Influence of different treatment and amount of Spanish broom and hemp fibres on the mechanical properties of reinforced cement mortars

Abstract

This paper presents experimental investigations into the behaviour of cement mortar micro-reinforced with natural hemp and Spanish broom fibres. The fibre treatment process was carried out with: alkali (2.5, 5, 6, 8, 10 and 15% NaOH solution, and 2.5 or 5% NaOH and 2% Na2SO3 mixed solution), seawater, and a combination of alkali (5% NaOH) and seawater. The changes in fibre structure caused by the chemical treatment were monitored by FTIR, TG/DTG and XRD analysis. Fibres were added to mortar specimens in amounts of 0.34, 0.5, 0.68 and 1 vol%. The flexural and compressive strengths were tested on mortar specimens after 56 days. The σ–δ diagrams are presented, and the specific fracture energy is determined based on the curve from the plot of load (N) vs. displacement (mm). The tensile strength of the fibres was determined on specimens treated in the same way. Treatment in different solutions showed that increased pH values of the treatment medium have a great influence on the increase in crystallinity, for both Spanish broom and hemp fibres. The results presented here showed that natural fibres do not have a significant influence on the mechanical properties of the mortar (compressive and flexural strengths), but do significantly increase its ductility. In addition, it has been shown that specimens with a lower proportion of natural fibres give better mechanical properties and higher ductility of the material. It was observed that both the mortar preparation and the method of fibre installation significantly affect the mortar properties. Seawater as a means of treating fibres was proven to be the most ecologically and economically acceptable treatment method. Spanish broom fibres showed large potential for reinforcing cement composites.