Effect of SiO2/Al2O3 molar ratio on mechanical behavior and capillary sorption of MK-based alkali-activated composites reinforced with PVA fibers

This paper investigates the effect of SiO2/Al2O3 molar ratio on the mechanical behavior of polyvinyl alcohol (PVA) fiber-reinforced alkali-activated matrices (PVA-AAM) based on the activation of metakaolin (MK) as a source material. Different volume fractions (0, 1 and 2%) of PVA fibers were used to reinforce MK-based matrices with different compositions (SiO2/Al2O3 molar ratios, i.e. 3.0, 3.4 and 3.8). The amount of activation solution was adjusted to maintain same workability for all fresh mixes and account for the fiber addition. The mechanical properties assessed were compressive and flexural strengths as well as toughness, followed by optical microscopy to observe the fractured surfaces. Capillary sorption test was conducted to estimate the durability of the composites. Test results show that the matrices of PVA-AAM can be designed for the development of high performance composites, with significantly improved deformation and toughness, as it is the case for matrices with higher SiO2/Al2O3 molar ratio and 2% PVA fiber. Adjustments in the content of the activation solution may reduce the mechanical strength. However, as the amount of activation solution increases in the mixes, so does the toughness of the PVA fiber-reinforced composites, which indicates a good correlation between the amount of soluble silica in the fresh AAM and toughness in bending.