## 1 Introduction
In the study of [PERSON] [10], single-layered or double-layered TRM overlays consisting of PBO textile and a cement-based matrix were applied on concrete prisms. Single-lap/single-prism shear bond tests were conducted after specimens' exposure at 50 \({}^{\circ}\)C and 100 \({}^{\circ}\)C for 8 h. The bond capacity of the double-layered TRM strips was reduced for both exposure temperatures while the capacity of the single-layered strip was negatively affected only for the higher exposure temperature. In the study of [PERSON] and [PERSON] [11], TRM strips with three or four dry carbon textile layers were applied on concrete prisms through a polymer-modified cementitious mortar for the realization of single-lap/double-prism tests. Two testing procedures were followed. According to the first one, specimens were heated at a target temperature (50 \({}^{\circ}\)C, 75 \({}^{\circ}\)C, 100 \({}^{\circ}\)C, 150\({}^{\circ}\)C, 200 \({}^{\circ}\)C, 300 \({}^{\circ}\)C, 400 \({}^{\circ}\)C, and 500 \({}^{\circ}\)C) for 60 min and they were then tested under the same temperature. These specimens were not seriously affected in terms of TRM bond capacity up to a temperature of 400 \({}^{\circ}\)C while their bond load was less than or equal to half of the untreated specimens' load for a temperature of 500 \({}^{\circ}\)C. According to the second procedure, specimens were loaded up to a certain percentage of their bond strength (25%, 50%, and 75%) at ambient conditions and they were then heated up to failure (temperature at failure: approximately 300 \({}^{\circ}\)C when stressed to 25% and 50% of their bond strength and approximately 75 \({}^{\circ}\)C when stressed to 75% of their bond strength). Review of the existing literature on the topic reveals the lack of commonly accepted testing protocols for the investigation of the heating effect on the TRMs' shear bond performance (either during or post heating) when bonded on various substrates. Temperatures examined are subjectively characterized as 'elevated' or 'high' and heating regimes are arbitrarily selected, which renders comparisons between different experimental campaigns difficult or even invalid. Specimens' treatment prior to testing with a special focus on the moisture content of the TRM overlay (but also of the substrate) is yet another parameter that deserves special attention should rational testing procedures be drafted. Once there, the role of bond critical parameters like the number of textile layers, the textile geometry, the type of the matrix, and the type of substrate on heat-struck TRM/substrate joints remains to be investigated. Although there is no clear definition of what is considered to be the range of \"elevated temperatures\" as opposed to that of \"high temperatures\", one would identify (from the available literature) 300 \({}^{\circ}\)C as the boundary temperature between them. Realistic exposure conditions to higher (or much higher) temperatures should be simulated with fire-resembling time-temperature histories (since these temperatures are frequently the result of fire events). The \"elevated temperatures\" range is of relevance when the aim is to assess the properties of concrete-like materials (TRM, in this case) with surface temperatures close to the ones reached in this paper. Practical examples of situations resulting into such surface concrete (TRM) temperatures are: (i) hot weather exposure (where concrete surface temperatures close to 50 \({}^{\circ}\)C or higher can be recorded, [12]) and (ii) exposure to climatic conditions inside nuclear reactor containments (where the maximum allowed--accident-inflicted or short-term--surface temperatures on concrete elements is set to approximately 175 \({}^{\circ}\)C, [13]). This paper presents the experimental assessment of the residual bond capacity of two externally bonded TRM systems on masonry substrates post their exposure to elevated temperatures.