Improving sulfate resistance of 100% recycled coarse aggregate concrete by simultaneous application of limestone powder and EDTA-2Na

This study investigated the performance of 100% recycled coarse aggregate concrete (RAC) containing limestone powder (5% and 10%) and EDTA-2Na (0.4% and 0.8%) in 5% Na2SO4 solution for 360 days. Value engineering and environmental analysis were conducted to determine the optimum proportion of 100% RAC. Results showed that the 28-d compressive strength of RAC decreased by 12.2% when using 100% recycled coarse aggregate. After the sulfate attack, the 100% RAC seriously deteriorated because of the weak interface transition zone. Adding 5% limestone powder refined the pore structure of 100% RAC and improved its sulfate resistance, although the 28-d compressive strength decreased. Adding the proper amount of EDTA-2Na (0.4%) can reduce the mass loss of concrete during the sulfate attack, which is attributed to the promotion of hydration of cement and the decrease in calcium ions by chelating. Besides, the crystals of ettringite in the specimen containing EDTA2Na was thicker and longer, less damaging to concrete than the thinner needle -like ettringite crystals observed in 100% RAC. The value engineering and environmental analysis showed that applying 100% RAC containing 5% limestone powder and 0.4% EDTA-2Na in a sulfate environment was optimum and had good ecological and environmental effects.