Bond strength between concrete substrate and metakaolin geopolymer repair mortars at ambient and elevated temperatures

Ordinary Portland cement (OPC) is commonly adopted as an effective binder in the production of concrete and cementitious mortars. The metakaolin (MK) based geopolymer (GP) binder offers a sustainable alternative to the OPC due to its essential environmental and technical benefits in reducing the carbon footprint. In the present study, two conventional and six GP repair mortars were used. Three GP mortars were plain (without fibers), and the remaining three were produced by mixing Polyvinyl-alcohol (PVA) fibers. The GP mixes were produced by varying sand content, alkaline solids to MK, and sodium silicate to NaOH ratios, resulting in different molar ratios. The test specimens were prepared by overlaying a 5 mm thick layer of repair mortar on a concrete substrate for conducting pull-off strength tests. This research was undertaken to investigate the effect of exposure to elevated temperatures on the performance of bond strength of GP mortar used as a repair material. The test specimens were subjected to ambient temperature and elevated temperatures of 200 and 400 °C for a duration of 3 h before conducting pull-off tests. The test results revealed that the selected GP mixes could be a promising alternative repair material for structures due to their good bond strength performance. The addition of fibers in stable mixes of GP mortars enhanced the bond strength at ambient as well as when exposed to 200 °C, through crack control mechanism.