Improving performance of recycled aggregate concrete with superfine pozzolanic powders

Abstract

Phosphorous slag (PHS), ground granulated blast-furnace slag (GGBS) and fly ash (FA) were used as replacements of Portland cement to modify the microstructure of recycled aggregate concrete (RAC). A new manufacturing method named “W3T4” was proposed to improve the performances of interfacial transition zone (ITZ) between recycled aggregate and mortar. The mechanical properties and the durability of RAC were tested, which show that this new manufacturing method improves the properties of RAC, and the GGBS with finest size makes a great contribution to the performance of RAC due to its better filling effect and much earlier pozzolanic reaction. Combined with GGBS, the effects of PHS on the retardation of setting time can be alleviated and the synergistic effect helps to make a more compact RAC. For the RAC with 25% of the recycled aggregate (RA) replacement and 10% PHS + 10% GGBS additives, the compressive strength increases by 25.4%, but the permeability decreases by 64.3% with respect to the reference concrete made with nature aggregates. The micro-mechanisms of these improvements were investigated by the scanning electron microscope (SEM). The SEM images show that the new manufacturing method, adding superfine pozzolanic powders and super-plasticizer benefits, makes a much denser ITZ in RAC.