Investigation of Mineral Admixtures on Mechanical Properties of Alkali-Activated Recycled Concrete Powders Cement

Recycled concrete powders (RCPs) are collected during the treatment of recycled aggregates using devices that suction dust. However, RCPs have not been effectively utilized as mineral admixtures in concrete due to their low activity and high capacity for water absorption. In this study, alkali-activated recycled concrete powders cement (AARCPC) was prepared using chemical activation, and then the composition, fluidity, setting time, strength and micro-structure of hydration products in AARCPC were studied. We found that the addition of mineral admixtures significantly improved the strength of hardened paste at various ages, and that the effect of slag powders on the mechanical properties was significantly better than that of fly ash. Replacing AARCPC with 50% slag caused the 28 d and 90 d compressive strength of pastes to reach 79.5 and 84.4 MPa, respectively. The optimal ratio of the various minerals that make up AARCPC was 60% recycled concrete powder, 20% slag powder and 20% fly ash. In particular, hydration with fly ash and slag of AARCPC promotes better fluidity and compactness. AARCPC showed higher strength and has the potential to replace Portland cement and be applied to concrete.

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