A multi-criteria evaluation and optimization of sustainable fiber-reinforced concrete developed with nylon waste fibers and micro-silica

Nylon waste fibers similar to new nylon fibers possess high tensile strength and toughness; hence, they can be used as an eco-friendly discrete reinforcement in high-strength concrete. This study aimed to analyze the mechanical and permeability characteristics and life cycle impact of high-strength concrete with varying amounts of nylon waste fiber and micro-silica. The results proved that nylon waste fiber was highly beneficial to the tensile and flexural strength of concrete. The incorporation of a 1% volume of nylon waste fiber caused net improvements of 50% in the flexural strength of concrete. At the combined addition of 0.5% volume fraction of nylon fiber and 7.5% micro-silica, splitting tensile and flexural strength of high-strength concrete experienced net improvements of 49% and 55%, respectively. Nylon fiber-reinforced concrete exhibited a ductile response and high flexural toughness and residual strength compared to plain concrete. A low volume fraction of waste fibers was beneficial to the permeability resistance of high-strength concrete against water absorption and chloride permeability, while a high volume (1% by volume fraction) of fiber was harmful to the permeability-resistance of concrete. For the best mechanical performance of high-strength concrete, 0.5% nylon waste fiber can be used with 7.5% micro-silica. The use of micro-silica minimized the negative effect of the high volume of fibers on the permeability resistance of high-strength concrete. The addition of nylon waste fibers (at 0.25% and 0.5% volume) and micro-silica also reduced carbon emissions per unit strength of concrete.