Effect of the modification of Pinus Kraft pulp with aluminum sulfate in cementitious composites

The use of aluminum sulfate (AS) as a chemical treatment for plant fibers aims to protect them against the aggressions of the alkaline environment provided by cement. This research aimed to understand the effects of treatment with AS (chemical modification) at concentrations of 0%, 4% and 11% on the surface of Kraft pulp of Pinus spp. and to evaluate the composites generated on the 28th day of curing and after 200 cycles of accelerated aging. The results suggest that AS is a surface modifying agent and will be homogeneously deposited on the surface of plant fibers. In addition, the experimental data showed that treatment with AS reduced water absorption by approximately 3% and apparent porosity by 10% in cementitious composites. In contrast, the limit of proportionality increased with both AS concentrations. Furthermore, the modulus of elasticity of the composites produced with the fibers treated with AS increased considerably in relation to that of the fiber-cement sample with 0% AS. The modulus of rupture (MOR) of the 4% AS treatment sample was considerably greater than that of the control sample, both on the 28th day and after the aging cycles. On the other hand, no considerable changes were observed in the MOR of the composites produced from fibers treated with 11% AS compared to the control. The specific energy of the fiber-cement composites with 4% and 11% AS was considerably lower than that of the control sample. These data reflect the methods of applying cementitious composites, which can be used in the manufacturing of covering tiles that yield better results in terms of the modulus of elasticity (MOE). On the other hand, those composites that obtained higher MOR and specific energy (SE) values may be suitable for the production of both tile and flat plates.