Assessing the compressive strength of concrete incorporating volcanic scoria as partial replacement for gravel

Volcanic scoria has attracted increasing attention as a sustainable lightweight aggregate due to its low density, local availability, and economic advantages. This study investigates the feasibility of partially replacing conventional gravel with volcanic scoria in concrete production and evaluates the resulting effects on compressive strength, workability, density, and production cost. Concrete specimens were produced with six replacement levels of gravel by volcanic scoria (0, 20, 40, 60, 80, and 100%) while maintaining a constant water–cement ratio of 0.55. Laboratory investigations included sieve analysis, water absorption, slump test, and compressive strength tests at curing ages of 7, 14, and 28 days. The moderate improvement in compressive strength observed at 20–40% replacement levels is attributed mainly to improved particle packing and internal aggregate interlocking resulting from the rough and porous texture of volcanic scoria. The optimal replacement ratio is 40% replacements of gravel with volcanic scoria, which conducts to the highest value of compressive strength. However, replacement levels above 60% resulted in progressive strength reduction. Increasing volcanic scoria content also caused reduced workability and lower concrete density due to its porous and lightweight nature. In addition, comparative cost analysis revealed an approximate 24% reduction in aggregate-related cost at the optimum replacement level. These findings demonstrate that volcanic scoria can serve as an effective and economical partial substitute for gravel in lightweight and low-cost concrete production, provided the replacement ratio does not exceed 40%.