Age-Adjusted Effective Elastic Modulus of High-Performance Concrete at Early Age

One of the key parameters governing the stresses due to restrained deformation, and thereby the associated risk of cracking, is the elastic modulus of concrete. The early-age evolution of the elastic modulus is intrinsically a function of the development of hydration degree. For concrete subjected to sustained loads, the elastic modulus evolves with creep and relaxation properties. Many design methods use the concept of effective elastic modulus or age-adjusted effective elastic modulus to account for such effects. The challenge with the existing approaches is the lack of in-depth knowledge and reliable test data to accurately determine creep and aging effects for predicting elastic modulus evolution under sustained loading conditions. This paper first provides a brief review of the current approaches to determine the elastic modulus evolution under sustained loading at early age. Second, a method is proposed to directly obtain the age-adjusted effective elastic modulus (E_aaef(t, t₀)) evolution experimentally by utilizing an advanced Temperature Stress Testing Machine. Such evolution of E_aaef(t, t₀) in a high-performance concrete subjected to a sustained tensile stress of 30% of the 3-day tensile strength is experimentally obtained. The test data are compared with the pure elastic modulus evolution. The creep and aging coefficients are derived based on the newly-measured test data. Differences between obtained early-age creep coefficients and that predicted by existing approaches are comparatively investigated. In addition, on the basis of newly-measured test data and analytical investigations, a convenient approach to determine E_aaef(t, t₀) using time-dependent profiles of reduction factors is proposed.