Compressive strength of sandless concrete

Abstract

Sandless concrete is made of cement, coarse aggregates and water, and chemical admixtures in some cases. This study aims to develop sandless concrete for regions facing a shortage of sand. The effect of aggregate gradation, aggregate-cement ratio (A/C) and water-cement ratio (W/C) on the compressive strength of sandless concrete was investigated and reported herein. In the laboratory tests carried out, the aggregate-cement ratio was varied from 2.0 to 3.5 in steps of 0.5 and the water-cement ratio from 0.30 to 0.55 in steps of 0.05. The coarse aggregate gradations varied from the upper to the lower bound of the ASTM C33-03 requirement for aggregate size number 89, which has a nominal size between 9.5 mm and 1.18 mm. Compressive tests indicated that the sandless concrete fails at the interface between the aggregates and cement. The compressive strength of sandless concrete was not significantly affected by the aggregate gradation except for the case where the water-cement ratio was greater than 0.45. The effect of aggregate-cement ratio was also not significant if the content of cement paste was sufficient to cover the aggregates and fill the voids between the aggregate particles, that is, as long as the aggregate-cement was less than 3.5, which is explained by the "excess paste theory". There exists a linear relationship between the compressive strength and the water-cement ratio. It was deduced that a 28-day cube compressive strength of 30~50 MPa can be readily achieved with a water-cement ratio of less than 0.5 and aggregate-cement ratio less than 3.