Combined Effect of Silica Fume and Nanosilica on the Performance of Injection Grouts for Consolidation of Heritage Buildings

This chapter presents a research on the joint effect of silica fume (SF) and nanosilica (NS) on the fresh and hardened properties of natural hydraulic lime-based grouts for mechanical strengthening of old stone masonry walls. Old buildings were mainly built based on multi-leaf stone masonry walls using lime-based mortars. Due to reduced quality of the used mortar and the presence of internal cracks and voids in the walls, the load bearing capacity of such walls is mostly insufficient. A successful technique for the repair and strengthening of the historical buildings is grout injection, where the grout is injected into the wall to achieve increased bonding between the stones, leading to improved mechanical properties of the injected walls.
For proper strengthening by grout injection, suitable fresh and hardened grout performance and materials compatibility with the existing ones should be assured, which requires an adequate grout design. In this sense, this study investigates the contribution of SF and NS on the rheological properties, mechanical strength and durability of injection grouts, in which grouts formulated with different SF, NS and high range water reducer (HRWR) contents were produced. Taguchi’s method was used to obtain the optimal contents of parameters involved in the grouts design. It was found that, even for reduced NS content, the plastic viscosity and the yield stress increase significantly, which increases the HRWR amount needed in order to not impair the grouts fluidity. On the other hand, the combined effect of SF and NS had substantial and positive changes on the mechanical strength and microstructure of the hardened injection grouts. The results obtained allow concluding that SF and NS should be used together to exploit their synergetic behaviour.