Three-dimensional reconstruction and sulfate ions transportation of interfacial transition zone in concrete under dry-wet cycles

The interface transition zone (ITZ) is widely recognized as the weakest phase in cement-based materials, and playing a critical role in the durability of concrete. The purpose of this paper is to investigate the performance difference and the diffusion of sulfate ions in cement matrix and ITZ under dry-wet cycles. Therefore, the three-dimensional structure of cement matrix and ITZ was reconstructed by CEMHYD3D and cellular automaton, which was used for exploring the formation and evolution law under the cycling conditions of corrosion. The unsteady diffusion equation of sulfate ions was established based on Fick's second law and the impact factor m of diffusion coefficient was introduced to analyze sulfate ions transportation. The simulation results were compared and discussed with the measured results. Results indicate that the porosity of ITZ is higher than cement matrix with the same water-cement ratio. Yet, the content difference of ettringite between cement matrix and ITZ hardly changed with the increase of water-cement ratio. The corrosion depth of sulfate ions in ITZ is approximately 2 mmdeeper than cement matrix and the sulfate ions concentration in ITZ is greater than that of cement matrix at the same corrosion depth. Moreover, the diffusion rate of sulfate ions increases multiplying under dry-wet cycles and the increase of sodium sulfate concentration also accelerates the early corrosion rate. However, the influence of sodium sulfate concentration on the corrosion rate becomes insignificant as the water-cement ratio increases to 0.5. This study provides new insights in sulfate ions transportation about ITZ and cement matrix, the results of which are expected to provide a new direction for designing sulfate resistant concrete. (C) 2021 Elsevier Ltd. All rights reserved.