EFFECT OF CORE DIAMETER ON CONCRETE CORE STRENGTHS

Data are analyzed from studies by others concerning the effect of specimen diameter on the magnitude and precision of the compressive strength of concrete cores. The data indicate that the effect of damage to the cut surface of the core counteracts and overwhelms any effect that might be inferred by the weakest link theory or attributed to systematic bias caused by testing procedures. Based on the analyses, the predicted average strength of a 2-in. -diameter core is 94 percent of the predicted 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 reflect the considerable scatter of the data and therefore should be used with caution. The large variability commonly attributed to small-diameter specimens is often caused by the large variability of the in situ concrete strength within the element being cored. The data also indicate that the effect of the core length-to-diameter ratio on the compressive strength is more significant for 2-in.-diameter cores than for 4-in.-diameter cores.