Determination of Shrinkage, Tensile and Compressive Strength of Repair Mortars and Their Adhesion on the Concrete Substrate Using "Twist-off" and "Pull-off" Methods

Abstract

The damage of concrete structures may arise due to physical or chemical agents. Some materials are needed to repair and reinforce these structures. Cement-based mortars are commonly used to repair these structures. Since some executors are not aware of the correct application of the repair mortars and their handling after application, the repair layer separated from the concrete after a while. Also, considering the differences between the environmental and the laboratory conditions of the concrete structures, it is important to determine the important parameters of the materials at the site of the structure. Therefore, in this paper, using the methods of "pull-off" and "twist-off," the amounts of compressive strength, tensile strength, and shrinkage of repair mortars under different curing and their adhesion to the concrete substrate are investigated. Moreover, the correlation between the results of the above methods and the mechanical properties of the repair mortars and the applied stress distribution method in the above methods is presented using nonlinear finite element analysis (Abaqus/CAE). The curing procedures used in this study include "water immersion," "curing agents," and "abandoning in the laboratory (open space)" that have been evaluated at various ages. The results show a direct relationship between compressive and tensile strength with the shear bond strength and tensile bond strength of repair mortars on a concrete substrate. The curing process also improves the bond strength and mechanical properties of the mortar and dramatically reduces its shrinkage. Since there is a high correlation coefficient between the results of the "pull-off" and "twist-off" methods and the compressive/tensile strength of the repair mortars and high consistency with the results of the nonlinear finite element analysis, they can be used for the in situ determination of the mechanical properties of the mortars.