Sustainable Concrete Reinforced with Sisal Fibers: Experimental Assessment of Density, Porosity, and Mechanical Performance

Natural fiber-reinforced concrete has attracted increasing attention as a sustainable alternative to conventional construction materials. In this study, the structural, physical, and mechanical behavior of reinforced concrete slabs incorporating sisal fibers was experimentally investigated. Three formulations were prepared according to the Moroccan standard NM 10.1.184: a reference concrete without fibers (MS), and concretes reinforced with 1 wt.% (MA3) and 2 wt.% (MB3) sisal fibers. The sisal fibers exhibited an average length of 60 mm and a diameter of 0.9 mm. The samples were characterized using X-ray diffraction (XRD), hydrostatic weighing measurements, Schmidt hammer testing, and mechanical compression and flexural tests after 90 days of curing.

The results revealed that increasing the sisal fiber content significantly modified the physical and mechanical properties of the concrete slabs. The apparent density decreased from 1576.9 kg m⁻³ for the reference sample to 1510.8 kg m⁻³ for the slab containing 2 wt.% sisal fibers. Simultaneously, the water absorption values ranged from 12.0% to 7.4%, indicating a substantial modification of the pore structure and fiber–matrix interactions. Mechanical testing demonstrated a progressive reduction in compressive strength from 38 MPa to 17 MPa, while the Young’s modulus decreased from 12 MPa to 7.4 MPa as the sisal fiber content increased from 0 to 2 wt.%. Similarly, the flexural strength declined from 8.7 MPa to 5.2 MPa. Microstructural observations suggested that fiber agglomeration, reduced matrix compactness, and weak fiber–cement interfacial bonding contributed to the increase in porosity and the deterioration of mechanical performance.

The findings demonstrate that although sisal fibers provide an environmentally friendly reinforcement solution, their incorporation at high contents can adversely affect the mechanical integrity of concrete slabs due to increased porosity and heterogeneous fiber dispersion. These results provide valuable insights into the optimization of natural fiber-reinforced cementitious composites for sustainable construction applications.