Effect of Aggregate Gradation on the Workability of Fresh Concrete

A Compacting Factor Test Study

Abstract

This study investigates the effect of aggregate gradation on the workability of fresh concrete using the compacting factor test. Two concrete mixtures were prepared with different aggregate gradations. Sample 1 consisted of a well-graded combination of fine and coarse aggregates with a mix ratio of 1:2:4 and a water-cement ratio of 0.50, while Sample 2 contained uniformly graded coarse aggregate with a mix ratio of 1:4 and a water-cement ratio of 0.30. The compacting factor values obtained were 0.986 for Sample 1 and 0.813 for Sample 2, representing a difference of 0.173. The results indicate that well-graded aggregates significantly improve the workability of fresh concrete by enhancing particle packing and reducing internal voids. The compacting factor of Sample 1 lies at the upper boundary of the valid range specified in BS 1881-103 and is interpreted as a methodological observation rather than a measurement error. The study also acknowledges that variations in both the water-cement ratio and mix proportion between the two samples may have influenced the observed workability. Further investigations using identical mix proportions and water-cement ratios are recommended to isolate the influence of aggregate gradation more accurately.