Rheological characterisation of injection grouts using rotational rheometry

The overall goal of this chapter is to contribute to the understanding and improvement of the rheological performance of injection grouts for consolidation of stone masonry buildings. It is a well known fact that old masonries such as heritage or ordinary buildings represent a large portion of the construction area in many European cities. They frequently present a bad state of conservation and have particular technical needs and specific weaknesses that require special approaches. Grout injection is an interesting technique to repair and consolidate such stone masonries. It consists of introducing a suspension (grout) into the masonry inner core in order to upgrade the cohesion of the masonry and increasing its monolithic behaviour. Therefore, it is essential to evaluate the effectiveness of the grouts in terms of keeping their adequate flow capacity. For this purpose, rheology appears as a useful tool in the controlling and optimisation of grouts design. Notwithstanding, during rheological measurements many disturbing effects may arise, such as the wall slip, which can play a significant role leading to an inaccurate rheological parameters determination. Despite the large number of research related to wall slip on several fluids with yield stress, the wall slip is still a concern for rheological measurements of grouts. Thus, this study aims to determine the degree of wall slip during rheological measurements of natural hydraulic lime-based grouts for stone masonry consolidation. For the determination of wall slip stress controlled measurements at various gaps and different shear stresses were performed. Overall, the results revealed that wall slip is function of the shear stress and the grout composition. Results from this research can help to define an adequate measurement protocol to correctly infer the rheological properties of injection grouts based on rotational rheometry.