Point load test application for estimating compressive strength of concrete structures from small core

To estimate a compressive strength from existing concrete structures by core drilling are usually gathered with a diameter specimen of 100mm or three times of maximum coarse aggregate size and examined by uniaxial compressive strength (UCS) test as stated in JIS A1170. To get an alternative solution with smaller specimen, point load test (PLT) has been selected which is a simple test and widely accepted in rock materials research, but relatively new in concrete. The reliability of PLT is examined by extracting a lot of core drilled specimen from ready mixed concrete blocks with maximum coarse aggregate size, G_max of 20mm in representative of architectural structures and 40mm in representative of civil structures on the range of concrete grade from 16 to 50. The reference of strength is resulted from concrete core diameter of 100 and 125mm with h/d ratio of 2.0, and examined by UCS test with compressive strength of concrete core of f'^cc in results. The core specimen diameters are 35 and 50mm with h/d ratio of 1.5 and 2.0, and examined by PLT with point load index of IS in results. The estimation of compressive strength is conducted by making a linear approximation for I_S to f'^cc for each group of G_max and h/d. This study also evaluates the reliability of test results for each core specimen and proposes a new geometric correction factor.