Effect of Adding Natural Fibers on the Performance of Concrete

The construction sector contributes nearly 29% of the total carbon dioxide emissions globally, and this is largely due to the use of non-renewable materials such as Portland cement and synthetic fibers.The authors of this article are reporting on the utilization of natural fibers, more specifically date palm fibers (DPF) and sheep wool fibers (SWF), as green and long-lasting composites contributing to the reduction of environmental impact along with the increase of mechanical performance.Seven mixes were prepared for concrete: plain concrete (A0), single fiber mixes of DPF or SWF at 1.5% and 3.0%, respectively (A1, A2, A4, A5), and combined DPF+SWF mixes at total fiber content of 1.5% (A3) and 3.0% (A6).The fibers underwent chemical treatment with sodium hydroxide and sulfuric acid, were cut into 20 mm pieces, and were incorporated into Type I Portland cement concrete.Slump, flow table, and Vebe tests were used to measure fresh state properties.Hardened state properties -compressive strength (ASTM C39), splitting tensile strength (ASTM C496), and flexural strength (ASTM C78) -were measured at 7, 14, and 28 days, and an additional test for compressive strength at 56 days was done to evaluate long-term performance.The findings indicated the use of natural fibers had a negative effect on the workability of the concrete (the Vebe time of A4 went from 8 to 26 seconds).Nevertheless, the hybrid combination A3 (0.75% DPF and 0.75% SWF) performed the best overall, and its 28-day flexural strength was 3.55 MPa (almost the same as A0's 3.53 MPa), the compressive strength was 26.85 MPa (≈70% of A0), and the splitting tensile strength was 2.95 MPa (≈80% of A0).After 56 days, A3 had the highest compressive strength of 38.55 MPa which was slightly over the control's (36.50 MPa) thus indicating a beneficial long-term synergic effect of fiber hybridization.Single DPF mixes (A2, A5) suffered the most with the largest drops in compressive strength, while the SWF mixes (A1, A4) were more balanced in their performance.