Application of X-Ray CT to Study Diffusivity in Cracked Concrete Through the Observation of Tracer Transport

Ivan Sandi Darma, Takafumi Sugiyama and Michael Angelo B. Promentilla

Journal of Advanced Concrete Technology, 11, 266-281, 2013

This paper demonstrates the application of microfocus X-ray computed tomography (CT) to study solute transport in cracked concrete. Cracks in a cylindrical specimen of ordinary Portland cement (OPC) and fly ash mortar were induced using a splitting tensile test. Cesium Carbonate(Cs2CO3) was then used as a tracer in the in-situ diffusion test with the aid of X-ray CT. Image analysis was also employed to measure the 3D crack geometry and tracer diffusivity from these CT images. The geometric tortuosity of the crack was approximately 1.25 irrespective of the crack opening width and whether fly ash was added or not. On the other hand the constrictivity increased for the fly ash mortar having roughly the equivalent crack opening width. The measured diffusivity in the crack was controlled by both crack opening width and constrictivity. Results obtained from microtomographic images suggest that the entire crack space may not always be filled with the tracer. The diffusive transport of solute in cracks thus can be restricted from microstructure’s point of view. Smaller crack opening would increase such restricted diffusion. Indications also suggest that the addition of fly ash would lead to the reduction of diffusivity through uncracked body of the mortar.

Though being widely applied in other areas, the CT scanning technique is not effectively used or much studied for application in the field of structural engineering. The results obtained from this study convince that there is a potential for effective use of the technique in tracing and clearly understand the actual 3-dimensional substance transports in the concrete mass. The system, when more improved, and the future obtained data will enhance the precision of simulation of substance transport phenomena and durability behavior of concrete structures.
(Prof. Somnuk Tangtermsirikul)
X-ray Computed Tomography is a powerful analytical tool. This high-tech method is applied to study movement of dissolved ions in water filled cracks. Results obtained with this method may improve prediction of chloride penetration into cracked concrete.
(Prof. Folker H. Wittmann)