Percussion-drill method for casting concrete cube samples to assess the characteristics of precast zero-slump concrete

Precast concrete products are load-tested to confirm compliance, but the workability of the concrete, being generally zero-slump concrete, is often not tested for quality control, as would be done with normal- or high-slump concrete. An industry practice in South Africa uses the percussive action of a rotary percussion drill to compact control cube samples. However, variability in specimen compaction leads to variations in the density and compressive strength results, making the procedure unreliable. This indicates a need for a simple, standardised quality control method for preparing zero-slump concrete cube samples with compaction equivalent to that achieved by precast machines. This technical note aims to (i) report on a practical and economical procedure (i.e. percussion-drill method) that has been formulated for quality control based on the concrete density achieved by precast machines, and (ii) apply this method to mix optimisation with the specific objective of partial replacement of the cement in a factory mix with a suitable fine filler to reduce cost and the carbon footprint of a precast facility. It was shown that the percussion-drill method was able to obtain reliable results (density, compressive strength) for quality control purposes and was successfully employed in the replacement of 17% to 32% of cement by volume with quartz flour in a factory mix. This resulted in a significant cost saving and a reduction in nett carbon emissions at the factory.