CHAPTER 4 MIX DESIGN OF CONCRETE WITH MANUFACTURED SAND

Transcription

1 54 CHAPTER 4 MIX DESIGN OF CONCRETE WITH MANUFACTURED SAND 4.1 GENERAL The design of concrete mix requires complete knowledge of the various properties of the ingredients used in concrete. This chapter discusses the properties of materials used and the mix proportioning of M 20, M 30 and M 40 grades of concrete with the replacement levels of manufactured sand from 0 to 100%. Besides it considers the specific gravity and fineness modulus values of each replacement level of manufactured sand. 4.2 MATERIALS Cement Portland pozzolana cement conforming to IS was used for this experimental investigation. The physical and chemical properties of cement are shown in Tables A 1.1 and A Coarse Aggregate Locally available crushed aggregate of 20mm down size conforming to graded aggregate as per IS: was chosen for the present investigation. The coarse aggregate was tested as per the procedure given in IS: and the results are given in Table A 1.3.

2 Fine Aggregate Locally available river sand was used as fine aggregate. The natural river sand was replaced by the manufactured sand. Here the manufactured sand varied from 0 to 100% as ten increments and designated as A, B, C, D, E, F, G, H, I, J and K respectively. The physical and chemical properties of the fine aggregate are given in Tables A 1.4 and A 1.5. The particle size distribution curve of the fine aggregate is shown in Figure 4.1. Figure 4. 1 Particle size distribution analysis of MS Figure 4.1 shows the grading curves of natural sand and the various proportions of manufactured sand. In the figure, L.L represents the lower limit and the U.L represents the upper limit of the particle size distribution curves of sand. From the figure, it is noticed that the particles of size less than 300 microns are higher for the proportions of 80 %, 90 % and 100 %manufactured sand.

3 Water Water is a key ingredient in the manufacture of concrete. A potable tap water was used in this research. 4.3 MIX DESIGN (IS ) It involves Mix design is a process that consists of two interrelated steps. 1) Selection of suitable ingredients (cement, aggregate, water and admixtures) of concrete. 2) Determining their relative quantities ( proportioning ) to produce as economically as possible, concrete of the appropriate workability, strength and durability. In this thesis, mix proportions for M 20, M 30 and M 40 grade concrete were arrived at for the different replacement levels of natural sand with manufactured sand as ten increments. This meant considering the specific gravity and fineness modulus values of each replacement level of manufactured sand. In the process, the mixes were named as A, B, C, D, E, F, G, H, I, J and K for 0 to 100% respectively. Concrete mixes were designed as per IS Mix proportions of M 20, M 30 and M 40 grade concrete are given in Tables 4.1 to 4.3 and Figures 4.2 to 4.4.

4 57 Table 4.1 Ingredients of M 20 grade concrete D Cement F.A C.A Water (Lit) A/C ratio (based on surface index value) A : 70 1 : 2.26 B : 70 1 : 2.28 C : 69 1 : 2.23 D : 67 1 : 2.04 E : 67 1 : 2.04 F : 67 1 : 2.03 G : 66 1 : 1.94 H : 66 1 : 1.94 I : 66 1 : 1.95 J : 67 1 : 1.99 K : 67 1 : 2.00

5 58 Figure 4.2 Percentages of ingredients for M 20 grade concrete Table 4.2 Ingredients of M 30 grade concrete D Cement F.A C.A Water (Lit) A/C ratio (based on surface index value) A : 70 1 : 2.36 B : 70 1 : 2.37 C : 69 1 : 2.26 D : 68 1 : 2.11 E : 68 1 : 2.11 F : 68 1 : 2.09 G : 67 1 : 2.01 H : 67 1 : 2.01 I : 67 1 : 2.01 J : 67 1 : 2.06 K : 67 1 : 2.01 Figure 4.3 Percentages of ingredients for M 30 grade concrete

6 59 Table 4.3 Ingredients of M 40 grade concrete D Cement F.A C.A Water (Lit) A/C ratio (based on surface index value) A : 77 1 : 3.32 B : 77 1 : 3.34 C : 76 1 : 3.16 D : 74 1 : 2.91 E : 74 1 : 2.91 F : 74 1 : 2.89 G : 74 1 : 2.78 H : 74 1 : 2.78 I : 74 1 : 2.78 J : 74 1 : 2.78 K : 74 1 : 2.78 Figure 4.4 Percentages of ingredients of M 40 grade concrete

7 DISCUSSION OF TEST RESULTS Properties of Materials From Figure 4.1, it is found that the particle sizes of manufactured sand for the proportions A to H lie within the lower and upper limits. But the proportions I, J and K (80, 90 and 100% manufactured sand) exceed the upper limit. This represents that the finer fractions below 300 microns are higher in these proportions, which may affect the workability and the strength of the concrete Mix Design From Tables 4.1 to 4.3 and Figures 4.2 to 4.4, it is observed that for the constant cement content, the fine aggregate content is increased while increasing the proportions of manufactured sand due to the coarser particles of manufactured sand. It is also noticed that the water content is slightly reduced with the increase in proportions of manufactured sand due to the high surface moisture content of manufactured sand, which may increase the strength of the concrete. 4.5 CONCLUDING REMARKS According to the findings of this research, the gradation of the manufactured sand, the increased amount of aggregate/cement ratio and the reduced amount of water cement ratio, the workability of the concrete may get reduced and the strength of the concrete may be increased. The presence of large amount of fines in 80, 90 and 100% manufactured sand may reduce the strength of the concrete in these proportions.