Properties and Tensile Softening Laws of Hybrid Basalt Fiber Reinforced Recycled Aggregate Concrete

The performance of hybrid basalt fiber (BF)-reinforced concrete made with recycled concrete aggregates (RCAs) and dune sand as an eco-friendly construction material is examined. Test variables comprised the base concrete grade (normal- and high-strength concrete (NSC and HSC)), the hybrid BF volume fraction (νf = 1.0 and 1.5%), and the RCA replacement percentage (30, 60, and 100%). The workability of the concrete mixtures was evaluated via the slump test. The mechanical properties were assessed using compression, splitting tensile, and four-point flexural tests. The durability characteristics were examined using bulk resistivity and ultrasonic pulse velocity (UPV) tests. The addition of hybrid BFs was detrimental to the slump and compressive strength of the concrete mixtures. In contrast, improvements of up to 32 and 40% were recorded in the splitting and flexural strengths of NSC mixtures made with 30–100% RCA. The HSC mixtures exhibited respective improvements of up to 26 and 34% at RCA replacement percentages of 30–60%. The bulk resistivity and UPV values of NSC and HSC mixtures remained almost unaltered with the addition of hybrid BFs. New idealized tensile softening laws were developed for RCA–based concrete reinforced with hybrid BFs. The tensile softening laws were implemented into numerical models that simulated the flexural behavior of the tested concrete prisms with good accuracy.

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