Amazon açaí fibre–Portland cement compatibility: a challenge to produce cement-bonded fibreboards?

Abstract

The açaí waste from the Amazon contains short fibres that show potential for reinforcing cement-bonded fibreboards (CBFBs), although their compatibility with the cement matrix is still unknown. The aim of this work was to characterise raw and pretreated açaí fibres and analyse their compatibility with Portland cement by different techniques, alongside developing a CBFB. The fibres were subjected to thermal (180, 200 and 220°C), cold and hot water, alkaline (NaOH) and bleaching (NaOH–H2O2) pretreatments. The chemical and water pretreatments raised the fibre crystalline indexes (28–57%). The chemical pretreatments individualised the fibre bundles and removed hemicelluloses. Alkali-pretreated and raw fibres had the highest (96%) and lowest (65%) cement compatibility indexes. Portlandite and ettringite appeared after 24 h for most pastes, but were delayed for raw and 220°C-pretreated fibres. In contrast, only the raw fibre specimens reached the required compression strength of 34 MPa after 28 days; hence, they were chosen to produce a CBFB. The boards showed proper thickness swelling (1.4%), but low bending strength (modulus of elasticity = 647.8 MPa; modulus of rupture = 1.9 MPa). Overall, the fibre modifications improved the compatibility with cement, but not the composite's mechanical strength. Açaí-fibre CBFB is a promising building material, but future studies must overcome its poor mechanical performance.