relationship between compressive split tensile of self compacting concrete

International Journal of Mechanics and Solids ISSN 0973-1881 Volume 3 Number 2 (2008) pp. 157–168 © Research India Publications http://www.ripublication.com/ijms.htm

Relationship between Compressive, Split Tensile, Flexural Strength of Self Compacted Concrete

T. Seshadri Sekhar1 and P. Srinivasa Rao2

1Research Scholar, J.N.T. University, Hyderabad. E-Mail: [email protected]

2Professor and Head, J.N.T.U. College of Engineering, Anathapur, A.P. E-Mail: [email protected]

Abstract

Concrete is a mostly used construction material in the world. As the use of Concrete becomes more widespread the specifications of Concrete like Durability, Quality, Compactness and Optimization of Concrete becomes more important. Self Compacting Concrete (SCC) is a very fluid Concrete and a homogeneous mixture that solves most of the problems related to ordinary Concrete. Besides, SCC gets compacted under its own weight and there is no need for an internal vibrator for the body of the mould. This specification helps the execution of construction components under high compression of reinforcement.

The elimination of vibration for compacting concrete during placing through the use of Self Compacting Concrete leads to substantial advantages related to better homogeneity, enhancement of working environment and improvement in the productivity by increasing the speed of construction The resulting concrete is characterized in the fresh state by methods used for Self Compacted Concrete, such as slump-flow, V-funnel and L- box tests respectively.

This paper concentrates mainly on studying the properties like Compressive Strength, Split Tensile Strength and Flexural Strength of SCC mix proportions ranging from M30 to M65 Grades of Concrete. An attempt also has been made to obtain a relationship between the splitting tensile strength, Flexural Strength and Compressive strength by the test results. Keywords: Self Compacting Concrete, Segregation Resistance, Filling ability, Passing Ability, Water-Powder Ratio.

158 T. Seshadri Sekhar and P. Srinivasa Rao

Introduction Self compacting concrete is a concrete which can be placed and compacted under its own weight with little or no vibration effort, while being cohesive enough to be handled without segregation or bleeding at the same time. It is used to facilitate and ensure proper filling and good structural performance in restricted areas and heavily reinforced structural members. SCC was developed in Japan in the late 1980s to be mainly used for highly congested reinforced structures in seismic regions. Recently, this concept has gained a wider use in many countries for different applications and structural configurations due to the fact that it can provide a better working environment by eliminating the vibration noise. The several advantages reported in using SCC are reduced the construction time and labor cost, eliminating the need for vibration, reduced noise pollution, improved compactability even in highly congested structural members, and finally a better construction ensuring good structural performance. Definition Self Compacting Concrete is defined as a category of high performance concrete that has excellent deformability in the fresh state and high resistance to segregation, and can be placed and compacted under its self weight without applying vibration Properties of Self Compacted Concrete in Fresh State Filling ability: The property of Self Compacted Concrete to fill all corners of a formwork under its own weight is known as filling ability. Passing ability: The property of Self Compacted Concrete to flow through reinforcing bars without segregation or blocking. Resistance to segregation: The property of Self Compacted Concrete to flow without segregation of the aggregates. Performance of SCC SCC is the modified concrete with the use of chemical and mineral admixtures in the concrete. It is designed generally with high content of powder/fine material. To facilitate flow and penetration through congested reinforcement zones, it is desirable to avoid 20 mm aggregate. If more coarse aggregate is used, flow rate will be diminished due to frictional loss and stresses. The lower the maximum size of aggregate, higher would be the permissible input of coarse aggregate, but within the range specified. In European Method it was recommended that: The Water-Binder ratio by volume be 0.8 to 1.10. Total binder content, including powders if any, should be between 400-600 Kg/m3 Water to Cement ratio to be selected based on Strength and Durability requirements. (Water content generally does not exceed 200 lt/m3) Max Cement Content should be 350-450 Kg/m3 Cement having C3A content more than 10% should not be used in SCC because of its role in early setting. It may cause problems of poor workability retention.

Relationship between Compressive, Split Tensile, Flexural Strength 159

There appears to be no codal specifications for SCC in any country except the guidelines by EFNARC European Federation for Specialist Construction Chemicals and Concrete Systems, formulated in Europe. However the Technology developers have evolved certain study methodologies based on application needs. Literature Review Okamura (1) proposed a mix design method for SCC based on paste and mortar studies for superplasticizer compatibility followed by trail mixes. However, it is emphasized that the need to test the final product for passing ability, filling ability, and flow and segregation resistance is more relevant Vengala(2) found that use of fine fly ash for obtaining Self Compacting Concrete resulted in an increase of the 28 day Compressive Strength Concrete by about 38%. Self Compacting Concrete was achieved when volume of paste was between 0.43 and 0.45. Subramanian and Chattopadhyay (3)described the results of trails carried out to arrive at an approximate mix proportioning of Self Compacting Concrete. Self Compatibility was achieved for Water to Powder ratio ranging from 0.9 to 1.1 when Coarse Aggregate and Sand content were restricted to 46 % and 40% of the mortar volume respectively. Dr.Srinivasa Rao. P(4) had proposed the relation ship between Splitting Tensile Strength and Compressive Strength by the test results and found that Split Tensile Strength is proportional to 0.78 power of Compressive Strength for normal concrete. Dr.Malathy(5)had developed the mix design for different grades of concretes and studied the flow properties and strength properties for Self compacting Concrete. Research Significance In fact, concrete researchers have shown that the true tensile strength, as determined from the split cylinder test, is between 65 and 75 per cent of the modulus of rupture for normal concrete. It has been well established that the splitting tensile test of the cylindrical specimen gives more reasonable tensile strength estimation than the direct tensile test or the modules of rupture test. The acceptance of the split cylinder test is based on the fact that the stress distribution is reasonably uniform along the vertical diameter of the cylinder, which has been shown to be the plane of principle tensile stress for about 80 per cent of its length. In a number of recent investigations of the behaviour of actual concrete dams during earthquakes, it has become apparent that a limiting factor has been that the tensile strength of any concrete is only a fraction of its compressive strength. However, ACI building code provisions are primarily based on tests of relatively mature concrete elements, and provisions may not provide consistent safety margins when applied to young concrete. In ACI, such strengths as modulus of rupture, shear, and splitting tensile strength of concrete are expressed in terms of the square root of the compressive strength. These empirical relationships were derived from tests on relatively mature concrete specimens, and the square root function was probably chosen as a matter of convenience so that calculations could be readily performed with a slide rule. However, recent research has shown that a square root relationship between splitting tensile strength and


compressive strength is not the most appropriate relationship for maturing concrete. It is evident that most concrete researchers believe, from analyses of test data that the true test data is representative of power relation, which lies between 0.6 and 0.8. as given below The Relationships between f t and f 1c Suggested by the Various Investigators for ordinary Concrete

S No.

Investigation Suggested ft – f1c

relationship ft, f1

c in N/mm2

Year of publication

Strength valid upto MPa

Remarks

1 Akazawa ft = 0.209 (f1c)

0.73 1953 ------ ------ 2 Carneiro and Barcellor

ft = 0.185 (f1c)

0.735 1953 ------ ------

3 Vinayaka ft = 0.88 (f1

c)0.716

1959 ------ ------

4 Sen and Desayi ft = 0.628 (f1

c)0.73

1962 ------ Converted using their equation fc cylinder = 0.848 fc cube

5 Carino and lew ft = 0.272 (f1

c)0.71

1982 ------ ------

6 Raphael ft = 0.313 (f1

c)0.667

1984 ------ ------

7 ACI Building code 318-89

ft = 0.556 (f1

c)0.5

1989 Strength between 13.79 to 61.38

For conversion fc cylinder = 0.81 fc cube was used

8 N.. Gardner ft = 0.313 (f1

c)0.667

1990 57.23 ------

9 Oluokun ft = 0.206 (f1

c)0.79

1991 62.07 For conversion fc cylinder = 0.8 fc cube was used

f1

c = cylinder compressive strength For a newly development material like Self Compacting Concrete studies on Compressive, Split Tensile and Flexural strength are of paramount important for instilling confidence amongst the engineers and builders. The literature indicates that while some studies are available on the Compressive Strength, Split Tensile Strength and Flexural Strength of Self Compacting Concrete , a comprehension study which involve relationship between the parameters Compressive Strength, Split Tensile Strength, Flexural Strength are not available Self Compacting Concrete. Hence, considering the gap in the existing literature, an attempt also has been made to obtain a relationship between the splitting tensile strength, Flexural Strength and Compressive strength by the test results. Experimental Programme The objectives of the experimental study that was conducted are given below. To study the Compressive, Flexural Strength and Split Tensile Strength behavior at 28,90 and 180 days for M30 to M65 Grades of Concrete. To develop Mathematical Relationship between Compressive Strength, Split Tensile Strength and Flexural Strength.


Materials Cement Ordinary Portland cement of 53 grades available in local market is used in the investigation. The Cement used has been tested for various proportions as per IS 4031-1988 and found to be confirming to various specifications of are 12269-1987.The specific gravity was 2.96 and fineness was 2800cm2/gm. Coarse Aggregate Crushed angular granite metal of 10 mm size from a local source was used as coarse aggregate. The specific gravity of 2.60 and fineness modulus 6.05 was used. Fine Aggregate River sand was used as fine aggregate. The specific gravity of 2.61 and fineness modulus 2.77 was used in the investigation. The test results are shown in Table No 1.0.

Table 1.0: Properties of Fine and Coarse Aggregates

S.No Property Fine Aggregate Coarse Aggregate 1. Specific Gravity 2.61 2.60 2. Loose Bulk Density 1.55 1.49 3. Rodded Bulk Density 1.65 1.57

Viscosity Modifying Agent A Viscosity modified admixture for Rheodynamic Concrete which is colourless free flowing liquid and having Specific of gravity 1.01+0.01 @ 250C and pH value as 8+1 and Chloride Content nil was used as Viscosity Modifying Agent. Admixture The Modified Polycarboxylated Ether based Super Plasticizer which is Brown Color and free flowing liquid and having Relative density 1.08+0.01 and pH value as 7+ 1 and Chloride Content nil was used was Super Plasticizer Fly Ash Type-II fly ash from Vijayawada Thermal Power Station was used as cement replacement material. The chemical properties of the fly ash are shown in Table No2.0 & 3.0

Table 2.0: Physical Characteristics of VTPS fly ash

S.No Characteristics Experimental Results 1. 2. 3. 4. 5.

Fineness in m2/kg (Blain’s permeability) Lime reactivity Compressive strength @ 21 days Drying shrinkage % Autoclave expansion %

577 4.0 > 80% of the corresponding plain cement mortar cubes 0.08 0.68


Table 3: Chemical Composition of VTPS Fly Ash

S.No Characteristics Percentage 1. 2. 3. 4. 5. 6.

SiO2 +Al2o3+Fe2O3 SiO2 MgO Total sulfur as SO3 Available alkali as sodium oxide(Na2O) Loss of ignition

86.7 54.0 0.10 0.11 2.16 4.0

Test Specimens Test specimens consist of 150X150X150 mm cubes, 150 X 300 mm cylinders and 100X100X 500 mm beams were casted using different concrete mixes as given in Table No 4.0 and tested as per IS 516 and 1199.

Table 4: Mix Proportions for Various Grades of Self Compacted Concretes

Grade of Concrete

Cement (Kg/m3)

Fly ash (Kg/m3)

Coarse Aggregate

(kg/m3)

Fine aggregate (Kg/m3)

Water (Kg/m3)

W/ P SP (kg/m3)

V.M.A (Kg/m3)

M 30 225 225 865 898 179 0.40 4.50 0.315 M 35 231 231 862 864 175 0.37 4.62 0.370 M40 258 258 835 836 176 0.34 5.16 0.413 M 45 330 220 826 827 176 0.32 5.50 0.440 M 50 360 240 797 796 180 0.30 6.00 0.480 M55 360 240 812 813 168 0.28 6.00 0.480 M 60 400 250 785 785 172 0.26 9.75 0.460 M 65 450 250 760 760 174 0.24 11.20 0.490

Discussion of Test Results Water Powder Ratio: The Water to Powder by weight was kept at about 0.26 for M60 grade of Concrete. For M65 Grade of Concrete Water to Powder ratio by weight was kept about 0.24 in the Mix. These values are given in Table No. 4.0. Workability Table No 5.0 provides a summary of the workability properties of the Self Compacted Concrete mixes in the fresh state. As it is evident, the basic requirements of high flowability and segregation resistance as specified by guidelines on Self Compacted Concrete by EFNARC are satisfied. The workability values are maintained by adding suitable quantities of superplasticizers.


Table 5.0: Rheological Studies of Self Compacted Concrete for Various grades of Concrete

Permissible limits as per Efnarc Guidelines

( Ref 6.0)

M 30 M 35 M 40 M 45 M 50 M 55 M 60 M 65

Min Max V-Funnel 10 sec 8 sec 5 sec 8 sec 10 sec 8 sec 5 sec 8 sec 6 sec 12 sec Abrams slump flow

650mm 660mm 700mm 680mm 660mm 680mm 720mm 700mm 650mm 800mm

T 50cm slump flow 5 sec 3 sec 2 sec 2 sec 4 sec 2 sec 3sec 2 sec 2 sec 5 sec H2/H1=0.8 0.82 0.90 0.80 0.8 0.85 0.88 0.84 0 .82 1.0 T 20= 1sec 2 sec 1 sec 1 sec 1sec 1 sec 2 sec 2 sec 1sec 2 sec

L-Box

T40= 2 sec 3 sec 2 sec 2sec 2 sec 3 sec 2 sec 2sec 2sec 3sec

V-Funnel at T 5

min 12 sec 11 sec 11 sec 11 sec 12 sec 13sec 12 sec 14 sec 11 sec 15 sec

Compressive Strength The Compressive Strength Values are observed to be varied from 33.94 to 66.29 N/mm2 for 28 days, 40.38 to 77.55 N/mm2 for 90 days and 43.44 to 82.19 N/mm2 for 180 days. These Values are tabulated in Table No 6.0. The increase in Compressive Strength Values compared with 28 days Strength is given in Table 7.0 and variation is given in fig 1.0. The Test set up is given in Plate no 1.0

0

20

40

60

80

100

28 90 180

Age in Days

Com

pres

sive

Str

engt

h (M

pa)

M 30

M35

M40

M45

M50

M55

M60

M65

Figure 1: Variation of Compressive Strength with age.

Plate No 1.0: Test set up for measuring Compressive Strength


The increase in Compressive strength for all the Grades of Concretes at 90, 180 days are observed to be 20 to 30% when compared with 28 days Strength. These results can be explained by the delayed pozzolanic activity of supplementary powder. Initially, cement hydration and the resulting calcium silicate hydrate is the principal source of strength in concrete. But as time progresses, the influence of supplementary powder (Fly Ash) becomes noticeable. Largely pozzolanic in composition, supplementary cementitious materials convert weak calcium hydroxide released by cement hydration into calcium silicate hydrate. Table 6: Compressive Strength, Flexural Strength, Split Tensile Strength of Various Grades of Self Compacted Concretes at different ages.

Grade of Concrete

No of Days

Compressive Strength

Flexural Strength Split Tensile Strength

28 33.94 3.15 3.01 90 40.38 3.65 3.52

M 30

180 43.44 3.90 3.68 28 38.90 3.49 3.25 90 45.90 4.11 3.86

M35

180 49.24 4.36 4.12 28 41.21 3.88 3.68 90 49.03 4.61 4.39

M 40

180 51.27 4.65 4.50 28 45.95 4.22 4.08 90 54.22 5.02 4.81

M45

180 57.88 5.14 5.12 28 53.00 4.59 4.44 90 61.48 5.37 5.18

M50

180 63.93 5.58 5.44 28 56.00 5.01 4.67 90 65.70 5.87 5.48

M55

180 68.73 6.13 5.72 28 61.64 5.46 5.21 90 71.50 6.38 6.04

M60

180 73.97 6.66 6.18 28 66.29 5.95 6.44 90 77.55 6.96 7.54

M65

180 82.19 7.40 7.62


Table 7: Percentage increase Compressive Strength, Flexural Strength, Split Tensile Strength of Various Grades Of Self Compacted Concrete Compared with age (28 Days)

Grade of Concrete

No of Days Compressive Strength

Flexural Strength Split Tensile Strength

28 ---- ---- ---- 90 19 16 17

M 30

180 28 23 23 28 ---- ---- ---- 90 19 18 19

M35

180 28 25 27 28 ---- ---- ---- 90 19 19 19

M 40

180 25 20 22 28 ---- ---- ---- 90 18 19 18

M45

180 26 22 26 28 ---- ---- ---- 90 16 17 17

M50

180 21 22 23 28 ---- ---- ---- 90 17 17 17

M55

180 22 23 23 28 ---- ---- ---- 90 16 17 16

M60

180 20 22 19 28 ---- ---- ---- 90 17 17 17

M65

180 24 24 18 Split Tensile Strength The Split Tensile Strength Values are observed to be varied from 3.01 to 6.44 N/mm2 for 28 days, 3.52 to 7.54 N/mm2 for 90 days and 3.68 to 7.62 N/mm2 for 180 days. These Values are tabulated in Table No 6.0. The increase in Split Tensile Strength Values compared with 28 days Strength is given in Table 7.0 and variation is given in fig 2.0. The Test set up is given in Plate no 2.0.

0

2

4

6

8

10

28 90 180

Age in Days

Split

Ten

sile

Str

engt

h (M

pa)

M30

M35

M40

M45

M50

M55

M60

M65 Figure 2: Variation of Split Tensile Strength with Age


Plate No 2.0: Test set up for measuring Split Tensile Strength The Split Tensile Strength for all the Grades of Concretes at 90, 180 days are observed to be varied from 15% to 25% when compared with 28 days Split Tensile Strength Strength. Flexural Strength The Flexural Strength Values are observed to be Varied from 3.15 to 5.95 N/mm2 for 28 days, 3.65 to 6.96 N/mm2 for 90 days and 3.90 to 7.40 N/mm2 for 180 days. These Values are tabulated in Table No 6.0. The increase in Flexural Strength Values compared with 28 days Strength is given in Table 7.0 and variation is given in figure 3.0 The Test set up is given in Plate no 3.0.

0

2

4

6

8

28 90 180

Age in Days

M30

M35

M40

M45

M50

M55

M60

M65 Figure 3: Variation of Flexural Strength with Age.

Plate No 3.0: Test set up for measuring Flexural Strength


The Flexural Strength for all the Grades of Concretes at 90, 180 days are observed to be varied from 15% to 25% when compared with 28 days Flexural Strength. Mathematical Relationship between Compressive, Split Tensile and Flexural Strength: Mathematical equations were obtained expressing Compressive Strength, Split Tensile Strength and Flexural Strength for Self Compacted Concrete. fig 4.0 shows the graphical behaviour of Compressive Strength and Split Tensile Strength , fig 5.0 shows the graphical behaviour of Compressive Strength and Flexural strength . The mathematical relationship between both between Compressive Strength – Split Tensile Strength and Compressive Strength – Flexural Strength of Self Compacted Concrete depicts that they are obeying Power Law.

y = 0.0753x1.0382

R2 = 0.9574

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70

Compressive Strength (Mpa)

Split

Ten

sile

Stre

ngth

(M

pa)

Figure 4: Relationship between Compressive Strength and Split Tensile Strength

y = 0.119x0.929

R2 = 0.9908

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70

Compressive Strength (MPa)

Flex

ural

Str

engt

h (M

Pa)

Figure 5: Relationship between Compressive Strength and Flexural Strength at 28 days. The Relation between Compressive Strength – Split Tensile Strength is given by ft 28 = 0.08 fck

1.04 The Relation between Compressive Strength – Flexural Strength is given by fcr28 = 0.12 fck 0.9


Conclusions 1. The Relation between Compressive Strength – Split Tensile Strength is given by

ft 28 = 0.08 fck 1.04

2. The Relation between Compressive Strength – Flexural Strength is given by fcr28 = 0.12 fck .09

3. The increase in Compressive Strength for all the grades of SCC mixes compared with 28 days strength varied between 20 to 30% .

4. The increase in Flexural Strength for all the grades of SCC mixes compared with 28 days Flexural strength varied between 15 to 25%.

5. The increase in Split Tensile Strength for all the grades of SCC mixes compared with 28 days Split Tensile strength varied between 15 to 25%.

6. The Relationship between Compressive, Split Tensile and Flexural Strength designed SCC mixes are In accordance with power’s law.

References [1] Okumura.H, Ozawa. K. Ouchi. M. (2000), “Self Compacting Concrete”,

Structural concrete, No.1. [2] Jagadish Vengala Sudarsan, M.S., and Ranganath, R.V.(2003), “Experimental

study for obtaining self-compacting concrete”, Indian Concrete Journal, August, pp. 1261-1266.

[3] Subramanian .S and Chattopadhyay (2002),”Experiments for Mix Proportioning of Self Compacting Concrete”, Indian Concrete Journal, January, Vol., PP 13-20.

[4] Dr.P.Srinivasa Rao and P. Sravana (2005)” Relationship between Splittting Tensile and Compressive Strength of Concrete” , Construction Review Journal June, 39-44.

[5] Dr.R.Malathy and T.Govindsamy (2006) “ Development of Mix Design Chart for various Grades of Self Compacting Concrete”, Indian Concrete Institute Journal Oct-Dec ,pp 19-28.

[6] EFNARK, “Specifications and guidelines for self compacting concrete”, www.efnarc.org

relationship between compressive split tensile of self compacting concrete

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