Core Strengths of High-Strength Concrete
George C. Hoff and Radoslav Elimov
Appears on pages(s):
Drilling; fly ash; high-performance concretes; high-strength concretes;
offshore structures; silica fume
The effects of varying L/D ratios and core size on the strength of cores from large elements of high-strength concrete (HSC) made both in the laboratory and the field were examined. One-hundred and fifty four cores (65 mm and 100 mm nominal diameters) representing 5 laboratory mixtures having moist-cured cylinder compressive strengths from 114 to 142 MPa at 5-years age and 101 cores (70 mm and 100 mm nominal diameters) representing an actual field placement of 28,150 m3 of concrete in an offshore concrete structure having continuously moist-cured compressive strengths at l-year from 88 to 92 MPa were evaluated. The results indicate that for 100 mm (nominal) diameter cores of HSC, there is no need to apply the ASTM C 39 correction factors to the observed strength of cores with L/D’s from 2.0 to 1.0. The use of cores with a smaller diameter (e.g., 70 mm) exhibit lower strengths (78% to 82%) than companion larger diameter cores and have a higher degree of variability and thus are not recommended for use with HSC. At early ages (e.g., 28-days), the observed strength of HSC cores may be very close to the strength of continuously moist-cured control cylinders. At substantially later ages (e.g. 5 years), the observed strength of the cores may be fairly close to the strength of air-cured control cylinders but be only 70% to 80% of the strength of continuously moist-cured cylinders.