Study on the durability of eco-friendly recycled aggregate concrete with supplementary cementitious materials: The combined action of compound salt solution of MgSO4, Na2SO4, and NaCl and dry-wet cycles

Abstract

Focusing on eco-friendliness and sustainability, recycled aggregate concrete (RAC) has been recently substituted for natural aggregate concrete (NAC) in new constructions. In Northwest China, high-concentration corrosive ions of magnesium, sulfate, and chloride exist in soil and groundwater, which have a severe adverse effect of exposing RAC’s durability. To improve the efficient utilization of RAC in the environment of the aggressive ion, the durability experiment of eco-friendly RAC with supplementary cementitious materials (SCMs) under the combined action of 7.5 %Na2SO4 + 7.5 %MgSO4 + 5 %NaCl and dry-wet cycles was investigated. Results show that RAC with the ternary blend of cement-fly ash-granulated blast furnace slag had the best durability among all the RAC mixtures. The 10 % fly ash + 20 % silica fume and 10 % fly ash + 20 % metakaolin negatively affected the durability improvement of RAC. At the same D&W cycles, the relative content of hydration and corrosive products of RAC with SCMs was lower than that of RAC without SCMs, and Friedel’s salt and Mg10(OH)18Cl2·5H2O were not found. The mineral phase composition of RAC exposed to the compound salt solution was related to the relative content of portlandite. Furthermore, grain volume increasing from brucite and gypsum, salt crystallization pressure from blödite and MgCl2, and solid volume changing from thenardite to mirabilite mainly degraded RAC’s durability.