The Effect of HRWR and AEA on the Air System of Vibrated Concrete

2015 ◽  
Author(s):  
Ahmad Ghadban ◽  
Mohammed Albahttiti ◽  
Kyle Riding ◽  
David Lange
Keyword(s):  
Rheological Properties ◽  
Precast Concrete ◽  
Air Entrainment ◽  
System Stability ◽  
Unit Weight ◽  
Time Duration ◽  
Freeze Thaw ◽  
Air Content ◽  
Air System ◽  
The Stability

Air entrainment in concrete railroad ties is typically included to prevent freeze-thaw damage. Uniformly-distributed microscopic air voids in concrete ties helps to resist against freeze-thaw. The air entrainment system stability with time after mixing is dependent on a number of factors which include chemical, environmental, and construction related parameters. These resulting differences in the air void system can in turn lead to different performances of concrete under freeze-thaw loading. Vibration is mainly used to consolidate concrete but can also alter the air structure of concrete. This study investigates the effect of different chemical admixtures and rheological properties on the stability of the air system inside vibrated concrete. Form vibration of 75 Hz frequency and 3 g or 10 g peak acceleration was applied to the tested concrete after the lapse of several time durations. This was done to investigate the stability of the air system of concrete as time passes on under different vibration conditions. The testing included slump, unit weight, temperature, rheology and fresh air content before vibration and after vibration for each elapsed time duration. Fresh air content tests showed that the air loss increases linearly with time for almost all mixtures. Concrete rheological properties immediately after mixing were not a good indicator of the concrete air system stability after delayed placement. Tall oil based air entraining agents (AEA) was found to produce slightly lower air instability; however, the differences between AEA were small. The results showed that for precast concrete railroad ties, any instability with time of entrained air should not be a significant problem for precast concrete railroad tie plants if the concrete is placed and consolidated within 30 minutes from mixing at room temperatures.

scholarly journals Impact of Air Entrainment on the Microstructure and Mechanical Performance of High Performance Mortar

2014 ◽  
Vol 629-630 ◽  
pp. 358-365
Author(s):  
Jeroen Dils ◽  
Veerle Boel ◽  
Geert de Schutter
Keyword(s):  
Pore Structure ◽  
High Performance ◽  
Mercury Intrusion Porosimetry ◽  
Mechanical Performance ◽  
Air Entrainment ◽  
Air Bubbles ◽  
Mercury Intrusion ◽  
Freeze Thaw ◽  
Air Content ◽  
Air Entraining Agents

High performance self-compacting mortar has the ability to push out air bubbles under its own weight. Consequently, the resistance against freeze-thaw cycles with or without deicing salts can decrease due to the total air content reduction. In order to assure the necessary expansion zones1,2 air entraining agents (AEA) are commonly used to increase the amount of stable air bubbles. Depending on the mixture, the workability and rheology decrease or increase by the entrained air bubbles3. This will depend on the ratio between the surface tension and the shear stress applied during the test. If the latter can overcome the first, the bubbles will deform and increase the fluidity of the mixture. Besides the influence on the durability and the fresh concrete, air entraining agents also alter the pore structure and the mechanical performance of the mortar. The effect of AEA on these properties is the subject of this paper. The pore structure is examined on two different levels. On the one hand, mercury intrusion porosimetry is used to investigate the capillary porosity, ranging from 10 nm to 10 μm. On the other hand air void analysis and fluorescence microscopy is performed to evaluate the larger air bubbles ranging from 0.1 mm to 1 mm4. Both techniques showed an overlap in their measuring range. Consequently it was possible to compare the techniques critically. Similar as in literature, mercury intrusion porosimetry underestimates the amount of larger air bubbles in mortar, due to its measuring principle5. Furthermore, the bubbles with a diameter of 80 μm increase significantly by the addition of AEA. This confirms the average air bubble size often used in literature to explain the influence of AEA on the workability and rheology3. The influence of air entraining agent on the mechanical performance was tested by the compressive and bending tensile strength. In conclusion, a good balance is necessary between the air content necessary for a proper freeze-thaw resistance without changing the mechanical performance drastically.

scholarly journals Durability Evaluation of Concrete with Multiadmixtures under Salt Freeze-Thaw Cycles Based on Surface Resistivity

2021 ◽  
Vol 2021 ◽  
pp. 1-18
Author(s):  
Shibin Luo ◽  
Wei Liang ◽  
Hua Wang ◽  
Wensheng Wang ◽  
Rongjun Zou
Keyword(s):  
Flexural Strength ◽  
Concrete Strength ◽  
Air Entrainment ◽  
Surface Resistivity ◽  
Mineral Admixtures ◽  
Chloride Permeability ◽  
Freeze Thaw ◽  
Air Content ◽  
Rapid Chloride Permeability ◽  
Function Relationship

According to the climatic characteristics of seasonal frozen area in northeast China, the concrete strength tests, surface resistivity, rapid chloride permeability, and freeze-thaw test under salt solution were carried out to study the influences of mineral admixtures and air content on the conventional properties and salt freeze-thaw resistance of concretes. Then, the correlation analysis of surface resistivity with strength and rapid chloride permeability were further investigated. Subsequently, the changes of cumulative mass loss and relative dynamic elastic modulus varying with salt freeze-thaw cycles were analyzed to study the influences of mineral admixtures and air content on salt freeze-thaw resistance of concrete. The test results showed that fly ash (FA) was not conducive to improve the strength and salt freeze-thaw resistance of concrete. However, blast furnace slag (BFS) and silica fume (SF) could improve the compressive and flexural strength of concrete, in which SF can improve its strength more significantly. Increasing the air content of concrete will lead to the reduction of its compressive strength, and the flexural strength first increased and then decreased. Nevertheless, the addition of air-entrainment agent (AEA) has the best effect on improving the salt freeze-thaw resistance of concrete. Moreover, surface resistivity of concrete has a good exponential function relationship with strength and a good power function relationship with rapid chloride permeability. Therefore, it is of great significance for engineering quality control and quickly and nondestructive testing.

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 Effect of Photoinitiator on Precursory Stability and Curing Depth of Thiol-Ene Clickable Gelatin

Polymers ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1877
Author(s):  
Kai-Hung Yang ◽  
Gabriella Lindberg ◽  
Bram Soliman ◽  
Khoon Lim ◽  
Tim Woodfield ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Visible Light ◽  
Rheological Properties ◽  
Swelling Ratio ◽  
Sodium Persulfate ◽  
Photo Polymerization ◽  
Gelation Kinetics ◽  
The Stability ◽  
Over Time

Recent advances highlight the potential of photopolymerizable allylated gelatin (GelAGE) as a versatile hydrogel with highly tailorable properties. It is, however, unknown how different photoinitiating system affects the stability, gelation kinetics and curing depth of GelAGE. In this study, sol fraction, mass swelling ratio, mechanical properties, rheological properties, and curing depth were evaluated as a function of time with three photo-initiating systems: Irgacure 2959 (Ig2959; 320–500 nm), lithium phenyl-2,4,6-trimethylbenzoylphosphinate (LAP; 320–500 nm), and ruthenium/sodium persulfate (Ru/SPS; 400–500 nm). Results demonstrated that GelAGE precursory solutions mixed with either Ig2959 or LAP remained stable over time while the Ru/SPS system enabled the onset of controllable redox polymerization without irradiation during pre-incubation. Photo-polymerization using the Ru/SPS system was significantly faster (<5 s) compared to both Ig2959 (70 s) and LAP (50 s). Plus, The Ru/SPS system was capable of polymerizing a thick construct (8.88 ± 0.94 mm), while Ig2959 (1.62 ± 0.49 mm) initiated hydrogels displayed poor penetration depth with LAP (7.38 ± 2.13 mm) in between. These results thus support the use of the visible light based Ru/SPS photo-initiator for constructs requiring rapid gelation and a good curing depth while Ig2959 or LAP can be applied for photo-polymerization of GelAGE materials requiring long-term incubation prior to application if UV is not a concern.

Stability of Ring-Type MEMS Gyroscopes Subjected to Stochastic Angular Speed Fluctuation

2017 ◽  
Vol 139 (4) ◽  
Author(s):  
Samuel F. Asokanthan ◽  
Soroush Arghavan ◽  
Mohamed Bognash
Keyword(s):  
Angular Velocity ◽  
Degrees Of Freedom ◽  
Microelectromechanical Systems ◽  
Damping Ratio ◽  
Operating Conditions ◽  
System Stability ◽  
System Response ◽  
Ring Type ◽  
Mems Gyroscopes ◽  
The Stability

Effect of stochastic fluctuations in angular velocity on the stability of two degrees-of-freedom ring-type microelectromechanical systems (MEMS) gyroscopes is investigated. The governing stochastic differential equations (SDEs) are discretized using the higher-order Milstein scheme in order to numerically predict the system response assuming the fluctuations to be white noise. Simulations via Euler scheme as well as a measure of largest Lyapunov exponents (LLEs) are employed for validation purposes due to lack of similar analytical or experimental data. The response of the gyroscope under different noise fluctuation magnitudes has been computed to ascertain the stability behavior of the system. External noise that affect the gyroscope dynamic behavior typically results from environment factors and the nature of the system operation can be exerted on the system at any frequency range depending on the source. Hence, a parametric study is performed to assess the noise intensity stability threshold for a number of damping ratio values. The stability investigation predicts the form of threshold fluctuation intensity dependence on damping ratio. Under typical gyroscope operating conditions, nominal input angular velocity magnitude and mass mismatch appear to have minimal influence on system stability.

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.

Design of Electrostatic Precipitator Power System Based on Auto Disturbance Rejection Controller

2013 ◽  
Vol 846-847 ◽  
pp. 190-194
Author(s):  
Shu Jun Yin ◽  
Xue Ren Li ◽  
Ji Geng Luo
Keyword(s):  
Power Supply ◽  
Disturbance Rejection ◽  
Power Supply System ◽  
Electrostatic Precipitator ◽  
Supply System ◽  
System Stability ◽  
Engineering Practice ◽  
Single Chip ◽  
High Voltage Power Supply ◽  
The Stability

The paper designs a three-phase high voltage power supply system based on active disturbance rejection controller which make single-chip microcomputer ATmega128 as the main control chip and the system improve the stability and control precision of dust removing power. Engineering practice shows that, the DC power supply system has the advantages of convenient operation, high work efficiency, system stability.

Stability of two-layer stratified flow in inclined channels: applications to air entrainment in coating systems

1996 ◽  
Vol 312 ◽  
pp. 173-200 ◽  
Author(s):  
Yuan C. Severtson ◽  
Cyrus K. Aidun
Keyword(s):  
Spectral Decomposition ◽  
Air Entrainment ◽  
Density Variation ◽  
Generalized Eigenvalue ◽  
Long Wave ◽  
Inclined Channels ◽  
The Stability ◽  
Air Liquid Interface ◽  
Sommerfeld Equation ◽  
Interfacial Mode

To understand the physics of air entrainment in thin-film liquid coating and other applications, the stability characteristics of general stratified two-layer Poiseuille-Couette flow are examined in inclined channels. Only one mode of instability, the interfacial mode, is obtained in the long-wave asymptotic limit. The generalized eigenvalue problem, formed by spectral decomposition and solution of the general two-layer Orr-Sommerfeld equation, is solved to obtain all of the critical modes. Analysis of the air/liquid interface corresponding to experiments reveals that because of the large density variation between the two layers, the interfacial mode is the only mode of instability in air entrainment. Results from the stability analysis of the flow near the contact line where air entrainment occurs are consistent with previous experimental observations.

scholarly journals Assessment of Fennel Oil Microfluidized Nanoemulsions Stabilization by Advanced Performance Xanthan Gum

Foods ◽  
2021 ◽  
Vol 10 (4) ◽  
pp. 693
Author(s):  
Rubén Llinares ◽  
Pablo Ramírez ◽  
José Antonio Carmona ◽  
Luis Alfonso Trujillo-Cayado ◽  
José Muñoz
Keyword(s):  
Essential Oil ◽  
Rheological Properties ◽  
Xanthan Gum ◽  
Mechanical Energy ◽  
Physical Stability ◽  
Processing Condition ◽  
Oil In Water ◽  
Mechanical Spectra ◽  
The Stability ◽  
Fennel Oil

In this work, nanoemulsion-based delivery system was developed by encapsulation of fennel essential oil. A response surface methodology was used to study the influence of the processing conditions in order to obtain monomodal nanoemulsions of fennel essential oil using the microchannel homogenization technique. Results showed that it was possible to obtain nanoemulsions with very narrow monomodal distributions that were homogeneous over the whole observation period (three months) when the appropriate mechanical energy was supplied by microfluidization at 14 MPa and 12 passes. Once the optimal processing condition was established, nanoemulsions were formulated with advanced performance xanthan gum, which was used as both viscosity modifier and emulsion stabilizer. As a result, more desirable results with enhanced physical stability and rheological properties were obtained. From the study of mechanical spectra as a function of aging time, the stability of the nanoemulsions weak gels was confirmed. The mechanical spectra as a function of hydrocolloid concentration revealed that the rheological properties are marked by the biopolymer network and could be modulated depending on the amount of added gum. Therefore, this research supports the role of advanced performance xanthan gum as a stabilizer of microfluidized fennel oil-in-water nanoemulsions. In addition, the results of this research could be useful to design and formulate functional oil-in-water nanoemulsions with potential application in the food industry for the delivery of nutraceuticals and antimicrobials.

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