The suitability of vegetable fibres for the reinforcement of concrete

Abstract

The use of vegetable fibres as a sustainable alternative to non-natural fibres for reinforcing concrete was investigated in this research. For plant-based fibres, previous studies have identified issues such as the variability in properties and biodegradability in the alkaline pH of concrete. The study was divided into four different sections along with the literature review. First, the properties of untreated flax and hemp fibres were assessed. Second, the fibres were subjected to surface treatments using NaOH (at concentrations of 5%, 15%, and 15%), KMnO4, stearic acid, and EDTA solutions for various durations (4, 6, 10, 15, and 24 hours) to minimize variability and degradation caused by the alkaline pH of concrete. The effects of each treatment were evaluated, and the treatments that yielded the most satisfactory results were selected. For flax fibres, the 4-hour stearic acid treatment, which was a novel treatment in this study, was chosen. For hemp fibres, the 24-hour NaOH 10% treatment was selected, which provided original results for the reinforcement of concrete. Thirdly, the effects of an alkaline environment on the tensile strength and elastic modulus of treated and untreated fibres were assessed. Lastly, the effect of long fibres (40 ± 5mm) on certain properties of concrete was investigated. The addition of treated fibres increased the peak flexural tensile strength and reduced the elastic modulus of the concrete by at least 50% after 28 days. The mixes containing treated fibres exhibited significantly lower fracture energy values than the basalt fibre reinforced blend. Both types of fibre reinforced concretes using surface-treated fibres showed higher values for residual tensile strength. Additionally, the addition of fibres improved the thermal conductivity of the concrete, and a reduction in density was observed based on the volume of added flax fibres.