Problem definition and Objectives: In recent years, construction engineering has increasingly shifted toward the use of lightweight, durable, and environmentally compatible materials. Cement-based composites, as emerging construction materials, offer considerable potential for development depending on the availability of regional raw materials such as wood, cellulosic fibers, and waste paper. Given the limited wood resources and the growing demand for composite products, the use of fibers recovered from recycled printing-paper waste has been suggested as an economical and environmentally sustainable alternative. Accordingly, waste printing-paper fibers were employed in the present study. One of the major challenges in producing such composites is the inherent incompatibility of lignocellulosic fibers with Portland cement, which restricts the formation of strong and stable interfacial bonding within the composite matrix. Previous studies have shown that the incorporation of calcium chloride can enhance cement hydration and improve fiber–cement compatibility. The combined use of recycled cellulosic fibers with additives such as calcium chloride or nanosilica has also been reported to improve durability, phase cohesion, flexural performance, and reduce thickness swelling in wood–cement composites. Therefore, calcium chloride was utilized in this research to improve the setting behavior of cement in the presence of waste paper fibers. The primary objective of this study was to determine the optimum mixing ratio of recycled printing-paper fibers and cement, together with an appropriate dosage of calcium chloride, in order to enhance the physical and mechanical properties of the resulting composite.
Methodology: In this study, cellulosic fibers derived from waste printing paper were used as the reinforcing agent, while Type II Portland cement served as the matrix. Calcium chloride powder was employed as a setting accelerator and to improve the fiber–cement interfacial bonding at two levels (3% and 5% by cement weight). The specimens were prepared with three different fiber-to-cement ratios (30:70, 25:75, and 20:80 by weight) and cured for 28 days. Subsequently, they were tested for physical and mechanical properties according to EN standards. The obtained results were analyzed to evaluate the effects of the mixing ratios and calcium chloride content on the performance of the paper fiber–cement composites.
Results: The results showed that increasing the cement content from 70 to 80% led to a decrease in water absorption and thickness swelling, as well as an improvement in the density of the samples measured. In contrast, the effects of 3 and 5% calcium chloride on the physical and mechanical properties of the samples were not independently significant observed. The highest mechanical properties, including modulus of rupture, modulus of elasticity, and internal bond strength, were obtained in the 20:80 cement-to-fiber ratio prepared. The use of calcium chloride in limited amounts contributed to the acceleration of setting and the improvement of fiber–cement bonding facilitated. However, at higher contents, a slight reduction in physical properties was observed due to porosity formation and volumetric stresses induced. Overall, optimizing the cement-to-fiber ratio and controlled application of calcium chloride played a crucial role in enhancing the performance of paper fiber–cement composites achieved.
Conclusion: The mixing ratio of recycled printing-paper fibers and cement plays a decisive role in improving the physical and mechanical properties of cement-based composites, as demonstrated in this study. An increase in the cement content to 80% led to higher density and enhanced mechanical strength, while water absorption and thickness swelling decreased. In contrast, raising the fiber content to 30% resulted in greater water absorption and thickness swelling, a phenomenon attributable to the porous structure of the fibers that provided additional capillary pathways for moisture penetration. The incorporation of 3% calcium chloride accelerated the hydration process and strengthened the fiber–cement interfacial bonding, whereas increasing its level to 5% caused a relative decline in both physical and mechanical properties because of salt crystallization and increased porosity. A significant interaction effect between cement and calcium chloride was observed only for internal bonding. The optimal performance was obtained in the formulation containing 20% fibers, 80% cement, and 3% calcium chloride. Overall, the use of recycled printing-paper fibers as a sustainable and environmentally compatible substitute has the potential to enhance composite performance and reduce the environmental impacts of building materials.