Image Analysis Technique for Monitoring Early Age Shrinkage Strains with Depth from the Top Surface of Monolithic Cementitious Prism Specimens

摘要

This paper describes the use of the image analysis technique for monitoring the variation of early age shrinkage strains with respect to the depth from the top surface of ordinary Portland cement mortar and concrete prism specimens starting as early as 30 min after adding water to the mixture. The applicability of the image analysis technique was demonstrated on both sealed and unsealed cementitious prism specimens. As expected, in situations where the top trowelled surface is protected from moisture loss, the shrinkage strains are similar with depth from the top trowelled surface. On the other hand, magnitudes of shrinkage strains monitored vary with depth when the top trowelled surface is exposed to a dry environment from an early age. The results also showed that the effect of settlements on early age shrinkage strains monitored can be minimized by adopting the current image analysis testing arrangement. Furthermore, when the early age shrinkage strains monitored using the image analysis technique were benchmarked against the results obtained via laser sensors, comparable shrinkage strains values were observed on the sealed prism specimen. On the other hand, the laser sensors were found to provide an "average" value of shrinkage strains that develop across the whole cross section of the unsealed prism specimen.