WASHOUT RESISTANCE

Fig. 6.5 Setting behavior of washout-resistant concrete (Rakitsky [41])...

Silica fume has been used as a cohesion inducing agent to improve adhesion and sag and washout resistance. Incorporation of silica fume in dry-mix... 

Washout resistance Silica fiime shotcrete is very resistant to washout by water. It is thus well suited to operations where freshly applied shotcrete will be exposed to running water or tidal flushing, e.g. rehabilitation of marine structures in the intertidal zone, construction of dikes, and creek channelization. 

Fig. 7.27 Bleeding characteristics of washout-resistant concrete, total bleed = 0.0145 ml cm-2 (Rakitsky [78]).

Washout resistance Silica fume shotcrete is very resistant to washout by water. It is thus well suited to operations where freshly applied shotcrete will... 

The welding will need more electrical and pressure power since a thicker layer of adhesive acts as an insulator. Usually this is addressed as squeezability, which means the property of the adhesive to flow under a small pressure when the metal sheets are put together. The challenge for the adhesive formulator is to balance a low viscosity at the application temperature of 80°C with a rather high viscosity at room temperature to achieve a good washout resistance and at the same time a good squeezability. 

Inhaled tobramycin (TOBI ) is typically administered to patients 6 years of age and older in alternating 28-day cycles of 300 mg nebulized twice daily, followed by a 28-day washout or off period to minimize development of resistance. Longterm intermittent administration improves pulmonary function, decreases microbial burden, and reduces the need for hospitalization for IV therapy.24,25 Due to minimal systemic absorption, pharmacokinetic monitoring is not necessary with normal renal function. Lower doses of nebulized tobramycin solution for injection have been used in younger children, and studies are underway using 300 mg twice daily in children under age 6. 

Photocrosslinking. The second class of photopolymer chemistry that is used in some commercial products is based on the reaction of unsaturated moieties attached to an organic polymer. These photopolymer materials include the [2+2] cycloaddition of the ethylenic groups in poly(vinyl cinnamate) polymers and in the newer styryl pyridinium (10) and thiazolium (77) derivatives of poly(vinyl alcohol). The main advantage of this chemistry is that, unlike free-radical photopolymerization, they are insensitive to the presence of oxygen. This photopolymer mechanism is principally used in applications employing a washout development process (e.g. resists). 

For simplicity, we assume that the enzymes are immobilized inside the reactor, i.e., there is no outflow of enzymes nor any washout. At the same time we assume that there is no mass transfer resistance. Then the governing equation is... 

Dry deposition is parameterized via a resistance approach in which resistances depend on particle size and density, land-use classification and atmospheric stability (Wesely 1989 Zanetti 1990). Wet deposition is included via below cloud scavenging (washout), using a parameterization based on precipitation rates (Baklanov and Sprensen 2001) and scavenging by snow is parameterized using the scheme by Maryon and Ryall (1996). The terminal settling velocity is considered in both the laminar case, in which Stake s law is used and the mrbulent case in which a iterative procedure is employed (Naslund and Thaning 1991). For very small particles a correction for non-continuum effects is used. 

The most commonly used test for measuring water resistance is the water washout test method (ASTM D-1264, IP 215) in which a greased ball bearing is rotated at 600 rpm in an assembly with specified clearances in the covers to allow entry of water from a water jet that impinges on the face of one cover. The loss in grease pack after 1 h of operation is a measure of the resistance to water. The test serves only as a relative measure of the resistance of a grease to water washout. 

---