Comparison at the short and long term of the mechanical performance of FRCs with recycled, natural and commercial fibers

This paper presents a comparative study on the mechanical performances of four types of fiber-reinforced concrete (FRC), using commercial steel fibers (CSFs), commercial polypropylene fibers (CPPFs), natural fibers (NFs) and recycled polyethylene terephthalate fibers (rPETFs). The evaluation was conducted at both short-term (ST) and long-term (LT) curing stages. To assess durability by comparing the long-term mechanical performance after thermal cycles, the FRCs were cured considering two different thermal cycles methodology: freeze–thaw (FT) cycles according to the European Assessment Document (EAD) and thermal cycle conditions typical of hot-climate (HC) regions. In the ST program, eight FRCs were mechanically characterized, differing in fiber type and dosage, while maintaining the same cementitious matrix. FRCs included: 20 kg/m3 for CSF, and both 2.5 kg/m3 and 5.0 kg/m3 in the case of CPPF, NF, and rPETF. In the LT program the dosage of CSF 20 kg/m3 and for the other fibers only a 5.0 kg/m3 dosage was analyzed. The evaluated parameters include workability, E modulus, cylindrical compressive strength , cubic compressive strength , flexural cracking strength and residual flexural strength of the FRCs. For the non-commercial fibers, peak tensile strength were also assessed, and the carbonation surface of the specimens was observed. Finally, from the analysis of the FRCs - CMOD curves, the toughness of the mixtures was evaluated to compare the fracture energy both in ST and in LT. This experimental study aims to address the gaps in scientific literature regarding FRCs considering thermal cycles effects to support informed decisions on the selection of the most effective reinforcement fibers.