Maturity testing through continuous measurement of E-modulus: an inter-laboratory and inter-technique study

Nowadays, many construction companies use maturity-based approaches to support decisions that have strong impact on costs and sustainability of the construction process, such as: age of pre-stressing operations, decision of propping/formwork removal; instant of subjection to load, etc. Current approaches to quality control through maturity consist in evaluating the compressive strength evolution of the concrete mix at a reference curing temperature (usually 20°C), together with the determination of the apparent activation energy (Ea) of the mix. The value of Ea is usually obtained from one of these three sources: (i) reference recommendations based on the type of cement; (ii) calorimetric testing; (iii) testing of compressive strength evolution at several distinct temperatures. The only technique of determining Ea that really addresses a mechanical property is the latter one, demanding however the deployment of many specimens and tests. Furthermore, the destructive character of this technique limits the possibility of maintaining the same specimen for the entire Ea testing, thus increasing the variability/scattering of results. The present study intended to evaluate the possibility of assessing mechanical-based activation energy for concrete through continuous or quasicontinuous assessments of E-modulus since very early ages. E-modulus is a mechanical property depending on the advancement of the hydration reaction and the temperature stories during the curing, with the interesting characteristic of allowing non-destructive testing to be carried out. This paper presents an inter-laboratory and inter-technique comparative study of E-modulus evolution at several temperatures. Three laboratories were involved, contributing with specific testing techniques applied to a single mix of normal strength concrete: 1) BTJASPE (BéTon au Jeune Age, Suivi de la Prise et du module d'Elasticité), available at IFSTTAR in France; 2) EMM-ARM (Elasticity Modulus Measurement through Ambient Response Method) available at the University of Minho in Portugal; 3) TSTM (Temperature Stress Testing Machine), available at Université Libre de Bruxelles in Belgium.