An experimental campaign on the use of Flax-TRMs for seismic strengthening of masonry structures

Past earthquakes have shown that conventional masonry buildings are often most vulnerable to damage in case of an earthquake. Several approaches have been deployed in the past to strengthen the masonry structures against extreme loading events. One of the most widely used strengthening mechanism is the application of externally bonded inorganic composite systems on masonry substrate. In recent years, with a focus on environmental conservation and sustainability, there are continuous efforts to use ecofriendly materials and innovative methods in construction instead of conventional materials and methods. Several studies have been conducted in the past to characterize such materials and to determine their suitability for short- and long-term applications. One such class of composite materials is the Natural Fiber Reinforced Cementitious Matrixes (NFRCMs) or Natural Textile Reinforced Mortars (N-TRMs). N-TRMs consist of layer/s of plant-based uni- or bi-directional textile embedded in inorganic mortar matrix that can enhance the tensile and toughness properties of the substrate. Different studies have been conducted in the past on plant-based textiles such as jute, sisal, hemp, flax and other commonly produced natural textiles for their characterization and eventual determination of mechanical response of the composite systems in which they are embedded. However, there is still, a considerable research gap to study the effects of textile pretreatment, mortar mix design and textile reinforcement amount on TRM performance. This experimental campaign characterizes the plant-based bi-directional flax fabric locally produced in Italy and further studies the mechanical properties of flax-TRMs with different amount of textile reinforcement. The inorganic matrix used in this study is designed keeping in view the sustainability principles to have the least environmental impact. The experimental plan reports the tensile properties of individual flax yarns, threads and subsequently the fabric strips while determining the change in these properties with a proposed pre-treatment. It further investigates the microscopic structure and pull-out behavior of pre-treated and untreated flax threads from the mortar while extending the study to introduce pretreated short jute fibers into the mortar matrix and reports its effect on the composite system’s mechanical response. Eventually, masonry assemblages are prepared and reinforced with different flax-TRMs studied in first phase to correlate the response of diagonal compression test on walls with tensile response of composite prisms. The experimental results found that with pre-treatment, flax-TRM’s mechanical performance in terms of peak tensile strength and reduced crack width is considerably improved. The study further compares the response of textile embedded in normal mortar to the textile embedded in fiber-reinforced mortar. The results show a considerable improvement of tensile strength and reduction in crack width of flax-TRMs embedded in fiber-reinforced mortar in comparison to conventional mortar. Additionally, the experimental test results on masonry wall assemblage prove the enhanced peak load capacity and a higher post peak strength gain of the masonry units reinforced with pretreated flax-TRMs in comparison to untreated flax-TRMs. Nonetheless, this study paves the way for further studies to enhance the mechanical response of flax-TRMs adapting sustainable alternatives.