TITLE:
Mix Design and Mechanical Behaviour of Structural Concrete in Tropical Coastal Environments
AUTHORS:
Babacar Diouf, Mariama Ba, Bator Cisse
KEYWORDS:
Concrete Mix Design, Compressive Strength, Water-to-Cement Ratio, Cement Dosage, Bridge Construction, Tropical Environment
JOURNAL NAME:
Open Journal of Civil Engineering,
Vol.16 No.3,
September
4,
2026
ABSTRACT: This paper presents a comprehensive experimental investigation into the mix design and mechanical behaviour of five structural concrete grades (C20/25 to C40/50) used in the construction of the 4th Abidjan Bridge, Côte d’Ivoire. Mix proportions were established using the Dreux-Gorisse method and two cement types: CPA-CEM I/52.5N (ordinary Portland cement) and CHF-CEM III/B 42.5 L-LH/SR (blast-furnace slag cement). The influence of three key parameters—cement content, water-to-cement ratio (w/c), and cement type—on fresh-state consistency and 7- and 28-day compressive strength was systematically assessed through standardised slump tests (NF EN 12350-2) and compression tests on cylindrical specimens (NF EN 12390-3). Results demonstrate that increasing cement content from 275 to 400 kg/m3 is associated with a 55% increase in 28-day compressive strength, while reducing the w/c ratio from 0.62 to 0.44 is associated with a 50% strength gain; because cement type, aggregate proportions and admixture dosage also varied among the mixes compared, these values reflect differences between complete mix formulations rather than isolated effects of cement content or w/c ratio alone. At identical cement dosages (380 kg/m3), CEM I develops 7-day strengths approximately 21% higher than CEM III/B, whereas 28-day strengths converge within 3%, although the mixes compared also differed in w/c ratio and superplasticiser dosage. The mean compressive strength of each grade, based on at least three specimens, exceeded the corresponding target strength class defined under NF EN 206-1; a mean value alone, however, does not constitute the statistical characteristic-strength or conformity assessment required by the standard. The findings are consistent with recent literature on hydration kinetics, capillary porosity, and admixture performance, and provide actionable quality-control guidelines for ready-mix concrete production in tropical coastal settings.