# Experimental Study on Shear Strengthening of RC Beams with an FRP Grid-PCM Reinforcement Layer
## 1 Introduction
the advantages of FRP grids bonded with a cement-based material are summarized as follows: (a) the stress transfer between the FRP grid and cementitious materials is more efficient, caused by the improving of the impregnation [32; 35]; (b) the drawbacks observed with the FRP sheets/plates with respect to uneven pasting and empty drums can be effectively avoided, especially when the strengthening areas are excessively large; and (c) for FRP grid strengthening, the rivets are usually considered to be a temporary anchor to attach the FRP grid on the external surface of concrete beams such that better bonding at the interface may be obtained to some extent. As mentioned before, FRP grids are usually fixed and bonded to concrete by spraying or laminating a thin covering of normal mortar. However, normal mortar is easily broken due to its properties of low tensile strength and brittleness. Thus, several cementitious materials used as a thin strengthening layer, such as engineered cementitious composite (ECC) matrix [33; 34; 36] and polymer cement mortar (PCM) [37; 38; 39], have been proposed by scholars from all over the world to take the place of normal mortar with low strength. PCM, a new inorganic material used in strengthening fields, is made by pouring a small volume of organic polymer (e.g., acrylic copolymer [40], arene-perfluoroarene [41; 42]) into a kind of cement mortar. The purpose of this is to improve the performance of the original inorganic materials, as it displays such properties as high tensile strength, superior corrosion and seepage resistance, lower incidence of dry cracking, as well as better bonding performance between PCM and the original concrete substrate [37; 43; 44]. A large number of relative studies on various FRP composites in shear strengthening have been discussed in recent years. For example, [PERSON] et al. and [PERSON] et al. [6; 45; 46] demonstrated the current state of research regarding RC members retrofitted by CFRP grid-PCM layer, indicating that regardless of the flexural or shear reinforcement effect, the load-carrying capacity of RC members retrofitted by CFRP grid-PCM was adequate. [PERSON] et al. [47] summarized the development and application of new structural materials, such as FRP composites, showing that the load capacity and ductility of strengthened structures were increased compared to unreinforced structures. [PERSON] et al. [48] and [PERSON] et al. [49] considered that the debonding failure of FRP composites with various formations (e.g., FRP grids/sheets) usually appeared on the concrete surface prior to concrete crushing during the shear resistance process. [PERSON] et al. [50] conducted several shear tests with RC beams externally bonded with FRP grid and UHTCC. The results showed that the shear strengthening effect produced by this method was very good, and studied the shear-compression failure and partial debonding of FRP grids regarding the ultimate state for these beam specimens with different reinforcement ratios. [PERSON] et al. [51] assessed the strengthening effect by comparing FRP grids and FRP sheets, indicating that the load-carrying ability and safety of beams reinforced with FRP grids were better than FRP sheets. In addition, [PERSON] et al. [52] and [PERSON] et al. [53] noted that the structural effectiveness of FRP composites in strengthening RC members was quite important to predict the load capacity of the strengthened beams. Therefore, previous investigators have pointed out that the evaluation method, which determines the contribution of the FRP composites for RC beams in shear, should carefully consider the effective strain of the FRP composites [54; 55; 56; 57]. However, existing calculated methods in shear are not suitable for the FRP grid because its stress transfer mechanism is different from traditional FRP composites (e.g., FRP sheets, FRP plates, and FRP bars). Moreover, at present, few studies have explored the reinforcement range and reinforcement amount of I-shaped RC beams, especially those strengthened by FRP grids.