Effect of ultrafine pozzolanic powders on durability of fabricated hydraulic lime

Fabricated hydraulic lime (FHL), prepared by fully mixing hydrated lime and hydraulic components containing activated Si/Al, shows quicker strength development and better water resistance than that of hydrated lime, and has the advantage of raw material supply to replace natural hydraulic lime (NHL) for the restoration of ancient sites. As ultrafine pozzolanic powders such as nano-SiO2, silica fume, slag, fly ash and circulating fluidized bed combustion ash can not only improve the hydraulic activity, but also be beneficial for the permeability of FHL paste in the ancient sites, this study investigated the influence of the above ultrafine pozzolanic powders on the durability of FHL, and obtained an optimal FHL through orthogonal test, and its durability was compared with NHL. The results showed that nano-SiO2 had a significant improvement on the water and sulphate resistance of FHL paste as well as its early compressive strength; silica fume greatly influenced the water resistance and later compressive strength; slag is the most important factor to improve the sulphate resistance of FHL; fly ash and circulating fluidized bed combustion ash had a smaller effect on the durability of FHL. The optimum FHL is composed of 1% nano-SiO2, 2% silica fume, 10% slag, 10% fly ash, 6% circulating fluidized bed combustion ash and 69% hydrated lime, which owned much better water and sulphate resistance than NHL mortar. The superior durability of FHL pastes was mainly due to the diversification of the internal hydration products and the close connection from XRD and SEM analysis. FHL with excellent durability proposed in this paper may have a positive impact on the restoration of ancient sites. In the future, the reinforcement effect of FHL prepared in this study on cultural relics sites will be discussed.