Conservation and strengthening of historic masonry buildings should preserve their significance and ensure their structural stability. The condition of a structure and the extent of the damage determine the type of actions needed. It is important that the selected strategy maintains the existing aesthetic value of the masonry, as well as its structural integrity and the function of components, both during and after any intervention. Grouting is a well-known technique, which can be durable and mechanically efficient, whilst preserving the historic value. The selection of a grout for repair is based on the physical and chemical properties of the existing masonry. Compatibility between the existing and the injection material is a major factor in the success of the intervention. Parameters such as rheology, fluidity, and stability of the mix should be considered to ensure the effectiveness of grout injection. Many commercial ready-mix grouts are available but the use of lime-based grouts formulated in laboratory, with the addition of materials like fly ashes, silica fume, bentonite, hydraulic lime, or metakaolin, have been proposed by different researchers. This article addresses the development of ternary grouts, which show satisfactory mechanical and physical properties, and are viable low-cost alternatives to the commercial grouts.
Conservation, repair and strengthening of historic masonry buildings should preserve their significance and ensure their structural stability. The condition of a given structure and the extent of damage determine the type of action needed. Grouting is a well-known remedial technique, which can be durable and mechanically efficient whilst preserving the historic value. Still, the selection of a grout for repair must be based on the physical and chemical properties of the existing materials. Parameters such as rheology, injectability and stability of the mix should be considered to ensure the effectiveness of grout injection. In addition, the bond strength of the grout to the existing material is the most relevant mechanical property. Several commercial lime based grouts are available but it is unclear what are the applicable standards and requirements. This paper evaluates the behavior of commercial grouts under laboratory conditions. First, the properties of the grouts as an independent product are assessed with the objective to perform a comparative analysis of their behavior subjected to different conditions (temperature and working time of grout after mixing). Then, the behavior of the grouts when used in combination with stones used in the construction of masonry buildings is addressed (granite, schist and limestone), again considering different conditions (dry, wet and saturated). It is shown that the performance of the commercial products is rather different and careful selection of injection materials in practical applications is recommended.
Heritage masonry structures often show signs of deterioration due to ageing, soil settlements, extreme events or other actions. Repairing these structures using grout injection is an interesting technique since it preserves the historical character of the existing materials, even if filling voids and bringing a bonding addition. A high-performance grout for use in these structural repairs should meet several performance criteria, including fluidity, strength, compatibility and durability. The main objective of this study is to assess the bond characteristics of four commercially available (CA) grouts available in Europe, as this is possibly the most needed mechanical performance of grouts. The bond mechanism was studied in composite grout/stone specimens, as the shear bond strength of the grout–stone interface is the main property affecting the behaviour of grouted walls. In-depth characterization of the tensile strength of the interface between grout and stone required the preparation of specimens with the selected CA grouts and three usual stones in historical buildings: limestone, schist and yellow granite. The moisture content of the stones was also varied, as this is difficult to control in real case studies. Therefore, the tests were performed with dry, moist and saturated stones. Significant differences were found between the different grouts, stressing the need for adequate material selection.
