Employing limestone and calcined clay for preserving the strain-hardening response of PET fiber-reinforced cementitious composites
Ameer Hamza Ahmed, Cesare Signorini, Mariam Chikhradze, Marco Liebscher, Marko Butler, Viktor Mechtcherine
Abstract
The degradation of polyethylene terephthalate (PET) fibers in alkaline environments limits their use in strain-hardening cementitious composites (SHCC). Prolonged PET exposure to alkaline environments has a detrimental effect on its mechanical performance, mainly due to the physicochemical transformation caused by alkaline hydrolysis. This study presents a tailored cementitious matrix design containing high amounts of limestone and calcined clay, replacing 75 wt% of Portland cement, to attain and maintain the strain-hardening response of composites incorporating PET fibers as dispersed reinforcement. Analytical and mechanical tests were carried out at different curing ages, ranging from 7 to 60 days, to study the effects of aging on virgin PET fibers, both within the matrix and outside it (in the pore solution). The results showed a pronounced degradation of the PET fibers in the test pore solution at pH 12.5, manifested by a progressive reduction in the load-bearing capacity of the individual fibers with prolonged immersion. Conversely, when the PET fibers were aged in-matrix under laboratory conditions and tested under tension, the performance of the corresponding composites showed resilience to aging, exhibiting reasonable tensile strength and remarkable strain capacities that exceeded 4 %.