Air content

The water quality (air content) and the water flow influenced the measurements using one channel. Therefore the four channel system was first tested in the laboratory with a stationary tube. The best results were obtained using tap water and a well controlled flow in a water-filled chamber. A great difference in the concentration of air in the different grades of water was obvious, and the tap water was superior to soft water during these measurements. 

Bottles of carbonated beverage are tested for carbonation using a Zahm-Nagel or Ashcroft carbonation tester. The carbonation can be calculated from the measured pressure and temperature values. Canned beverage is tested for carbonation and air content using a Zahm air tester. 

Admixtures include materials other than cement, water, or aggregate added immediately before or during mixing. Admixtures serve a broad range of purposes including the control of setting, control of workabiUty, and control of air content. 

Temperature, air content, pressure, and chemical composition of the fluid can affect the tendency of the fluid to cavitate. For example, the presence of minute air bubbles in the fluid can act as nucleation sites for cavitation bubbles, thereby increasing the tendency of the fluid to cavitate. Increasing pressure decreases susceptibility to cavitation decreasing pressure increases susceptibility to cavitation. 

Figure 10-86A. Influence of air content on the heat transfer coefficient of steam containing air. (Used by permission Edmister, W. C., and Marchello, J. M. Petro/Chem. Engineer, June 1966, p. 48. Petroleum Engineer International.)...

This scheme is selfexplanatory. Important in the formation of PBDD by Ullmann reaction of brominated phenoxy radicals. Influences of added water, air content and other factors on PBDD/F yield and pattern have also been studied in detail (ref. 11). 

Air content of freshly mixed concrete by the pressure method Air content of freshly mixed concrete by the volumetric method Unit weight, yield, and air content of concrete Specific gravity, absorption, and voids in hardened concrete Resistance of concrete to rapid freezing and thawing Scaling resistance of concrete surfaces exposed to deicing chemicals... 

Pan shina T.N. Materialy po toksikologii fosfamida i gigienicheskomu normirovaniyu ego soderzhaniya v vozdukhe rabochey zony (Materials on Phosphamide Toxicology, and Health Standards for Work Zone Air Content) Dis.. ..Candidate of Medical Sciences. Kiev, 1964. 

Gasification reactor atmosphere (level of oxygen or air content)... 

Soil air is made up of the same basic constituents as atmospheric air however, the ratios of various gases are different and more variable. First and most importantly, virtually all void volume of the soil can be occupied by either air or water. The amount of air in soil is thus inversely related to the amount of water present. When the air content is around 25 % or more of the void volume, as shown in Figure 5.1, the soil is considered to be aerobic and oxidation reactions predominate. When all the void volume is occupied by water, the soil is anaerobic and reducing reactions predominate. 

Funicular saturation Similar to residual saturation, except that each grain is surrounded by a water film and has a large air content. 

The physical and chemical parameters which influence iron oxide formation vary with time and space, e. g. through changing water/air content. Microenvironments exist in pores of different sizes and with different degrees of filling. For example, hematite was identified in coatings at the (dry) surface of a basalt boulder, whereas goethite occurred in a nearby (moister) crack (Bender-Koch et al., 1995 a). In another case, goethite was the dominant oxide next to the root surface, whereas lepidocrocite predominated a few mm away from it (Schwertmann Fitzpatrick, 1977). Often, however, the exact conditions under which Fe oxides form are difficult to determine. 

The initial plastic state of the fresh concrete subsequent to the mixing process, where properties such as the air content, density and workability are normally measured by relevant standard tests, and utilized as a means of control of production. The magnitude of these properties is affected by the addition of water-reducing admixtures, either intentionally or as a side effect, which could result not only in a change in the characteristics in the plastic state, but could also be reflected in changed properties in the hardened state. 

The presence of a water-reducing admixture can alter the air content of concrete, either as a deliberate measure (the air-entraining water-reducing admixtures) or as a side effect of the material in lowering the surface tension of the aqueous phase. 

Category of water-reducing admixture Chemical type Additional air content (% by volume) Reference... 

Product type Mix details Air content Bleeding Reference... 

Series Mix Air- entraining agent Water-reducing admixture Cement content (kg m - ) Water- cement ratio 28-day compressive strength (N mm-2) Air content (%) Slump (mm) Durability factor ASTM C290 1967... 

The initial plastic state of the fresh concrete when properties such as the workability as measured by slump or flow table test or air content can be determined by the relevant standard method. 

The later plastic state when the concrete may be transported, handled and placed changes in air content and workability may occur and setting time may be a factor in the finishing operation. 

Different types of superplasticizers alter the air content of fresh concrete in varying degrees and the effect is also dependent on the way the superplasticizer is used. In general, the following observations are noted ... 

When superplasticizers are used to reduce the water-cement ratio, normally any increase in air content will be minimal, especially in high-cement-content mixes. When it is a requirement to intentionally air-entrain such mixes, the dosage required to obtain a given air content is often considerably increased, presumably because of the reduced aqueous medium in the concrete. 

Water-cement ratio (by wt) Nature of mix Air content (%) Paste content (%) Voids in concrete (%) Specific surface area (mm) Void spacing factor (mm)... 

The apparatus shown in Fig. 3.5 was used, and was filled completely with cement paste. Admixture additions were made by injecting with a hypodermic needle through the rubber cap. Pastes prepared in this way had air contents of less than 0.6% by volume, were free from any premature stiffening tendencies and were homogeneous. 

The same apparatus was used, but quantities of paste were removed to give an air space in the vessel. On rapid agitation the volume increased, dependent on the air content required. Paste viscosities were measured, using a Stormer viscometer, which is a type of concentric cylinder viscometer. Although it is possible to obtain results in absolute terms, for comparative purposes the times for 100 revolutions of the rotor under a fixed applied torque were recorded. 

Table 3.5 The effect of water-cement ratio of cement pastes on the air content, specific surface area and computed spacing factor...

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