The effects of pre-compress on the mortar/concrete bond and their in-situ compressive strength using “pull-off” and “twist-off” methods

The paper aimed to quantify the compressive strength of cementitious materials using in-situ “pull-off” and “twist-off” tests. Apart from determining the correlation coefficient, calibration plots and equations are presented to convert the results of in-situ tests to mortar compressive strength. The crack distribution was calculated in the tests using the nonlinear ABAQUS software. Additionally, the methods mentioned above were used to investigate the effect of pre-compression on mortar/concrete shear and tensile adhesion strength. Thus, the effect of pre-compression on the tensile and shear adhesion strength of mortar/substrate concrete was investigated using the scanning electron microscopy (SEM) method and physical adsorption theory. The results indicated that pre-compression positively affected adhesion and could be measured using the simple twist-off machine instead of the other machine. By applying 0.1 kg/cm2 of pre-compress, the tensile and shear adhesion between the mortar and concrete layers increased by 5.8% and 8.8%, respectively, after 90 days. Additionally, a linear relationship between the results of “twist-off” and “pull-off” tests and those obtained from experimental tests was observed.