Evaluation of transport properties of deteriorated concrete due to calcium leaching with coupled CT image analysis and random walk simulation

Abstract

Concrete may deteriorate when chronically in contact with water due to the leaching of calcium ions. This study conducted a natural diffusion test for calcium ions with a minute cylindrical specimen of 3 mm in diameter and 6 mm in height to determine leaching at 20 and 80 °C in 33 days. One piece of limestone as aggregate was inserted inside each specimen to investigate the effect of the interfacial transition zone (ITZ). Changes in mass transfer in the leaching and non-leaching regions in bulk cement paste were evaluated using synchrotron X-ray computed tomography (CT) in a micrometer order. A deeper dissolution front of Ca(OH)2 inside the specimen was observed for a higher temperature leaching test. Random walk simulation was performed to obtain diffusion parameters. Results showed that the calcium diffusion coefficient of non-deteriorated ITZ is about ten times as high as that of the non-leaching region. For the leaching region, the diffusion coefficient is about 50 times and 100 times as high as that of the non-leaching region at 20 °C and 80 °C, respectively. In addition, the Ca(OH)2 dissolution front appeared deeper inside the specimen in the direction where aggregate is close or exposed to the dissolution front because of ITZ.