What if concrete’s carbon problem could be tackled using seafood waste? New research shows that discarded seashells can strengthen low-carbon concrete while significantly cutting emissions.
Study: Experimental Investigation of Low Carbon Concrete Using Ground Seashell Powder as Filler and Partial Cement Replacement. Image Credit: Reimar/Shutterstock.com
Researchers have taken a closer look at how ground seashell powder, typically treated as waste, can be used as a filler material and partial cement replacement in low-carbon concrete. Their findings, published in Construction Materials, offer a potential solution to one of the construction industry’s most pressing challenges: reducing the carbon footprint of traditional concrete.
Environmental Benefits of Seashells in Concrete
The construction sector is a major source of global CO2 emissions, with Ordinary Portland Cement (OPC) production alone responsible for roughly 7–8 % of the total. This has driven a search for supplementary cementitious materials (SCMs) that can reduce the environmental impact of concrete.
Seashells, especially scallop shells, are abundant byproducts of the seafood industry and are rich in calcium carbonate - a key ingredient in cement. When finely ground, these shells can replace a portion of OPC in concrete, offering dual benefits: reducing emissions and helping address shell waste disposal.
Methodology for Assessing Seashell Powder in Concrete
To explore this potential, researchers processed discarded scallop shells by cleaning, drying, and grinding them into two particle sizes:
- 63–125 microns, used as a filler material
- 0–63 microns, used as a cement replacement
These powders were incorporated into concrete at a 15 % cement replacement level, with some also used as fillers.
A control mix targeting 40 MPa compressive strength was prepared using 52.5-grade type I (CEM I) cement. Multiple concrete mixes combining seashell powder with cement and aggregates were tested for workability, density, strength, modulus of elasticity (via stress–strain tests), alkalinity, and overall mechanical performance.
To understand the microstructure, the team used scanning electron microscopy (SEM) and X-ray diffraction (XRD), examining pore distribution and the role of calcium-rich shells in hydration and bonding. Environmental performance was assessed by calculating carbon emissions reductions based on material processing and lab-scale electricity use.
Key Findings: Performance and Sustainability
The results were encouraging. Replacing part of the cement with seashell powder reduced CO2 emissions by up to 36 % while maintaining performance at moderate replacement levels. At 15 % replacement, compressive strength remained comparable to the control mix. However, at 45 % total cement reduction (30 % replacement + 15 % filler), compressive strength declined by approximately 25 %.
Concrete density decreased slightly, from 2515 kg/m3 in the control mix to 2458 kg/m3 at 30 % replacement, suggesting potential applications in lightweight construction. This change reflects a modest 2.27 % reduction in density.
Setting time also shifted. At 30 % replacement, initial setting time increased by 30 %, likely due to the shells’ porous nature absorbing water. Meanwhile, the final setting time decreased by 12 %.
Microstructural analysis supported the strength findings. SEM imaging revealed denser pore networks, fewer microcracks, and indications of added calcium-silicate-hydrate (C-S-H) gel, attributed to the high calcium content of the shells. However, XRD showed that while C-S-H content remained low (≤3 %) and poorly crystalline, other changes were evident. Specifically, portlandite decreased while calcite increased - a sign of secondary filler effects influencing hydration behavior.
Importantly, the alkalinity of all mixes stayed within a safe pH range of 12–13, supporting the passive protection of embedded steel. This suggests that corrosion resistance would not be compromised.
Practical Applications for the Construction Industry
These findings carry strong implications for the construction industry, especially as it moves toward low-carbon alternatives. By using waste seashells to replace a portion of cement, this approach reduces emissions and promotes circular economy practices.
Seashell-modified concrete strikes a balance between sustainability and performance. It's particularly well-suited to coastal regions, where shell waste is readily available. Potential applications include pavements, precast elements, and lightweight blocks, areas where strength demands are moderate and environmental benefits are prioritized.
As construction regulations increasingly focus on emissions, seashell-derived concrete offers contractors and builders a practical, cost-effective route to lower-carbon projects, without sacrificing critical performance benchmarks.
Conclusion: A Pathway to Greener Concrete Solutions
This study presents a compelling case for using discarded seashells as a low-carbon material in concrete production.
At moderate replacement levels, especially the 15% cement replacement with an additional 15 % filler, seashell powder cuts emissions while maintaining reliable mechanical properties.
Higher substitution levels showed trade-offs in strength and stiffness, indicating that further optimization is needed. Large-scale trials will be essential to validate durability over time and better understand the hydration dynamics involved. Still, the outlook is promising.
If adopted at scale, seashell-based concrete could help reduce reliance on carbon-intensive cement and offer the construction industry a viable way to support climate goals and material circularity.
Journal Reference
Abbas, A.; Kudukkan, A. (2025, November). Experimental Investigation of Low Carbon Concrete Using Ground Seashell Powder as Filler and Partial Cement Replacement. Constr. Mater. 5, 82. DOI: 10.3390/constrmater5040082, https://www.mdpi.com/2673-7108/5/4/82
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