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Material Specification

The Contractor shall provide thermally stable cable trench backfill around the cables and conduits that meets the following requirements. Backfill can be dry mix or flowable slurry.

The Contractor shall provide the design details of the proposed backfill material including details such as the components in the mix, source quarry/s, particle size distribution, dry density and thermal resistivity curve as described below.

The thermal fill shall surround the cables and conduits such that at least a minimum coverage is achieved as shown on the project trench cross section drawings.

The backfill material shall have the following certified properties:

  • Maximum thermal resistivity of [1.2] k.m/W at full dry-out (0% moisture)
  • Stable and consistent thermal resistivity curve down to 0.5% moisture
  • Non shrink, non-cracking properties after placement and curing, for the life of the cable
  • For direct buried cables, screened to less than 4.75mm to ensure large particles cannot damage cable sheathing
  • Compacted to 98% maximum dry density in several layers to ensure placement of the product matches the conditions under which it was tested. The placement method must prevent damage to cables and conduits.
  • Tested by a NATA registered laboratory using the ASTM D5334-08 and IEEE442 test methods
  • Test sample frequency and sample randomness as specified below
  • Test certificates from a NATA registered laboratory shall be provided for each test sample
  • If flowable, must be vibrated using conventional immersion concrete vibrating equipment operated by trained and experienced operators, for the entire length of the trenches to eliminate air voids. Excess vibration shall be avoided to prevent separation of components.
  • If flowable, average slump shall be 110mm with a range of 90mm to 130mm.