Development of cementless ultra-high performance fly ash composite (UHPFC) using nucleated pozzolanic reaction of low Ca fly ash

Abstract

This study developed ultra-high performance fly ash composite (UHPFC) by enhancing the pozzolanic reactivity of low-calcium fly ash (FA). Although it did not include Portland cement, the composite exhibited outstanding performance in workability, mechanical properties, and strength development. At room temperature (20 °C), the hydrated lime-activated FA containing silica fume showed a distinct acceleration period. Moreover, 3 days of steam curing at 60 °C guaranteed its final strength (∼110 MPa) before 7 days because of the synergistic effect between the ultrafine filler and steam curing. At 60 °C, the reactivity of FA was dramatically improved only when nucleation sites were provided by silica fume. Furthermore, increasing the curing temperature reciprocally affected FA and silica fume in the reaction; while FA was a leading participant in the pozzolanic reaction, silica fume mostly played a role as a physical filler, providing the nucleation site for reaction products.