Periwinkle Shells vs Gravel for Concrete: Cost Comparison in Nigeria

Quick answer: In coastal and riverine areas of Nigeria, periwinkle shells can cost 30–60% less than granite gravel because they are locally abundant, while granite must be quarried inland and transported long distances at significant cost. However, periwinkle shell concrete has lower compressive strength than granite concrete and is generally only appropriate for non-structural or lightly loaded applications — not for structural columns, beams, or suspended slabs without engineering approval.

What Are Periwinkle Shells, and Why Are They Used?

Periwinkle shells are the discarded shells of periwinkle snails, a common seafood in Nigeria's coastal and riverine communities. In states like Lagos, Rivers, Bayelsa, Delta, and parts of Akwa Ibom and Cross River, periwinkle shells accumulate in large quantities as a food-processing by-product and are often available cheaply or even free in bulk near waterside markets and fishing communities.

Because granite chippings (the standard coarse aggregate for concrete) must be quarried — mostly from inland states like Ogun, Oyo, and Ondo — and then transported to coastal sites, granite is often one of the more expensive line items in a Lagos or Niger Delta building budget. Periwinkle shells offer a locally sourced alternative that some builders in these areas have used for decades, particularly for filling, blinding, and lightly loaded concrete work.

Cost Comparison: Periwinkle Shells vs Granite Gravel

The actual saving depends heavily on how far your site is from a granite quarry versus how close you are to a periwinkle shell source. In Lagos waterside areas or the core Niger Delta, the saving can be substantial. Further inland, granite may already be locally available and the cost advantage of periwinkle shells disappears.

The Structural Trade-Off — Read This Before Choosing Periwinkle Shells

Cost is only half the picture. Periwinkle shell concrete has been studied extensively by Nigerian civil engineering researchers, and the consistent finding is that it produces lower compressive strength than granite concrete at the same mix ratio — typically in the range of 15–35% lower, depending on shell grading and mix design. This matters because:

• Periwinkle shells are irregularly shaped and more porous than granite, which affects how well the concrete compacts and bonds
• Strength reduction is generally acceptable for blinding concrete, mass fill, non-structural floor slabs on grade, and pavement/walkway work
• Strength reduction is not generally acceptable for structural columns, ring beams, suspended floor slabs, or any load-bearing structural element — these require an engineer to specify and verify the mix design if periwinkle shells are to be used at all

Do not substitute periwinkle shells for granite in structural concrete without your structural engineer's explicit approval and a verified mix design. Saving on aggregate cost is not worth compromising the structural integrity of columns, beams, or slabs that carry the load of your building.

Where Periwinkle Shell Concrete Makes Sense

• Blinding concrete under foundations — a non-structural levelling layer where strength requirements are minimal
• Mass fill and site levelling — where the concrete is not carrying structural load
• Compound paving and walkways — lightly loaded surface applications
• Non-structural floor slabs on solid ground — where a structural engineer confirms the application does not carry significant load

Where Granite Remains the Right Choice

• Foundation footings and any reinforced concrete in the foundation
• Columns, ring beams, and lintels
• Suspended (German) floor slabs and any upper-floor structural slab
• Any element your structural engineer has designed assuming standard granite concrete strength

The Bottom Line

Periwinkle shells are a genuine, long-used cost-saving option for non-structural concrete in Nigeria's coastal and riverine regions, and the saving can be meaningful where granite transport costs are high. But this is a decision for your structural engineer to confirm on an element-by-element basis, not a blanket substitution to save money across the whole project. For structural work, granite remains the default for good reason.