Extending the use of ternary cementitious system in rapid repair engineering through the incorporation of fly ash

This paper investigates the effect of fly ash [FA] on the hydration and strength development of composite cement pastes with ternary cementitious systems [OPC-CSA-CŠ]. The fluidity, setting time, swelling rate, and compressive strength of cement pastes with 0 %, 5 %, 10 %, 15 % and 20 % [mass fraction] fly ash substituted for OPC cement were tested. The hydration process, hardening, and microstructure of the cement slurry were analyzed by hydration heat, XRD, TG-DTG, SEM, and MIP test techniques. The results showed that with increasing FA content, the flowability of cement slurry improved, the setting time was shortened first and then lengthened, and the doping of FA can inhibit the shrinkage of the volume of the cementitious system at the later stage. When the FA content was 10 %, the flowability increased by 9.6 %, and the initial and final setting times were shortened by 23.4 % and 12.1 %, respectively. Simultaneously, the nucleation effect of FA provides a precipitation surface for Ca(OH)2 and C-S-H, which spreads the generated hydration products, accelerating the early hydration reaction rate and generating more AFt, improved its compressive strength. At the later stage of hydration, the micro-filler effect of FA made the unhydrated particles cut the large pores in the cement pore space into small interconnected pores, which improves the overall compactness of the slurry. The above results further develop the utilization value of FA and effectively expand the application of the ternary cementitious system in rapid repair engineering.