EFFECT OF CORE DIAMETER ON CONCRETE CORE STRENGTHS

Data are analyzed from studies by others concerning the effect of spec imen diameter on the magnitude and precision of the compressive streng th of concrete cores. The data indicate that the effect of damage to t he cut surface of the core counteracts and overwhelms any effect that might be inferred by the weakest link theory or attributed to systemat ic bias caused by testing procedures. Based on the analyses, the predi cted average strength of a 2-in. -diameter core is 94 percent of the p redicted average strength of a 4-in. - diameter core and 92 percent of that of a 6-in. -diameter core. These overall average values do not r eflect the considerable scatter of the data and therefore should be us ed with caution. The large variability commonly attributed to small-di ameter specimens is often caused by the large variability of the in si tu concrete strength within the element being cored. The data also ind icate that the effect of the core length-to-diameter ratio on the comp ressive strength is more significant for 2-in.-diameter cores than for 4-in.-diameter cores.