Global Engineers & Technologists Review, Vol.3 No.4
(2013)
3.5 Fresh and Hardened of Concrete The test carried out on the fresh concrete was the slump test; this test was carried out using the standard procedure as outlined in BS 812 and the slump was measured as the difference between the height of the mould and that of the highest point of the specimen. Meanwhile for the hardened of concrete specimens were cured in water after casting and testing of the hardened concrete was done at an age of either 7 or 28 days. 3.6 Compression and Flexural Test The concrete cubes and cylinders compressive strength was determined at seven days and twenty eight days. The tensile strength of the concrete was determined using the splitting tensile test according to the procedure in ASTM C496. Both the cube and cylinders were tested at 7 and 28 days for splitting tensile strength for both the normal and sand replaced concrete. The arrangement for the flexural test was as shown in Figure 1. A manual Compression machine was used for this test according to BS 1881-118. Beam specimens measuring 500 x 150 x 150 mm were moulded and cured for 28 days before testing for flexural strength.
Figure 1: Specimen geometry and setup.
The beams were tested for flexure using Universal Testing Machine, where the beams were loaded at one point, center, load applied at a small strain monitoring the deflection until first crack appeared. Loading was continued until the ultimate failure was achieved. The load-deflection data at mid span section for plain concrete beams with different proportions of natural river sand and rock sand was determined. Load deflection curves were plotted.
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RESULT AND DISCUSSION
Three sand samples from different sources were tested for bulking. The findings show that the bulking of sand samples ranged between 35 % and 44 %. Four sand samples from different sources and the crushed rock sand were analyzed for silt content and the results shows that all the four sand samples tested had silt content values below the maximum allowed value of 5 % while the crushed rock sand sample had an average silt content of 11 % compared to the maximum allowable content of 8 % as per required in BS 812. Two sand samples and the crushed rock sand were tested for specific gravity and water absorption. The specific gravity for sand samples varied between 2.55 and 2.63 while that of crushed rock sand 2.55. The water absorption rate for sand ranged between 1.21 % and 1.83 % while that of the crushed rock sand averaged 2.4 %. The higher values of specific gravity and water absorption rate from rock sand are as a result of high the high fineness of the material. Three sand samples selected from different sources were tested for particles size distribution and their results compared with the gradation envelope for fine aggregates. For this sand to qualify as zone two (2) material, there was need to blend two or more materials which would give the required gradation. Having only one norminal size of the rock sand, a second batch of norminal size 1.18 mm was created by sieving the initial batch through this sieze and therefore discarding the material retained on this sieve. The two norminal sizes 5 mm and 1.18 mm were sieved again and their grading curves plotted as Figure 2.
Figure 2: Grading of CRS as received compared with zone two fine aggregate envelope. Š 2013 GETview Limited. All rights reserved
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