Effect of recycled aggregate and supplementary cementitious material on mechanical properties and chloride permeability of concrete

With impending demand for sustainable development, construction wastes as recycled aggregate (RA) to produce recycled aggregate concrete (RAC) is inevitable. However, RA makes adverse effect on performance of RAC. To enhance its performance, the supplementary cementitious materials (SCM), including ground granulated blast furnace slag, red mud, and glass powder, were used to partially substitute cement. In this investigation, the plain cement concrete and mineral-admixture concrete with four replacement ratios of RA were poured. For each mixture, the compressive strength, dynamic elastic modulus, and resistivity were determined; Besides, chloride penetration test was conducted in a tidal cycling simulation device, in which specimens with dimension of 100 x 100 x 400 mm3 were used to explore the effect of drying-wetting time ratios RD/W on chloride diffusion. It was found concrete with 50% RA exhibits improved compressive strength and equivalent chloride resistance through 25% SCM addition. Concrete containing 100% RA achieves equivalent or even superior chloride resistance to control group as SCM added by 45%. With the increase of RD/W, the diffusion of chloride is more serious. Considering the inhomogeneity of concrete pores, a double-porosity transport model solution was derived based on Fick's second law. Combined with test results, a time-dependent model was then established to predict chloride concentration in concrete containing RA and SCM. Furthermore, an analytical solution of cumulative chloride content diffused into concrete was derived to quantify chloride permeability. Subsequently, a linear correlation between chloride permeability and resistivity is confirmed. This investigation will encourage the use of RA in marine engineering, thereby leading to a more sustainable and cleaner production.

Automated summary

This study investigates the use of supplementary cementitious materials to enhance the performance of recycled aggregate concrete. The results show that concrete with 50% recycled aggregate exhibits improved compressive strength and equivalent chloride resistance with the addition of 25% SCM. Additionally, the diffusion of chloride becomes more serious with the increase of drying-wetting time ratios.