Size Effect of Coarse Aggregate Within Concrete Matrix on the Mechanical Properties of Concrete

Abstract

This investigation focuses on how aggregate size affect the performance of plain concrete. Three concrete grades (M10, M15, and M20) with varying water-cement ratios (.3, 0.35, 0.4, 0.5, 0.55, and 0.6) and coarse aggregate sizes (7 mm, 18 mm, and 22 mm) were examined. Slump tests evaluated workability, while compressive strength tests assessed mechanical properties. The results consistently indicates that larger aggregate sizes tend to reduce the compressive strength (of concrete mixes. This trend was observed across M10, M15, and M20 concrete mixes. As aggregate size increases, the  generally decreases. This was due to the reduced interlocking and load transfer efficiency within the concrete matrix, as larger aggregates have fewer contact points with the cement paste, leading to weaker bonds and lower overall strength. Larger aggregate sizes greater 7 mm but less than 24 mm enhance the workability of concrete, as specified by higher slump values. However, this increased workability does not necessarily translate into higher compressive strength. The ease of mixing and placing concrete with larger aggregates must be balanced against the potential reduction in strength. Smaller aggregate sizes, such as 7 mm, tend to provide better compressive strength due to improved interlocking and load transfer mechanisms. Concrete mixes with smaller aggregates showed higher compressive strength​ values compared to those with larger aggregates. For instance, a concrete mix with a water-cement ratio of 0.55- and 7 mm aggregate achieved a compressive strength of approximately 34.22 Mpa at 28 days, which decreased as the aggregate size increased to 18 mm and 22 mm.