Chemical prestressing of concrete thin plates reinforced with mineral-impregnated carbon fibre (MCF) composites

Mineral-impregnated carbon fibre (MCF) is a new type of reinforcement that has superior mechanical properties at elevated temperatures to conventional polymer-impregnated composites. However, its specific manufacturing process results in an inherent looseness, which adversely affects its structural performance under loading. Therefore, chemical prestressing was used herein to enhance the structural performance of the MCF reinforcement by introducing tensile stress inside this reinforcement, which can transform it from a passive into an active state, as well as prestressing the concrete. For this aim, sixteen concrete plates of dimensions 700x100x20mm3 and reinforced with MCF reinforcement were cast. CSA (calcium sulfoaluminate) was used as an expansive additive with replacement ratios by weight of cement of 0 % (control), 10 %, 12.5 %, and 15 %. Based on this, the specimens were divided into four groups, each of which consisted of 4 specimens. Distributed fibre optic sensor (DFOS) technology was used to measure the concrete expansion and to track the development of stresses with time. All specimens were tested under a direct tension load to determine the influence of expansive concrete. The results showed that high expansion rates can be achieved when using the proposed expansive concrete mixture; however, such expansion may lead to a limited negative effect on the strength of the resulting concrete, especially at high CSA replacement ratios. Nevertheless, expansive concrete can significantly enhance the structural performance of the MCF-reinforced concrete plates. This includes higher stiffness before cracking and higher cracking stress, which was approximately doubled for specimens with 15 % CSA compared to the control specimens with 0 % CSA. Furthermore, enhanced cracking behavior was also observed for all the specimens made of expansive concrete