Investigation of In-Situ Compressive Strength of Fiber-Reinforced Mortar and the Effect of Fibers on the Adhesion of Mortar/Steel

Abstract

The proper connection between mortar and steel is one of the crucial issues in civil engineering. This paper has investigated the effect of polypropylene fibbers on the bond between cement mortar and steel, using “Twist-off” and “pull-off” tests. Moreover, in order to assess the in-situ mechanical properties of fibre-reinforced mortars, the correlation of records obtained from semi-destructive methods of “Twist-off” and “pull-off” with those of laboratory tests was determined, and calibration curves were provided, using the regression analyses. The mentioned tests were modelled with the ABAQUS software to evaluate the distribution of stresses and cracks developed during the semi-destructive tests. The results show that the addition of polypropylene fibbers reduces the shrinkage of mortars by about 13% and this has a direct effect on the bond between the mortar and steel. So that the shear and tensile bond of fibre-reinforced mortars at 90 days is 75% and 94% higher than conventional mortars, respectively. The reason for this is the effect of fibbers on the process of hydration of mortars and also to prevent excessive opening of cracks, which is shown by SEM. According to the results, instead of using an expensive and imported pull-off device, a cheap and internal twist-off device can be used to measure adhesion. Also, to evaluate the compressive strength of mortars, twist-off and pull-off tests can be used by placing the readings obtained in the equations y = 0.156x + 0.329 and y = 0.055x-0.001 instead of x, respectively, to evaluate the compressive strength of mortars.

Keywords

• bond
• fibre
• finite element method
• mortar
• steel