Effect of chemical and thermal activation on the microstructural and mechanical properties of more sustainable UHPC

To boost the hydration reaction of blended UHPC with a high BFS content, KOH was added. The use of [KOH]3 significantly increased the amount of hydrated products, reducing the porosity of UHPC4 1.6-fold at 3 days and increasing its compressive strength by 42% at the same age. However, this activation mode was not enough to ensure the required compressive strength of UHPC1. Thermal activation at 90 °C for 2 days was therefore tested. Results showed the acceleration of the reaction of solid components, which increased the consumption of portlandite and hence the development of hydrated products. This resulted in improving the packing density of blended UHPC, decreasing its porosity and enhancing its compressive strength. In comparison with reference concrete at 90 days, the compressive strength of UHPC3-T increased by 7% and that of UHPC4 was 12.5% lower.