Microstructure and macro properties of sustainable alkali-activated fly ash mortar with various construction waste fines as binder replacement up to 100%

Utilizing construction waste fines as eco-friendly binder for sustainable alkali-activated materials provides new approach to recycling construction waste. This work investigated the characterization of alkali-activated fly ash mortar (AAM) incorporating construction waste fines at varied types and replacement levels. The results showed that incorporating waste paste powder containing abundant hydrated products refined the pore size of AAM, but mixing waste mortar powder and waste concrete powder that contained massive inert quartz and calcite adversely affected the alkali-activated reaction and pore structure of AAM. The incorporation of construction waste fines was found to reduce the fluidity but increased the drying shrinkage of AAM. At identical replacement level of construction waste fines, the waste paste powder incorporated AMM has lower fluidity and greater drying shrinkage than the waste mortar powder or waste concrete powder incorporated AAM. Substituting waste paste powder for fly ash improved the mechanical strength of AAM, but the strength decreased as waste mortar powder or waste concrete powder was incorporated. Particularly, the AAM blended with 100% construction waste fines still owned good strength. Mixing construction waste powder reduced the chloride diffusion coefficient and chloride ingress depth of AAM, and the waste paste powder mixed AAM had better chloride resistance than the waste mortar powder or waste concrete powder mixed AAM. Therefore, the hydrated products in construction waste fines was revealed to benefit the micro-characteristics of alkali-activated materials, and optimizing the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.

Automated summary

Utilizing construction waste fines as an eco-friendly binder for sustainable alkali-activated materials provides a new approach for recycling construction waste. This study investigated the effects of different types and replacement levels of construction waste fines on the properties of alkali-activated fly ash mortar (AAM). The results showed that incorporating waste paste powder containing hydrated products improved the pore structure of AAM, while incorporating waste mortar powder or waste concrete powder with inert quartz and calcite had a negative impact on the alkali-activated reaction and pore structure of AAM. Adjusting the type and replacement level of construction waste fines can achieve sustainable AAM with good mechanical strength and chloride ingress resistance.