Aggregate Testing and Hydraulic Concrete Mix Design for Bridge Construction in an Aggressive Marine Environment: A Case Study of the émile Badiane and Tobor Bridges, Ziguinchor, Senegal

Abstract

This paper evaluates basalt aggregates from the Diack quarry and develops two concrete mixes for bridge construction in an XS1 saline environment. The study applies the Dreux-Gorisse and Féret-Bolomey mix design methods to a conventional C35/45 concrete and a self-compacting C35/45 concrete using CEM III/B cement. The reported aggregate properties meet the cited compliance limits, and both proposed mixes satisfy the prescriptive binder-content and effective water-to-cement ratio requirements for XS1 exposure. Basalt aggregates from the Diack quarry were characterized for physical properties (particle size distribution, specific gravity, bulk density, water absorption) and mechanical properties (Los Angeles and Micro-Deval coefficients) in accordance with applicable NF EN standards. All reported aggregate test results were within NF EN 12620 compliance limits. Two concrete formulations were derived: a conventional structural concrete B40 (C35/45) using the Dreux-Gorisse method, and a Self-Compacting Concrete (BAP, C35/45) using the Féret and Bolomey approaches, both incorporating slag cement CEM III/B 42.5 N-SR and a polycarboxylate superplasticizer. All granular fractions were used in saturated surface-dry (SSD) conditions, and effective water contents were corrected for aggregate absorption prior to mix proportioning. The resulting mix designs achieved effective water-to-binder ratios of 0.449 (B40) and 0.376 (BAP), satisfying the XS1 class requirements for minimum binder content (≥330 kg/m 3 ) and maximum w/c ratio (≤0.55). Fresh-state performance targets for the BAP (slump flow ≥ 650 mm, yield stress τ 0 η < 20 Pa·s) and an estimated service life exceeding 100 years under DuraCrete assumptions represent design objectives that require experimental validation prior to site implementation. The study demonstrates that locally sourced basalt aggregates are suitable for high-performance bridge concrete in estuarine West African environments, provided appropriate cement selection and admixture optimisation are applied.