Combine use of 100% thermoactivated recycled cement and recycled aggregate for fully recycled mortar: Properties evaluation and modification

Abstract

The large-scale recycling of concrete waste and its high-value utilization are key research topic in the field of sustainable building materials. This paper investigated the properties of fully recycled mortar made with thermoactivated recycled cement and recycled fine aggregate (RFA) up to 100%. The 600 °C thermoactivated recycled cement contained active compounds such as C2S and CaO. Substituting recycled cement for ordinary Portland cement reduced the hydration reaction and enlarged the pore structure of paste, but mixing active admixture could improve the micro-structure of recycled cement paste. Incorporating recycled cement and RFA decreased the mechanical strength of mortar, as well as elevated the drying shrinkage and transport properties. The detrimental impact of incorporating recycled cement on the performance degradation was more prominent than that of RFA incorporation. Nevertheless, the properties of fully recycled mortar with both 100% recycled cement and RFA still achieved a relatively satisfactory level. Besides, recycled mortar made with recycled cement derived from cement paste waste exhibited superior performance to that made with recycled cement from concrete waste. Substituting active admixture for 10% recycled cement could obviously improve the strength and permeability resistance of fully recycled mortar. Therefore, optimizing the replacement rate of recycled cement, RFA and active admixture is expected to prepare the fully recycled mortar with good performance. The maximal utilization of concrete waste could be achieved through preparing fully recycled mortar with the use of recycled cement and RFA completely instead of natural sand and ordinary Portland cement. This approach resulted in lower CO2 emissions and provided superior environmental benefits.