Build-up Thickness Research Articles

Tests to characterise properties of fresh dry-mix shotcrete

The intent of this project is to study the fundamental characteristic properties of dry-mix shotcrete. Although several factors are known empirically to influence the shooting properties of the dry process shotcrete, it is generally not clear how and why these variables are important, particularly with regard to the maximum buildup thickness. With this in mind, different dry-mix shotcrete mixtures were shot, and rebound and maximum buildup thickness were evaluated for each. In particular each mixture was shot at a different consistency, which was evaluated from the force required to push a needle into the fresh shotcrete. Relationships were found between the penetration resistance of a fresh mixture and its fresh tensile strength or maximum buildup thickness (cohesiveness). However, distinct relationships were obtained for the different mixtures tested, which implies that consistency (penetration stress) is not sufficient by itself to characterise fresh dry-mix shotcrete. The addition of silica fume or air-entraining admixture allowed one to shoot better quality shotcretes. However, these additions had an opposite effect on the fresh tensile strength.

Absorption and Scattering of 90Sr/90Y Beta Particles Transmitted Through Aluminium and Plastic Filters

Absorption and scattering of 90 Sr/ 90 Y beta particles transmitted through aluminium and plastic filters have been studied. From measurements of the ionisation current by the extrapolation chamber, it was shown that a build-up in absorbed dose rate occurred over the first 0.1 mm of aluminium thickness before attenuation started to dominate. This build-up thickness corresponded to a δ particle energy of 150 keV. The attenuation at large thicknesses followed an exponential function which predicted a half-value thickness of ∼112 mg.cm -2 and a range (99% attenuation) of ∼1000 mg.cm -2 . Angular distributions of the absorbed dose rate for 90 Sr/ 90 Y beta particles transmitted through aluminium and plastic filters have also been measured. These distributions followed the multiple scattering Gaussian curves for small projected angles and the single scattering tails for large projected angles. The mean square angle of the Gaussian distribution was approximately a linear function of the filter thickness. The peak height, however, dropped rapidly with increasing filter thickness at small thicknesses but slowly at large thicknesses. Both the mean square angle and the peak height were slightly dependent on the filter material.

Dimensional factors affecting magnetic properties of wound cores

The magnetic properties of wound cores constructed from electrical steel strips have been found to be affected by their geometry, in particular the inner and outer diameters, the strip width and the build-up thickness of the toroids. Assessment of the effect of aspect ratio and winding ratio have been carried out in various sizes of toroid. An increase in aspect ratio resulted in better magnetic performance, whereas increase in winding ratio degraded the original magnetic properties. However, when the inner and outer diameters are varied with constant build-up and strip width, better performance is obtained by increasing the winding ratio.The initial rate of rise of temperature technique using thermistors has been used to measured power loss on the inner and outer wraps of a wound toroid. The power loss of a 60 × 44 × 40mm toroid at 1.0 T before stress relief annealing was 0.88 and 0.52 W kg−1 at the inner and outer layers respectively. After stress relief annealing, the power loss fell to 0.44 and 0.43 W kg−1 at the inner and outer layers respectively. This indicates the higher stress produced by small diameter wrapping can be reduced by normal stress relief annealing.

Development and Hydrocarbon Potential, Carbonate Platforms Offshore Northeastern America: ABSTRACT

The Jurassic-Lower Cretaceous carbonate platforms and banks form a discontinuous belt extending from the Grand Banks to the Bahamas (over 6,000 km). The thickness of the carbonate buildups progressively increases southward along the margin, attaining a thickness of more than 5 km on the Bahamas. The platforms also become younger southward, which has been interpreted as an indication of a northward motion of the North American plate. Six types of carbonate buildups recognized document variability of depositional, paleo-oceanographic, and tectonic processes along the margin. The composition of the buildups closely resembles the recent deposits of the western Great Bahama Bank, since oolitic shoals were present near the shelf edge and skeletal, peloid wackestones and biomicr tes were deposited in the inner part of the platform. Coral-hydrozoan, sponge and algal stromatolite bioherms and reefs are important constituents of the Late Jurassic-Early Cretaceous shelf edge. The hydrocarbon prospectivity of the carbonate front differs for the individual carbonate platform types which prevents construction of a single model for evaluation of their hydrocarbon potential. Porosity has locally developed as a result of secondary dolomitization in a mixing zone. Hydrocarbons were at least locally generated and migrated through the porous carbonate rocks. The major critical factor is presence of a rich source rock. The latest deep sea drilling on the northwestern African and eastern North American margins, together with the interpretation of the Mesozoic paleogeography of the shelf, allows the elucidation of this important factor in a time and space framework of margin development. End_of_Article - Last_Page 585------------

Mesozoic carbonate platforms and banks of the eastern North American margin

The Jurassic—Lower Cretaceous carbonate platforms and banks form a discontinuous belt extending over distance of 6000 km from the Grand Banks up to the Bahamas. Six types of carbonate buildups are recognized and document the variability of depositional, paleo-oceanographic and tectonic processes on the eastern North American margin. The composition of the carbonates closely resembles the Recent deposits of the western Great Bahama Bank since oolitic shoals were present near to the shelf edge, and skeletal, peloid wackestones and biomicrites were deposited in the inner part of the platform. Coralstromatoporoid and sponge bioherms were only rare constituents of the carbonate banks. The thickness of carbonate buildups progressively increases southward along the margin, attaining a thickness of more than 5 km on the Bahamas. The carbonate platforms also become younger southwards, which is thought to reflect the northward movement of the North American plate of less than 1.5 cm/yr. The carbonate platforms were seeded over the continental basement following the taphrogenic period of plate tectonics. Building of carbonate ramps which characterized the Early Jurassic, has began during the transitional period between continental rifting and early drift. The second stage in construction of the carbonate platforms and offshore banks proceeded mainly after separation of the continental plates.

Mesozoic Carbonate Platforms and Banks of Eastern North American Margin: ABSTRACT

The Jurassic-Lower Cretaceous carbonate platforms and banks form a discontinuous belt extending from the Grand Banks to the Bahamas, a distance of over 6,000 km. Six types of carbonate buildups are recognized that document the variability of depositional, paleo-oceanographic, and tectonic processes on the eastern North American margin. The texture of the carbonates closely resembles recent deposits of the western Great Bahama Bank in that oolitic grainstones were present near the shelf edge, and skeletal, peloid wackestones and mudstones (biomicrites) were deposited in the inner part of the platform. Coral-stromatoporoid and sponge bioherms were rare constituents of the carbonate banks. The thickness of carbonate buildups progressively increases southward along the margin attaining a thickness of more than 5 km in the Bahamas. The platforms also become younger southward, which is thought to reflect the northward movement of less than 1.5 cm/year of the North American plate. The carbonate platforms were seeded over the continental basement following the taphrogenic period of plate tectonics. The building of carbonate ramps characteristic of the Early Jurassic began during a transitional period between continental rifting and early drift of the continental plates in the North Atlantic. The second stage in construction of the carbonate platforms and offshore banks proceeded mainly after separation of the continental plates. End_of_Article - Last_Page 941------------

Perturbation of isodose distributions adjacent to cavities in tissue-equivalent media during irradiation by 10-35 MeV electrons.

Quantitative determination of the effect of cavities on the dose measured by an ionization chamber at a suitable point behind the cavity has shown that the percentage of dose increase varies markedly as.a function of the build-up layer, the diameter and thickness of the cavity, and the electron energy. A study of dose distribution showed that cylindrical cavities similar in size to those encountered in the head and neck may result in a localized dose of up to 160% of that measured at the depth of maximum dose within a homogeneous tissue-equivalent medium.

The importance of build-up thickness in the dose increase produced adjacent to voids in tissue-equivalent material exposed to 10-35 MeV electrons.

The increase in dose adjacent to voids was systematically measured as a function of void diameter for combinations of incident electron energy and void thickness, utilizing build-up layer thicknesses of 1/4 inch, 1/2 inch, and 1 inch. Plots of “percentage void dose” vs. void diameter are shown. Marked changes in dose are observed when the build-up layer thickness is varied.

Environment of Deposition of Late Cretaceous Fruitland Formation Coal Deposits of San Juan Basin, New Mexico and Colorado: ABSTRACT

The Fruitland Formation in the San Juan basin contains large resources of subbituminous and bituminous coal. The thickest beds are in the lowermost part of the formation and in many places lie directly on the underlying Pictured Cliffs Sandstone. The coal beds were deposited in a coastal-swamp environment. This environment shifted northeast together with the Pictured Cliffs shoreline as the Late Cretaceous sea withdrew from the San Juan basin. The coal swamps trended northwest, parallel with the shoreline. The thickness of vegetal matter buildup in these coastal swamps is related closely to the manner in which the Pictured Cliffs shoreline retreated from the basin area. The retreat of the sea was primarily the result of sediment infilling along the edge of a subsiding dep sitional basin. When sediment influx was great, the shoreline regressed rapidly, swamps soon were filled and covered, and the resultant coal beds were thin. When sediment influx was moderate, the shoreline remained geographically stable, shoreline sandstone deposits built up vertically, swamp deposits of vegetal matter also built up vertically, and the resultant coal beds were thick. When sediment influx was small, the shoreline transgressed continental deposits, swamps were filled and covered by marine sandstone, and resultant coal beds were thin. Another paleoenvironmental factor affecting swamp configuration was streams passing through the coastal swamp area to the sea. This process tended to limit the length of swamps. In addition, variations in the paleotopography of the coastal swa p area due to the presence of bars and dunes limited the areas which the swamps occupied. End_of_Article - Last_Page 214------------