Effects of Temperature-Control Admixtures on Shrinkage and Mechanical Properties of Fly Ash Concrete: Experiments and Modeling

The mitigation of early-age shrinkage and thermal cracking remains a pressing challenge in mass concrete structures. This study introduces a novel temperature-control admixture (TCA), formulated with gel-forming inorganic compounds, designed to suppress internal temperature rise while improving the mechanical stability of fly ash concrete. Four concrete mixes with TCA dosages of 0, 0.05, 0.10, and 0.15% were experimentally evaluated under controlled environmental conditions. Results show that the optimal dosage of 0.10% achieved a 27.3% reduction in shrinkage and a 12.2% increase in compressive strength at 28 days compared to the control. Furthermore, existing shrinkage models (Eurocode 2, fib Model Code 2010, AS 3600, Bazant B4) consistently overestimated shrinkage by up to 294% due to their inability to capture TCA-induced modifications in hydration and moisture transport. To address this, a modified prediction model incorporating admixture and fly ash-dependent correction factors was proposed, reducing the mean prediction error to just 10% and achieving a coefficient of variation as low as 0.08. This work provides a semi-empirical modeling approach that captures the influence of microencapsulated TCAs on concrete shrinkage and offers useful insights for the design and optimization of advanced concrete systems.