Testing Concrete E‐modulus at Very Early Ages Through Several Techniques: An Inter‐laboratory Comparison

Abstract

The design of concrete structures is based on calculation rules, which often do not take into account the very early age behaviour of the material. However, during this period, structural concrete is subjected to strains due to the hydration process of cement. If these strains are restrained by concrete itself or surrounding boundaries, stresses start to build up that can lead to the formation of cracks. Among the parameters involved in the stress build up, the stiffness evolution is of major importance. This paper reports the use of eight different techniques aimed at stiffness evolution assessment, applied on the same concrete mix, in a round robin experimental test within three laboratories. The observations are compared after having expressed the results at the same equivalent age. Both the loading stress rate and amplitude are observed to have an effect of limited importance on the determination of the quasi-static elastic modulus, which might be explained by very short term creep. Ultrasonic measurements provide values of E-modulus that are higher than the values provided by the quasi-static tests at the time of the concrete setting. Similar mechanisms associated to very short term creep could explain the difference between the quasi-static and high-frequency elastic modulus.

Longitudinal restraining devices for the evaluation of structural behaviour of cement‐based materials: The past, present and prospective trends

“…Since then, this testing method was adopted by several research groups, universities and institutions worldwide, contributing to a breadth of investigations regarding the early age viscoelastic behaviour of concrete. Some of them comprised of the evaluation of cracking sensitivity of concretes due to autogenous shrinkage at various temperatures with and without reinforcement, 72–75 self‐induced stresses in high‐performance concrete, 76,77 effects of mix composition and mineral additions 78,79 or even the determination of the elastic properties of concrete since setting 80–84 . The TSTM apparatuses used in these studies had the similar operating principles and testing set‐up configurations, with some differences originating from the positioning of sensors, size of specimen, existence of thermal regulation system, loading control system, deformation threshold value and starting time of tests, as already mentioned for a few studies in Staquet et al 85…”

Embedding ultrasonic transducers in concrete: A lifelong monitoring technology

“…Assuming a value of the dynamic Poisson's ratio of ν dyn ≈ 0.3 at 28 days [38], the dynamic E-modulus is 36 GPa.…”

Influence of cyclic movement on the hardening process of grout: case of offshore wind turbine installation

“…Then loads are applied at ages of 2, 3, 7, 14 and 28 days. A complete description of the device, the test protocol and the data processing is indicated in [4,17,18].…”