Evaluation of the grout injectability and types of resistance to grout flow

Grout injection is an efficient technique commonly used for structural consolidation of multi-leaf stone masonries, which often present high porosity (especially in the inner core) due to the presence of internal voids. Since porosity and void size distribution are not constant within masonry, the efficiency of grouting varies along the injection. Thus, it is essential to study the injectability of grouts in porous media with different characteristics along the height of injection. To evaluate the efficiency of grout injection this work used 11 different porous media, in the shape of small scale cylinders. For each porous medium, grout injection velocity and injected mass were measured. The reliability of various rules of thumb used to check grout injectability was also verified. From the injection tests different resistances to grout penetration were detected, created by the porous medium to the flow. The knowledge of these resistances is crucial to estimate the grout penetration in the internal voids. In contrast with literature, the injection tests show that Darcy's law and front resistance are not adequate to estimate the grout injection. Therefore, an additional resistance is introduced (resistance of suspension – R_s). This resistance, as well as the overall resistance to grout flow are reduced when the pre-wetting of the porous medium (before grout injection) is done. The performance of the grout injection performance was also analysed in the hardened state with ultrasonic tomography.