Experimental assessment and modelling of effective tensile elastic modulus in high performance concrete at early age

This paper focuses on the age-adjusted effective elastic modulus (E_a(t,t₀)) in high performance concrete subjected to sustained tensile loading conditions at early age. First, the existing approaches to determining E_a(t,t₀) are discussed, underlining their limitations. Second, a novel experimental approach is put forward to capture E_a(t,t₀) using an advanced Temperature Stress Testing Machine and a unique direct tensile test setup. In this approach, both pure elastic modulus (E(t)) and E_a(t,t₀) can be directly measured, whereas, in existing methods, the predictions are based on empirically determined values/models of ageing and creep coefficients. A unique set of test data obtained based on the proposed approach is presented to assess the early-age evolution of E_a(t,t₀) and its key influencing factors. Such obtained experimental values are used to compute the evolutions of the reduction factors (k(t,t₀)) simply by obtaining the ratio between experimentally determined values of E(t) and E_a(t,t₀). The applicability of existing approaches for predicting k(t,t₀) is evaluated, and the causes for discrepancies between experimental values and predictions are discussed. Finally, an empirical model is proposed in this paper to quantify the k(t,t₀) profiles. It is shown that the proposed model is convenient, easily adaptable for different types of concrete without the need for an extensive test database, and yet realistically reflects the nonlinearity of k(t,t₀) profiles at early ages.