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.
NEAR-SURFACE MOISTURE GRADIENTS AND IN SITU PERMEATION TESTS
Abstract Both the durability of concrete and permeation test results are influenced by the degree of saturation of capillary pores in concrete. In a laboratory, the moisture distribution of a test sample can be standardised by oven drying, however, this is not feasible for tests carried out in situ. Therefore, an investigation was carried out to monitor the moisture distribution in the near surface concrete over an extended period and study its effects on in situ air permeability and sorptivity test results. The results indicated that moisture distributions in the near surface concrete within 10 mm of the exposed face are highly susceptible to changes in exposure conditions. However, when the internal relative humidity of the near-surface concrete layer was less than 80%, the results of the in situ permeation tests could be used to identify the variation in quality of concrete.
Factors influencing relative humidity in concrete
The effects of water/cement ratio, cement type, curing and exposure condition on time-dependent relative humidity profiles in drying concrete are examined. The water/cement ratio of the concrete and the period of initial moist curing were found to have little effect on the measured relative humidities for laboratory exposure, but the latter dropped more rapidly in concretes made with pulverized fuel ash or ground granulated blastfurnace slag than in those made with ordinary Portland cement. The relative humidities in the concretes subjected to laboratory exposure were represented concisely by a set of simple equations. High relative humidities were measured in concretes exposed outdoors, although these were less high when the exposed surface was sheltered from rain. The effects of moisture on several aspects of concrete performance are briefly reviewed, and the benefits of relative humidity measurements are indicated.