Investigation of Biomineralization on the Strength, Durability Properties of Fiber-Based RAC

Abstract

In concrete,recycling waste materials plays a crucial role in preserving natural resources, managing construction and demolition waste (CDW) and reducing environmental impact. Given the extensive use of aggregates in concrete, integrating recycled aggregates can significantly enhance the sustainability of construction practices. This study investigates an innovative approach to improving the mechanical strength and durability of recycled aggregate concrete (RAC) through biomineralization and fiber reinforcement. The novelty of this research lies in the synergistic use of basalt fibers (BF), polyvinyl alcohol (PVA) fibers, and bacterial self-healing mechanisms to enhance RAC performance. Experimental results indicate that fiber-reinforced RAC exhibits superior compressive and splitting tensile strength compared to conventional RAC with 50% or 100% recycled aggregate. Among the fiber types, basalt fibers consistently outperformed PVA fibers in enhancing mechanical properties. This study provides a novel strategy for optimizing RAC performance, making it a more viable and sustainable alternative for construction applications.

Introduction

Concrete is the second most used material after water, but its continued use raises sustainability concerns due to natural resource depletion and the generation of construction and demolition (C&D) waste. Recycled aggregates (RA) from C&D waste offer a partial solution, but their use in concrete—forming Recycled Aggregate Concrete (RAC)—leads to lower mechanical strength and durability compared to Natural Aggregate Concrete (NAC).

To improve RAC performance, recent studies have explored three main strategies:

1. Pretreatment of RA

2. Addition of fibers (e.g., Basalt Fiber [BF], Polyvinyl Alcohol [PVA] fiber)

3. Bacterial-induced calcite precipitation (BICP) using bacteria like Bacillus megaterium.

Key findings:

• Basalt fibers (BF) significantly improved compressive and tensile strength due to their high modulus and crack-bridging capabilities.

• PVA fibers offered good bonding and durability improvements but showed limited strength enhancement at low dosages.

• Bacteria (BICP) enhanced RAC by precipitating calcium carbonate (CaCO?), filling voids and cracks, and densifying the concrete structure. Strength gains of over 20% were observed in bacterial-treated mixes.

Experimental program:

• Ordinary Portland Cement (OPC), natural and recycled aggregates, PVA and basalt fibers (12 mm), and Bacillus megaterium were used.

• Concrete samples were tested for compressive and split tensile strength at 7, 28, and 56 days.

• SEM imaging confirmed improved microstructure due to bacterial CaCO? precipitation and denser interfacial transition zones (ITZ) in fiber-reinforced RAC.

Results:

• 50% and 100% RCA replacements showed strength reduction in plain RAC.

• Fiber + bacteria combinations led to significant improvements in strength:

  • BF + bacteria: Up to 20.5% compressive and 20.3% tensile strength improvement.

  • PVA + bacteria: Up to 34% tensile strength gain.

• SEM analysis confirmed denser microstructure and reduced porosity in bacterial and fiber-reinforced mixes.

Conclusion

Through extensive testing and analysis, the compressive strength, split tensile strength, and microstructural properties of fiber-reinforced recycled aggregate concrete (RAC) were thoroughly investigated. Based on the research findings, the following conclusions were drawn: 1) The incorporation of PVA fiber had a minor effect on compressive strength, likely due to reduced compactness and increased interfacial transition zone (ITZ) formation between the cement mortar and PVA fibers. In contrast, basalt fiber (BF) significantly improved compressive strength, with a 9.24% increase in 50R0.2B and a 7.39% increase in 100R0.2B at 28 days. 2) The inclusion of bacteria proved to be highly effective in enhancing the strength of RAC. The compressive strength of fiber-reinforced bacterial concrete increased by 8.5% in 50R0.2P and 16.5% in 50R0.2B at 28 days compared to the 50R mix. 3) The split tensile strength of 100R0.2P exhibited significant improvements of 29.37% and 36.45% at 28 and 56 days, respectively. A similar enhancement was observed in the 100R0.2B mix, with tensile strength increases of 11%, 12.68%, and 20.30% compared to the 100R mix. 4) SEM analysis revealed that conventional RAC contains loose calcium hydroxide (CH) crystals and voids, leading to a weaker microstructure. However, the addition of fibers not only reduced these voids but also facilitated the development of additional calcium silicate hydrate (CSH) gel. This improvement in microstructural integrity enhanced ITZ properties, with BF incorporation further strengthening the mechanical and durability characteristics of RAC.

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Copyright

Copyright © 2025 Harshit Varshney, Rizwan A. Khan, Iqbal Khaleel Khan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.