Within-Batch Variability in Stiffness of Rapid-Setting Concrete Produced Using a Volumetric Concrete Mixer

The objective of this research was to evaluate the variability in stiffness of three types of rapid-setting concrete batched using a volumetric concrete mixer: 1) air-entrained, 2) non-air-entrained, and 3) low-permeability. The rapid-setting concrete mixtures tested in this study were batched using a volumetric concrete mixer operated by a paving contractor, and 10 cylindrical specimens of each type of concrete were cast. The specimens were subjected to nondestructive stiffness testing at 3, 7, 14, and 28 days. Based on the calculated values of Young’s modulus for the specimens, the variability in stiffness was quantified for each type of concrete at each curing time by computing the coefficient of variation (CV). The results indicate that the low-permeability concrete was more variable than the air-entrained concrete, which was in turn more variable than the non-air-entrained concrete; while higher variability in stiffness appears to be associated with higher numbers of admixtures, all batches exhibited a CV lower than 4% at all curing times, indicating minimal overall variability.