration on the flow and

rheological properties were evaluated using cement pastes pre-

pared at water-to-cement ratios (w/c) of 0.48 and 0.42. These w/c

ratios were selected in order to produce pastes with different

consistency levels ranging from highly flowable to relatively

cohesive. Flow was evaluated by determining the average dia-

meter of the paste after spreading on a horizontal surface. An

ASTM C230 mini-slump cone (top diameter, bottom diameter

and height of 70, 100 and 50 mm respectively) was used for

testing. A rotational viscometer connected to a datalogger was

used to evaluate the static yield stress (�0) and viscosity (�) of

the cement pastes. The vane used consisted of four blades

arranged at equal angles around the main shaft; it measured

24 mm in height and 12 mm in diameter (Assaad and Harb,

2012). The vane geometry offers an important advantage in

rheological measurements as it reduces slip and most likely

enables shearing to take place along a cylindrical surface

circumscribed by the vane. The transformation from torque–

rotational speed to shear stress–shear rate was made in accor-

dance with the details provided by Nehdi and Rahman (2004). A

cylindrical bowl, 90 mm in diameter and 100 mm high, was used

for testing.

Right after mixing, the cement paste was poured into the

cylindrical bowl and allowed to rest for 1 min prior to measuring

the �0 value. This property can be defined as the stress above

which the material turns from a solid to a liquid state (Moller et

al., 2009). The testing protocol consisted of subjecting the paste

to a very low rotational speed of 0.3 r/min and recording the

changes in shear stress as a function of time. Typical shear

stress–time profiles determined for various cement pastes are

plotted in Figure 2. The profiles show a linear elastic region until

a yielding moment where the stress exerted on the vane shaft

reached a maximum value, indicating that the majority of the

bond was broken, then followed by stress decay towards a steady-

state region. The maximum stress is taken as the �0 value.

Following determination of �0 values, the vane was stopped and

the specimen stirred to mitigate the formation of preferential

shear planes due to particle orientation. The paste was then

allowed to rest for 1 min for � measurements. The testing

protocol consisted of maintaining the vane impeller at a relatively

high rotational speed of 60 r/min and recording the decay in

viscosity as a function of time (as is typically shown in Figure 3).

The plots obtained are commonly referred to as thixotropic

breakdown curves (Assaad et al., 2003). They are characterised

by a peak initial viscosity, which corresponds to the initial

0

2

4

6

8

10

0 10 20 30 40

Shea

r st

ress

: Pa

Time: s

Control0·13% amine-based GA0·12% glycol-based GA

Figure 2. Typical shear stress–time profiles for determining �0 at

0.3 r/min; w/c ¼ 0.48

0

2

4

6

8

10

12

14

16

0 1 2 3 4 5 6 7 8

Vis

cosi

ty: P

a s

Time: s

Control; w/c 0·42�

0·14% amine-based GA; w/c 0·48�

0·12% glycol-based GA; w/c 0·42�

Figure 3. Typical viscosity–time profiles for determining �equil at

60 r/min

31

Advances in Cement ResearchVolume 27 Issue 1

Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution

structural condition, and thereafter decay with time towards an

equilibrium value (�equil) where a balance between flocculation

and deflocculation is reached. It is to be noted that the peak

initial viscosity and �equil followed similar trends throughout

testing; therefore, only the �equil values are reported and discussed

in this paper.

All flow and rheological measurements were determined immedi-

ately after mixing (i.e. T1 ¼ 0–5 min) and after 30 and 60 min

later, referred to here as T2 ¼ 30–35 min and T3 ¼ 60–65 min.

The cement pastes were covered with wet burlap during the rest

period to prevent water evaporation and were stirred vigorously

using a spatula prior to each test.

Tests on mortars

The compressive strength was determined according to ASTM

C109 (ASTM, 2012b). Tests were performed using mortars

prepared with 450 g of ground cement, 1350 g of normalised

sand (as per EN 196-1) and a w/c ratio of 0.485. The cubes

were demoulded after 24 h and then stored side-by-side in

saturated limewater until the time of testing after 7 d and 28 d.

The mixing procedure was similar to the one described earlier

for cement pastes, except that sand particles were added in this

procedure.

Test results and discussionThe various properties of cements containing amine- or glycol-

based GAs along with �0 and �equil values determined at T1, T2

and T3 are summarised in Tables 2 and 3 respectively. It is to be

noted that several cement mixtures were ground two or three

times in order to evaluate the reproducibility of responses.

Acceptable repeatability was obtained: the coefficients of varia-

tion (CoV, taken as the ratio between standard deviation and

mean values, multiplied by 100) for Blaine fineness, R38, water

demand, setting time and compressive strength were 3.8%,

5.1%, 4.6%, 7.4% and 5.7% respectively. The CoV values for �0

determined at T1, T2 and T3 were 8.8%, 9.1% and 11.3%

respectively, and the values for �equil were 9.2%, 11.3% and

16.1% respectively.

Effect of GAs on Ec values

As expected, the addition of an increased concentration of GAs

led to consecutively reduced Ec values (Tables 2 and 3). For

example, Ec decreased from 42 kWh/t for the control cement to

37.1 kWh/t and 34.2 kWh/t with the addition of 0.09% and

0.14% of amine-based GAs respectively; these values correspond

to decreases in energy consumption of 11.7% and 18.6%. This

phenomenon is normally attributed to the organic polar nature of

the GAs, which partially neutralises electrostatic surface charges

(Engelsen, 2008), thus improving the efficiency of grinding by

reducing agglomeration and attractive forces of the newly ground

particles. It is important to note that the decrease in Ec was

coupled with an increase in R38 and R90 values, given the reduced

amount of energy provided during the grinding process (Assaad

et al., 2009). Hence, R38 increased from 28.3% for the control

cement to 36.7% and 41.6% when amine- and glycol-based GAs

were used at 0.14% and 0.12% respectively.

For given GA concentration, slightly higher decreases in Ec were

achieved with the use of amine-based GA compared with the

glycol-based GA. For example, at a dosage of 0.11%, the targeted

Blaine was achieved at Ec values of 35.7 kWh/t and 36.9 kWh/t

for cement ground with the amine- or glycol-based GA respec-

tively.

Compliance of tested cement to ASTM C465

The water demand required to achieve normal consistency slightly

decreased when the cement mixtures were ground with increased

GA concentrations (see Tables 2 and 3; note that ASTM C465

(ASTM, 2010) does not specify any limitation in the case that a

decrease in water is encountered). For example, the water

required decreased from 27.25% for the control cement to 27.1%

and 26.5% when the glycol-based GA was used at concentrations

of 0.08% and 0.12% respectively. As noted earlier, coarser cement

particles characterised by higher R90 and R38 values resulted when

reducing the amount of energy provided during grinding. For a

given Blaine fineness (or packing density), this reduces the

quantity of water required to lubricate the cement grains and

achieve the targeted consistency (Ahmad and Qureshi, 2004).

As shown in Figure 4, the final setting time increased gradually

with the use of higher GA concentration, until exceeding the

ASTM C465 limitation of 235 + 60 ¼ 295 min (the R38 values

are also shown in Figure 4). It is well established that the setting

of cement is a percolation process in which isolated or weakly

bound particles are connected together by the formation of

hydration products when mixed with water (Bentz, 2008): the

finer the cement, the faster this process is. Therefore, given that

coarser cement particles are produced because of lower Ec, this

can reduce this process and lengthen the dormant period prior to

setting.

The variations in ˜(Compression) determined after 7 d and 28 d

for mortars made with cement ground with amine- or glycol-

based GAs are plotted in Figure 5 (H values are also shown).

˜(Compression) is calculated from

˜(Compression) ¼ f GA � f cont

f cont

� �100

where fGA is the strength determined using cement containing

GAs and fcont is the strength determined using control cement.

The increase in strength for mortars prepared with cement

containing low to relatively moderate amounts of amine-based

GA is mostly attributed to the presence of TIPA, which strength-

ens the C-S-H compounds and densifies the interfacial transition

zone between the cement paste and sand particles (Perez et al.,

2003; Sandberg and Doncaster, 2004). This is corroborated by the

relative increase in H values from 278 J/g for the control cement

32

Advances in Cement ResearchVolume 27 Issue 1

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Offprint provided courtesy of www.icevirtuallibrary.comAuthor copy for personal use, not for distribution

to 318 J/g for 0.11% of amine-based GA (Figure 5). At higher

concentrations, the slight decrease in ˜(Compression) can be

related to the coarser cement particles that reduce strength

development (Ahmad and Qureshi, 2004).

The decrease in strength was much more pronounced in the case

of mortars prepared with cement ground with glycol-based GA.

At a dosage of 0.11%, ˜(Compression) dropped to 7.6% and

8.7% after 7 d and 28 d respectively (i.e. below the ASTM C465

(ASTM, 2010) limit of 5%). From Figures 4 and 5 it can be

concluded that the maximum permissible GA concentration as

per ASTM C465 requirements is slightly higher than 0.13% for

the amine-based GA and around 0.10% for the glycol-based GA.

Flow and rheological variations over time

Responses determined immediately after mixing

(T1 ¼ 0–5 min)

Variations in static yield stress (�0) determined at T1 on 0.48 w/c

pastes prepared using cement ground with different concentra-

tions of amine- or glycol-based GAs are illustrated in Figure 6

(variations in R38 and flow values are also shown). Regardless of

the GA type, �0 appears to decrease when the cement is ground

using increased GA concentrations. For example, a decrease from

9.2 Pa for the control cement to values of 7.2 Pa and 6.8 Pa was

obtained when amine- or glycol-based GA was used at a dosage

of 0.11%. Similar trends are obtained for �equil determined at T1

for 0.42 and 0.48 w/c pastes (Figure 7).

GA dosage: % of mass

0 0.03 0.06 0.09 0.11 0.13 0.14

Ec: kWh/t 42 40.4 38.6 37.1 35.7 34.8 34.2

H at 7 d: J/g 278 272 290 284 318 281 256

Blaine fineness: cm2/g 3460 3430 3505 3375 3405 3390 3340

R90: % 8.6 8.1 8.2 9.3 9.8 9.5 11.6

R38: % 28.3 25.8 22 30.1 28.6 32.8 36.7

Water demand: % 27.25 27.3 27.35 27.1 27.5 27 26.9

Final setting time: min 235 240 235 255 275 290 330

Flow: mm (w/c ¼ 0.48)

T1 195 190 200 195 200 205 210

T2 180 180 190 175 175 170 170

T3 160 165 170 165 155 160 145

�0: Pa (w/c ¼ 0.48)

T1 9.2 10 8.8 7.6 7.2 7.6 7.2

T2 11.1 11.2 10.3 12.4 12.8 14.5 15.3

T3 14.8 14 14.8 14.4 18.9 20 21.6

�equil: Pa s (w/c ¼ 0.48)

T1 2.3 2.2 2.2 2.4 2.1 2.0 1.9

T2 2.5 2.4 2.6 2.5 2.6 2.9 3.1

T3 3.1 3.2 3.0 3.3 3.8 4.1 4.7

Flow: mm (w/c ¼ 0.42)

T1 150 150 160 155 160 165 165

T2 140 145 140 140 135 135 130

T3 125 135 125 125 115 120 110

�0: Pa (w/c ¼ 0.42)

T1 30.4 28.8 29.6 28 28.8 26.4 25.6

T2 33.7 34.3 31.5 38.4 42.3 48.7 56.0

T3 50.5 48.6 56.7 52.2 66.6 71.1 83.7

�equil: Pa s (w/c ¼ 0.42)

T1 4.1 4.1 3.9 3.7 3.8 3.7 3.5

T2 4.4 4.5 4.3 4.6 5.3 5.5 6.8

T3 6.3 5.8 6.4 6.6 8.1 8.6 9.4

7 d compression: MPa 35.6 35.9 38.5 38.4 39 35.8 37.8

28 d compression: MPa 47.2 48.8 50.1 51 52.1 49.6 46.2

Table 2. Properties for cement ground with amine-based GA;

temperature of cement sampled after grinding ¼ 35 � 38C

33

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The decreases in �0 and �equil at T1 compared to the control

cement paste can be attributed to a combination of physical and

chemical phenomena. As explained earlier, coarser particles are

produced when the cement is ground at lower Ec, thus requiring

less water to achieve a given consistency (Tables 2 and 3). Hence,

given that the cement pastes were prepared at a fixed water

content, this can increase flowability (as shown in Figures 6 and

7) and lead to lower �0 and �equil values. Concurrent with this

effect, the decrease in rheological properties can be related to a

chemical effect resulting from the interaction between GA

molecules and cement grains. In fact, the organic GA molecules

arrange their dipoles to saturate the charges of the newly formed

grains, thus creating repulsive forces between neighbouring

cement particles and resulting in improved flowability (Anna et

al., 2008; Katsioti et al., 2009).

For given GA concentration, it is interesting to note that cement

mixtures ground with amine-based GA exhibited lower flowabil-

ity and higher �0 and �equil values than those registered when the

glycol-based GA was used. For example, �0 increased from

18.4 Pa to 28.8 Pa and �equil from 3.3 Pa s to 3.8 Pa s when the

glycol- or amine-based GAs were used respectively, at a dosage

of 0.11% in 0.42 w/c pastes. The corresponding flow values at T1

reduced from 175 mm to 160 mm respectively (Figure 7). Addi-

tional discussion regarding the effect of GA type on flow and

rheology is provided later in the paper.

GA dosage: % of mass

0 0.03 0.06 0.08 0.10 0.11 0.12

Ec: kWh/t 42 40.7 39.2 38.4 37.5 36.9 36.3

H at 7 d: J/g 278 282 269 302 270 254 249

Blaine fineness: cm2/g 3460 3485 3475 3520 3515 3400 3345

R90: % 8.6 7.8 8.4 9 8.9 10.5 14.2

R38: % 28.3 25.2 24 29.1 34.3 35 41.6

Water demand: % 27.25 27.05 27.2 27.1 27.3 26.85 26.5

Final setting time: min 235 255 265 260 300 320 355

Flow: mm (w/c ¼ 0.48)

T1 195 210 210 225 220 230 230

T2 180 185 190 210 205 210 215

T3 160 175 175 180 180 175 190

�0: Pa (w/c ¼ 0.48)

T1 9.2 8.8 8 7.5 7.6 6.8 6.4

T2 11.1 10.4 10 9.1 9.6 7.7 8

T3 14.8 14.3 13.2 12.4 12.8 12.5 11.6

�equil: Pa s (w/c ¼ 0.48)

T1 2.3 2.2 2.1 2.1 1.9 1.7 1.7

T2 2.5 2.4 2.2 2.1 2.1 1.9 2.0

T3 3.1 3.0 2.8 2.6 2.5 2.7 2.3

Flow: mm (w/c ¼ 0.42)

T1 150 145 160 175 170 175 180

T2 140 155 155 150 160 170 165

T3 125 140 140 135 145 145 150

�0: Pa (w/c ¼ 0.42)

T1 30.4 28.8 25.6 21.6 22.4 18.4 17.6

T2 33.7 32 31.2 32.9 29.6 28 29.5

T3 50.5 45.3 47.8 45 42.3 39.2 41.1

�equil: Pa s (w/c ¼ 0.42)

T1 4.1 4 3.6 3.3 3.2 3.3 2.9

T2 4.4 4.2 4.2 4.3 4.0 3.6 3.3

T3 6.3 5.9 5.4 5.6 4.8 4.3 4.6

7 d compression: MPa 35.6 35.1 37 36.7 35.3 32.9 32.5

28 d compression: MPa 47.2 48.7 47 49.5 45 43.1 42

Table 3. Properties of cement ground with glycol-based GA;

temperature of cement sampled after grinding ¼ 35 � 38C

34

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Responses determined at T2 ¼ 30–35 min and

T3 ¼ 60–65 min

Typical variations of �0 determined during the three time intervals

on 0.42 w/c pastes prepared with cement ground with various GA

concentrations are plotted in Figure 8. The effect of incorporating

higher GA concentrations of either amine- or glycol-based GA

led to reduced �0 values during the first time interval (T1). As

earlier discussed, this can be related to a combination of

220

260

300

340

380

0 0·03 0·09 0·11 0·13 0·14 0·03 0·08 0·10 0·11 0·12

Fina

l set

ting

time:

min

41·635·034·329·125·236·732·828·630·125·828·3

Dosage: %

Glycol-based GAAmine-based GAControl

Permissible increase insetting, as per ASTM C465(235 60 295 min)� �

R38: %

Figure 4. Variations in setting time for cement ground with

various concentrations of amine- and glycol-based GAs (R38

values are also shown)

�15

�10

�5

0

5

10

15

0

Δ(C

ompr

essi

on):

% o

f co

ntro

l

After 7 d

After 28 d

H: J/g

Amine-based GA

Permissible 5% decrease incompression, as per ASTM C465

0·120·110·100·080·060·030·140·130·110·090·060·03

249254270302269282256281318284290272278

Control

Dosage: %

Glycol-based GA

Figure 5. Variations in compressive strength for mortars made

using cement ground with various concentrations of amine- and

glycol-based GAs (heat of hydration (H) values are also shown)

35

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Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

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phenomena including coarser grains and interactions between GA

molecules with cement particles. At longer elapsed times (T2 and

T3), however, the tendency changed depending on the type of GA

used. Hence, for example at 0.42 w/c ratio, �0 decreased from

50.5 Pa at T3 for the control cement paste to 47.8 Pa and 39.2 Pa

when the glycol-based GA was used at dosages of 0.06% and

0.11% respectively. The corresponding flow at T3 increased from

125 mm to 140 mm and 145 mm respectively. This suggests that

0·120·110·100·080·060·030·140·130·110·090·060·03Dosage: %

Flow: mm 230230220225210210210205200195200190195

Control Glycol-based GA

6

7

8

9

10

11

0

Stat

ic y

ield

str

ess:

Pa

Amine-based GA

28·3

30·1

25·2

29·1

41·6

36·7

25·8

28·6 34

·3

Figure 6. Variations in �0 at T1 (¼ 0–5 min) for 0.48 w/c cement

pastes containing various concentrations of amine- and glycol-

based GAs; flow values are also shown and the numbers above

the bars are values for R38 (in %)

Dosage: %

180175170175160145165165160155160150150

Glycol-based GAControl

2·5

3·0

3·5

4·0

4·5

1·5

1·7

1·9

2·1

2·3

2·5

0 0·03 0·06 0·09 0·11 0·13 0·14 0·03 0·06 0·08 0·10 0·11 0·12

η equ

il(w

/c0·

42):

Pa s

�

η equ

il. (w

/c0·

48):

Pa s

�

w/c 0·48�

w/c 0·42�

Flow: mm(w/c 0·42)�

Amine-based GA

Figure 7. Variations in �equil at T1 for 0.42 and 0.48 w/c cement

pastes containing various concentrations of amine- and glycol-

based GAs (flow values at 0.42 w/c are also shown)

36

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Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

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the repulsive forces initially created between these later GA

molecules and the cement preserved their performance over

longer elapsed times, resulting in improved flowability and

reduced �0 measurements (Table 3).

Contrary to the effect of the glycol-based GA, the pastes contain-

ing the amine-based GA led to reduced flowability and increased

�0 values at T2 and T3 (Table 2). For example, �0 increased from

50.5 Pa at T3 for the control paste to 56.7 Pa and 83.7 Pa when

the amine-based GA was used at dosages of 0.06% and 0.14%

respectively. In fact, when cement comes into contact with water,

it is the aluminate phases (C3A and C4AF) that react first to form

a gel based on complex sulfoaluminate hydrates (Ramachandran,

1976). This gel exerts a barrier effect and governs the mass flow

between the inner part of the cement grain and pore water, thus

controlling the rheological behaviour and hydration of the silicate

phases. Given that TEA and TIPA have been identified to rapidly

react with the aluminate phases (Perez et al., 2003; Ramachan-

dran, 1976) (especially when present at high percentages in the

tested clinker; see Table 1), this can increase the viscosity of the

interstitial phase including gel structuration and formation of

colloidal crystals between connected cement grains. This there-

fore explains the reduction in flowability and increase in �0

measurements at T2 and T3 for pastes prepared with cement

containing the amine-based GA.

It is to be noted that a fairly good correlation exists between �0

and �equil, given as �equil ¼ 0.093�0 + 1.39, having a correlation

coefficient (R2) of 0.95. Practically speaking, this indicates that

the effect of GAs on �0 and �equil measurements is independent

from the rotational speed, time interval or testing protocol used.

The relationships between flowability and rheological measure-

ments determined at T1, T2 and T3 for all the tested cement pastes

are plotted in Figure 9. As can be seen, the higher the flow, the

lower the �0 and �equil values, with R2 greater than 0.88.

Effect of temperature increase

The �0 and �equil values, along with other cement properties,

determined for mixtures ground with or without GAs after being

heated to a temperature of 105 � 58C for a period of 2.5 h are

summarised in Table 4. It is important to note that the tests were

conducted 24 h after the heating process, during which time the

0·120·110·100·080·060·030·140·130·110·090·060·03Dosage: %

Control

10

20

30

40

50

60

70

80

90

100

0

Stat

ic y

ield

str

ess:

Pa

T1

T2

T3

Amine-based GA Glycol-based GA

Figure 8. Variations in �0 determined at T1 (0–5 min), T2

(30–35 min) and T3 (60–65 min) for 0.42 w/c cement pastes

containing various concentrations of amine- and glycol-based

GAs

y 920·47e� �0·023

2

x

0·89R �

240220200180160140120

y 33·29e� �0·014

2

x

0·92R �

0

10

20

30

40

50

60

70

80

90

100

Rheo

logi

cal p

rope

rty

Flow: mm

Static yield stress at 0·3 r/min: Pa

Equilibrium viscosity at 60 : Pa sr/min

Figure 9. Relationships between flowability with respect to �0 and

�equil determined at T1, T2 and T3 for all tested cement pastes; 84

data points were used for each plot

37

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Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

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cement samples were allowed to cool to ambient temperature.

The cement fineness and setting time were almost unaffected by

the temperature rise (compare Tables 2 and 3 with Table 4).

Slight variations in water demand and compressive strength (not

exceeding 4%) were noted, reflecting the negligible effect of

temperature on these properties.

The variations in �0 for cement mixtures ground with 0.06% and

0.11% amine- and glycol-based GAs before and after heating are

illustrated in Figure 10. Generally speaking, the increase in

temperature appeared to yield minor variations in �0, particularly

for the cement ground with glycol-based GA, which remained

within the CoV of responses obtained from the repeatability tests.

The effect of temperature was slightly more pronounced when the

cement was ground with amine-based GA at high dosage of

0.11%: �0 increased from 32.0% to 39.9% at T3 when the cement

temperature increased from 358C to 1008C. Knowing that the

decomposition temperatures of amine and glycol molecules are

well above 2008C (DCC, 2003), this indicates that the increase in

temperature encountered during the clinker grinding process will

not remarkably alter cement properties containing different types

and concentrations of GAs.

GA dosage: % of mass

Control Amine-based GA Glycol-based GA

0 0.06 0.11 0.06 0.11

Ec: kWh/t 42 38.6 35.7 39.2 36.9

H at 7 d: J/g 281 293 315 271 248

Blaine fineness: cm2/g 3460 3495 3405 3475 3400

R90: % 8.6 8.2 9.8 8.4 10.5

R38: % 28.3 22 28.6 24 35

Water demand: % 27.25 27.55 27.5 27.15 26.7

Final setting time: min 235 240 285 270 320

Flow: mm (w/c ¼ 0.48)

T1 195 200 195 205 225

T2 180 190 170 185 210

T3 165 165 150 170 175

�0: Pa (w/c ¼ 0.48)

T1 9.3 8.9 6.6 8.1 6.4

T2 11 9.8 13.1 10.6 8.3

T3 14.5 17 20.5 12.8 12.4

�equil: Pa s (w/c ¼ 0.48)

T1 2.3 2.2 2.1 2.3 1.7

T2 2.6 2.9 3.1 2.3 2.1

T3 3.3 3.5 4.1 3 2.9

Flow: mm (w/c ¼ 0.42)

T1 150 160 155 165 175

T2 140 145 135 160 165

T3 125 120 115 140 140

�0: Pa (w/c ¼ 0.42)

T1 31.3 31.8 29.6 27 19.6

T2 35.1 36.7 46.8 33 30.1

T3 53.6 60.2 75 53.7 46.8

�equil: Pa s (w/c ¼ 0.42)

T1 4.3 4.4 4.1 3.7 3.4

T2 4.6 5.1 5.9 4.5 3.9

T3 6.7 7 8.8 6 4.7

7 d compression: MPa 35.4 39 39.2 37.4 32.5

28 d compression: MPa 47.7 50.2 51.6 46.8 41.7

Table 4. Properties determined after heating the powder cement

to 105 � 58C

38

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Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

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Rheological variations due to GAs and comparison with

ASTM C465 limitations

The variations in rheology due to GAs were evaluated based on

˜�0 and ˜�equil indices. ˜�0 is determined as

˜�0 ¼�0GA � �0cont

�0cont

� �100

where �0GA is the static yield stress determined using the paste

prepared with cement containing GA and �0cont is that determined

using the control cement paste; ˜�equil is calculated similarly.

Two thresholds of �50% and �25% based on the range of data

obtained from this experimental programme were proposed for

these indices. The former value of �50% reflects a wide relative

tolerance in variations of rheology due to the addition of GAs.

Conversely, �25% can be considered as a rigorous requirement

so as to minimise changes in fresh cementitious properties

resulting from eventual variations in rheology.

The relationship between ˜�0 and ˜�equil for all tested cement

pastes determined at various elapsed times is given in Figure 11,

along with the �25% and �50% threshold regions (note that the

data points rejected by ASTM C465 based on Figures 4 and 5 are

also plotted). As can be seen, all data points fulfilling ASTM

C465 requirements are shown to fall within the �50% threshold

region. Nevertheless, when the threshold is reduced to �25%, a

significant number (around 26%) of data points fulfilling ASTM

C465 requirements fall outside the region. This indicates that the

�25% allowable variations in rheology become prevalent over

the physical ASTM C465 requirements for water demand, setting

time and/or compressive strength. In other words, the maximum

permissible GA concentrations determined as per ASTM C465

should be revised to reflect acceptable variations in rheology. In

the case of the GAs tested in this study, the maximum amine-

based GA dosage should thus be reduced from 0.13% to less than

about 0.11%, whereas the maximum dosage for the glycol-based

GA should be decreased from around 0.10% to 0.08%.

ConclusionThis work reported here is part of a comprehensive research

project undertaken to assess the impact of GAs on the rheological

and mechanical properties of Portland cement. Based on the

above results, the following conclusions can be warranted.

j For a given cement Blaine fineness of 3460 cm2/g, setting

times are increased with the use of increased GA

concentration until exceeding ASTM C465 limitations. An

increase in compressive strength was noted when amine-

based GA was added, mostly due to the presence of TIPA.

The maximum permissible amine-based and glycol-based GA

concentrations as per ASTM C465 requirements are slightly

higher than 0.13% and around 0.10% respectively.

j Regardless of the type of GA, noticeable improvements in

flowability and reductions in �0 and �equil were observed

immediately after the end of mixing. This was related to the

coarser cement particles that require less water for proper

lubrication associated with a dispersion mechanism of cement

agglomerates due to the GA molecules.

j The dispersion mechanism associated with glycol-based GA

molecules persisted at longer elapsed times from mixing, and

resulted in improved flowability and reduced �0 and �equil

measurements. Contrarily, a reduction in flowability and

increases in �0 and �equil were noted over time with the use of

T 35°C�T 35°C� T 100°C�T 35°C� T 100°C��20

�10

0

10

20

30

40

50Va

riatio

n in

sta

tic y

ield

str

ess:

%

T1

T2

T3

0·06%amine-based

0·11%amine-based

0·06%glycol-based

T 100°C�

Figure 10. Effect of temperature rise on variations in �0 for 0.42

w/c cement pastes determined during T1, T2 and T3

39

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Rheological properties of cement pastescontaining amine- and glycol-basedgrinding aidsAssaad and Issa

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the amine-based GA. This was related to the presence of

TEA and TIPA, which react with C3A and C4AF, causing an

increase in viscosity of the interstitial phase and gel

structuration between connected cement grains.

j The temperature rise in real grinding mills does not lead to

significant variations in cement properties (including

flowability, �0 and �equil), given that the decomposition

temperatures of amine and glycol molecules are well above

1058C.

j The developed ˜�0 and ˜�equil indices were found to be

suitable to assess variations in the rheology of cement pastes

due to the addition of GAs. When the threshold is set at

�25%, the maximum permissible GA concentrations that

were originally based on ASTM C465 limitations should be

reviewed to reflect acceptable variations in rheological

properties.

AcknowledgementsThis project is funded by the University Research Council of the

Lebanese American University, Byblos, Lebanon. The authors

also wish to acknowledge experimental support provided by the

laboratory personnel of Holderchem Building Chemicals, Baabda,

Lebanon.

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�75

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Advances in Cement ResearchVolume 27 Issue 1

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