Properties and modification of sustainable foam concrete including eco-friendly recycled powder from concrete waste

Reusing recycled powder (RP) including recycled concrete powder (RCP) and recycled mortar powder (RMP) as an eco-friendly alternative binder benefits the reclamation of construction waste and reduces the cement demand. Considering that foam concrete (FC) which contains high volume cement and supplementary cementitious material (SCM) has been largely used in building engineering owing to its low density and good thermal insulation performance, and thus, substituting RP for partial cement in preparing FC is more sustainable. This work studied the influence of RP type and replacement on the performance of newly-made FC, and some feasible modification methods for improving the performance of RP blended in FC were further provided. A series of micro and macro tests were conducted. The results show that the utilization of RP has no distinct impact on the dry apparent density, thermal conductivity and porosity of its prepared FC. When the RP replacement rate is below 15%, the compressive strength of FC containing RP is slightly lower than that of FC without RP, while the compressive strength of FC decreases significantly as high-volume RP incorporates. Incorporating polyvinyl alcohol (PVA) fiber decreases the drying shrinking of FC containing RP, and the RP-prepared FC incorporating 0.3% PVA fiber has lower drying shrinkage and higher strength than that without fiber incorporation. The addition of metakaolin (MK) improves the mechanical strength of RP blended in FC, and the compressive strength increases by 32.9-34.9% as 10% MK incorporates.