Nondestructive evaluation of volumetric shrinkage of compacted mixtures using digital image analysis

Adapting image processing technology to engineering disciplines can be useful in the evaluation of the mechanical behavior of materials. Not only characteristics of granular materials, but also particulate levels of colloids can be studied using image analysis. Attempts to identify the volume change of soils or compacted specimens have been made since late 1990s. Some of the previous studies were related with the determination of the deformation field during triaxial tests while the rest were directly related with the measurement of the volumetric shrinkage strains of expansive soils. Unlike with other studies, considered volumetric shrinkage strain levels in this study were limited to 6%. The strain levels were limited, because it was noted that the maximum allowable volumetric shrinkage strain levels were 5% for evaluating the hydraulic behavior of compacted soils. The principal purpose of this study is to show the ability of image processing techniques on the quantification of the volumetric shrinkage of the compacted soils even in the small strain levels. For this purpose, a special test setup was established and a computer algorithm was developed to identify volume of the specimens from digitized images. Initially, volume changes of compacted bentonite-zeolite mixtures at various bentonite contents were measured by means of vernier caliper. Comparison of the digital measurement results with those of the manual readings showed that they were in good agreement. It appears that the proposed methodology would provide nondestructive, stable and repeatable volume measurements and is a promising approach for the quantification of volumetric shrinkage strains of compacted bentonite-zeolite mixtures even at small strain levels.