Factor influencing point load tests on concrete

The main purpose of this paper is to predict the in-situ compressive strength of concrete by means of point load strength test (PLT) as a partially destructive test method. This test method is examined by extracting core specimen from concrete blocks and applying two point loads to the lateral surface of the core specimen. The failure in the core specimen is occurred in the direction of applying load where most normal stresses are tensile, while some compressive stresses are generated in the contact surface of load cell with the core specimen. In this study, point load index (PLI) in which a force is divided by the square of the distance between the platen points and cube compressive strength (CS) was determined under wet and dry curing conditions at the ages of 7, 14, 28 and 42 days. The effects of various parameters such as core diameter and length to diameter (L/D) ratio were considered experimentally and numerically by means of finite element method using ABAQUS software. A three dimensional finite element model (FEM) was constructed to study the stress magnitude and stress distribution at the failure surface. The results showed that the PLI in wet curing conditions were about 12 % higher than those in dry curing conditions. In addition, The PLI increased particularly steep when the L/D ratio is less than 1, while then becomes less steep when the L/D ratio is between 1 and 1.8. Meanwhile, it seems that there is no significant difference among PLI values for the ratios of L/D more than 1.8.