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In a recent article published in the journal Scientific Reports, researchers investigated the potential of cocoa pod husk extract as a sustainable, bio-based concrete retarder to improve setting time and workability while maintaining mechanical performance.
Study: The use of cocoa pod shells as a bio-based concrete retarder. Image Credit: BrandFotos/Shutterstock.com
Cocoa Pod Husk Retarder Potential
This research addresses the need for sustainable and bio-based alternatives to petrochemical concrete admixtures, focusing specifically on retarding admixtures that regulate cement hydration and setting time.
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Conventional retarders derived from petrochemical sources pose environmental concerns, driving interest in renewable agricultural byproducts. Cocoa pod husks, a major waste product from global cocoa production, contain cellulose, hemicellulose, lignin, and organic compounds that have potential as eco-friendly additives.
While prior studies explored cocoa pod husk ash as a supplementary cementitious material, this study pioneers the investigation of a water-extracted cocoa pod husk extract (CPHE) as a Type B concrete retarder.
The work aims to evaluate CPHE's influence on cement hydration kinetics, setting behavior, mechanical properties, and workability, with validation under real-world mixing conditions and compliance with ASTM standards for Type B retarders, contributing to sustainable construction technology.
CPHE Extraction and Testing
The study proceeded in two phases. The first phase involved identifying CPHE’s retarding capacity and mechanical effects at different dosages
using mortar specimens. CPHE was produced by hydrolytic aqueous extraction from powdered, dried cocoa pod husks and characterized for total organic carbon content.
Cement pastes and mortars were prepared with CPHE additions ranging from 1% to 5% by weight of cement. Setting times were measured using penetration resistance testing, and compressive strength was assessed at early (three and seven days) and later (14 and 28 days) ages.
The second phase involved validating CPHE’s compliance as a Type B retarder according to ASTM C494/C494M-24 through tests on concrete, including setting time, compressive and flexural strength, and drying shrinkage. Large-scale mixing trials at a ready-mix concrete plant compared CPHE performance to commercial retarders like citric acid and sucrose at equivalent total organic carbon concentrations.
Microstructural characterization employed thermogravimetric analysis (TGA), scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDX), and microbial analysis to elucidate retardation mechanisms.
Hydration Delay and Strength Analysis
The addition of CPHE significantly delayed cement setting times, with 3% dosage producing the most effective retardation, extending initial and final setting times by approximately 30% and 50%, respectively.
This retardation fell within ASTM’s acceptable limits for Type B retarders. Early-age compressive strength showed a modest decrease at three and seven days, attributed to the delayed hydration, but strength rebounded to nearly equivalent levels of the control by 14 and 28 days. Flexural strength remained consistently high, exceeding 98% of the control mix at all ages, indicating negligible adverse impact on structural performance.
Analysis of the hydration products suggested that CPHE delayed the nucleation and growth of calcium silicate hydrate (C–S–H) and calcium hydroxide (CH). The researchers proposed that this may be a result of natural organic acids and phenolic compounds in the extract adsorbing onto C3S and C3A cement particles, slowing hydration.
The researchers proposed that these interactions may have reduced the availability or release of Ca2+ ions required for hydration-product formation. Additionally, polysaccharides present in CPHE mildly increased pore solution viscosity, inducing a diffusion-controlled hydration mechanism contributing further to setting delay.
Microstructural SEM images showed reduced formation and interconnection of ettringite crystals and calcium silicate phases at early ages in CPHE specimens compared to control. Energy-dispersive X-ray analysis identified elemental compositions consistent with hydration products whose formation was delayed. Total organic carbon analysis verified dissolved organic species in CPHE that interact chemically with cement hydration processes.
In large-scale ready-mix concrete trials, CPHE improved fresh concrete workability and notably reduced slump loss during mixing and transport. Its performance matched or exceeded commercial retarders such as citric acid and sucrose when normalized by total organic carbon concentration.
Importantly, the long-term mechanical and dimensional stability of the concrete with CPHE satisfied all ASTM Type B retarder requirements, including compressive and flexural strength thresholds and controlled drying shrinkage.
Compared to other bio-based retarders reported in prior literature, such as lignosulfonates, molasses, tannins, and date seed extracts, CPHE demonstrated a broader effective dosage range without the risk of flash or indefinite retardation, which are common issues with hyper-potent sugar-based retarders.
Sustainable Concrete Retarder Insights
This study demonstrates that cocoa pod husk extract has potential to act as an effective, sustainable bio-based concrete retarder conforming to ASTM C494/C494M-24 Type B standards. At an optimal dosage of 3%, CPHE substantially extends cement setting times without compromising long-term mechanical strength or flexural performance, and maintains dimensional stability within acceptable limits.
Leveraging an abundant agricultural waste stream with simple extraction, CPHE offers a promising eco-friendly alternative to petrochemical concrete admixtures, advancing sustainable concrete production and contributing to waste valorization initiatives.
Further research should explore CPHE’s long-term effects on pore solution chemistry and reinforcement corrosion resistance to fully assess durability implications.
Journal Reference
Tsai C.J., Huang Y.C. and Chuang, C.-W. (2026). The use of cocoa pod shells as a bio-based concrete retarder. Scientific Reports. DOI: 10.1038/s41598-026-63231-6, https://www.nature.com/articles/s41598-026-63231-6.