Effects of alkali-treated recycled carbon fiber on the strength and free drying shrinkage of cementitious mortar

Abstract: The waste management of carbon fiber−polymer composites has serious environmental implications if the wastes are sent to landfill or incineration. This laboratory investigation explored the viable chemical treatment for recycled carbon fiber (RCF) with residual cured epoxy on its surface, and evaluated the effects of alkali-treated RCF on the strength properties and volume stability of cementitious mortar. A total of seven mortar mixtures were designed to incorporate the untreated RCF and RCF treated by 1, 2 and 3 mol/L NaOH solution, respectively. The dosage of RCF was 1% by volume of the mortar and the water-to-binder ratio was 0.50. The compressive strength, splitting tensile strength and free drying shrinkage of RCF reinforced mortars were evaluated. The mechanical and shrinkage behaviors of cement mortars were enhanced by the RCF (untreated or treated by 1 mol/L NaOH). The scanning electron microscopy revealed that the treated RCF had better adhesion to the mortar matrix than the untreated one. The incorporation of RCF treated by 1 mol/L NaOH is a viable solution to reuse this waste in mortar. The RCF treated by NaOH solution of higher concentrations had a negative effect on the behaviors of mortar because of more damaged RCF and more Ca(OH) 2 in the mortar (if mixed with the waste NaOH solution).