Performance evaluation and development of tensile softening law for concrete reinforced with different sizes and combinations of basalt fibers

This research examines the performance of concrete reinforced with different sizes and combinations of basalt fibers (BF). Test parameters comprised the base concrete grade [normal-strength concrete (NSC) and high-strength concrete (HSC)] and BF configuration (short with length of 20 mm, long with length of 50 mm, and hybrid combination at ratio of 1:1). The BF volume fraction (ν_f) was 1.0%. The tests included slump, compression, splitting, flexure, bulk resistivity, and ultrasonic pulse velocity (UPV). The base concrete grade had no effect on the slump reduction, splitting and flexural strength gains caused by BF when short BF were used. The slump reduction caused by BF was aggravated when long or hybrid BF were used. The use of BF slightly reduced the compressive strength by up to 13%. Short BF resulted in a minor increase of up to 8% in the splitting and flexural strengths, irrespective of the base concrete grade. Hybrid BF resulted in similar or higher splitting and flexural strength gains, except in one case where long BF were more effective. The splitting tensile strength gain caused by long BF was more pronounced for NSC (25%) than HSC (14%). NSC mixtures exhibited higher flexural strength gains (18–20%) than those of their HSC counterparts (10–16%), when long or hybrid BF were used. The use of BF improved the bulk resistivity but had no effect on UPV. Simulation models were developed for the tested concrete prisms. A new tensile softening law was established for BF-reinforced concrete based on inverse analysis of test data.