Promoting utilization rate of ground granulated blast furnace slag (GGBS): Incorporation of nanosilica to improve the properties of blended cement containing high volume GGBS

Utilization of high volume ground granulated blast furnace slag (GGBS) to produce cement-based materials (CBMs) meets the requirements of sustainable development. However, high volume GGBS will significantly reduce some properties of CBMs. Incorporation of nanosilica is a potentially feasible approach to solve the problem. In present paper, effects of nanosilica (1 wt%, 2 wt% and 3 wt%) on hydration and microstructure of blended cement incorporating high volume GGBS (80 wt%) have been studied by testing setting time, compressive strength, hydration heat, hydration products and pore structure. Results reveal that nanosilica shortens the initial and final setting time of blended cement by 10.75%–20.56% and 10.45%–23.00%, respectively. Furthermore, nanosilica enhances early hydration heat release rate of cement and GGBS. Meanwhile, nanosilica increases cumulative heat release of blended cement by 23.40%–26.46%. However, nanosilica hinders cement hydration after curing for 7 d. Results of thermal analysis indicate that 80 wt% GGBS significantly reduces the content of chemically bound water, while nanosilica improves the parameter by 1.32%–5.91% at 56 d. Additionally, 80 wt% GGBS increases cumulative porosity by 31.89% at 28 d, but nanosilica decreases cumulative porosity by 3.05% at 28 d. Both high volume GGBS and nanosilica can decrease average pore diameter and enhance microstructure of cement paste. Ultimately, nanosilica increases the 28 d compressive strength by 8.27%–19.23%, which partially compensates for the reduction of compressive strength caused by high volume GGBS. This paper can provide the essential foundation for the theory of nanosilica-modified CBMs with high volume GGBS, help to improve the effective utilization rate of GGBS and realize sustainable development of CBMs. •Properties of blended cement with high volume GGBS and nanosilica are studied.•Mechanism of nanosilica reinforced GGBS-containing cement paste is discussed.•Nanosilica increases compressive strength of blended cement with GGBS.•Nanosilica enhances the microstructure of cement pastes with high volume GGBS.•Nanosilica improves the effective utilization rate of GGBS in blended cement.