EFFECT OF CORE LENGTH-TO-DIAMETER RATIO ON CONCRETE CORE STRENGTHS

Data are analyzed to determine the effect of the specimen length-to-di ameter ratio (l/d) on the magnitude and precision of the compressive s trength of concrete cores. The data represent strength tests of 758 co re specimens, all 4 in. in diameter, obtained from 10 different elemen ts cast from ordinary portland cement concretes with strengths between 2000 and 14,000 psi. Strength correction factors are determined for c onverting the strength of a core with an l/d between 1 and 2 to the st rength of an equivalent standard specimen with an l/d of 2. The data i ndicate that both the core moisture condition and the core strength si gnificantly affect the strength correction factors. The proposed stren gth correction factors differ only slightly from those currently recom mended in ASTM C42-90. The single-operator coefficient of variation is found to be independent of the core length-to-diameter ratio. Typical values are 4 percent if the effect of spatial variation of the in sit u strength is accounted for, or 5 percent otherwise.