Cover thickness

Specifications and Test Methods. The American Society of Electroplated Plastics pubHshes a comprehensive book covering most technical aspects of testing and control (24). A number of ASTM standards have been issued that cover thickness, adhesion, and thermal-cycling resistance of the total plated film. Some specifically for plated plastics include ... 

Note 5 In calculating paint requirements up to 50% more than the theoretical dry film weight requirement should be allowed to cover thick coatings, wastage, repairs, losses (typically 30% for air spray 15% airless spray 10% electrostatic spray 5% roller or brush) etc. Manufacturers should be asked to quote percentage volume solids in their paint to facilitate calculations. 

Switzerland accommodates a substantial part of the Alpine chain, and there are over 700 road or railway tunnels in the country. The cover thickness is often considerable, which can lead to rock/water inflow temperatures of 40—50 °C. An examination of the geothermal potential of Swiss tunnels screened 150 tunnels, from which 15 objects were selected for more detailed studies (Arbeitsgemeinschaft ZEWI 1995, 1996, 1998 Fig. 7). Their heat potential is estimated to be greater than 30MWt (Table 3). The flow rates range from 360L/min (Ascona) to... 

Chapters 1 to 5 deal with ionophore-based potentiometric sensors or ion-selective electrodes (ISEs). Chapters 6 to 11 cover voltammetric sensors and biosensors and their various applications. The third section (Chapter 12) is dedicated to gas analysis. Chapters 13 to 17 deal with enzyme based sensors. Chapters 18 to 22 are dedicated to immuno-sensors and genosensors. Chapters 23 to 29 cover thick and thin film based sensors and the final section (Chapters 30 to 38) is focused on novel trends in electrochemical sensor technologies based on electronic tongues, micro and nanotechnologies, nanomaterials, etc. 

Over a considerable fraction of the high-latitude global ocean, sea ice forms a boundary between the atmosphere and the ocean, and considerably influences their interaction. The details and consequences of the role of sea ice in the global climate system are still poorly known. Improved knowledge is needed of the broad-scale time-varying distributions of the physical characteristics of sea ice, particularly ice thickness and the overlying snow-cover thickness, in both hemispheres, and the dominant processes of ice formation, modification, decay and transport which influence and determine ice thickness, composition and distribution. We do not know how accurate present model predictions of the sea ice responses to climate change are, since the representation of much of the physics is incomplete in many models, and it will be necessary to improve coupled models considerably to provide this predictive capability. 

A smooth fall of the equilibrium thickness is clearly seen when the counterion concentration is raised. For films of h = 60 - 80 nm the equilibrium is determined by the equality of Uei with the hydrostatic pressure (pa = 25.5 Pa) Ylvw was not accounted for. Studying films of small thickness, the authors considered for the first time film structure, i.e. the presence of a free aqueous core and adsorption layers (see Section 2.1.3). This is important for the treatment of not only the results from optical thickness measurements but of ne( and Ylvw as well. It was established that ne/ covered thickness h2 equal to the thickness of the... 

It was necessary to use a film thickness of 200 pm for the total photo protection of multivitamin infusions containing ascorbic acid, thiamine hydrochloride, nicotin-amid, and pyridoxine hydrochloride. For amiodarone hydrochloride and a special quinolone infusion, which showed sensitivity to all wavelengths in the UV region up to 400 nm, the photo protection was considerably lower. However, a reduction of drug losses from 59% and 75% to 5% and 7% was still attainable using this cover thickness. It was concluded, that the limit of application for these particular UV protective covers is photolability of drug solutions with activation spectra above 385 tun. 

Figure 6.7 Initiation time of corrosion as a function of cover thickness and apparent diffusion coefficient assuming that the surface chloride concentration is 5 % and the critical threshold is...

Action Exposure class Minimum cover thickness (mm) to ... 

As the environmental aggressiveness increases, it is theoretically possible to maintain a constant level of durability by increasing the thickness of the concrete cover. In reality, however, the cover thickness cannot exceed certain limits, for mechanical and practical reasons. In particular a very high cover may have less favourable barrier properties than expected. In extreme cases, a thick unreinforced layer of concrete cover may form (micro)cracks due to tensile forces exerted by drying shrinkage of the outer layer, while the wetter core does not shrink. In practice, having cover depths above 70 to 90 mm is not considered realistic. 

Table 11.6 Maximum acceptable values of D,pp (10 the concrete cover thickness, the service life and the content of 4% chloride by mass of cement [16] m /s, assumed constant) as a function of chloride threshold (C,h) for a constant surface ...

Ax = reduction term for the cover thickness (mm), depending on the risk class of the structure. 

Cover thickness (mm) Time to depassivation (y) Time to depassivation (y)... 

Table 12.5 Initiation time for chloride-induced corrosion estimated for different concrete cover thicknesses, utilising apparent diffusion coefficients of chlorides (D,pp) evaluated on specimens submerged in the North Sea for 16 y (concrete of 420 kg/m of Portland cement, OPC, or blast furnace slag cement with 70% GGBS and identical curing procedures) [18]...

Bamforth [23] suggested the recommendations given in Table 12.6 that show how the use of normal Portland cement does not produce concrete adequate for a service Hfe of 75 y in a chloride-containing environment, unless class C50/60 concrete and concrete covers of 100 mm are used. Cements with a high percentage of mineral additions allow the use of more reasonable concrete cover thicknesses and lower classes of strength. 

In a recent independent study [13], 15% by mass solutions of monqfluoropho-sphate were applied repeatedly to reinforced concrete specimens w/c 0.65, cover thickness 12 mm) with various levels of chloride contamination. The embedded bars, pre-corroded under cyclic wetting and drying conditions for about 6 months prior to the MFP treatment, showed a reduction in corrosion rate only at low chloride concentrations (Figure 13.5) [13]. Repeated drying and MFP-immersion cycles... 

Alkanolamine-hased inhibitors have been tested in similar conditions. For ongoing chloride-induced corrosion with a chloride level of about 1-2 % by mass of cement, in mortar specimens no reduction in corrosion rate was found (Figure 13.6) except at low chloride concentrations. This is confirmed by two other studies [1,11,14] pre-corroded rebars in mortar (w/c 0.75, cover thickness 25 mm) did not show any detectable effect on the corrosion rate of embedded steel once active corrosion had been initiated, despite the fact that the specimens had low cover and porous mortar [14]. It seems that for penetrating or migrating inhibitors the favourable effects found in solution do not occur when applied to hardened mortar or concrete laboratory specimens with ongoing steel corrosion. It is thus necessary to look for information regarding the transport of inhibitor blends in mortar or concrete. 

For the replacement of the original concrete, an alkaline material with high resistance to chloride penetration should be applied with a sufficient cover thickness to prevent corrosion initiation during the design life of the repair (Chapter 19). Effects of possible diffusion of chlorides into the repair mortar from the concrete substrate should also be considered. A chloride resistant coating or mortar layer can also be applied on the concrete surface to limit further chloride penetration (Chapter 14). 

Variability. The examples of Figures 19.1 and 19.2 summarise the process of evaluation of the depth of concrete removal when a single rebar is considered and measurement of carbonation, chloride and cover thickness are available locally. In a real structure carbonation and chloride penetration may vary due to spatial variation of exposure conditions (microclimate) and of concrete properties (e. g. cracking or had compaction), etc. The cover depth may also be very variable. 

Cover thickness. The thickness of the cover produced by the repair material should be designed, as in the case of new stractures, to be sufficient to protect the reinforcement for the required time. Therefore, it depends on the resistance of the repair material to carbonation and chloride contamination (Section 19.4.3), on the aggressiveness of the environment and on the design life of the repair. Often for geometrical and aesthetic reasons the original thickness of the concrete cover is reconstmcted however, if this is not sufficient to obtain the required durability, it should be increased or additional protection should be used (Section 19.5). 

The shape of the microcapsules is usually that of the encapsulated substance and the cover thickness depends on the microencapsulation conditions and is varied according to the intended uses of the products. It may be possible to process the resulting composition directly into goods (e.g. by pressing), or the polymeric cover may enable better combination of the nanoparticles with other polymers. 

Figure 12.9 shows chloride content change at the concrete rebar surface as a function of time. Simulations were performed for a cover thickness of 5.08 cm and different surface chloride contents. It is clear that an increase in surface chloride content results in more chloride ions at the rebar surface, leading to faster corrosion initiation. 

Similar studies have been carried out for the bottom of the deck, which has a cover thickness of 7.62 cm, and the results are shown in Fig. 12.10. The chloride concentration at the rebar surface increases more rapidly for 5.08 cm cover thickness compared to 7.62 cm. Because the top of the deck is not in the splash zone, the surface chloride content is lower than the bottom part. Corrosion onset will start at the bottom deck first and lead to eventual structure failure. 

Fig. 12.9 Change in surface chloride concentration for 5.08 cm cover thickness.

Figure 12.11 presents surface chloride content change for different cover thickness at threshold concentration of 7.36 kg/m NaCl. The threshold chloride content of 0.83 kg/ is marked by the straight Hne in the plot. This graph shows rebars at the bottom of the deck will start corroding after 2500 days ( 7 years), while those at the top will start... 

Fig. 12.10 Change in surface chloride content for 7.62 cm concrete cover thickness.

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