Effect of 40-day seawater treatment of Spanish broom fibers on the mechanical properties of reinforced cement mortar

Recently, there has been increasing interest in natural fibers as reinforcement for cement composites. Natural fibers are low-cost, low-density, non-abrasive, biodegradable, and non-toxic materials. The limits for the application of natural fibersare their high absorption of water, improper adhesion to a matrix material, high dispersion of mechanical properties, and decomposition of fibers in cement composites due to the influence of alkalis. Some of these problems can be overcome by treating the fibers. The most common chemical treatment method uses alkaline, which dissolves lignin and hemicellulose in fibers. Treatment of fibers with seawater, which is a more natural and environmentally friendly process, can be used as an alternative to chemical treatment. This paper considered Spanish broom fibers treated with seawater for 40 days. After the seawater treatment, half of the Spanish broom branches were immediately washed, and the fibers were separated under tap water. The other half of the branches were left to dry for a few days, and the fibers were washed with tap water after separation from the dry woody part. The fibers of the second group broke under a low tensile force. Thirteen series of cement mortars were made: a reference mortar and mortars reinforced with fibers of 1, 2, and 3 cm in length and in amounts of 0.5% and 1% of the total volume. Compressive strength and flexural strength were tested on 28-day-old specimens. Reinforced mixtures had weaker mechanical properties than the reference mixture. Specimens reinforced with fibers that were immediately washed inwater had a 3–8% higher flexural strength, and the compressive strength of the reinforced specimens was almost the same. The mixture with the first group of fibers (1 cm long and added to the mixture in a ratio of 0.5%) achieved the highest strength of all reinforced specimens.