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Insulating Underground Pipe and Ducting with Perlite Insulating Concrete

Lightweight perlite insulating concrete can play a multiple role in underground pipe and duct installations. In addition to providing quality thermal insulation, perlite concrete insulation also can serve as a supporting envelope. This latter advantage is of special importance when pipe or ducts are laid under roadways, parking lots or other areas subject to traffic. Perlite concrete pipe insulation provides a monolithic (seamless) insulation for the length of a pipe or duct. Additionally, perlite insulating concrete is permanent, fire-proof, rot proof and vermin proof.


Where there is stable or compacted soil, pipe or ducting may be supported on precast perlite concrete support blocks in the bottom of a trench and a perlite concrete cover poured into the trench area. Depth of concrete cover and pipe spacing will depend on the size of pipe or duct to be insulated as well as operating temperatures. The perlite cover should be waterproofed by encasing the perlite concrete with a polyvinyl chloride (PVC) membrane. Internal vent drain lines may be required. If operating temperatures are in excess of 800 F (427 C). Aluminite cement should be employed. Prior to pouring concrete, pipe and ducts should be wrapped with a parting material such as was coated corrugated paper to prevent the perlite concrete from adhering to the pipe and to permit free longitudal movement of the pipe as a result of temperature changes.


When disturbed soils are encountered in the trench area, a perlite concrete base pad should be poured first. Precast perlite concrete support blocks are then placed on top of the base pad and the installation proceeds as for installations in compacted soils


Expansion loops and ells must be carefully designed as there will be pipe or duct movement in the perlite concrete insulation as a result of temperature changes. Depending on the design, metal pan blockouts can be used to isolate the pipe or ducts from the insulation in those areas where there is excessive movement. Double wraps of 1.5 inch (4 cm) foil faced fiberglass may also be used to accommodate pipe movement at elbows, expansion loops, expansion "Z's" and U-bends.


Where there is heavy traffic loading on the soil above an insulated pipe as when running a pipe under parking lots or highways, the designer should take this loading into account.

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed.  Your supplier may be able to provide you with more precise data.  Certain compositions or processes involving perlite may be the subject of patents.
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