Effect of Partial Replacement of Crushed Granite with Local Coarse Aggregate in Concrete

Abstract

This study investigated the effect of partially replacing crushed granite with locally available sandstone (locally referred to as “wili-wili stone”) on selected fresh and hardened properties of concrete. The experimental programme was conducted at the Civil Engineering Laboratory of Nnamdi Azikiwe University, Awka, using Ordinary Portland Limestone Cement, sharp sand, crushed granite and local sandstone aggregate. Granite was replaced with sandstone at 0%, 10%, 20% and 30% levels. Concrete mixtures of 1:1:2, 1:2:4, 1:3:6 and 1:4:8 were investigated. Slump, 28-day compressive strength and aggregate water absorption were determined. The results showed a consistent reduction in slump as the sandstone content increased. For the 1:1:2 mixture, slump decreased from 76 mm at 0% replacement to 56 mm at 30% replacement; corresponding reductions were observed for the other mix proportions. The water absorption of sandstone was 1.76%, compared with 1.13% for granite, indicating greater water demand associated with the local aggregate. The compressive strength response depended strongly on the mix proportion. In the 1:2:4 mixture, the mean 28-day strength increased from 7.32 N/mm² for the control to 9.33 N/mm² at 10% replacement, but declined at 20% and subsequently recovered to 8.41 N/mm² at 30%. In the richer 1:1:2 mixture, strength increased progressively to 12.45 N/mm² at 30% replacement. Conversely, the 1:3:6 mixture remained below the control at all replacement levels, while the 1:4:8 mixture showed an irregular response. These results demonstrate that a single universal optimum replacement percentage cannot represent the suitability of local sandstone; performance is strongly dependent on mixture proportion and aggregate moisture condition. For the conventional 1:2:4 mix investigated, 10% replacement provided the highest measured 28-day compressive strength and a relatively small loss of workability. The study concludes that properly characterized local sandstone can serve as a partial coarse-aggregate replacement, provided its higher absorption is considered during mix proportioning and quality control.