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

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 degrees C), the hydrated lime-activated FA containing silica fume showed a distinct acceleration period. Moreover, 3 days of steam curing at 60 degrees C guaranteed its final strength (similar to 110 MPa) before 7 days because of the synergistic effect between the ultrafine filler and steam curing. At 60 degrees 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.

Automated summary

This study developed an ultra-high performance fly ash composite (UHPFC) by enhancing the pozzolanic reactivity of low-calcium fly ash (FA). The composite showed outstanding performance in workability, mechanical properties, and strength development. Steam curing and the presence of silica fume had a significant effect on improving the reactivity of the fly ash.