Formulation of High-Performance Cement Grouts for the Rehabilitation of Heritage Masonry Structures

Heritage masonry structures are an integral part of our landscape. Heritage structures located in Canada and the United States are relatively young compared to European heritage structures but they can show signs of deterioration due to our harsh climate. Repairing these structures using grout injection is a very interesting technique since it involves preserving the historical character of the structures. The formulation of injection grouts for such repair must be based not only on physical properties of the deteriorated mortar, but also on chemical properties. Compatibility between the existing medium and the repair material is a major factor in avoiding new deterioration related to poor mechanical behaviour of injected grout or chemical reactions with deteriorated mortar. Other parameters such as rheology, injectability and stability of repair grouts must be considered to ensure the effectiveness of grout injection. Many mineral additives and chemical admixtures are available for the formulation of cement-based grouts used to make repairs. Some of these products have been tested in the laboratory to optimise high-performance cement grouts used to repair heritage hydraulic masonry structures in Canada. The characteristics of these grouts and their performance during field work are presented in this paper. The effectiveness of the grouting treatment was controlled by sonic tomography conducted before and after grouting: several techniques are illustrated and their results are very sensitive to the actual grout intake in the different locations of the structure treated.