Durability Assessment of Concrete Incorporating Tannery Sludge and Crumb Rubber: Implications for Sustainable Structural Applications

Sustainable valorisation strategies in construction materials are essential to tackle the combined environmental problems caused by increased tannery sludge (TS) generation and end-of-life tire disposal. This study examines the durability and environmental impact of concrete using TS as a partial substitute for Portland limestone cement (PLC) and crumb rubber (CR) as a partial replacement for fine aggregate (TSCRC). Experimental assessments were performed on water absorption, sulfuric acid attack, accelerated carbonation, and heavy metal (chromium) leaching across different curing durations and exposure conditions. The findings demonstrated that water absorption diminished with curing age due to the ongoing densification of the matrix. The control concrete demonstrated the lowest absorption rates, ranging from 3.8% at 7 days to 2.7% at 90 days, while the 5% TS and 10% TS mixtures showed reductions of 4.1% to 3.1% and 4.5% to 3.5%, respectively. Exposure to acid resulted in gradual mechanical deterioration. The depth of carbonation also increased proportionally with higher replacement levels, indicating greater permeability to carbon dioxide. Leachate analysis verified that chromium mobility rose with TS dosage, although concentrations stayed relatively low because of immobilization within the hydration products. The findings collectively suggest that a preliminary replacement range of 5–10% TS and 0–5% CR achieves optimal industrial waste incorporation while ensuring the necessary durability for sustainable concrete purposes.