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Insulating Concrete for Underground Pipes and Ducting

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 can also 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 dipe or duct. Additionally, perlite insulating concrete is permanent, fire-proof, rot-proof and vermin-proof.

Stable or Compacted Soils

Where there is stable or compacted soil, pipe 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 800oF (427oC) Aluminite cement should be employed. Prior to pouring concrete, pipe and ducts should be wrapped with a packing material such as coated corrugated paper to prevent the perlite concrete from adhering to the pipe and to permit free longitude movement of the pipe as a result of temperature changes.

Disturbed or Loose Soils

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 or Ells

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 (4cm) foil faced fibreglass may also be used to accommodate pipe movement at elbows, expansion loops, expansion "Z"s and U-bends.

Heavy Traffic Areas

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