The effect of initial compression on the interface of repair/concrete and the evaluation of the compressive strength of mortars

One of the key factors that reduce the bond strength between repair mortars and concrete substrate is improper compaction of the repair layer when applied to concrete. Due to the fact that compacting has a direct effect on the adhesion of the interface of two layers, so the lack of proper compaction causes small cavities between the two layers and as a result causes a decrease in bond strength. Therefore, in this paper, by applying semi-destructive tests, by applying initial compression for 24 hours on the mortar applied to the concrete substrate, the effect of compression on bond between the repair layer and the concrete has been studied. The effect of one week of curing on the dry shrinkage of repair mortars is also presented. In the following, the compressive strength of repair mortars was evaluated using the "twist-off" and "pull-off" tests. In this regard, calibration diagrams were drawn between laboratory tests and semi-destructive tests and linear equations were presented to convert the original results from semi-destructive tests to the compressive strength of mortars. ABAQUS software was used to investigate cracks and stresses in mortars. The results show an increase in bond strength between the repair mortar and the concrete substrate by applying initial compression. Applying initial compression of 0.5 kg/cm2 on unhardened mortar increased the shear and tensile strength between the repair and concrete layers at the age of 90 days by 36.9% and 31.4%, respectively. Also, a linear relationship with high correlation was observed between the readings obtained from the above tests with the compressive strength of repair mortars.