Effect of nylon fibres on mechanical and thermal properties of hardened concrete for energy storage systems

The use of recycled materials in new concrete production is very appealing because of the low cost of the raw materials and the landfill space saving, as well as the enhancement of the resulting concrete’s properties. This paper focuses on the production of concrete for thermal energy storage systems using polyamide fibres from post-consumer textile carpet waste. We investigated the influence of a fibre content of 5 kg/m3 on the mechanical and thermal properties of fresh and hardened concrete with a w/c ratio of 0.35, comparing it with plain concrete. The nylon fibre-reinforced concrete was slightly more ductile and tougher than the plain concrete because the fibres have an important role after failure. The tensile strength, maximum load-bearing capacity and modulus of elasticity decreased slightly with the addition of nylon fibres, but drying shrinkage was lower than for plain concrete. Given that heat capacity and thermal conductivity are the most important parameters for thermal energy storage purposes, we measured these parameters for all the samples at 25 °C, and after a thermal treatment at 300 °C. The heat capacity values were 0.63 and 0.81 J g−1 K−1 for fibre-reinforced concrete (FC) and plain concrete (C), respectively, and the thermal conductivity values were 1.16 and 1.02 W m−1 K-1.