Characterization of shrinkage behavior in concrete materials using cure reference method
A novel experimental technique was developed to investigate the shrinkage behavior in cementitious materials. The Cure Reference Method (CRM), previously developed for residual strain measurements in composites, was used to determine the shrinkage that develops in concrete materials during the curing or drying process. This technique involves the replication of diffraction grating on the concrete specimen during the curing process and the use of high sensitivity moiré interferometry. A specially-designed stage was created to help obtain a set of the consecutive phase shifted fringe patterns. Instead of the intensity-based methods, an automated fringe analysis program was used to analyze fringe patterns to obtain full-field displacement and strain information. Shrinkage as a function of time, location, humidity, temperature, water/cement (w/c) ratio and size was measured for unsealed cement paste specimens. Also, a method of combining CRM and removing drying effect was used to explore the relative contribution of non-drying shrinkage (autogenous shrinkage) to the total shrinkage in cement pastes. Furthermore, CRM technique was applied to explore the effect of fine aggregates (sand) on the shrinkage behavior. The effect of sand quantities was investigated to observe how shrinkage responded to this influential factor. The method of removing drying effect was modified to explore the relative contribution of autogenous shrinkage to the total shrinkage in the specimen with the fine aggregates (mortar specimen). The effect of coarse aggregates (gravel) on shrinkage was also displayed.
An inverse method based on finite element moisture diffusion model and optimization was developed in order to obtain the material properties of cement paste from the complex geometry used in the tests. Once the material parameters were determined, they can be the inputs in finite element analysis for the predictions. The tests in different drying conditions, with different geometry of the specimens, and for the reinforced specimens were performed and their results were compared with FEA to validate the constructed model and the obtained materials properties.
Ring tests were performed under both normal and extreme low humidity conditions for crack investigation. Also, the FEA of the ring test under normal humidity has shown that the numerical result had good agreement with that from the experiment.
Finally, stresses were predicted in FEA model for both free shrinkage and restrained (ring test) shrinkage cases.
0548: Mechanical engineering