Preliminary studies on the suitability of coal fly ash geopolymer mortars for strengthening existing concrete and masonry structures

Nowadays externally bonded fiber reinforced cementitious matrix composites represent a possible alternative to traditionally used fiber reinforced polymer composites for strengthening existing damaged structures. This work investigates the possibility of using a geopolymer mortar instead of cementitious matrix for this technology. Indeed, compared to cement based materials, geopolymers show both competitive properties and sustainable characteristics but research on the use of geopolymer for strengthening and rehabilitation of reinforced concrete and masonry structures is still very limited. First of all, different coal fly ash geopolymer mortars have been prepared and characterized by varying the molar concentration of sodium hydroxide solution used as the alkali activator (4M, 6M, 8M). Then, they have been used as matrices to embed and bond continuous high strength galvanized steel fibers and basalt fibers on concrete and masonry substrate, respectively. Physical and mechanical properties of the geopolymer mortars have been evaluated after room temperature curing. Moreover, the interfacial bond behavior between the fiber reinforced geopolymer matrix and the support (i.e., concrete and masonry) has been studied by means of specific mechanical tests (single-lap direct shear test). Obtained results show that geopolymer mortars are promising for this kind of application and can potentially replace cementitious mortars used in fiber reinforced inorganic matrix composites.