Showing papers on "Air entrainment published in 1989"

The kinetics of wetting: the dynamic contact angle

Abstract: From measurements of dynamic contact angles, whereby a continuous solid strip is drawn into a large liquid pool, we obtained an operational equation: $$cos\theta _d = cos\theta _o - 2(1 + cos\theta _o )Ca^{1/2}$$ which predicts that under air entrainment conditions, the velocity is independent from the nature of the strip.

Study of air entrainment and aeration devices

Abstract: Cavitation erosion damage to spillway surfaces may be prevented with the use of aeration devices (aerators) introducing air in the layers close to the channel bottom in order to reduce cavitation damage. The performance of a spillway aerator are studied on steep spillway model with high velocities (from 4 m/s up to 15 m/s) and new air concentration and velocity measurements were performed. The data are presented and analysed developping new equations. The behaviour of the air demand relationship between the air discharge and the subpressure in the cavity beneath the nappe is analyzed. All these results provide a better understanding of the air entrainment processes above a spillway aerator and the quantity of air entrained can be obtained. Experimental data at the impact point of the jet are shown. The results indicate a strong deaeration process occuring in the impact region and reducing the effect of the aeration occuring above the aerator.

Effects of Air Entrainment on Plunge Pool Scour

Abstract: Plunge pool scour depths are normally assumed to be dependent on unit flow q and head drop H, with a surprising variation among authors concerning the importance of H. It is hypothesized by the writer that this process may be linked to plunge pool air entrainment. Tests are carried out using a hydraulic model on which q, H and the air/water ratio β in the plunge pool could each be varied separately. Scour depths are found to depend only on q and β with the apparent effects of H recorded in the past being possibly due to associated variations of β with H. Equations are developed explaining the results in terms of forces on the particles of bed material. These are shown to apply to a wider body of model test data and also to prototype data. Particular areas of relevant future research are also identified. It is proposed that any future plunge pool scour studies should recognize air entrainment as a significant variable.

Method of controlling air entrainment in concrete compositions

Abstract: A method of controlling the level of entrained air in hydraulic cement compositions is disclosed comprising the sequential steps of preparing a hydraulic cement composition in the form of an aqueous slurry containing an air entraining plasticizer and a defoamer, and increasing the air content of the composition by adding to said composition an air entraining agent. This method prevents undesired air entrainment, while allowing controlled amounts of air to be entrained if desired for freeze/thaw durability.

The oscillatory behaviour of medium-scale pool fires

Abstract: This paper describes an investigation of the formation of the large-scale structures which govern air entrainment and mixing in the continuous flame zone of a 30 cm diameter acetone pool fire. Flow visualization was combined with Laser Doppler Anemometer velocity and thermocouple temperature measurements to determine the pulsation frequency of the fire and to identify the regions of the fire involved in the evolution of these structures. The visible fire structure and the pulsation frequency were also examined when the boundary conditions on the burner were varied. The flow visualization studies and the velocity and temperature profiles suggested a detailed description of the stages occurring during the development of large-scale structures in the fire. The frequency of oscillation of the fire varied only slightly with the reduction of fire radiation back to the surface of the fuel and with minor blockages in the entrainment of air at the edges of the fire. When the flow of air into the base of the fire was altered more significantly, the visible structure of the fire and its frequency of oscillation were affected to a larger extent. It appears that the large-scale structures are more a result of instabilities in the fluid dynamics external to the fire, than the variations in flame chemistry due to the local accessibility of fuel and air. An initial phenomenological model of the entrainment processes and their effect on fire behaviour formulated as a result of these experiments has provided further insight into the complex processes which interact in the continuous flame zone of a medium-scale pool fire.

Domestic sewage as mixing water in concrete

Abstract: Reviews of the characteristics of domestic sewage and refinement in its composition upon biological treatment imply its suitability for use in concrete technology. A typical domestic sewage was characterized and used in this study as mixing water. Setting time, air content, specific gravity, and strength tests were performed on cement paste, mortar, and concrete specimens made with distilled water showed that untreated domestic sewage increases the initial setting time, entrains air, and reduces the strength of mortar and concrete, and therefore is not recommended for use in concrete technology. However, average biologically treated domestic wastewater is inistinguishable from distilled water when used as mixing water.

Technical review of calcium nitrite corrosion inhibitor in concrete

Abstract: Calcium nitrite has been used as a corrosion inhibitor against chloride attack and as a set accelerator in concrete for more than 20 years Considerable data are available concerning its effects on corrosion inhibition, setting times, freeze-thaw resistance, strength, and other properties Although much of the data have been published in the open literature, a full-scale review is not available This paper reviews past and present research on the properties of calcium nitrite in concrete While the bulk of the data have been generated by WR Grace & Co, considerable information is available from outside sources, including the US Federal Highway Administration (FHWA), departments of transportation, universities, and independent test laboratories It is shown that calcium nitrite is an effective corrosion inhibitor for steel in concrete, based upon extensive corrosion testing in laboratory and field concrete specimens The effects of mix design and concrete cover on corrosion resistance with calcium nitrite are also discussed Furthermore, in most cases, calcium nitrite improves the compressive strength of the concrete mix and, with proper air entrainment, is freeze-thaw durable In conclusion, the data generated in the last 20 years show that calcium nitrite is a proven corrosion-inhibiting admixture to be used to protect concrete structures in a chloride environment

Pipeline design for water engineers

Abstract: 1. Economic Planning. Introduction. Pipeline economics. Basics of economics. Balancing storage. 2. Hydraulics. The fundamental equations of fluid flow. Flow head loss relationships. Minor losses. Pressure and flow control in pipes. Types of valves. Cavitation in control valves. 3. Pipeline System Analysis and Design. Network analysis. Optimization of pipeline systems. 4. Water Hammer and Surge. Rigid water column surge theory. Mechanics of water hammer. Elastic water hammer theory. Protection of pumping lines. 5. Air in Pipelines. Introduction. Problems of air entrainment. Air intake at pump sumps. Air absorption at free surfaces. Hydraulic removal of air. Air valves. Head losses in pipelines. Water hammer. 6. External Loads. Soil loads. Superimposed loads. 7. Concrete Pipes. The effect of bedding. Prestressed concrete pipes. 8. Steel and Flexible Pipe. Internal pressures. Tension rings to resist internal pressures. Deformation of circular pipes under external load. Stress due to circumferential bending. Stiffening rings to resist buckling with no side support. 9. Secondary Stresses. Stresses at branches. Stresses at bends. The pipe as a beam. Temperature stresses. 10. Pipes, Fittings and Appurtenances. Pipe materials. Line valves. Air valves. Thrust blocks. Forces induced by supports. Flow measurement. Telemetry. 11. Laying and Protection. Selecting a route. Laying and trenching. Thrust bores. Pipe bridges. Underwater pipelines. Joints and flanges. Coatings. Linings. Cathodic Protection. Thermal insulation. 12. Pumping Installations. Influence of pumps in pipeline design. Types of pumps. Terms and definitions. Impeller dynamics. Pump characteristic curves. Motors. Pumpstations. General References and Standards. Books for Further Reading. Appendix. Symbols for pipe fittings. Properties of pipe shapes. Properties of water. Properties of pipe materials. Conversion factors. Author Index. Subject Index.

Effect of air entrainment on airway pressure during endotracheal gas injection.

Abstract: Turbulent jets in endotracheal tubes induce air entrainment and airway pressure changes. We attempted to understand the physical explanation for these effects, which open up to a wide range of applications in intubated patients. An in vitro study was performed on standard size endotracheal tubes with diameters of 8, 7, and 3 mm and several capillaries molded into the wall (less than 1 mm diam) allowing gas injection at approximately 1-2 cm from the tracheal end of the endotracheal tube. This produced a jet velocity-dependent gain in tracheal pressure (Ptr) during inspiration. Data have been interpreted with a theory, based on the classic momentum theorem, which indicates that the mechanisms involved resemble those of axisymmetrical confined jets: air entrainment by turbulent friction with a longitudinal increase in lateral pressure. The difference with axisymmetrical systems lies in the nonconservation of the total thrust in our system because, secondary to wall friction and to the nonaxial incidence of the jets, only a fraction of the jet momentum flux is transformed into pressure. This suggests faster mixing in the present lateral jet system, as shown by 1) the independence of Ptr on tracheal geometry and 2) the very rapid increase in lateral pressure. The present study supports the idea that pressure changes in the airways, which are potentially beneficial in intubated patients, can be satisfactorily generated by turbulent jets.

Air-void stability part i: influence of silica fume and other parameters

Abstract: Thirty concrete mixes were prepared to analyze the influence of silica fume and other parameters on the stability of air-void system during mixing and agitation. For each mix, four sets of samples were cast over a period of 90 min after initial water-cement contact. The modified point count method (ASTM C 457) was used to determine the characteristics of the air-void system on each set of samples. Results indicate that silica fume and type of mixing have little influence on the production and stability of the air-void system but that superplasticizers can cause a significant increase of the spacing factor value. This inflkuence of superplasticizers was found to vary quite significantly with the characteristics of the cement and also with the type of superplasticizer and air-entraining agent. Results show that it is difficult to estimate the value of the spacing factor from the air content of fresh concrete.

Properties of Concrete Incorporating Low Quantity of Cement and High Volumes of Low-Calcium Fly Ash

Abstract: This paper presents the results of investigations forming part of a long-term study of concrete that incorporates low quantities of cement and high volumes of low-calcium (ASTM Class F) fly ash. Two types of low-calcium fly ashes from sources in Nova Scotia and Alberta were studied. For comparison purposes, a control concrete containing only ASTM Type I cement was also investigated. A large number of concrete test cylinders and prisms were subjected to determinations of strength, modulus of elasticity, drying shrinkage, freezing and thawing durability, carbonation, and permeability to chloride ions. The test results up to 1 year corroborate the results of previous investigations on concrete incorporating high volumes of low-calcium fly ash. At 7 and 28 days, the compressive strength and the modulus of elasticity were about 47 MPa and 37 GPa, respectively. Air-curing of test specimens did not seem to affect the compressive strength development significantly up to the testing period of 91 days. Resistance of all concretes to repeated cycles of freezing and thawing was found to be excellent with durability factors > 99, when tested after 14 days of the initial moist curing. The drying shrinkage strains of the fly ash concretes were comparable to or lower than that of the control concrete. Further, permeability tests carried out on one of the fly ash concretes indicated exceedingly low permeability to chloride ions at 1 year.

Some recent problems with air-entrained concrete

Abstract: Several problems are identified in regard to air-entrained concrete, which include the accuracy of the pressure air meter (ASTM C 231), the accumulation of air voids at the coarse aggregate surface, excessive loss of air volume in transit or in pumping, and the need for greater precision and detail in specification requirements for air-entrained concrete. Data are presented from four recent construction projects from a wide geographical range in the United States.

Air-void stability, part ii: influence of superplasticizers and cement

Abstract: Eighteen concrete mixes wre prepared to analyze the influence of superplasticizers on the stability of the air-void system during mixing and agitation. For each mix, four sets of samples were cast over a period of 90 min after initial water-cement contact. The modified point count method (ASTM C 457) was used to determine the characteristic of the air-void system on each set of samples. Results indicate that superplasticizers can cause a significant increase of the value of the spacing factor. This influence of superplasticizers was found to vary very significantly with the characteristics of the cement and also with the type of air-entraining admixture. A methodology similar to the one used in this study is recommended to assess the production and the stability of the air-void characteristics in relation to the composition of the mixes and materials that are used.

Sediment Entrainment in Channel with Rippled Bed

Abstract: An expression for the entrainment in a channel with rippled bed has been developed considering the entrainment mechanism. The flow structure behind the ripple has been modeled on an eye‐shaped line vortex. Afterwards, the pickup rate of the sediment particle and its motion has been calculated under the vortex activity. The ripple characteristics, such as, configuration, frequency of formation and the shear stress (due to the vortex) on the sand surface have been obtained as functions of the bulk parameters. Combining these characteristics, the entrainment rate at the lee‐side of the ripple has been calculated. Also the entrainment rate from the stoss side has been taken as a basis for the calculations concerned with the total entrainment rate. Then, the ratio of the lee‐side entrainment to the total value has been obtained as a function of the ripple characteristics described above. It can be concluded that the results have been found to be satisfactory when compared with former investigations and experim...

Observation of a dynamic wetting process using Laser‐Doppler velocimetry

Abstract: The purpose of this study is to observe the dynamic wetting process of a slide coater flow (Ca = 0.16; Re = 14.4; St = 0.0142; ΔeP = 2.5), using a specially-developed Laser-Doppler measuring technique. The measurements, carried out with glycerol solutions, reveal that the observed contact line is apparent and that a thin air film is entrained between the web and the liquid surface. The liquid is accelerated along the lower free surface and attains approximately 50% of the web velocity at the apparent contact line. Downstream from the apparent contact line, the liquid is further accelerated along the air film to the web velocity at the real contact line. The apparent contact angle increases with the capillary number Ca and air entrainment occurs at Ca = 0.25.

Laboratory investigation of concrete sealers

Abstract: Laboratory studies are described that were performed to assist specifiers in the selection of sealers for the protection of concrete traffic surfaces of existing parking garages that have been exposed to chlorides. The study is limited to products marketed in Canada and include the following generic types: acrylics, oligomeric alkoxysiloxanes, epoxies, blends, urethanes, alkoxysilanes, silicates/ siliconates, polysiloxanes and silicones, stryrene-acrylate copolymers, chlorinated rubbers, oils, siloxane/methacrylate, and synergistic system. Considerable differences were found in the effectiveness of the various sealers; they were more effective on good concrete than on inferior concrete. Thus, the properties of concrete must be considered in selecting a sealer. Only 35% of all sealers penetrated the concrete to a measurable extent. Air entrained concrete has a higher water absorption and chloride penetration of coated and uncoated concrete.

Sources of Ambient Noise in the Ocean: AN Experimental Investigation.

Abstract: : The general characteristics of underwater sound produced at the ocean surface have been known for many years and recent measurements have also described the sound of rainfall. The mechanisms which produce these sounds have remained a mystery. This report describes a series of laboratory experiments in which various simple mechanisms in the 0.5-100 kHz frequency range were examined. A large part of the work describes the sounds made by the impact of a drop of water on the water surface. It is found that two types of sound are emitted: first, a sharp spike radiated when the drop first strikes the surface and second, a damped sinewave emitted when a bubble is entrained below the water surface. For a certain range of drop sizes and velocities a bubble will always be entrained; this phenomenon has been named regular entrainment. The hydrodynamics of a drop impact are discussed in an attempt to show why regular entrainment occurs; a qualitative explanation is described using computer modelling. The sound of rainfall on water is studied in detail; an important feature of the acoustic spectrum is a peak at about 14 kHz. It is shown that this peak is caused by regular entrainment and not by initial impacts as one author has suggested. Experimental results enable us to predict the spectrum levels which rain of a given intensity would produce; the predictions compare reasonably well with real rain data. Other experiments examined the sound of a breaking wave and of bubbles interacting with a submerged jet of water. Theses.

Effect of length of freezing period on durability of concrete

Abstract: Concretes with different entrained air void systems were subjected to long and short cycles of freezing and thawing in 4% sodium chloride solution. Results indicated that the long freeze-thaw cycles were more severe than the short freeze-thaw cycles for the same number of cycles, even where air void spacing factors were no greater than 0.008 in. These findings agree with the ice accretion theory of frost damage in concrete.

Freeze-thaw deterioration of concrete pavements

Abstract: Under winter exposure conditions, solar radiation effects along with the presence of de‐icing salts have a pronounced impact on the deterioration of concrete pavements. The rapid changes and differences in temperature between the pavement's dry surface and saturated subsurface can cause both thermal and hydraulic stress. As subsequent cycles of freezing and thawing occur, a subsurface plane of cracks will form in which ice lenses can grow parallel to the surface and eventually cause failure of the subsurface paste. Once the subsurface has failed, the surface will spall off in sheets. This thin brittle layer will then crumble under traffic, and leave the aggregate exposed. By using both laboratory and field data this paper discusses concepts of how de‐icers and freeze‐thaw cycles limited to the upper portion of the concrete pavement contribute to scaling by setting up thermal gradients and lowering the immediate surface moisture content.

Resistance of Condensed Silica Fume Concrete to the Combined Action of Freezing and Thawing Cycling and Deicing Salts

Abstract: This paper will present results of investigation to determine the combined effect of deicing salts and repeated cycles of freezing and thawing on condensed silica fume concrete. The concrete mixtures tested in this phase included mixtures incorporating silica fume as an 8 percent replacement by mass for cement, along with control mixtures (no silica fume), both covering a range of water-to-cementitious materials ratio of 0.40 to 0.65. All mixtures were air entrained and some contained a superplasticizer. For each mixture, freeze-thaw resistance and scaling resistance to deicing salts were determined using ASTM standard procedures. For some selected mixtures, scaling resistance was also determined using slight variations in the testing procedures. In general, concrete incorporating silica fume is slightly more susceptible to scaling than concrete without silica fume. Preliminary results clearly indicate that the methods of preparing and curing the test specimens has a significant influence on the scaling resistance of the concrete, but further investigations are needed to establish possible correlations between the degree of scaling, type of curing, method of specimen preparation, and percentage of silica fume in the concrete.

Cryogenic Frost Resistance of Lightweight Concrete Containing Silica Fume

Abstract: This paper will discuss longitudinal thermal strains of high-strength, air-entrained, lightweight concrete containing silica fume that were monitored during a single frost cycle between 15°C and -157°C to measure the coefficients of thermal length changes at different temperatures. The immunity of such concrete to repeated exposures to liquified petroleum and natural gas temperatures was also evaluated. Scanning electron microscopy was employed to observe the deterioration of concrete prior to and after five frost cycles to -73° C. The coefficients of thermal length changes of air-dried and water-saturated concretes were calculated to be 3.2 and 4.1 x 10-6 cm/cm/C, respectively, before freezing, and 2.9 and 3.0 x 10-6 cm/cm/C at post-freezing temperatures. The strength deterioration study indicated that dried concrete cycled to -40° C can experience maximum drops in compressive and splitting tensile strengths of 7 and 3.5 percent, respectively. These reductions can be expected to increase to 15 percent if the extreme cooling temperature is lowered to -73° C. Water-saturated concrete can lose 12 to 17 percent of its initial strength after five freeze-thaw cycles to either temperature range.

Measurement of Residence Time, Air Entrainment Rate, and Base Pressure in the Near Wake of a Cylindrical Body in Supersonic Flow

Abstract: The air entrainment rate into the near wake was calculated from the residence time. THe residence time was measured by injecting carbon dioxide (CO 2 ) into the near wake and then monitoring the time required for dissipation of the gas after the injection was shut off. The dissipation was monitored using a radiometer that measured absorption of radiation from an infrared (IR) source in the 4.3-μm CO 2 band. The test body was 2 1/2in. in diameter and 5 in. long. Residence time varied from 14.4 ms at an air velocity of 150 ft/s to 8.98 ms at 312 ft/s

Air entrainment concrete cutting machine

Abstract: The utility model relates to an air entrainment concrete cutting machine, which belongs to the improvement of the air entrainment concrete cutting machine. The air entrainment concrete cutting machine comprises a cutting machine mould, horizontal and vertical cutting steel wires whose both ends are positioned by a positioning mechanism, and a vertical cutting device by electric drive (hands). The utility model has the advantages of simple structure, low cost, simple operation, high rate of products meeting standards, convenient change of the specification and the size of the product, agility and easy implementation. The air entrainment concrete cutting machine is suitable for middle and small air entrainment concrete factories for the use of cutting blocks and sheet materials.

Freeze-thaw tests of concrete in seawater

Abstract: The paper discusses the freeze-thaw durability of air-entrained concrete (w/c=0.44, 4 % air) in seawater for marine construction. Two laboratory procedures were used. The first procedure approximates the field freeze-thaw conditions the concrete undergoes in the tidal zone. The second procedure was similar to the one recommended in ASTM C 666, Procedure A. The experiments were performed in fresh water and seawater. The results of the study suggest that, in the performance of concrete under arctic conditions, surface effects probably play an important role in the deteriorative mechanisms.

Influence of Different Pozzolan Types upon the Effect of Plastifying Admixture

Abstract: This paper presents the results of an investigation where the effect of lingo-sulphonate addition on the properties of cement paste and concrete, which incorporated pozzolans has been studied. Measurements of adsorption and zeta-potential were made on the systems of pozzolans/Ca(OH)2-solutions/ lingo-sulphonate, and upon the heat evolution from cement pastes containing pozzolans and ligno-sulphonate. The results indicated that the effect of lingo-sulphonate was dependent upon the type and quality of the pozzolan used. When testing in concrete, the above measurements showed to have pointed the direction but not the magnitude, in which concrete properties such as water demand, air content, setting time and strength development were affected. They also gave the basis for the explanation of most of the phenomena observed in concrete.

The use of air-entraining and plasticizing admixtures for producing concrete with good saltfrost resistance.

Abstract: The use of air-entraining and plasticizing admixtures for producing concrete with good saltfrost resistance.

Fatigue strength of roller compacted concrete. proceedings, 4th international conference on concrete pavement design and rehabilitation, purdue university, april 18-20, 1989

Abstract: Although the experiences on the performance of Roller Compacted Concrete (RCC) under heavy traffic and severe environmental conditions have been satisfactory, there are still some questions about the structural strength and fatigue characteristics of RCC. Laboratory information on durability of RCC helps to predict field performance. This paper presents laboratory results on attempts to improve the durability of RCC by air entraining a cement mortor prior to the addition of coarse aggregate. Also, some strength correlations are presented to give a more complete view of the RCC properties.