The influence of alkaline treatment on the mechanical performance of geopolymer composites reinforced with Brazilian malva and curaua fibers

Abstract

Lignocellulosic fibers obtained from the curaua (Ananas erectifolius) and malva (Malva sylvestris) plants in Brazil can be used as suitable reinforcements for geopolymers (GPs) owing to their high strength, ready regional availability, and low cost. In this work, the tensile and flexural strengths of untreated and NaOH alkali‐treated curaua and malva fiber‐reinforced GP composites were measured according to ASTM standards. Curaua reinforced GP composites had an average tensile strength of 25.7 (±) 7.1 MPa and flexural strength of 18.9 (±) 4.72 MPa. Malva GP composites withstood 19.18 (±) 9.0 MPa in tension and 31.5 (±) 7.6 MPa in flexure. Additionally, pullout tests were performed to investigate the debonding mechanisms for both fibers, with and without alkaline treatment, finding increases in chemical bonding for the treated samples due to roughness enhancements through fiber surface modifications with alkali treatment. Thermogravimetric analysis and X‐ray diffraction were used to characterize the physical fiber modifications after alkali treatment, evidencing lignin and hemicellulose removals. Scanning electron microscopy and energy‐dispersive X‐ray spectroscopy were used to further examine the fiber–matrix interaction, with proofs of interfacial tailoring.

Abaca fiber as an efficient reinforcement for high mechanical performance in metakaolin‐based geopolymers

“…To assess the reliability of the mechanical responses observed in compression, flexural, and splitting tensile tests, Weibull statistics were employed, following established guidelines outlined in previous studies 17,51 . The parameters were determined by plotting the relationship between the observed data and the corresponding Weibull distribution: $$$$\begin{equation}\;\ln \left[ {\ln \left[ {{\mathrm{\;}}\frac{{N + 1}}{{N + 1 - i}}} \right]} \right] = {\mathrm{\;}}m\ln \left( {\frac{\sigma }{{{\sigma _0}}}} \right).\end{equation}$$$$…”

“…The geopolymer design used to prepare the composites consisted of a successful formulation previously employed in other published studies, 17,45 as follows:…”

“…To assess the reliability of the mechanical responses observed in compression, flexural, and splitting tensile tests, Weibull statistics were employed, following established guidelines outlined in previous studies. 17,51 The parameters were determined by plotting the relationship between the observed data and the corresponding Weibull distribution:…”

“…The geopolymer design used to prepare the composites consisted of a successful formulation previously employed in other published studies, 17,45 as follows: $$$$\begin{eqnarray}{{\mathrm{K}}_2}{\mathrm{O}} \bullet 2{\mathrm{Si}}{{\mathrm{O}}_2} \bullet 11{{\mathrm{H}}_2}{\mathrm{O}} + 2{\mathrm{Si}}{{\mathrm{O}}_2} \bullet {\mathrm{A}}{{\mathrm{l}}_2}{{\mathrm{O}}_3} \to {{\mathrm{K}}_2}{\mathrm{O}} \bullet \nonumber\\ {\mathrm{A}}{{\mathrm{l}}_2}{{\mathrm{O}}_3} \bullet 4{\mathrm{Si}}{{\mathrm{O}}_2} \bullet 11{{\mathrm{H}}_2}{\mathrm{O}}\end{eqnarray}$$$$…”

“…Raw natural fibers are hydrophilic and porous, leading to undesired moisture absorption and the deterioration of typical cementing microstructures. [11][12][13] Thermal, biological, and chemical treatments [14][15][16] have been proposed to enhance fiber durability and efficiency to some extent by removing non-cellulosic components, 14,17 such as the amorphous contents and reducing their porous nature. However, these processes are still not feasible for large-scale applications due to time, cost, and uniformity constraints, thereby limiting their practical use in the construction market.…”