Freeze-thaw resistance and service life prediction of fly ash incorporated ultra-high ductility magnesium phosphate cement-based composites

Abstract

To develop ultra-high ductility magnesium phosphate cement-based composites (UHDMC) suitable for cold areas and fully utilize solid waste, the effects of fly ash (FA) substitution and freeze-thaw cycles on the mechanical properties and freeze-thaw resistance of UHDMC specimens were explored. The mechanism of freeze-thaw damage was revealed by mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM). Freeze-thaw damage model for UHDMC was established to predict its service life. The results showed that, after 300 freeze-thaw cycles, the compressive strength retention rate of the UHDMC specimens with FA substitution from 10 % to 30 % was above 88.7 %, and the tensile strain maintained above 3.48 %, still presenting the characteristics of multi-cracking and strain hardening. Meanwhile, after 600 freeze-thaw cycles, the mass loss rate and the dynamic elastic modulus of UHMPC specimens with FA substitution from 10 % to 30 % were below 1.38 % and above 81.1 %, respectively. The mechanical properties were mainly related to the total porosity and macropores. The effect of the water solubility of prismatic struvite-K crystals and the secondary hydration production of filamentous struvite potassium crystals on the matrix presented well explanation for the excellent freeze-thaw resistance of UHDMC specimens with FA substitution from 10 % to 30 %. At last, a freeze-thaw damage model for UHDMC specimens with FA substitution below 30 % based on the Weibull probability distribution function was established, predicting that their service life was up to 232 years in the northeastern of China.