Effects of polypropylene fibers and measurement methods on the yield stress of grouts for the consolidation of heritage masonry walls

The injection of grouts is a consolidation technique suitable for overcoming the structural deterioration of old stone masonry walls. Grouting operations involve introducing a suspension (grout) into a masonry core with the aim of improving the load capacity of the wall, as well as reducing its brittle mechanisms. The yield stress of injection grouts will affect the injection pressure and their flow inside the masonry. However, the determination of some rheological properties such as yield stress in hydraulic grout is challenging, due to the combined effects of hydration reactions and interactions between the particles present in the suspension. In this study, the determination of the yield stress of natural hydraulic lime-based grouts with polypropylene fibers was carried out. The changes in yield stress with time, fibers content and hydration were evaluated by two measurement methods using a rotational rheometer. Additionally, the static and dynamic yield stress as well as the critical shear-strain rate were determined, which provided useful information on the grout design in order to achieve successful grouting operations.