concrete pipe lining

[BRIS]

Our client has specified concrete pipe with a coal tar epoxy lining for both storm and foul sewers. The specification is somewhat weak (that is it). I am looking for alternative lining materials, specifications and standards. Any suggestions?

 

[cvg]

Try T-lock

http://www.ameronpipe.com/products/tlock.htm

http://www.pubs.asce.org/

http://WWWdisplay.cgi?0206038

 

[RWF7437]

Also try using non-corrodable pipe like PVC or HDPE. Possibly be cheaper too.

 

[BRIS]

Thanks for the replies. The project is an aid funded project in a developing country. The client has specified concrete pipe because it is manufactured in-country whereas PVC, HDPE etc have to be imported and are economically more expensive. Some of the pipe has already been manufactured so we are looking for a post manufacture coating.

 

[Ussuri]

There are health and safety issues using Coal Tar Epoxy, its a pretty nasty product as it causes skin, eye, nose, throat irritation. Dependent on exposure it is also carcinogenic. I would question whether a developing country would have/use the protective equipment necessary such as respirators.

Most of the lining I know about is either cement (not much use on a concrete pipe), plastic in one form or another, or glass flake coating (which would prove hideously expensive)

Is clay piping a possibility? It is more resistant to erosion than concrete.

 

[cvg]

Coal tar specification, Referenced from Army Corps of Engineers Guide Specs

Drying Time Prior to Immersion

Minimum drying periods after final coat prior to immersion shall be: epoxy systems at least 5 days, vinyl-type paint systems at least 3 days, and cold-applied coal tar systems at least 7 days. Minimum drying periods shall be increased twofold if the drying temperature is below 65 degrees F and/or if the immersion exposure involves considerable abrasion.

Coal Tar-Epoxy (Black) Paint (Formula C-200a)

Mixing

Component B shall be added to previously stirred Component A and thoroughly mixed together with a heavy-duty mechanical stirrer just prior to use. The use of not more than 1 pint of xylene thinner per gallon of paint will be permitted to improve application properties and extend pot life. The pot life of the mixed paint, extended by permissible thinning, may vary from 2 hours in very warm weather to 5 or more hours in cool weather. Pot life in warm weather may be extended by precooling the components prior to mixing; cooling the mixed material; and/or by slow, continuous stirring during the application period. The mixed material shall be applied before unreasonable increases in viscosity take place.

Application

Spray guns shall be of the conventional type equipped with a fluid tip of approximately 0.09 inch in diameter and external atomization, seven-hole air cap. Material shall be supplied to the spray gun from a bottom withdrawal pot or by means of a fluid pump; hose shall be 1/2 inch in diameter. Atomization air pressure shall not be less than 80 psi. High-pressure airless spray equipment may be used only on broad, simply configured surfaces. Brush application shall be with a stiff-bristled tool heavily laden with material and wielded in a manner to spread the coating smoothly and quickly without excessive brushing. The coverage rate of the material is approximately 110 square feet per gallon per coat to obtain 20 mils (dry thickness) in a two-coat system. The paint shall flow together and provide a coherent, pinhole-free film. The direction of the spray passes (or finish strokes if brushed) of the second coat shall be at right angles to those of the first where practicable.

Subsequent Coats

Except at the high temperatures discussed later in this paragraph, the drying time between coal tar-epoxy coats shall not be more than 72 hours, and application of a subsequent coat as soon as the undercoat is reasonably firm is strongly encouraged. Where the temperature for substrate or coating surfaces during application or curing exceeds or can be expected to exceed 125 degrees F as the result of direct exposure to sunlight, the surfaces shall be shaded by overhead cover or the interval between coats shall be reduced as may be found necessary to avoid poor intercoat adhesion. Here, poor intercoat adhesion is defined as the inability of two or more dried coats of coal tar-epoxy paint to resist delamination when tested aggressively with a sharp knife. Under the most extreme conditions involving high ambient temperatures and sun-exposed surfaces, the drying time between coats shall not exceed 10 hours, and the reduction of this interval to a few hours or less is strongly encouraged. Where the curing time of a coal tar-epoxy undercoat exceeds 72 hours of curing at normal temperatures, 10 hours at extreme conditions, or where the undercoat develops a heavy blush, it shall be given one of the following treatments before the subsequent coat is applied:

a. Etch the coating surface lightly by brush-off blasting, using fine sand, low air pressure, and a nozzle-to-surface distance of approximately 3 feet.

b. Remove the blush and/or soften the surface of the coating by wiping it with cloths dampened with 1-methyl-2-pyrrolidone. The solvents may be applied to the surface by fog spraying followed by wiping, but any puddles of solvent must be mopped up immediately after they form. The subsequent coat shall be applied in not less than 15 minutes or more than 3 hours after the solvent treatment.

Ambient Temperature

Coal tar-epoxy paint shall not be applied when the receiving surface or the ambient air is below 50 degrees F nor unless it can be reasonably anticipated that the average ambient temperature will be 50 degrees F or higher for the 5-day period subsequent to the application of any coat.

Safety

In addition to the safety provisions in paragraph SAFETY AND HEALTH PROVISIONS, other workmen as well as painters shall avoid inhaling atomized particles of coal tar-epoxy paint and contact of the paint with the skin.

System No. 7

A special primer shall be used under the coal tar-base paint only if/as recommended by the coating manufacturer. The materials shall be heavily applied by brush or with heavy-duty spray equipment at a coverage rate that will give a minimum total dry film thickness of 20 mils at any point for the completed system. The paint shall not be thinned unless recommended by the manufacturer. If brushed, the final strokes shall be at right angles to those of the preceding coat. Application and drying time between coats shall be as recommended by the coating manufacturer.

When used for concrete exposed to such environments, the surface preparation instructions should include: blast clean to etch surfaces and remove contaminants. Obviously, the use of coatings to upgrade the chemical resistance of concrete has limitations and should not be relied on to solve an exposure situation in which uncoated concrete would be quickly damaged to a gross degree.