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.

Air Entrainment and the Fabrication of Concrete Railroad Ties

2015 ◽  
Author(s):  
Mohammed T. Albahttiti ◽  
Ahmad A. Ghadban ◽  
Kyle A. Riding ◽  
David Lange
Keyword(s):  
Prestressed Concrete ◽  
Air Entrainment ◽  
Vibration Exposure ◽  
Vibration Acceleration ◽  
Manufacturing Plants ◽  
Air Content ◽  
Concrete Properties ◽  
Air Void

Handling and vibration can affect the air content of prestressed concrete railroad ties. The amount and variation in vibration experienced in concrete railroad ties were investigated to determine the concrete fabrication conditions typically used. Two methods of fabrication were investigated by measuring the concrete properties and vibration exposure during placement at two concrete tie manufacturing plants. In addition to measuring the vibration distribution in concrete railroad ties, a pair of ties were selected for hardened-air void analyses to determine any variation of air content in relation to the height of the ties. The vibration results indicate the existence of constructive and destructive wave-interferences in tie cavities. These interferences may contribute to large variations in the vibration acceleration throughout the length, depth, and width of concrete crossties during fabrication. This may account for the air-loss across the depth of the ties.

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 Scaling Resistance and Air Void Characteristics in Concrete Containing GGBS

2016 ◽  
Vol 62 (4) ◽  
pp. 181-192 ◽  
Author(s):  
J. Wawrzeńczyk ◽  
A. Molendowska ◽  
T. Juszczak
Keyword(s):  
Frost Resistance ◽  
Air Entrainment ◽  
Test Results ◽  
Fundamental Factor ◽  
Air Content ◽  
Concrete Mixtures ◽  
Spacing Factor ◽  
Void System ◽  
Surface Scaling ◽  
Air Void

AbstractIn this paper we discuss the test results for concretes containing various amounts of ggbs as compared to concretes made with Portland cement. The main objective of these tests is to evaluate the influence of varying air content in such mixtures on the structure and frost resistance of concrete. The authors suggest that the approach presented here allows for a safe design of concrete mixtures in terms of their frost resistance.The results indicate that concrete can be resistant to surface scaling even at the W/C ratio markedly higher than 0.45. Increased addition of ggbs leads to a decrease in concrete resistance to surface scaling. Proper air entrainment is the fundamental factor for frost-resistant concrete, and the air void system has to be assessed (micropore content A300, spacing factor $\overline L $). The addition of ggbs increases pore diameters, thus, to obtain the appropriate air pore spacing factor, micropore quantities introduced have to be increased.

The effect of foam fractionated lignosulphonates on air entrainment in concrete

1982 ◽  
Vol 9 (2) ◽  
pp. 170-175
Author(s):  
K. F. Keirstead ◽  
D. DeKee ◽  
D. W. Kirk ◽  
S. U. Pillai
Keyword(s):  
Surface Tension ◽  
Air Entrainment ◽  
Hardened Concrete ◽  
Air Voids ◽  
Air Content ◽  
Low Concentrations ◽  
Tension Properties ◽  
Air Entraining Agents ◽  
Air Void ◽  
Mixing Water

One of the properties of air-entraining admixtures that may influence their efficiency is their surface tension when combined with mixing water. Lignosol SF is a standard air-entraining agent. With the objective of identifying a product with improved qualities, Lignosol SF was fractionated and two of its fractions, respectively with low (foamate) and high (retentate) surface tension properties were investigated as potential air-entraining agents. Measurements were made both of air content in wet concrete mix and of the air-void characteristics of the hardened concrete.The results showed that at low concentrations and water:cement ratios the performance of all the three products above are similar. However, the foamate fraction becomes more effective in entraining air with increases in concentration and water:cement ratio. Further, this foamate resulted in the hardened concrete having bubbles with a smaller mean diameter than those in the retentate. The spacing factors for both these products were within recommended limits. Keywords: admixtures; air-entrainment; air-voids; concrete; freeze-thaw resistance; Lignosol; spacing factor.

Effect of atmospheric pressure on air content and air void parameters of concrete

2015 ◽  
Vol 67 (8) ◽  
pp. 391-400 ◽  
Author(s):  
Xuefeng Li ◽  
Zhi Fu ◽  
Zhu Luo
Keyword(s):  
Atmospheric Pressure ◽  
Air Content ◽  
Air Void

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.

Pengaruh Penggunaan Batu Basalt Lampung dan Batubara dalam Bahan Baku terhadap Karakteristik Klinker

2020 ◽  
Vol 10 (1) ◽  
pp. 49
Author(s):  
Suharto Suharto ◽  
Muhammad Amin ◽  
Muhammad Al Muttaqii ◽  
Syafriadi Syafriadi ◽  
Kiki Nurwanti
Keyword(s):  
Experimental Study ◽  
Raw Materials ◽  
Coal Ash ◽  
Heating Time ◽  
Raw Material ◽  
Silica Sand ◽  
Cement Clinker ◽  
Duration Of Heating

Experimental study on the use of basalt stone originated from Lampung has been conducted to evaluate its potential for a partial substitute of raw material in production of cement clinker. The basalt stone contains minerals of anorthite, augite, and albite phases that are required for clinker formation. In this study, the main raw materials were 80% limestone, 10% silica sand, 9% clay and 1% iron sand. The raw material in these experiments were mixtures 90% or 80% of the main raw material and 10% or 20% of basalt stone. The effect of adding coal to raw materials was also studied to see the possibility of an increase in clinkerization temperature inside the raw material mixture, and at the same time to see the effect of coal ash on clinker composition. Clinker obtained from heating of raw materials at a temperature of 1100oC had LSF of 94.1% and 95.1% (heating time of 1 and 3 hours). If heating is carried out at 1200oC, the clinker had LSF of 97.7% and 98.0% (heating time of 2 and 3 hours, respectively). Depending on the temperature and duration of heating, the clinker mostly had SM in the range of 2.18-2.40% , and AM in the range of 0,78-1.80%. Characterization using XRD showed that the clinker consisted of larnite and gehlenite phases, and dominated by CaO.Batu basalt Lampung telah diuji potensinya sebagai pengganti sebagian bahan baku utama pembuatan klinker semen. Batu basalt tersebut memiliki mineral-mineral dalam fase anorthite, augite, dan albite yang diperlukan pada pembentukan klinker. Pada penelitian ini, bahan baku utama adalah batu kapur 80%, pasir silika 10%, tanah liat 9% dan pasir besi 1%. Campuran bahan baku klinker adalah 90% atau 80% bahan baku utama dan 10% atau 20% batu basalt. Efek penambahan batubara ke dalam bahan baku klinker juga dipelajari untuk melihat kemungkinan kenaikan temperatur klinkerisasi di dalam campuran bahan baku, dan sekaligus untuk melihat efek abu batubara terhadap komposisi klinker. Klinker hasil pemanasan bahan baku pada temperatur 1100oC memiliki LSF 94,1% dan 95,1% (lama pemanasan 1 dan 3 jam). Jika pemanasan dilakukan pada 1200oC, klinker memilik LSF 97,7% dan 98,00% (lama pemanasan 2 dan 3 jam). Tergantung pada temperatur dan lama pemanasan, klinker hasil percobaan ini umumnya memiliki SM 2,18-2,40%, dan AM antara 0,78-1,80%. Karakterisasi dengan XRD menunjukkan bahwa klinker terdiri dari fase larnite dan gehlenite, dan didominasi CaO.

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