Application of image analysis to monitor very early age shrinkage

Abstract

This paper Introduces a new approach to monitor the shrinkage of fresh cementitious materials using digital image analysis beginning within 30 minutes after adding water to the mixture. This method goes some way in overcoming the difficulties associated with the fixing and placing of targets for use with a number of shrinkage monitoring devices on fresh cementitious mixtures that have not set. These difficulties have given rise to occasions when useful information about very early-age shrinkage is not well documented in the literature. The very early-age shrinkage of concrete has significant effects on the behavior and durability of concrete in service, especially in the case of composite specimens comprising freshly-cast, low water-cement ratio (w/c cementitious materials on a hardened concrete substrate. This new method of monitoring shrinkage strains is presented herein and, where applicable, shrinkage strains monitored using this technique were compared with readings obtained using a laser sensor technique. Based on the results obtained, it was found that shrinkage strains monitored using image analysis compared well with and, as expected, are higher than that measured using a pair of laser sensors. Copyright © 2006, American Concrete Institute. All rights reserved.