Mechanical performance and structural application of a novel basalt‐fiber‐reinforced ultra‐high‐performance seawater‐sea‐sand concrete (UHPSSC) with basalt coarse aggregate

Abstract As unlimited resources, seawater and sea sand (SS) could be used as alternatives for fresh water and river sand in concrete constructions in areas with limited resources, such as mega‐cities and islands. To further improve the material efficiency, SS have been used to fabricate the ultra‐high‐performance seawater‐sea‐sand concrete (UHPSSC) in the literature. This work proposes a new type of UHPSSC, which incorporates basalt fibers to enhance the tensile property and coarse aggregate (CA) to improve the modulus. To investigate the contributing factors to the mechanical performance, 12 mixes of different fiber lengths, fiber volumes, and CA contents were designed and tested under compression and flexure. To verify the validity of the proposed UHPSSC in structural elements, six beam specimens reinforced with basalt‐fiber‐reinforced polymer (BFRP) bars were designed and tested. The influence of the tensile properties of the proposed UHPSSC and BFRP flexural reinforcement designs was analyzed. This research shows that with a proper mix design, the proposed UHPSSC has a maximum compressive strength of 140 MPa, exceeding the benchmark strength of 120 MPa for ultra‐high‐performance concrete. With different mix designs, the compressive strength of the proposed UHPSSC varies from 101.5 to 140.5 MPa and the flexural strength varies from 10.8 to 15.4 MPa at 28 days. At different curing ages, the basalt fiber length and volume have more significant impacts on the flexural strength but have limited impact on the compressive strength. Although an optimal CA content of 400 kg/m 3 was found for the compressive strength and the CA content could amplify the influences of the fiber length and volume on the flexural strength. With the flexural reinforcement ratio varying from 0.58% to 1.29%, the UHPSSC beam specimens failed with expected flexural failure and the ultimate capacities varying from 118 to 183 kN, showing a predictable manner. Improving the tensile strength of the proposed UHPSSC could effectively enhance the cracking load and expand the stiffness degradation phase.