PSI - Issue 42

Makashev Kuanysh et al. / Procedia Structural Integrity 42 (2022) 769–776 Makashev K./ Structural Integrity Procedia 00 (2019) 000 – 000

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same name used for the textile mesh impregnated in the cement based or limebased mortar and used for the strengthening Reinforced Concrete (RC) (Tetta, Koutas and Bournas, 2015; Elsanadedy et al., 2013) and Unreinforced Masonry (UM) structures (Ismail and Ingham, 2016). Over the past two decades TRM has been considered as a promising solution for strengthening existing structures (Makashev et al., 2022; Kouris and Triantafillou, 2018). However, one of the drawbacks of the TRM is the lower adhesive property compared to Fibre Reinforced Polymer (FRP) so, the bond between fibres and matrix is not as strong as in FRP. This is due to the cement grain is too large to fully penetrate between textile filaments, compared to epoxy resin. Coating of the fibres with epoxy resin make the fabrics rigid which, in turn, can eliminate the slippage among filaments and improve contact between matrix and fibres (Donnini, Corinaldesi and Nanni, 2016a). Based on the literature review, the three primary parameters such as textile materials, mortar matrix, and adhesion between TRM and masonry elements significantly affect the bond between TRM and masonry substrate. Carbon textile reinforced mortar (CTRM), in most cases, has a lower exploitation ratio (tensile coupon test result to bond test result) compared to the basalt and glass textile. Moreover, CTRM has the highest bond strength. Therefore, carbon textile can be more suitable for strengthening masonry bridges where structures subjected the high load in this case the high performance mortar can be more appropriate compared to lime-based mortar. Improving the bond performance between carbon textile and mortar matrix could lead to the better strengthening of UM elements. According to the literature, this could be done by applying epoxy resin to the textile. The application of epoxy resin coating on the textile fibre material was found to increase the rigidity of the textile and eliminate the slippage among the filaments. As a result, the contact between the matrix and the fibres was found to considerably improve (Donnini, Corinaldesi and Nanni, 2016b; Kariou, Triantafyllou and Bournas, 2019). Donnini et al. (2016) examined the effect of coating on the bond of carbon textile reinforced mortars to masonry. Varying pre-impregnation strategies were considered, namely, dry fabric (Dry), light impregnation (L), medium impregnation (M), and high impregnation (H). Furthermore, the layer of the quartz sand applied to the textile after the coating impregnated in the three-level light (L), medium (M), and high (H). The bond length used in the experimental campaign was equal to 150 mm. The mesh size of the textile was 20 x 20 mm. The weight of the dry textile was 180 g/m2. The application of light, medium, and high coating increased the weight by 36 %, 82%, and 205%, respectively. In addition, the application of light, medium, and high quartz sand layers increased the weight of the dry carbon by 390 %, 455 %, and 1000%, respectively. In total, 70 samples with a dimension of 410 x 60 x 10 mm were tested, for the tensile test using a clevis grip system, as described in Annex A of AC434 (AC 434-13), and 21 double-lap shear tests were performed (3 identical samples were used per variant). The failure mode for most samples was slippage fibres of the matrix. This was not the case for the high impregnation of the epoxy resin and epoxy resin with sand was slippage and failure of the matrix out of the bonded area. The authors concluded that the utilization of the epoxy resin has the potential to significantly improve the mechanical performance of the FRCM strengthening system. Barducci et al. (2020) investigated the bond performance of basalt TRM to masonry using both single- and double-lap shear tests with the objective of examining the effect of the matrix strength on the bond strength. For that purpose, the study considered the following types of mortar, i.e., • Commercial lime mortar matrix (MK); • Cement mortar matrix mixed in the laboratory (MC); • Lime mortar matrix mixed in the laboratory (ML); • Cement-lime mortar matrix mixed in the laboratory (MCL). A constant anchorage length used was across all specimens equal to 220 mm. The textile width was 95 mm. Two main failure modes were observed depending on the test setup. Fibre rupture out of the matrix was observed in all single-lap tests. Conversely, textile slippage was observed in all double-lap tests apart from double-lap specimens strengthened with the MK mortar. In this latter case, the specimens failed due to textile rupture. The authors concluded that the better bond performance showed by commercial lime mortar, i.e., the highest load values with the lowest Coefficient of variation (COV). Contrary to the worst result represented by cement-lime mortar matrix-based FRCM, i.e., lowest load values and consistent COV (Barducci et al., 2020). This paper presents the experimental results of the quasi-static single-lap bond tests. The main purpose of this experimental study was to investigate the bond at the TRM to masonry substrate interface considering the effect of the matrix strength on the bond strength.