CHAPTER 5 FRESH AND HARDENED PROPERTIES OF CONCRETE WITH MANUFACTURED SAND

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1 61 CHAPTER 5 FRESH AND HARDENED PROPERTIES OF CONCRETE WITH MANUFACTURED SAND 5.1 GENERAL The material properties, mix design of M 20, M 30 and M 40 grades of concrete were discussed in the previous chapter. In this chapter, the fresh concrete property such as workability and the hardened properties such as compressive strength, splitting tensile strength, modulus of rupture, modulus of elasticity and Poisson s ratio of concrete are studied. 5.2 TEST DETAILS Workability Workability is one of the important parameters of measuring the consistency of the fresh concrete. Slump test is the most commonly used method of measuring the consistency of the concrete. In this research work, the workability of the M 20, M 30 and M 40 grades of concrete with different proportions of manufactured sand varying from 0 to 100% as the increments of 10% in the order of A to K are measured by the slump cone apparatus as per IS: Compressive Strength In most structural applications, concrete is employed primarily to resist the compressive stresses. Therefore, concrete making properties of various ingredients of mix are usually measured in terms of the compressive

2 62 strength. Compressive strength is also used as a qualitative measure for other properties of hardened concrete. The compressive strength of concrete cube was determined based on IS: Three cubes of size 150mm x 150mm x 150mm were tested for each trial mix combination at the age of 7, 28, 56, 90 and 365 days of curing using a compression testing machine Splitting Tensile Strength This is an indirect test to determine the tensile strength of the cylindrical specimens of size 150mm diameter and 300mm height. Splitting tensile strength was determined in accordance with IS: The test was carried out by placing a cylindrical specimen horizontally between the loading surface of a compression testing machine and the load was applied until the failure of the cylinder, along the vertical diameter. In order to reduce the magnitude of the high compressive strength near the point of loading, narrow packing of plywood was placed between the specimen and the loading plates of the machine Flexural Strength Flexural strength of the concrete was measured by the prism specimens of size 100mm x 100mm x 500mm and tested as per IS: The bed of the testing machine was provided with two steel rollers of 38mm in diameter on which the specimen was supported, and these rollers were mounted at the distance of 40mm from center to center. The system of loading was symmetrical two point loading Modulus of Elasticity and Poisson s Ratio Concrete is not a perfectly elastic material. The modulus of elasticity was determined as per IS: , subjecting the cylinder to uni - axial compression and measuring the deformations by means of dial gauges

3 63 fixed between the certain gauge length which is shown in Figure 5.1. The stress strain curve was established from the readings. The modulus of elasticity was calculated from the stress strain curve. Poisson s ratio is calculated from the cylinder subjected to uni - axial compression and measuring the change in dimensions in longitudinal and lateral directions by means of dial gauges fixed on both the directions. Poisson s ratio was calculated as the ratio between the lateral and longitudinal strain. Figure 5.1 Modulus of elasticity test set up 5.3 DISCUSSION OF TEST RESULTS Workability Figure 5.2 shows the slump values of M 20, M 30 and M 40 grades of concrete with various replacement levels of manufactured sand from 0 to 100%.

4 64 Figure 5.2 Slump values of M 20, M 30 and M 40 grade concrete with MS From the Figure 5.2, it is observed that the slump values are reduced while increasing the replacement levels of manufactured sand for all the three grades of concrete. The shape and surface texture of the manufactured sand have a significant effect on the water requirement of the mix. The round shape and smooth surface texture of natural sand reduces the inter particle friction in the fine aggregate component, so that the workability is high in natural sand. Manufactured sand is angular in shape and the rough surface texture improves the internal friction in the mix, which reduces the workability of the concrete. The results indicate very low slump values in 80 %, 90 % and 100 % of manufactured sand due to the presence of a large amount of fines in it Compressive Strength Figures 5.3(a), (b) and (c) show the compressive strength of M 20, M 30 and M 40 grades of concrete. The rate of increase in strength of M 20, M 30 and M 40 grades of concrete are given in Figures 5.4 (a), (b) and (c).

5 65 Figure 5.5 shows the comparison between the compressive strength of M 20, M 30 and M 40 grades of concrete with MS. (a) M 20 grade concrete (b) M 30 grade concrete (c) M 40 grade concrete Figure 5.3 Compressive strength of M 20, M 30 and M 40 grade concrete with MS

6 66 (a) M 20 grade concrete (b) M 30 grade concrete (c) M 40 grade concrete Figure 5.4 Compressive strength achievements of M 20, M 30 and M 40 grade concrete with MS

7 67 Figure 5.5 Comparison between the compressive strength of M 20, M 30 and M 40 grade concrete with MS From Figures 5.3(a), (b) and (c), it is observed that the compressive strengths are increased with the increase in percentage of manufactured sand for all the three grades of concrete. This is due to the rough surface and angular particles of the manufactured sand crates better interlocking between the aggregate and the hydrated cement paste. From Figures 5.4 (a), (b) and (c), it is noticed that the rate of increase of strength at 7 days is higher for M 30 and M 40 grades of concrete when compared to the M 20 grade concrete due to the high cement content and less w/c ratio. Figure 5.5 indicates that there is no significant change for the proportions H and K. It states that even though the strength is increased for 100% manufactured sand, there is no significant improvement in the strength achievement beyond 70% of manufactured sand due to the large amount of fine particles present in 80, 90 and 100% of manufactured sand

8 Splitting Tensile Strength The tensile strength achievements of M 20, M 30 and M 40 grades of concrete are depicted in Figures 5.6(a), (b) and (c). (a) M 20 grade concrete (b) M 30 grade concrete (c) M 40 grade concrete Figure 5.6 Tensile strength achievements of M 20, M 30 and M 40 grade concrete with MS

9 69 Figure 5.7 Comparison between the splitting tensile strength of M 20, M 30 and M 40 grade concrete with MS Figures 5.6 (a), (b) and (c) show the tensile strength achievements of M 20, M 30 and M 40 grades of concrete with various proportions of manufactured sand from 0 to 100% at various curing periods. From the Figures, it is noticed that the splitting tensile strength achievement of the concrete is increased when the percentage of manufactured sand is increased up to 70%. The strength achievement is higher at an early period and it is also noted that it is increased for M 40 grade concrete when compared to the M 20 and M 30 grades of concrete due to the high cement content and less water content. Figure 5.7 shows the comparison between the splitting tensile strengths of M 20, M 30 and M 40 grades of concrete with the proportions of A, H and K. From the Figure, it is found that there is no significant change for the proportions H and K. It indicates that beyond 70% of manufactured sand, there is no improvement in the strength due to the presence of large amount of fines in the remaining proportions of manufactured sand.

10 Flexural Strength The flexural strength of M 20, M 30 and M 40 grades of concrete are shown in Figures 5.8(a), (b) and (c). (a) M 20 grade concrete (b) M 30 grade concrete (c) M 40 grade concrete Figure 5.8 Flexural strength of M 20, M 30 and M 40 grade concrete with MS

11 71 Figure 5.9 Comparison between the flexural strength of M 20, M 30 and M 40 grade concrete with MS Figures 5.8 (a), (b) and (c) show the flexural strengths of M 20, M 30 and M 40 grades of concrete with various proportions of manufactured sand from 0 to 100% during the various curing periods. From the Figures, it is found that the flexural strengths are increased with the increase in percentage of manufactured sand up to 70%. The flexural strength achievements are 80%, 137% and 144% at 7 days, 56 days and 365 days respectively, when compared to the conventional concrete of 28 days strength in M 20 grade concrete. For M 30 and M 40 grades of concrete, the strength achievements are increased at an early period and reduced at a later period. Figure 5.9 shows the flexural strengths of A, H and K proportions of three grades of concrete. From the Figure, it is clearly understood that there is no improvement in the flexural strength beyond 70% of manufactured sand. This is because beyond 70% the manufactured sand has a large amount of fine particles in it.

12 Modulus of Elasticity and Poisson s Ratio The modulus of elasticity of M 20, M 30 and M 40 grades of concrete with various proportions of manufactured sand at 28 days is shown in Figure Figure 5.10 Modulus of elasticity M 20, M 30 and M 40 grade concrete with MS Figure 5.11 Comparison between the modulus of elasticity of M 20, M 30 and M 40 grade concrete with MS From the Figure 5.10, it is clearly understood that the modulus of elasticity is increased with the increase in proportions of manufactured sand

13 73 up to 70%. Beyond 70% of manufactured sand, the elasticity values are reduced due to the presence of large amount of fine particles that reduce the filling of cement content in the voids. Figure 5.11 shows the modulus of elasticity of proportions A, H and K of all the three grades of concrete. It states that the modulus of elasticity is high for proportion H due to the presence of less amount of fines in it. Poisson s ratio values are experimentally determined as 0.15 to 0.16 for all the three grades of concrete with various proportions of manufactured sand Relationship Between the Mechanical Properties of the Concrete The relationship between the mechanical properties of the concrete are given in Figures 5.12 and Figure 5.12 Splitting tensile strength Vs Compressive strength Figure 5.13 Flexural strength Vs Compressive strength

14 74 The compressive strength and the splitting tensile strength results are plotted as a graph, shown in Figure Based on these results, an analytical equation was developed for determining the relationship between these two as follows: f t = f ck (5.1) whereas for normal concrete as per ACI , f t = 0.32 to 0.36 f ck. Hence the splitting tensile strength slightly increases for concrete with manufactured sand due to the angular particles in it. The flexural strength and compressive strength test results are plotted as a graph, and given in Figure An analytical equation for the relationship between these two was derived from the test results as given below: f r = f ck (5.2) whereas for normal concrete as per IS , f r = 0.7 f ck. Hence the flexural strength slightly increases for concrete with manufactured sand due to the angular particles of the manufactured sand. The relationship between the modulus of elasticity and compressive strength was calculated from the experimental results as, E = 5100 f ck (5.3) whereas for normal concrete as per IS , E = 5000 f ck. Hence the modulus of elasticity slightly increases for concrete with manufactured sand due to the angular particles of the manufactured sand.

15 CONCLUDING REMARKS follows: The conclusions from the experimental investigations are as Concrete with manufactured sand significantly improves the strength properties of the concrete. The rough texture and angular particles of manufactured sand create better interlocking between the particles and the cement paste which improves the strength properties of concrete just as the less w/c ratio increases the strength of the concrete. Blending of 70% manufactured sand with 30% natural sand has higher strength properties. The presence of small amount of fines in 70% manufactured sand increases the strength and elasticity properties of the concrete. Due to the presence of large amount of fines in 80, 90 and 100% of manufactured sand, there is no improvement in the strength development. The relationship between the compressive strength with splitting tensile strength, flexural strength and modulus of elasticity are higher than the standards set forth by IS specifications.