Using the tomography image, a method to characterize the 3D spatial distributions of increased porosity was proposed, and the increased porosity distributions of cement pastes with different leaching degrees were given using the current method. The leaching processes of CH/C-S-H and the contribution of CH/C-S-H leaching to porosity evolution were discussed. The proposed method can be applied to all cement- based materials with any leaching degrees. From the quantitative increased porosity results, we find that the CH leaching finished quickly on the sharp CH leaching front.
Although there has been much research of cracks of the cement-based materials using optical and electron microscopy two-dimensional(2D) imaging methods,the real three-dimensional(3D) crack shapes have not previously been revealed.Thanks to the focused ion beam(FIB) tomography and the follow-up image processing,two 3D subsurface cracks and a cluster of inner cracks were picked out and discussed in this research.It was found that the subsurface crack(its length is about 15 μm,width about 1 5 μm,and opening about 1 μm) was much larger than the inner crack(its length and width are about 1 5 μm,opening is from 200 nm to 1 μm),which arose from the sample preparation process.Besides,it was revealed that most of the inner cracks were in the form of clusters.
Porosity is one of the most important parameters for cement-based materials,which influences the mechanical property,transport property,and durability.The spatial and frequency distributions of local porosity of cement pastes are characterized using X-ray micro-tomography data and treating methods.The 3D spatial distributions for three cement paste specimens with different water cement(w/c)ratios show reasonable heterogeneity.The probability analysis also reveals this heterogeneity:the representative volume element(RVE)size based on porosity maps decreases with w/c ratio firstly,then increases with w/c ratio;and the heterogeneity on the characterized probe size or on the RVE size increases with w/c ratio.Average porosities obtained using the CT method are further compared with those by traditional methods.
