By giving discarded groundnut shells a second life, researchers have demonstrated how simple chemical treatments can turn this agricultural waste into a high-performance, eco-friendly reinforcement for concrete, enhancing its resistance to structural cracking and simulated blast impacts.
Study: Chemically treated groundnut shell fibers for enhanced mechanical and blast performance of concrete. Image Credit: Aviavlad/Shutterstock.com
A recent paper in Scientific Reports explores how chemically treated groundnut shell fibers affect the mechanical properties and simulated blast performance of high-performance concrete (HPC), offering a sustainable alternative to traditional reinforcement materials.
Rethinking Agricultural Waste
Natural fibers derived from roots, fruits, leaves, and stems are biodegradable, safe, and readily available, making them an attractive option for improving concrete performance. When used in dispersed form, these fibers provide both economic and mechanical benefits.
Traditionally, materials such as polypropylene and steel fibers are added to control early-age cracking and serve as secondary reinforcement. However, high-performance concrete remains particularly prone to early cracking due to its low water–cement ratio. This low water content accelerates strength development but also leads to self-desiccation and shrinkage cracking, which can compromise durability.
To counter these effects, internal curing agents - such as natural fibers, water-absorbing aggregates, wood fibers, and superabsorbent polymers - are introduced to supply additional moisture during hydration. Among natural fibers, banana and coir have shown promise in improving crack resistance, ductility, and energy absorption, though their success depends on the fiber type, treatment, and dosage.
Building on this understanding, groundnut shell fiber emerges as another viable option. Rich in cellulose, hemicellulose, and lignin, this agricultural byproduct offers strength, flexibility, and biodegradability at a very low cost. Derived from discarded groundnut shells, it is abundant and environmentally friendly, yet remains underexplored in construction research.
Testing Groundnut Shell Fibers in Blast-Resistant Concrete
In this study, researchers examined how chemically treated groundnut shell fibers affect the blast resistance and mechanical performance of fiber-reinforced concrete (FRC). The naturally sourced fibers underwent a sequential chemical treatment process involving alkali (NaOH), silane, and acetylation steps. Following treatment, the fibers were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and tensile testing to evaluate chemical and structural changes.
To assess mechanical performance, three different concrete mix proportions were prepared and compared against a conventional control mix. Both pre-treated and post-treated fibers were added at 0.5 %, 1 %, and 1.5 % volume fractions, and each variant was tested for its strength characteristics and resistance to simulated blast loading.
While most prior research on natural fibers has focused on static mechanical properties, relatively few studies have explored their role in enhancing blast resistance. This study aimed to fill that gap by analyzing how chemical treatments influence the fibers’ mechanical behavior and microstructure, and by evaluating their potential in high-performance, impact-resistant concretes. Blast performance was investigated using finite element simulations based on the ABAQUS/Explicit coupled Eulerian–Lagrangian (CEL) framework.
How the Fibers Were Processed and Evaluated
Groundnut shells were first cleaned using purified water, sun-dried, ground, and sieved to obtain 2 mm particles. Then, the shells were soaked in sodium hydroxide solutions of 4 %, 6 %, 8 %, and 10 % concentrations for three hours at room temperature. After rinsing with distilled water to remove residual alkali, the fibers were air-dried for 8 hours and then oven-dried for 6 hours at 100 °C.
For silane treatment, a 3 % oligomeric siloxane solution dissolved in a 40:60 water–methanol mixture was prepared and stirred for ten minutes. The alkali-treated fibers were immersed in this solution for three hours, washed, and oven-dried at 90 °C for four hours. Finally, the alkali-pretreated fibers underwent acetylation by soaking in acetic acid and treating using acetic anhydride at room temperature for three hours.
To evaluate groundnut shell fiber properties, single-fiber tensile tests were conducted on 50 individual samples each of treated and untreated fibers, with diameters measured using a Carl Zeiss optical microscope at four points for accuracy.
Over 50 fibers per type were tested, and tensile strength, failure strain, and modulus of elasticity were derived from stress–strain curves using Origin software. Fiber density was measured using a density gradient tube. Chemical analyses measured hemicellulose, wax, and moisture content. FTIR analysis examined chemical changes after sodium hydroxide treatment, while XRD analysis characterized crystalline structure modifications.
Treated Fibers Improve Strength and Reduce Blast Impact
The study found that untreated and pretreated groundnut shell fibers generally led to reductions in compressive, split tensile, and flexural strength. In contrast, sodium hydroxide post-treatment significantly improved concrete performance when fibers were used at optimized dosages.
The most notable gains were observed with 0.5 % post-treated fiber content, which improved compressive and tensile strengths by approximately 10–11 % over the control mix at 28 days. Flexural strength was optimized at 1.0 % post-treated fiber content. The chemical treatments enhanced fiber–matrix bonding by increasing the availability of hydroxyl groups and improving fiber crystallinity, as confirmed through FTIR and XRD analyses. FTIR spectra revealed stronger O–H and C–O bands associated with exposed hydroxyl and cellulose groups, while XRD patterns showed sharper peaks, indicating improved crystalline structure following treatment.
Finite element blast simulations supported these results, showing better stress distribution and significantly lower deformation in panels reinforced with treated fibers. Under a simulated 5 kg TNT blast, peak stress was reduced from approximately 200 MPa in untreated concrete to around 35 MPa in panels containing treated fibers. However, simulations also showed that higher fiber volumes (≥1.0–1.5 %) increased deflection due to reduced matrix continuity and poor fiber dispersion.
Overall, the findings suggest that post-treated groundnut shell fibers enhance energy absorption and crack-bridging capacity, though full-scale experimental validation under real blast conditions is still needed.
Post-treated fibers also acted as internal curing agents, slowly releasing absorbed water during hydration, thereby reducing shrinkage and improving overall hydration. However, untreated fibers reduced workability due to their high water absorption. Chemical treatments helped maintain the slump by limiting this absorption.
Still, at higher fiber volumes, the mix became harder to handle, and mechanical performance declined due to fiber clumping and reduced matrix continuity.
Conclusion: A Sustainable, Promising Reinforcement - With Room for Validation
In conclusion, the study demonstrated that chemically treated groundnut shell fibers can improve the energy absorption capacity and toughness of concrete when used in optimal proportions. While the findings on blast resistance are promising, they are based solely on numerical simulations. To fully confirm the material’s potential for real-world applications, large-scale experimental validation will be essential.
Journal Reference
Praveenkumar, T. R., Rath, B., Paramasivam, P., Gupta, R., & Tufa, M. A. (2025). Chemically treated groundnut shell fibers for enhanced mechanical and blast performance of concrete. Scientific Reports, 15(1), 1-18. DOI:10.1038/s41598-025-21957-9, https://www.nature.com/articles/s41598-025-21957-9
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