Experimental Study on the Estimation of Structural Strength Correction for Concrete Using Ordinary Portland Cement

This study investigates the influence of seasonal curing conditions on the compressive strength development of reinforced concrete, focusing on the gap between standard-cured cylinders and in situ structural performance. Concrete mixes with water-to-binder ratios of 0.35, 0.45, and 0.55 were cast under summer, autumn, and winter conditions. Large-scale specimens were instrumented to monitor the internal heat of hydration at center and outer regions, and 91-day core strengths were compared with 28-day standard-cured cylinders. Results revealed that seasonal temperature variations significantly affect hydration kinetics, producing thermal gradients that lead to spatial strength differences. Normal distribution analysis (₂₈S₉₁ values) was used to quantify strength deviations and derive correction factors. Outer-region cores consistently showed lower strengths, confirming them as conservative indicators for design. Based on μ + 2σ, correction factors of approximately 8 MPa are recommended for summer and winter conditions and 5 MPa for autumn, ensuring a conservative estimate of in situ strength. The proposed approach provides a rational, data-driven basis for mix design strength adjustments, improving the reliability of structural safety evaluations and supporting climate-responsive construction planning for durable and safe reinforced concrete structures.