Abstract
Low atmospheric pressure (LAP) can enormously affect properties of cement concrete in plateau areas. There are fewer studies and attendances on this issue than those of cement concrete in normal atmospheric pressure (AP), because of the limitations of both environmental conditions and instruments. In order to improve properties of cement concrete under LAP, influences of LAP on properties of cement concrete were reviewed in this work. The influence rules and mechanism on properties of cement concrete were summarized. The corresponding mechanism and techniques were put forward for enhancing the properties of cement concrete. The results of researchers show that LAP can significantly reduce the air entraining ability of the air entraining agent (AEA). Air content in concrete linearly decreases with the decrease of AP when other conditions are constant. If the initial air content is high, the decrease rate of air content increases with the decrease of AP. When the initial air content in cement concretes is similar, the greater the slump of cement concrete, the stronger its resistance to the decrease of air content caused by the decrease of AP. In addition, the condition of the bubble characteristics of hardened cement concrete under LAP is worse than that under normal AP. Therefore, the change of concrete properties under LAP is mainly attributed to these bubble characteristics, such as air content, bubble spacing coefficient, bubble radius and bubble specific surface area. In this work, nano-silica (negative charges) with cationic oligomeric surfactants is recommended as a new type of AEA to optimize the bubble characteristics under LAP in plateau areas.
Highlights
The altitude of plateau areas is high, and the air in these areas is thin, which forms a low atmospheric pressure (LAP) environment in these plateau areas
They proved that LAP reduced the air entraining ability of air entraining agent (AEA), which led to the decrease of air content in concrete
The AP affects the air entraining ability of AEA, which leads to a decrease in the air content of concrete under LAP
Summary
The altitude of plateau areas is high, and the air in these areas is thin, which forms a low atmospheric pressure (LAP) environment in these plateau areas. The influence rules and the mechanism of LAP on AEA and bubbles in cement concrete were summarized at first, and the microcosmic and macroscopic changes of workability, mechanical property and durability of cement concrete were deeply analyzed according to the changes of the bubble characteristics. In view of these influences, corresponding improvement techniques and some opinions on the mechanism for developing new AEA were put forward, which were beneficial to the development of any new AEA. This work can put forward theoretical and technical supports for improving the properties of cement concrete under LAP for its wide applications in construction and building materials in plateau areas
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