Strength development and environmental assessment of alkali-activated construction and demolition waste fines as stabilizer for recycled road materials

This study investigates the effects of curing temperature on alkali-activated fine particles of undivided construction and demolition waste (CDW) aggregates. Previous investigations demonstrated that such activated fines can stabilize the whole mixture thereby improving its mechanical properties. To comprehensively investigate the behaviour of the activated fine, its strength and leaching properties under different curing temperatures were compared to those of the four alkali-activated powders of CDW aggregate constituents (concrete, reclaimed asphalt, bricks and tiles, and natural aggregate). Flexural and compressive strength tests at 28 days of curing were performed on different pastes prepared with different liquid to solid (l/s) mass ratios (0.4, 0.5, and 0.6), and cured at 5, 20, 40, and 80 °C. All components showed satisfactory strength properties for l/s = 0.4, which was found to be optimal. A significant enhancement of the mechanical properties was observed for specimens treated at 80 °C. However, non-negligible strength values were obtained at other temperatures. In particular, the undivided fractions showed satisfactory results and a low variability in properties when cured at average roadside temperatures from − 5 to 40 °C. Following leaching tests, the environmental compatibility of alkali-activated materials was deemed satisfactory with the concentration of pollutants considerably below the threshold of the European Council Decision 2003/33/EC for non-hazardous waste.