ORIGINAL ARTICLE Durability of natural hydraulic lime (NHL) based TRM composites through hot water immersion method M. E. Gunes . B. Y. Pekmezci . Z. C. Girgin Received: 27 July 2020 / Accepted: 6 December 2020 / Published online: 13 January 2021 Ó RILEM 2021 Abstract The textile reinforced mortar (TRM) com- posites are widely utilized for the seismic strengthen- ing of masonry walls subjected to in-plane and out-of- plane actions. The probability of out-of-plane failure via snap-through mechanism is dominated by the flexural characteristics of relatively slender masonry wall. In this study, a rapid and early decisive procedure is proposed to direct the design of TRM composite through the bending tests combining accelerated ageing. The durability of natural hydraulic lime based TRM composites, which is unknown in the current literature, is addressed for glass, basalt and carbon textiles. The interaction between fiber mesh and matrix is discussed regarding fiber type, the influence of impregnation, flexural performance and failure modes. For total five types of fabrics, the flexural capacities are compared at ambient conditions and then through hot water ageing test (immersion at 50 °C during 10 days). The experimental findings indicate to the importance of the interaction between fiber and matrix about the durability and ductility of TRM composites. Keywords Textile reinforced mortar (TRM)  Natural hydraulic lime (NHL)  Bending tests  Durability  Accelerated ageing  Hot water immersion 1 Introduction Externally bonded systems have gained popularity in last decades for strengthening applications to current masonry structures. TRM systems are composed of high-strength fabric mesh dipped in inorganic matrix. This system originated as an alternative to fiber reinforced polymer (FRP) jackets, which have some disadvantages (due to organic binder, e.g. epoxy) such as the poor fire resistance, degradation risk in saline environment and freeze–thaw conditions, inconsis- tency with masonry/concrete substrates, sensitivity to UV and reversibility. Nowadays, bidirectional grids of glass, basalt and carbon type textiles gain popularity in TRM applications. Addressing the fiber types used in FRP and TRM composites, both glass and basalt fibers are rock based Supplementary Information The online version contains supplementary material available at (https://doi.org/10.1617/ s11527-020-01608-3). M. E. Gunes Building Science and Technology Division, Architecture Faculty, Karabuk University, Karabuk, Turkey e-mail: esatgunes@karabuk.edu.tr B. Y. Pekmezci Construction Materials Division, Civil Engineering Faculty, Istanbul Technical University, Istanbul, Turkey e-mail: pekmezcib1@itu.edu.tr Z. C. Girgin (&) Building Science and Technology Division, Architecture Faculty, Yildiz Technical University, Istanbul, Turkey e-mail: zcgirgin@yildiz.edu.tr Materials and Structures (2021) 54:24 https://doi.org/10.1617/s11527-020-01608-3