Long-Term Creep and Shrinkage Behaviour of High-Strength Concrete Incorporating Supplementary Cementitious Materials Under Nigerian Tropical Conditions

Time-dependent deformation in high-strength concrete, governed by creep and shrinkage, has significant structural consequences for long-span prestressed concrete bridges, high-rise columns, and thin-shell structures, yet creep and shrinkage databases for high-strength concrete incorporating supplementary cementitious materials under sustained tropical exposure conditions are largely absent for the Nigerian context. This study investigates the long-term creep and shrinkage behaviour of high-strength concrete mixes incorporating silica fume, fly ash from Egbin Power Station, and rice husk ash from the South South geopolitical zone under outdoor exposure conditions at research stations in Port Harcourt, Abuja, and Kano, representing three distinct Nigerian climatic zones. Cylindrical specimens were loaded to 30 percent of their 28-day compressive strength and maintained under sustained load over a 36-month measurement period. Specific creep, basic creep, drying creep, autogenous shrinkage, and drying shrinkage were measured at regular intervals and modelled using the fib Model Code 2010 creep and shrinkage models. Model predictions were compared against measured data and calibration factors for the tropical exposure environment were derived using non-linear regression. Results indicate that the current fib Model Code 2010 significantly overestimates drying shrinkage in the high-humidity coastal environment of Port Harcourt by 42 percent, while underestimating creep under the high sustained temperature of the Kano semi-arid zone by 28 percent. Silica fume inclusion at 10 percent cement replacement consistently reduced long-term creep coefficient by 19 to 24 percent across all three exposure locations. The study provides the first large-scale tropical climate correction dataset for international creep and shrinkage models using Nigerian supplementary cementitious materials. Keywords: creep, shrinkage, high-strength concrete, supplementary cementitious materials, tropical climate.