Analyzing the Effect of Polypropylene Fibers on Compressive Behavior, Shrinkage and Bond Strength of Repair Mortars/Concrete Substrate

The dry shrinkage of mortars is one of the primary causes for the reduction of bond strength between repair mortars and concrete substrates. Utilizing fibers in the mortars is one of the methods used to reduce shrinkage. The current study used polypropylene fibers in mortars to improve the bond between repair mortar and concrete substrate, and also to control the dry shrinkage of mortars. The “friction-transfer” and "pull-off” methods were used to determine the bond strength between the repair mortar and concrete substrate. In addition to determining the amount of shrinkage and bond strength, the amount of compressive strength of fiber reinforced mortar by using the above methods and by modeling finite element with ABAQUS software has been investigated. In addition, the methods of initiation and distribution of cracks and stresses were shown. In order to assess the in-situ compressive strength of polypropylene fiber-reinforced mortars, the correlation of records obtained from semi-destructive methods of “friction-transfer” and “pull-off” with those of laboratory tests was determined, using the linear and exponential regression analyses. Then, using calibration curves, the equations required to convert the results of in situ methods to the compressive strength of polypropylene fiber-reinforced mortars were presented. The results demonstrate the positive effect of fibers on shrinkage, shear and tensile bond strength and compressive strength of mortars. The correlation coefficients of the “friction-transfer” and “pull-off” methods are indicative of a strong linear relationship between the two methods that instead of using an expensive “pull-off” device, a simple and inexpensive "friction-transfer" device can be used.