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ABSTRACT
This research was aimed at examining the effect of gravel sizes on the mechanical properties of concrete by varying the sizes of gravel: 25, 20, 14, 10, 6.3mm and a combination of these sizes. This will enable the use of gravel as an alternative to quarry crushed granite in concrete production. It is an effort to broaden the choices of coarse aggregate in concrete production. Gravels were sourced, washed and sieved to obtain uniform grading of 25mm, 20mm, 14mm, 10mm, and 6.3mm. The gravel specimen were subjected to impact value and crushing value test to ascertain the resistance to impact load and crushing load. The result of ACV shows that the graded sizes of 25/ 20 and 10 /6.3 mm were 20.03 % and 27.8 %, while AIV for 25/ 20 and 10 /6.3 mm were 16.37 % and 25.0 % respectively. The result showed that workability increased with graded gravel sizes. The result showed that the compressive strength increased with increase in gravel sizes. At 28 days, the compressive strength of concrete made with graded gravel sizes of 25/20mm and10 /6.3mm for 1:2:4 were 26 N/mm2 and 15.03 N/mm2 . Also, gravel sizes of 25/20mm and10 /6.3mm for 1:1.5:2 gave 29.8 N/mm2 and 19 N/mm2 compressive strengths. This implies that combination of large gravel sizes produced stronger concrete when compared to combination of smaller sizes of gravel. The flexural resistance increased with increase in gravel sizes. At 28 days, the flexural strength of concrete made with graded sizes of 25/20mm and 10/6.3mm for 1:2:4 were 3.1 N/mm2 and 2.0 N/mm2 . Also, the graded sizes of 25/20mm and 10/6.3mm for 1:1.5:2 gave 3.3 N/mm2 and 2.26 N/mm2 flexural strengths. The result also showed that the density of concrete increased with the increase in gravel sizes. The linear model was adopted for modelling the effect of gravel sizes on the properties of concrete as a function of age, using mix proportions of 1:2:4 and 1:1.5:2 with a fixed water/cement ratio of 0.5 throughout the experiment. It can be concluded that concrete prepared with gravel sizes 25, 20 and 14 mm can have reasonable strengths. Using Gravels as alternative to quarry crushed stone should be encouraged in concrete production, as it is beneficial to provide economical infrastructural developments, especially for the construction of low rise buildings, rural roads and walkways.
