scholarly journals Impacts of Low Atmospheric Pressure on Properties of Cement Concrete in Plateau Areas: A Literature Review

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1384 ◽  
Author(s):  
Jinyang Huo ◽  
Zhenjun Wang ◽  
Huaxin Chen ◽  
Rui He
Keyword(s):  
Atmospheric Pressure ◽  
Bubble Radius ◽  
Hardened Cement ◽  
Nano Silica ◽  
Cement Concrete ◽  
Air Content ◽  
Normal Atmospheric Pressure ◽  
New Type ◽  
Low Atmospheric Pressure ◽  
Bubble Characteristics

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.

scholarly journals Effect of Low Atmospheric Pressure on Bubble Stability of Air-Entrained Concrete

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Xuefeng Li ◽  
Pengyu Yang
Keyword(s):  
Atmospheric Pressure ◽  
Fresh Concrete ◽  
Air Content ◽  
Spacing Factor ◽  
Normal Atmospheric Pressure ◽  
Design Requirements ◽  
Low Atmospheric Pressure ◽  
Vibration Time ◽  
Air Entraining Agents ◽  
Air Entrained Concrete

The effect of low atmospheric pressure of the environment on the air content and bubble stability of air-entrained concrete was investigated in Beijing and Lhasa. The results indicate that the reduction of atmospheric pressure can weaken the air-entraining capability of air-entraining agents (AEAs). The air content of fresh concrete decreased by 9%–39% when the atmospheric pressure dropped to 64 kPa. The bubble stability of concrete mixed at a low atmospheric pressure becomes worse. Within 50–55 min after mixing, the air content of concrete mixed at a low atmospheric pressure decreases greatly, and the void spacing factor increases obviously. The concrete mixed at a low atmospheric pressure will lose more air content when vibration time increases, leading to the decrease of air content and the increase of the spacing factor, which are more significant than the concrete mixed at normal atmospheric pressure. On the basis of the experiment results in this study, the type of AEAs must be carefully selected, and the vibration time must be strictly controlled to ensure that the air content of concrete will meet the design requirements in low atmospheric pressure areas.

Effect of Low Atmospheric Pressure on Air Content of Fresh Concrete

2014 ◽  
Vol 1079-1080 ◽  
pp. 202-206
Author(s):  
Xue Feng Li ◽  
Zhi Fu ◽  
Ying Xin Hui
Keyword(s):  
Atmospheric Pressure ◽  
Fresh Concrete ◽  
Test Chamber ◽  
Air Pressure ◽  
Air Content ◽  
Normal Atmospheric Pressure ◽  
Design Requirements ◽  
Low Atmospheric Pressure ◽  
Pressure Changes ◽  
Air Entraining Agents

The effects of atmospheric pressure changes on the air entraining capability of air-entraining admixtures was studied using a low-pressure test chamber to simulate plateau environments with thin air and low atmospheric pressure. Results indicate that the atmospheric pressure of the environment significantly affects the performance of air-entraining admixtures. The air content of fresh concrete decreases by approximately 20%–49% when the atmospheric pressure is 50 KPa with respect to the normal atmospheric pressure (101 KPa). The air content of fresh concrete decrease linearly as atmospheric pressure dropped. The higher the air content of fresh concrete mixed in ordinary pressure, the faster the air content of fresh concrete decreases with the drop of air pressure. The concrete with high slump shows more resistance to drop of air-content due to low air pressure than the concrete with low slump. Therefore, in order to meet the design requirements of air content of air-entrained concrete for different constructions in the plateau regions, it is necessary to increase the dosages of air entraining agents to according to different pressure conditions and types of air-entraining agent.

scholarly journals Effect of Low Atmospheric Pressure on Air Entrainment in Cement-Based Materials: An On-Site Experimental Study at Different Elevations

Materials ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 3975
Author(s):  
Xin Chen ◽  
Xu Liu ◽  
Bo Tian ◽  
Yong Ge ◽  
Lihui Li
Keyword(s):  
Experimental Study ◽  
Atmospheric Pressure ◽  
Raw Materials ◽  
Air Entrainment ◽  
High Elevation ◽  
Air Bubble ◽  
Air Content ◽  
Cement Based Materials ◽  
Low Atmospheric Pressure ◽  
Air Void

The efficiency and stability of air entrainment in concrete are sometimes found to be weaker at higher elevation. This phenomenon was attributed to the low atmospheric pressure by many researchers, however, the level of influence of atmospheric pressure on concrete air content dramatically varied among different studies. In order to clarify the effect of low atmospheric pressure on air entrainment in cement-based materials, an on-site experimental study was conducted with a rigorous control of irrelevant variables. The study focused on the air-entraining efficiency in cement paste, mortar, and concrete prepared in both low and standard atmospheric pressures. The air bubble stability in fresh mortar and air void characteristics of hardened mortar in different atmospheric pressures were also included. In the study, little effect of low atmospheric pressure on the air-entraining efficiency and air bubble stability in mortar with studied air-entraining agents (AEAs) was found. The air void characteristics were found to be similar between mortar with SJ-2 or 303R type AEAs prepared in different atmospheric pressures. Concrete with either SJ-2 or 303R type AEA prepared in low atmospheric pressure presented a satisfactory air content. These conclusions indicate that it is not necessary to worry excessively about the potentially adverse effect of atmospheric pressure on the frost resistance of concrete if a suitable AEA is applied. Additionally, a supplementary mortar study found that the low temperature of raw materials stored at high elevation would significantly weaken the air entrainment, reminding that potential causes in addition to low atmospheric pressure should also be taken seriously.

Study on Frost Resistance of Nano SiO2 Cement Concrete

2012 ◽  
Vol 198-199 ◽  
pp. 48-51 ◽  
Author(s):  
Zheng Rong Zhao ◽  
Jie Kong ◽  
Hong Xia Yang
Keyword(s):  
Frost Resistance ◽  
Hardened Cement ◽  
Cement Concrete ◽  
Cement Ratio ◽  
Water Cement Ratio ◽  
Ordinary Concrete ◽  
Air Content ◽  
Substantial Decline ◽  
The Relationship ◽  
Very High

According the test, this paper discussed the relationships among nano SiO2content of nano SiO2cement concrete ,air content, water-cement ratio and frost resistance property.Meanwhile, the relationship among the bubble parameter, structure of holes and the frost resistance is primarily discussed. The results show that the concrete mixed with some nano SiO2, with the increase of impervious holes in hardened cement paste, compared with ordinary concrete,both the ability of freezing-thawing resisting and compression strength will have an improvement. What’s more, when mixed with the air-entraining agent, freezing-thawing cycles number will have an obvious increase.When water-cement ratio is 0.35-0.39, the ability of frost resisting is very high but when water-cement ratio is larger than 0.39, freezing-thawing resisting performance is substantial decline.

Adaptation to Low Atmospheric Pressure

BMJ ◽  
1970 ◽  
Vol 2 (5700) ◽  
pp. 39-39
Author(s):  
S. Miles
Keyword(s):  
Atmospheric Pressure ◽  
Low Atmospheric Pressure

scholarly journals Adaptations and responses of the common dandelion to low atmospheric pressure in high altitude environments

2021 ◽  
Author(s):  
Carla C. M. Arce ◽  
Zoe Bont ◽  
Ricardo A. R. Machado ◽  
Paulo F. Cristaldo ◽  
Matthias Erb
Keyword(s):  
High Altitude ◽  
Atmospheric Pressure ◽  
The Common ◽  
Low Atmospheric Pressure ◽  
Common Dandelion
Sign in / Sign up

Export Citation Format

Share Document