Objective “This study presents a technical soil stabilization solution by utilizing Gorgan Bay Sludge Ash (GBSA), a processed, problematic environmental by-product, for the stabilization of clayey soils with varying plasticity characteristics.”

Methods: For this purpose, a wide range of clay soils, including four samples with plasticity indices of 21, 32, 40, and 68, were selected and mixed with 0, 5, 10, 15, 20, and 25 wt.% of sludge ash. The mechanical properties of the specimens were evaluated using Atterberg limits, standard Proctor compaction, and unconfined compressive strength (UCS) tests (at curing ages of 1, 7, 28, and 56 days).

Results: “Results showed that the addition of sludge ash up to an optimum ratio of 15% led to a 5–7% increase in maximum dry unit weight and a remarkable 193–270% improvement in unconfined compressive strength (UCS) across all tested samples. Beyond this optimum level (at 20% and 25% ash), the growth in dry density and UCS slowed or declined, which is attributed to clay particle flocculation as voids were filled by the heavier ash particles. In contrast, the plasticity index decreased continuously, showing a 58% to 75% reduction at 25% ash content. Ultimately, these combined effects—increased dry density and UCS alongside reduced plasticity—significantly enhance the engineering behavior of the stabilized soil.”

Conclusions: These findings identify Gorgan Bay sludge ash as an effective additive for stabilizing problematic clay soils and offer a practical, low-cost approach for the environmentally sustainable management of this sediment waste in the region.