Sustainable activation of sisal fiber-reinforced slag composites: Mechanical strength and microstructural insights through recycling of alkali-treated wastewaters

An alkali treatment is necessary for natural plant fibers employed as reinforcing additives in inorganic cementitious materials, aiming to diminish moisture sensitivity and facilitate interlocking between the matrix and additives. Recycling alkali-treated fiber wastewaters (ATFWs) is crucial to prevent significant environmental pollution. Sisal fiber (SF)-reinforced alkali-activated slag-based composites incorporating ATFWs were prepared and compared to the control, aiming to investigate the effects of alkali-treated SFs and recycled ATFWs on the long-term mechanical properties and microstructures. Initially, the influence of the treated duration of SFs was examined on the electrical conductivity (EC) of ATFWs. Subsequently, the effects of SFs and ATFWs on the 28-day and 360-day flexural and compressive strengths were investigated, including an observation of failure modes. Furthermore, the effect mechanism of ATFWs in SF-reinforced composites was detected concerning morphology, microstructure, and composition by using diverse analytical techniques such as Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), X-ray Diffraction (XRD), Fourier-Transform Infrared Spectroscopy (FTIR), and Thermogravimetric-Differential Scanning Calorimetry (TG-DSC). The results show that the inclusion of ATFWs diminishes electrical conductivity (EC) and density while augmenting the flexural and compressive strengths of the composites. When extending the treatment duration of SFs in a 10% NaOH solution from 1 hour to 3 hours for SF-reinforced composites, the 360-day flexural and compressive strengths for samples without SFs show an enhancement of 1.1 times and 0.9 times, those with 1% SFs exhibit an increase of 0.7 times and 0.5 times, and those with 2% SFs demonstrate an improvement of 0.3 times and 0.4 times, respectively. Furthermore, the incorporation of ATFWs enables the physical embedding and sequestration of organic components released from SFs in a matrix without local aggregation. Therefore, recycling ATFWs as an alkaline activator is deemed feasible to produce SF-reinforced SP-based composites. The research outcomes offer an innovative approach for whole-waste utilization in the realm of natural fiber-reinforced composites.