Effect of micro synthetic fibers content, spiral stirrups, curing, and high temperature on bond strength: A comparative study between experimental results and prediction models

Abstract Researchers are focused on investigating the potential to increase the bond performance between rebar and geopolymer concrete, a sustainable and environmentally friendly building material that has recently gained prominence. The effects of micro synthetic fiber additives and spiral stirrup arrangement on bond strength have not been sufficiently investigated in the literature; in this respect, the study fills an important gap. The aim of the study is to experimentally examine the effect of different parameters on the bond strength between rebar and geopolymer concrete based on granulated blast furnace slag, and produced with varying proportions of micro synthetic fibers. The pullout test was performed on a total of 432 cylindrical samples of 100 × 200 mm dimensions. Experimental parameters investigated were micro synthetic fiber volume (0%, 0.5%, and 1%), bond length (4d and 8d), curing conditions (ambient temperature, 4 h 80°C and 8 h 80°C), spiral stirrup usage, and the high temperature effect (150, 300, and 600°C). The results show that when micro synthetic fiber and spiral stirrup are used together, the bond strength is significantly increased. The use of 1% micro synthetic fiber and spiral stirrup arrangement increased the bond strength by ~4 times compared to samples without fibers or stirrups. Moreover, it has been observed that under high temperature, micro synthetic fibers improve bond performance up to 300°C, but at 600°C, fiber melting leads to a loss of performance. The study offers a new perspective in the design of environmentally sustainable and durable building elements. Lastly, commonly used bond strength prediction models did not give accurate results in geopolymer concretes containing micro synthetic fibers and exposed to high temperature; therefore, a new and appropriate model that takes such special situations into account needs to be developed in the near future.