Rice Husk Ash-Based Geopolymer Binder: Compressive Strength, Optimize Composition, FTIR Spectroscopy, Microstructural, and Potential as Fire-Retardant Material

• Published in: Polymers Vol. 13; no. 24; p. 4373
• Main Authors: Mohd Basri, Mohd Salahuddin, Mustapha, Faizal, Mazlan, Norkhairunnisa, Ishak, Mohd Ridzwan
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 14-12-2021; MDPI
• Subjects: Aluminosilicates; Aluminum; Aluminum silicates; Ashes; binder; Brittleness; Compressive strength; Construction materials; Design of experiments; Ductile-brittle transition; Fire resistant materials; fire-retardant; geopolymer; Geopolymers; Mathematical analysis; Mechanical properties; Microstructure; Moisture content; Optimization; Regression coefficients; Regression models; Response surface methodology; rice husk ash; Silica; Silicon; Sodium hydroxide; Statistical analysis; Statistical methods; Temperature; Thermal insulation; compressive strength; geopolymer; rice husk ash; stress-strain curve; optimization; fire-retardant; binder; ultimate stress; mechanical properties; response surface methodology (RSM)
• ISSN: 2073-4360; 2073-4360
• DOI: 10.3390/polym13244373

Compressive strength is an important property in construction material, particularly for thermal insulation purposes. Although the insulation materials possess high fire-retardant characteristics, their mechanical properties are relatively poor. Moreover, research on the correlation between fire-retardant and compressive strength of rice husk ash (RHA)-based geopolymer binder (GB) is rather limited. In addition, previous studies on RHA-based GB used the less efficient one-factor-at-a-time (OFAT) approach. In understanding the optimum value and significant effect of factors on the compressive strength, it was deemed necessary to employ statistical analysis and a regression coefficient model (mathematical model). The objective of the study is to determine the effect of different material behavior, namely brittle and ductile, on the compressive strength properties and the optimum material formulation that can satisfy both compressive strength and fire-retardant properties. The factors chosen for this study were the rice husk ash/activated alkaline solution (RHA/AA) ratio and the sodium hydroxide (NaOH) concentration. Compressive strength and fire-retardant tests were conducted as part of the experiments, which were designed and analyzed using the response surface methodology (RSM). The microstructure of geopolymer samples was investigated using a scanning electron microscope (SEM). Results showed that RHA/AA ratio was highly significant (
< 0.000) followed by NaOH concentration (
< 0.024). When the RHA/AA ratio was at 0.7 to 0.8 and the NaOH concentration was between 12 and 14 M, high compressive strength above 28 MPa was recorded. Optimum compressive strength of approximately 47 MPa was achieved when the RHA/AA ratio and NaOH concentration were 0.85 and 14 M, respectively. Brittle samples with low Si/Al ratio of 88.95 were high in compressive strength, which is 33.55 MPa, and showed a high degree of geopolymerization. Inversely, ductile samples showed low compressive strength and degree of geopolymerization. Water content within the geopolymer binder had a major effect on its fire-retardant properties. Semi-ductile GB showed the best fire-retardant properties, followed by semi-brittle and brittle GB. Using RHA as an aluminosilicate source has proven to be a promising alternative.