Fibers, Volume 12, Issue 5 (May 2024) – 3 articles

This paper investigates the durability of geopolymers and geopolymeric mortars made with metakaolin and alkaline activators, with and without a coconut fiber addition, after immersion for seven days into solutions of citric acid (1%, 2.5%, 5%, and 10%); hydrochloric acid (1%, 2.5%, 5%, and 10%); and sulfuric acid (1%, 2.5%, 5%, and 10%). The study focuses on mass changes, uniaxial compressive strength, flexural strength, and ultrasound pulse velocity measurements. X-ray diffraction and scanning electron microscopy are used to analyze the degradation products and microstructural changes. The aim is to assess the effect of acid exposure on the strength and stability of geopolymer materials and identify any protective effects of coconut fiber reinforcement. The samples are immersed in acid solutions of varying concentrations, and their mechanical properties are measured. The presence of coconut fibers slightly modifies the physical properties and the compressive strength, improving the mechanical flexural strength. Geopolymer and geopolymeric mortar materials experienced a weak decrease in strength when exposed to solutions of citric acid and a significant one when exposed to solutions of hydrochloric and sulfuric acids, attributed to depolymerization of the aluminosilicate binders. Brick waste geopolymeric mortars reinforced with coconut fibers showed the best performance in acid solutions with respect to geopolymers and quartz-rich sand geopolymeric mortars, suggesting a more stable cross-linked aluminosilicate geopolymer structure in this material. Full article

This study assesses the usability of natural materials available in Australia’s remote communities for making fibre-reinforced mudbricks. The present construction cost for housing in remote areas is too high to maintain the level of housing required for the remote Australian population. As this includes mostly First Nations communities, more culturally appropriate housing materials and construction methods are being considered. This study looks at mudbricks made from laterite soil reinforced by spinifex fibre, both available in abundance in remote communities. Hence, this material is more acceptable to communities as it is more sustainable, and the construction methods are more suited for First Nations engagement. Various mixes were tested for compressive strength and erosion resistance. Results suggest that spinifex can significantly improve compressive strength and reduce erosion effects; however, spinifex showed adverse effects at the early stage of the spray test. The results satisfy the minimum strength and erosion resistance requirements for construction and suggest that spinifex-reinforced mudbricks could potentially be considered as an alternative material in remote housing. Full article

Polymer-based composites are widely used in the automotive, security, aeronautical and space industries, to mention a few. This is because of their good mechanical properties, which are similar to those of metals but with the attraction of being lightweight. Kevlar^® is extensively used as a reinforcement in the security industry owing to its good ballistic properties. This investigation presents a mechanical characterization based on in-plane quasi-static tensile testing of Kevlar^® 29/phenolic resin with a polyvinyl butyral composite using a universal testing system. The methodology developed for the preparation of the coupons is based on pressure, temperature and time. As a result of this work, elastic moduli (E_L and E_T), Poisson’s ratio (ν_LT), shear modulus (G_LT) and strengths (X_T, Y_T, S) were obtained. It is worth mentioning that there is scarce or no characterization of this material in the literature, and those studies that do characterize it do not present the coupons’ thermoforming conditions or the reasons for the coupons’ dimensions (width, length and thickness). Full article