Pore Characteristics and Computed Permeability of Pastes Subject to Freeze-thaw Cycles at Very Early Ages by X-ray CT

Freeze-thaw cycling can damage microstructure of concrete and reduce the service life of concrete structures. This is especially detrimental for concrete subject to freeze-thaw cycles at very early-ages, such as within the first few days after constructions. Typical low and high water-to-cement (w/c) ratio pastes are investigated experimentally and numerically in this study. The pastes are subject to freeze-thaw cycles at the age of 1, and 7 days and then sealed-cured to the age of 45 days. The pore size distribution is measured and quantified by X-ray computer tomography (CT) with high resolution. The permeability of the corresponding pastes is predicted numerically based on the reconstructed microstructure results obtained from the CT measurements. The pore size distribution and the permeability variations of different pastes are investigated, and the key affecting factors are recognized. The Katz-Thompson and Navier-Stokes methods for computing permeability of paste are compared. The detectable pore size range by MIP, BSE, and X-ray CT in hardened paste is identified. The results of this study will offer suggestions for material design and curing strategies for concrete structures which are prone to experiencing freeze-thaw cycles at very early-ages

The Analysis of Chinese Sentence Semantic Chunk Share Based on HNC Theory

PACLIC 20 / Wuhan, China / 1-3 November, 200