Preparation and properties of gradient structure concrete member
Based on the dense packing powder theory, the refining and self-healing principles, and hydrophobic treatment, the special surface-layer materials and design are proposed in gradient structure concrete (GSC) member. According to service behavior, the GSC member is divided into serial structure and parallel structure. And it is fabricated corresponding to structural parameters by stacked press process, or pulled clapboard method, or suspended nets method. Use of small and full scale specimens for testing, the results are shown that: 1) the surface-layer strength of the GSC component improved by 30%, compared to that of a conventional single-layer component; 2) the width of the crack ranges from 0 to 0.1mm in the GSC component, whereas a conventional single-layer component are distributed with visible cracks(0.2–0.5mm);3) The permeating depth and chloride diffusion coefficient of the GSC component is respectively 0mm and 6.3×10–13 m2/s, whereas a conventional single-layer component is 15mm and 12.8×10–13 m2/s.
Effects of the component and fiber gradient distributions on the strength of cement-based composite materials
The effects of the component gradient distribution at interface and the fiber gradient distribution on the strength of cement-based materials were studied. The results show that the flexural strength and compressive strength of the mortar and concrete with interface component and fiber gradient distributions are obviously improved. The strengthes of the fiber gradient distributed mortar and concrete (FGDM/C) are higher than those of fiber homogeneously distributed mortar and concrete (FHDM/C). To obtain the same strength, therefore, a smaller fiber volume content in FGDM/C is needed than that in FHDM/C. The results also show that the component gradient distribution of the concrete can be obtained by means of multi-layer vibrating formation.
The Kelvin equation and the capillary condensation of water
The Kelvin equation1 relates the equilibrium vapour pressure of a liquid to the curvature of the liquid–vapour interface. It predicts that undersaturated vapours will condense in channels of sufficiently small dimensions. While the applicability of the Kelvin equation to organic liquids with meniscus radii as low as 4 nm has been verified by direct experiment2, its applicability to water for meniscus radii below 4 nm is unverified, and has been doubted3,4. We have used Fizeau interferometry to measure directly the capillary condensation of water in a wedge between fused silica surfaces. Measurements were made at relative vapour pressures (P/Ps) from 0.996 down to 0.945, corresponding to theoretical meniscus radii from ∼120 to 9nm. We findonly a small discrepancy between our experimental results and the Kelvin equation in the vapour pressure range covered, provided that correct account is taken of the effect of the adsorbed film, up to 200 nm thick, on the meniscus shape.