Effect of Temperature on the Basic Creep of High-Performance Concretes Heated between 20 and 80 degrees C
Résumé
This research concerns the uniaxial compressive basic creep of high-performance concretes (HPC) in the temperature interval 20-80 degrees C. A basic creep experimental program was performed on HPC envisioned for future storage structures of intermediate-level long-life nuclear wastes. The study determines the long-term evolution of delayed strains and estimates the long-term behavior of HPC under conditions characterized by temperature increases that could reach 70 degrees C attributable to heating by these exothermic wastes. The analysis of strains contributes to the understanding of basic creep at moderate temperatures and clarifies the effect of temperature. A campaign of uniaxial compressive basic creep tests was carried out on four formulations of HPC, two of which incorporated silica fume and stainless steel fibers, subjected to three different temperatures: 20, 50, and 80 degrees C. The comparative analysis of delayed strains assessed the effect of temperature on basic creep kinetics and magnitudes and on Young's modulus of HPC. Damage was observed at 80 degrees C, revealed by a decrease in the modulus of elasticity and a strong increase in creep capacity. From these results, the fitting of a nonlinear viscoelastic model, considering the effect of temperature using an Arrhenius law affecting the viscosities from 20 degrees C, a parameter linked to the intrinsic creep potential at temperatures between 50-80 degrees C, and a thermal damage, is proposed. The improved knowledge of the temperature effect on delayed behavior and its better integration in mechanical models are useful for the design of special structures (e.g.,massive structures and specific serviceability conditions in nuclear or hydroelectric power plants) sensitive to delayed strains and subjected to moderate temperatures.