INFLUENCE OF WATER/CEMENT RATIO ON THE FLEXURAL STRENGTH OF CONCRETE MADE WITH UNWASHED LOCAL GRAVEL

Summary

This paper studied the influence of water/cement ratio on the flexural strength of concrete made with unwashed
local gravel from Abagana in Anambra state. In the research work, concrete beams of dimensions 600mm x
150mm x150mm —three for each experimental point were made. The water/cement ratio, w/c ranged from 0.46
to 0.56 for the mix ratio of 1:1:2 and from 0.55 to 0.63 for the mix ratio of 1:2:4. The batching was by weight.
These beams were then tested based on the procedures prescribed in BS 1881: Part 118:1983. The graphs of
the flexural strengths against water/cement ratios were hyperbolic in nature. The equations of the graphs were
y = -636.6x2 + 645.6x - 160.35 and y = -636.36x2 + 752.41x - 219.62 for the mix ratios of 1:1:2 and 1:2:4
respectively, where y represented the flexural strength in N/mm2
and x represented the water/cement ratio, w/c.
As the water/cement ratio increased, the flexural strength of the samples rose to a peak before declining. The
mix ratio of 1:1:2 had a peak flexural strength of 3.33 N/mm2
at w/c = 0.51 and the mix ratio of 1:2:4, a peak of
2.79 N/mm2
at w/c = 0.59.

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