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 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 Stability of Air Content in Fresh Concretes with PCE-Based Superplasticizers

2019 ◽  
Vol 60 (1) ◽  
pp. 145-158 ◽  
Author(s):  
Fahim Al-Neshawy ◽  
Teemu Ojala ◽  
Jouni Punkki
Keyword(s):  
Fresh Concrete ◽  
Cement Content ◽  
Mixing Time ◽  
Air Entrainment ◽  
Concrete Durability ◽  
Mixing Times ◽  
Air Content ◽  
The Stability ◽  
Air Entraining Agents ◽  
Air Entrained Concrete

Abstract Air contents of concrete are necessary for concrete durability in freeze-thaw exposure. According to the Finnish concrete code, the target value for air content varies between 4% and 5.5% for XF - exposure classes. Lately in Finland, some cases showed an elevation of air contents up to 15% in fresh air-entrained concrete at construction site and in drilled concrete samples. The objectives of this study were to investigate the stability of air entrainment by measuring the air content elevation 30 minutes and 60 minutes after concrete mixing and investigating the concrete sensitivity to segregation. Composition of concretes used in this study include 7 different combination of PCE based superplasticizer and air-entraining agent admixtures, cement content of 425 kg/m3, two consistency classes S3 with water to cement ration of 0.33 and F5 with water to cement ration of 0.38. One cement type was used for all concrete mixes. The concretes were mixed for 2 minutes and 5 minutes mixing times. The results show that the elevation of the air content of fresh concrete depends on the consistency of the concrete and on the used combination of superplasticizer and air-entraining agents. The higher consistency classes concretes have more risk of air elevation with some combinations of PCE-based superplasticizers and air-entraining agents. The results also indicate that short mixing time would not be enough to achieve total effectivity of some air-entraining agents, especially for higher consistency classes concrete.

scholarly journals Maleic Rosin-based Gemini Surfactant as Air Entraining Agent for Concrete under Low Air Pressure

2021 ◽  
Vol 72 (2) ◽  
pp. 27-37
Author(s):  
Yang Li ◽  
Zhendi Wang ◽  
Ling Wang
Keyword(s):  
Dynamic Modulus ◽  
Gemini Surfactant ◽  
Fresh Concrete ◽  
Concrete Strength ◽  
Air Pressure ◽  
Test Results ◽  
Bubble Liquid ◽  
Air Content ◽  
Spacing Factor ◽  
Plateau Area

The effectiveness of Air entraining agent (AEA) in concrete under low air pressure in the plateau area decreased. A type of new AEA, named MRE was synthesized to increase bubbles` stability in fresh concrete under low air pressure. The performance of MRE solution and concrete with MRE were tested under 60 kPa and 100 kPa compared with commercially gemini AEA (DCC). The test results showed that the foam volume of MRE and DCC solution under 60 kPa was reduced by 3% and 9% than under 100 kPa. The bubble liquid film strength of MRE is 63% higher than that of DCC. For concrete with MRE and DCC under 60 kPa, the air content was 2% and 16% lower, the relative dynamic modulus of concrete reduced by 6% and 15%, and the bubble spacing factor under 60 kPa increased by 17% and 39% respectively compared with that under 100 kPa. MRE can increase the freeze-thaw resistance of concrete under low air pressure without affecting concrete strength and is suitable for high altitude concrete.

Influence of Air Content and Vibration Time on Frost Resistance of Air Entrained Concrete

2013 ◽  
Vol 857 ◽  
pp. 110-115 ◽  
Author(s):  
Xiu Hua Zheng ◽  
Yong Ge ◽  
Jie Yuan
Keyword(s):  
Frost Resistance ◽  
Hardened Concrete ◽  
Air Voids ◽  
Air Content ◽  
High Durability ◽  
Void Structure ◽  
Vibration Time ◽  
Air Void ◽  
Air Void Structure ◽  
Air Entrained Concrete

Air-entraining agent turely is one of the necessary compositions of the high durability concrete. The influence of air content and vibration time on the frost resistance of concrete was researched, and air void characteristics of hardened concrete was analysed. The results showed that the air contents could reduce the compressive strengthof hardened concrete excessively, but it made the spacing factor reduce obviously and significantly improve the frost resistance of concrete.The air voids with different structure in concrete were realized by vibration time. It was found that the air void structure and the frost resistance properties were influenced by the vibration time largely. The optimized vibration time is 30s, the appropriate vibration time is 20s~30s, no more than 35s.

Béton produit en bétonnière mobile et en usine conventionnelle : comparaison des caractéristiques du réseau de bulles d'air

1988 ◽  
Vol 15 (3) ◽  
pp. 306-314
Author(s):  
Gaston Larose ◽  
Michel Pigeon
Keyword(s):  
Key Words ◽  
Laboratory Tests ◽  
Fresh Concrete ◽  
Mobile Unit ◽  
Freeze Thaw ◽  
Air Content ◽  
Spacing Factor ◽  
Void System ◽  
Concrete Mixer ◽  
Air Void

The durability of concrete to freeze-thaw cycles is dependent upon the existence of an adequate air-void system. There are very few studies on the air-void system of field concretes. Laboratory tests have proven that the air content measurement on the fresh concrete is not sufficient to judge the aptitude of the air-void system to protect the concrete from frost damage.This paper is a comparison of the air-void systems of field concretes produced in either a conventional plant or a mobile unit the use of which is becoming more and more frequent. The concretes produced in the conventional plant generally had sufficient air-void systems for air contents in the usual range (5–7%). The mobile unit showed that a slightly higher air content (8%) was needed to produce an adequate air-void system. Key words: concrete, mobile concrete-mixer, air-void systems, air-entraining agent, spacing factor, surface area, air content.

Edit the Properties of the Fresh Concrete Admixing Additives and Steel Fibres

2015 ◽  
Vol 1106 ◽  
pp. 73-76
Author(s):  
Vladimír Suchánek ◽  
Matěj Slováček
Keyword(s):  
Mechanical Characteristics ◽  
Fresh Concrete ◽  
Research Centre ◽  
Air Content ◽  
Effective Change ◽  
Laboratory Facilities ◽  
Laboratory Results ◽  
Training And Research ◽  
Air Entraining Agents

This article describes experimental work carried out by the Department of Transport Structures of Jan Perner Transport Faculty, University of Pardubice in the laboratory facilities of the Training and Research Centre in Transport.This is an effective change of properties by admixing the additional air-entraining agents, or steel fibers, or combinations thereof to the delivered batches.The final chapter summarizes the laboratory results, including the effect of air content on the physico-mechanical characteristics and durability of concrete.

scholarly journals The Flexural Strength and Frost Resistance of Air Entrained Concrete

2012 ◽  
Vol 5 ◽  
pp. 364-369 ◽  
Author(s):  
Xiu Hua Zheng ◽  
Qin Fei Li ◽  
Jie Yuan ◽  
Yong Ge
Keyword(s):  
Flexural Strength ◽  
Frost Resistance ◽  
Test Results ◽  
Key Factors ◽  
Air Content ◽  
Void Structure ◽  
Vibration Time ◽  
Air Void ◽  
Air Void Structure ◽  
Air Entrained Concrete

The flexural strength and frost resistance properties of air entrained concrete were tested in this study. Although the flexural strength of concrete does not change largely with increasing of air content, it still has a maximum value with air content of 4%. The test results show that the frost resistance increase with increasing of air content. In air entrained concrete, the total air content is not the only factor that affect the final properties of the concrete, the air void structure parameters, including void size, shape, and distribution, are key factors as well. It was found that the air void structure and the frost resistance properties were influenced by the vibration time largely. The optimized vibration time is 30s.

scholarly journals Effects of Parameters of Air-Avid Structure on the Salt-Frost Durability of Hardened Concrete

2020 ◽  
Vol 10 (2) ◽  
pp. 632 ◽  
Author(s):  
Hui Zhang ◽  
Peiwei Gao ◽  
Zhixiang Zhang ◽  
Youqiang Pan ◽  
Weiguang Zhang
Keyword(s):  
Frost Resistance ◽  
Fresh Concrete ◽  
Close Correlation ◽  
Hardened Concrete ◽  
Air Content ◽  
Spacing Factor ◽  
Void Structure ◽  
Air Void ◽  
Frost Durability ◽  
Air Void Structure

Through laboratory testing, this research studied the connection between air-void structures of hardened concrete and fresh concrete and discussed the effects of the air-void structure on the salt-frost durability of the concrete. The results demonstrate that, in comparison with fresh concrete, the air-void spacing factor shows a close correlation with hardened concrete air-content and decreases in the form of a power function as the air-content increases. When the fresh concrete air-content is more than 6% and the hardened concrete air-void spacing factor is less than 0.18 mm, the influence of parameters of air-void structure on the salt-frost resistance of the concrete reduces. The air-void spacing factor more significantly affects the salt-frost resistance of the concrete compared with air content and the correlation reaches 0.93. Therefore, air-content and air-void spacing factor are recommended for dual control.

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