Evaluation of consolidation of different porous media with hydraulic lime grout injection

The grout injection is a technique widely used for structural consolidation of the multi-leafs stone masonry, which often present low compactness and weak links between the internal and external leaves. Grouts can be seen as mixtures of binder with water, with or without special additives. To ensure an adequate flow of the grout and a correct filling of the internal voids inside the masonry, it is essential to assure good fresh grout properties, such as stability, water retention and a rheological behaviour. The grout specification involves the knowledge of the flow capacity within the masonry inner core and physic-chemical compatibility with the original materials present in the historic materials. Thereby, the scope of this paper is to evaluate the injection performance of hydraulic lime based grouts as a function of the porous media to be injected. For this purpose, simplified models were created to allow injectability tests in controlled conditions. To enable the simulation of different permeabilities and internal structures of masonries, the models were created by filling plexiglass cylinders with different grain size distributions of limestone sands and crushed bricks. Since, these materials exhibit different water absorption coefficients, it also was possible to study the influence of water loss from grout to porous media in grout injectability. Another variable studied with influence on grout injectability was the water content of porous media. As it is not expected that masonries are always dried, the pre-wetting of some cylinders by simple injection of water is of extreme relevance to compare the results of grout injectability in the two opposite situations. The grout injection performance was analysed both in the fresh and hardened states. The injectability of the grout as well as its link to the materials within the inner core of old masonries was assessed by tomography and mechanical tests. The mechanical results showed good correlation with injectability and high dependence with the position of the specimen analysed on the cylinder injected, creating tensile strength gradients along the height of the cylinder. Regarding the tomography, the tomographs demonstrate the compactness of the porous media after grout injection. In fact, according to the results obtained, it can be stated that the tomography allows the evaluation of the grout injection capacity to improve the physical and mechanical properties of the inner core of old masonries.