This study aims to examine the impact of using basalt macro-fibers (BMF) on characteristics of concrete made with recycled concrete aggregates (RCA). Test variables included the initial concrete grade (normal- and high-strength concrete (NSC and HSC)), RCA replacement percentage (30 and 60%), and BMF volume fraction (νf = 0.5 to 1.5%). The compressive strength reduction in the plain concrete caused by RCA was sensitive to the RCA replacement percentage rather than the initial concrete grade. The splitting and flexural strength reductions of the plain HSC caused by RCA were more significant than those of their NSC counterparts. The use of BMF compromised the concrete workability. Such a detrimental effect increased with the BMF content and was more pronounced for the HSC with 60% RCA. Reinforcing of RCA-based concrete with BMF tended to improve the mechanical properties. In some instances, the use of BMF at νf > 1% caused a decay in the strength gain. The addition of BMF to RCA-based concrete had a potential to fully restore the original splitting and flexural strengths of plain concrete mixtures made with natural aggregates (NA). The increase in the compressive strength of the RCA-based concrete caused by BMF was, however, not sufficient to fully restore the original strength of the NA-based plain concrete. The resistances to water penetration and abrasion of the RCA-based concrete improved by up to 17% and 47%, respectively, due to the addition of BMF. Idealized tensile softening laws were established for RCA-based concrete reinforced with BMF.

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.

This study examines the fresh and hardened properties of normal- and high-strength concrete (NSC and HSC) reinforced with basalt macro-fibers (BMF) at a volume fraction (νf) of 0.5–1.5%. Workability tests were conducted on the fresh concrete to evaluate the slump, compacting factor, and vebe time. Mechanical tests were performed on the hardened concrete to examine the compressive strength, tensile properties, and flexural performance. Different durability characteristic tests were carried out to evaluate the water/chloride penetrability, bulk resistivity, and abrasion resistance of the hardened concrete. The addition of BMF reduced the concrete workability of both NSC and HSC at almost the same rate. A maximum slump reduction of 78%, on average, was recorded at νf of 1.5%. The compressive strength of the NSC slightly increased by 1–5% due to the addition BMF, whereas that of the HSC with BMF was, on average, 6% lower than that of their plain counterparts. The NSC with BMF exhibited significant improvements of 10–52% in the splitting tensile strength, 18–56% in the flexural strength, and 17–27% in the abrasion resistance. The enhancement caused by the addition of BMF was less pronounced for the HSC, where maximum respective improvements of 22, 25, and 4% were recorded. The NSC and HSC with BMF exhibited a similar reduction in the water absorption (max. of 12%), chloride penetrability (max. of 19%), and a comparable improvement in the bulk resistivity (max. of 21%), relative to those of their plain counterparts. The flexural test results along with an inverse analysis were employed to develop new tensile softening laws of concrete with different BMF volume fractions.

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This research investigates the effect of basalt fibers (BF) on the workability and early-age compressive and splitting tensile strengths of concrete made with 100% recycled concrete aggregates (RCA). The target concrete compressive strengths were 30, 45, and 60 MPa, whereas the basalt fibers had a length of either 20 or 43 mm. The addition of BF significantly decreased the workability, slightly improved the compressive strength, and remarkably increased the splitting tensile strength of the RCAbased concrete. The compressive strengths of the RCA-based concrete with different BF lengths and volume fractions were insignificantly different. The original compressive strength of the natural aggregate (NA)-based concrete was not fully restored, irrespective of the BF length and volume fraction. Basalt fibers had a more pronounced effect on improving the splitting tensile strength rather than the compressive strength. The original splitting tensile strength of the NA-based concrete was fully restored in most of the cases. Basalt fibers with a length of 43 mm were more effective in improving the splitting tensile strength of the RCA-based concrete than those having a length of 20 mm.