System for monitoring the evolution of the thermal expansion coefficient and autogenous deformation of hardening materials

This article presents an experimental system developed to determine the kinetic parameters of hardening materials. Kinetic parameters allow computation of the degree of reaction indices (DRIs). DRIs are used in predictive formulae for strength and are used to decouple the autogenous deformation (AD) and thermal deformation (TD). Although there are several methods to determine values for kinetic reaction parameters, most require extensive testing and large databases. A measurement system has been developed in order to determine kinetic parameters. The measurement system consists of optical fiber sensors embedded in specimens that are cured at varying temperatures and conditions. Sensors are used in pairs inside each specimen, and each pair has two deformation sensors that, aside from their axial stiffness, have the same characteristics. The study of the interaction between sensors and hardening material leads to establishment of a link between the deformations measured and the degree of reaction, by means of the newly developed concept of the equivalency point. The equivalency point is assumed to be an indicator of the degree of reaction and it allows the determination of the apparent activation energy (Ea) which defines the equivalent time. Equivalent time is a degree of reaction index (DRI) and it accounts for the combined effect of time and temperature in concrete. This new methodology has been used to predict the compressive strength and separate the AD and thermal expansion coefficient (TEC) in seven types of concrete. The measurement system allows gathering of data necessary for fast and efficient predictions. Due to its robustness and reduced dimensions it also has potential for in situ application.