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The interfacial transition zone (ITZ) is well known to be a zone of high porosity and lesser strength and is the weak zone in the fiber-reinforced matrix. This study aims to evaluate the improvement in the bonding between engineered polypropylene fibers and the surrounding mortar matrix. The improvement was implemented by modifying the ITZ, which develops between the fibers and the cementitious matrix. Two commercially available repair materials have been used in this study, Mix M and Mix P. Mix M served as the base material for the prepared fibers, whereas Mix P is a fiber-reinforced repair mortar and provides a comparison. A total of six types of mixes have been investigated. The improved bonding is tested by coating the polypropylene fibers with supplementary cementitious materials (SCM) using an innovative patented concept. In this study, silica fume and metakaolin are used as the SCM because of their fine size and pozzolanic capacity. The study involves multiple items of investigation, including mechanical tests such as compressive strength, direct tensile strength, and three-point bending tests. Energy-dispersive X-ray spectroscopy (EDS) of the different mixes helped in evaluating and analyzing the ITZ between the fiber and matrix.

Deterioration of concrete structures is one of the major issues faced by the construction industry. Repair and rehabilitation are necessary to extend the service life of such structures. This study aims to investigate the effect of repair material type, length of repaired region, and loading regime on the structural characteristics of the repaired reinforced concrete (RC) beams. To achieve this goal, a total of 30 repaired and non-repaired RC beams were prepared and tested under static and repeated loading conditions. Three types of sounding-based non-destructive test (NDT) methods are employed to determine the material deterioration and sub-surface delamination after repeated loading. Results showed that under static loading conditions, full-length repaired beams had better performance than 1/3-span repaired beams. Beams repaired with cementitious repair mortar containing modified binder and cementitious repair concrete in full length had a yield strength that was 14% and 9%, respectively, higher than that of beams repaired in 1/3 span. All RC beams with full-span repair outperformed the intact beams. After repeated loading, beams repaired with cementitious repair with modified binder over full length showed a 14% improvement in yield strength compared to control samples. It was found that repair materials that had a high compressive and flexural strength are beneficial. The resonant frequency drops correlate well with the yield strength results. The formulas proposed by Canadian Standards Association (CSA) 23.3 can effectively predict the moment resistance of both intact (control) and repaired RC beams. The ratio of experimental moment resistance values to its predictions ranges from 0.91 to 1.04.

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