Effect of nano-bentonite and <i>Bacillus subtilis</i> treatments on the water absorption behavior of RHA-based geopolymer SIFCON through interfacial transition zone modification

Mohammed Ali Abdulrehman; Khairunisak Abdul Razak; Khalid M. Eweed; Shah Rizal Kasim; Mohammed Ali Abdulrehman; Khairunisak Abdul Razak; Khalid M. Eweed; Shah Rizal Kasim

doi:10.3934/matersci.2026029

AIMS Materials Science

2026, Volume 13, Issue 3: 593-613. doi: 10.3934/matersci.2026029

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Research article

Effect of nano-bentonite and Bacillus subtilis treatments on the water absorption behavior of RHA-based geopolymer SIFCON through interfacial transition zone modification

1.
School of Materials and Mineral Resources Engineering, Universiti Sains Malaysia, 14300 Nibong Tebal, Malaysia
2.
Department of Materials Engineering, College of Engineering, Mustansiriyah University, Baghdad 10045, Iraq

Received: 19 February 2026 Revised: 12 June 2026 Accepted: 23 June 2026 Published: 29 June 2026

In this study, the individual effects of different modification strategies, namely 1% nano-bentonite and Bacillus subtilis (B. subtilis, 1.0 × 10⁸ CFU/mL) combined with 0.3% polyacrylamide (PAM), were investigated to improve the water resistance and mechanical performance of rice husk ash (RHA)-based geopolymer slurry-infiltrated fiber concrete (SIFCON). Our objective of this study was to reduce water absorption through interfacial transition zone (ITZ) refinement and matrix densification without compromising the mechanical properties of the composite material. In addition to microstructural observations using scanning electron microscopy (SEM), an extensive experimental investigation was performed, including compressive strength, splitting tensile strength, flexural strength, and water absorption tests. Our results showed that nano-bentonite boosted matrix compactness and ITZ quality lead to higher compressive strengths, up to 51.7 MPa, and lower water absorption than untreated mixes. In contrast, B. subtilis combined with PAM increased the matrix density via bacterial action and internal curing. This combination yielded the best results: a compressive strength of 52.9 MPa, a flexural strength of 22.92 MPa, and least water absorption at 1.46%. The optimum bacteria-treated mixtures exhibited up to 35% lower water absorption than the corresponding untreated mixtures. SEM observations confirmed a denser microstructure, reduced microvoid content, and improved fiber-matrix bonding in the modified composites. The novelty of this study lies in the comparative evaluation of biological and nano-modification approaches as separate ITZ enhancement strategies for the sustainable RHA-based geopolymer SIFCON. These findings demonstrate the potential of these modification techniques for the development of durable and environmentally friendly geopolymer composites.
- geopolymer SIFCON,
- rice husk ash,
- nano-bentonite,
- Bacillus subtilis,
- interfacial transition zone,
- bio-mineralization
Citation: Mohammed Ali Abdulrehman, Khairunisak Abdul Razak, Khalid M. Eweed, Shah Rizal Kasim. Effect of nano-bentonite and Bacillus subtilis treatments on the water absorption behavior of RHA-based geopolymer SIFCON through interfacial transition zone modification[J]. AIMS Materials Science, 2026, 13(3): 593-613. doi: 10.3934/matersci.2026029

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Abstract

In this study, the individual effects of different modification strategies, namely 1% nano-bentonite and Bacillus subtilis (B. subtilis, 1.0 × 10⁸ CFU/mL) combined with 0.3% polyacrylamide (PAM), were investigated to improve the water resistance and mechanical performance of rice husk ash (RHA)-based geopolymer slurry-infiltrated fiber concrete (SIFCON). Our objective of this study was to reduce water absorption through interfacial transition zone (ITZ) refinement and matrix densification without compromising the mechanical properties of the composite material. In addition to microstructural observations using scanning electron microscopy (SEM), an extensive experimental investigation was performed, including compressive strength, splitting tensile strength, flexural strength, and water absorption tests. Our results showed that nano-bentonite boosted matrix compactness and ITZ quality lead to higher compressive strengths, up to 51.7 MPa, and lower water absorption than untreated mixes. In contrast, B. subtilis combined with PAM increased the matrix density via bacterial action and internal curing. This combination yielded the best results: a compressive strength of 52.9 MPa, a flexural strength of 22.92 MPa, and least water absorption at 1.46%. The optimum bacteria-treated mixtures exhibited up to 35% lower water absorption than the corresponding untreated mixtures. SEM observations confirmed a denser microstructure, reduced microvoid content, and improved fiber-matrix bonding in the modified composites. The novelty of this study lies in the comparative evaluation of biological and nano-modification approaches as separate ITZ enhancement strategies for the sustainable RHA-based geopolymer SIFCON. These findings demonstrate the potential of these modification techniques for the development of durable and environmentally friendly geopolymer composites.

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