Thixotropic Thermal Grout (No-Set™) for High Voltage Electrical Conduits
Reliability on Conventional Methods
Prior to the development of No-Set™ Thermal Grout, the underground electrical industry had to rely on a conventional cementitious thermal grout to dissipate heat from the energized high voltage cables.
Cementitious grout naturally sets up and hardens over a relatively short period of time, thereby permanently locking the conduit or cable in place. Furthermore, due to the short setup time for the cement-based grout, the only viable method of installation was by way of tremie lines pulled in at the same time as the cable conduits. This standard methodology required multiple expensive spacers to keep the cable conduits in position while the grout was pumped under high pressure from the surface. Electrical engineers regularly questioned the degree of “fill” using tremie injection and the corresponding potential development of “hot spots”.
Conventional vs. Unconventional – Is there a better way?
The idea for No-Set™ was developed during a large electrical project in St. Lucie, FL in 2015. Mears Horizontal Directional Drilling experts, Steve Meaders, Special Projects Manager and Ron Halderman, P.E., Special Projects Director, discussed the idea of a better solution for their electrical clients.
The project (referred to as the “Reliability Project”) required the installation of two parallel 32-in. 7,020-ft bores 60-ft below river bottom. The 32-in. Fusible PVC casings housing four 10-in. and two 3-in. HDPE conduits. Mears’ contract for FPL’s St Lucie FL project required Mears to thermally grout the annular space around the HDPE electrical cable conduits and inside the 7000-ft long PVC casing installed under the river. Due to time restrictions, logistical issues and working constraints, the Mears’ team realized it was not practical to complete a conventional tremie grouting program with the standard cementitious grout product; therefore, the solution to create a contingency material was planned and No-Set™ was developed.
No-Set™ – What is it?
The newly developed grouting compound, referred to as No-Set™, is non-cementitious; rather, it relies on thixotropy (or more likely pseudo plasticity due to the quickness of response) to fully entrain sand grains in a homogeneous slurry during the interval from flow to static conditions.
As a result its desired thermal conductivity properties remain constant throughout repeated fluctuations of movement and no movement and are therefore not time-dependent. It furthermore allows 100% “fill” around the conduits or cable itself to be reasonably hypothesized. Installation of No-Set™ Thermal Grout, unlike cementitious grout, can now be segregated from other activities; it no longer creates a critical path.
No-Set™ – Application Benefits
Our standard drilling fluids (bentonite plus fresh water) are thixotropic; i.e., the property exhibited by certain gels of becoming fluid when stirred or shaken and returning to the semisolid state upon standing. When gelled under static conditions these fluids have the ability to entrain larger materials, such as sand, by becoming more viscous and thereby inhibiting the sand from quickly settling out of suspension.
Our objective was to develop a fluid/gel with enhanced thixotropy that would completely stop the sand from settling during a static state.
The thixotropic thermal grout had to be able to be easily prepared on a construction site, the components had to be easily procured, and quality control had to be consistently reproducible within required specifications.
No-Set™ – U.S. Trademark
No-Set™ is trademarked as a grouting compound and a chemical additive for horizontal directional drilling fluids.