Design and evaluation of hydraulic lime grouts for the strengthening of stone masonry historic structures

The present paper discusses an experimental procedure realized in order to design hydraulic lime based grouts adequate for the strengthening of stone masonry historic structures. With the aim to minimize incompatibility problems between the original materials and the grouts, several natural hydraulic lime based grouts, as well as a ternary (lime-pozzolan-cement) grout with reduced cement content, have been studied. The selection of the most suitable grouts was performed based on a set of criteria, namely injectability, mechanical and durability characteristics. The selected grouts were subsequently injected into cylindrical specimens that simulate the infill of three-leaf stone masonry. The experimental results obtained from mechanical tests carried out on the injected cylinders demonstrated that all grout mixes studied within this work were efficient in strengthening the infill material; they exhibited, however, differences in terms of durability properties. Finally, an empirical formula was developed to predict the compressive strength of the injected infill, as a function of the mechanical properties of grouts.