An experimental assessment of textile and wire reinforced horasan mortar strengthening of birick walls in historical buildings

It is quite important that original material properties of historical buildings are protected and passed to the next generations. Original material properties of historical buildings can be harmed irreversibly by wrong material choices in interventions aiming at strengthening of these buildings. Therefore, proper strengthening techniques should be preferred and the materials used in interventions to historical buildings need to be in harmony with the original materials of the building with respect to physical, chemical, mechanical and aesthetical aspects. It is known that horasan plaster and horasan mortar are used as binder and plaster in brick walls of historical buildings. In this study, we first built model brick walls similar to the brick walls of historical buildings by using materials compatible with the original materials of those historical brick walls. Then, we conducted experiments investigating the reinforcement of these model brick walls with textile and wire reinforced Horasan mortar First of all, an investigation to determine the mortars which will be used in the study was made. In the production of the mortars, brick ballast and river sand were used as aggregate, hydraulic lime and trass (natural puzzolana) were used as binder. Four series of mortar samples were constructed to determine the joint mortar which would be used in the construction of the model brick walls and the plaster mortar which would be used in the strengthening of the model brick walls constructed. While determining the binder:aggregate ratios of the joint mortar, the sample mortars produced were designed to represent the mortar properties of the historical buildings and to have low compression strength. While determining the binder:aggregate ratios of the plaster mortar which would be used to strengthen the model brick walls produced, mortar series were designed to be compatible with the original materials of historical buildings and to have high pressure endurance. In the mortar series designed, different binder:aggregate ratios by volume were tried. As to the mortars within the same series, binder: aggregate ratios by volume and water amount by mass were kept fixed. The aggregate particle size distributions and hydraulic lime:trass ratios of the mortars within the same series were made different. Compression and bending tests were conducted on the constructed mortar samples after the samples had awaited for either 7 days in a curing oven at high relative humidity, or 28 days or 90 days in ambient conditions. Unlike joint mortar samples, plaster mortar samples had awaited for 7 days in ambient conditions in closed polyethylene bags and cured with the samples own humidity. Later, these plaster mortar samples were taken out of the bags and had awaited in ambient conditions for 21 days. Then, compression and bending strength of these samples were determined. Furthermore, the samples which were humidified for 7 days in ambient conditions had, then, awaited in ambient conditions for 28 or 90 days. Then, compression and bending tests were applied to these samples. According to the results of these tests: • It was seen that determined that the grain size distribution of the aggregates used in mortar admixtures is an important factor in mechanical strength of the mortar. •It was determined that the mechanical strength of mortars changes as the binder: aggregate ratios of the admixture differ. •All of the natural puzzolana which were used as binders had binder effects. Some of these had thin aggregate impact. •It was determined that the mechanical strength of the mortars increases with the increase in awaiting time with time •It was seen that high relative humidity and high temperature significantly increases the mechanical strength of the mortars. •It was seen that humidifying the mortar with water in the first days of its applciation contributes to the mechanical strength of the mortar. In the experimental study, 42 model brick walls were constructed. The bricks used in the construction of these model brick walls were clay bricks. These bricks were cut in 9.5 cm x 4.5 cm x 2.5 cm dimensions, out of bricks the dimensions of which were 19 cm x 9 cm x 5 cm. The mortar used in the construction was horasan mortar with 1 cm thickness. The size of the model brick walls were determined to be 20 cm x 20 cm so that they fit into the machine into which the model brick walls would be loaded. While the plaster mortar used in strengthening the model brick walls was the same in all samples, the reinforcement type applied together with the mortar differed from sample to sample. Model brick walls were grouped into 4 series according to the reinforcement type used: •Strengthening with plain mortar (Series 1) •Strengthening with steel-mesh reinforced mortar (Series 2) •Strengthening with glass-fiber textile reinforced mortar (Series 3) •Strengthening with basalt mesh reinforced mortar (Series 4) The variables investigated in the series: •Damaged or non-damaged strengthening of the samples •One-sided or two-sided strengthening of the samples •Type of the reinforcement used in the samples In series 1, the strengthening was done by using only plain plaster mortar, without adding a reinforcement. Non-damaged wall samples were investigated by strengthening them one-sidedly or two-sidedly. Series 2, Series 3, and Series 4, each of which had 12 samples, were strengthened one-sidedly or two-sidedly, and they had been damaged or non-damaged. The samples which were damaged following diagonal load application were strengthened after they were repaired by using natural-hydraulic-lime based injection mortar. 42 strengthened wall samples awaited in laboratory conditions for 90 days. Then, uniaxial compression tests were applied to these walls after the walls were placed into the loading axis with an angle of 45 degrees. Co-evaluation of the horizontal and the vertical loads the samples were exposed to was ensured by using uniaxial compression loads applied onto the samples. For each variable investigated in the study, three model brick wall samples were tested. With the diagonal compression test applied to the model brick walls, the ultimate loads, shear stresses, vertical deformation capacities, and failure modes of the walls were determined. Mechanical properties of the samples were evaluated in two different ways according to the results. Firstly, breaking loads of the non-damaged model brick walls which were strengthened non-damagedly were investigated. The results of these were compared with the results of the 18 model brick wall samples the plain versions of which were tested. Efficiencies of the strengthening applications were compared. Secondly, the damaged model brick walls were strengthened and the efficiencies of these strengthening applications were compared with their initial states. According to the results: •It has been determined that the ultimate loads, shear stresses and deformation capacities of brick walls with fiber reinforced mortar are higher than other model brick walls •It has been determined that the ultimate loads, shear stresses and deformation capacities of two sided reinforced model brick walls are higher than one sided reinforced model brick walls. •Among the walls which were reinforced with reinforced mortar, ultimate load and shear stres were found to be the highest in the walls which were reinforced with wire mesh reinforced mortar, and lowest in speciments which were reinforced with basat fiber reinforced mortar. •Glass fiber and basalt fiber reinforced mortar specimens were found to be more ductile than other reinforced specimen. •The model brick wall samples plain or reinforced with mortar failed abruptly. •The failure in the model brick walls which were reinforced with fiber reinforced mortar was more ductile than the failure in the model brick walls which were plain or reinforced with mortar. •The mesh type was found to be quite influential on the failure modes of the speciments which were reinforce with fiber reinforced mortar. It has been observed that in the model brick walls which were reinforced with mortar and wire fiber reinforced mortar, the failure occurred abruptly while in the model brick walls reinforced with glass fiber reinforced mortar or basalt reinforced mortar the failure occurred in more ductile ways. •The adherence between the fiber and the mortar in the walls was found to be less in the walls which were reinforced with basalt reinforced mortar than those in the walls which were reinforced with glass fiber or wire reinforced mortar. Moreover, it has been observed that in the model brick walls reinforced with basalt reinforced mortar, the fibers and the mortar started to debond in the early phases of weight loading.