Thermal Grouting
Been There. Grouted That.™
Thermal grouting is critical for maintaining ampacity of underground cables. CJGeo performs thermal grouting for trenchless electrical installations throughout the United States. Our experience designing and installing thermal grout ranges from floating drilling fluid out of HDD shots to annular grouting on bored crossings and microtunnels.
CJGeo generates and places more than 100,000 cubic yards of grout every year throughout the country.
Typical Thermal Grouting Mix Design
CJGeo has developed multiple thermal grout mixtures. Each has been tested by GeoTherm, which is a standard industry requirement. Thermal grouts are typically specified by a maximum thermal resistivity, which is measured in rho. Generally, as grout dries, rho decreases, as the evaporating water leaves small voids. These voids are filled with air, which increases thermal resistivity.
Maximum allowable thermal resistivity values vary by utility owner. Most have a maximum allowable thermal resistivity at 0% moisture content, often accompanied by a maximum value at a single digit moisture content such as 4% or 6%. Occassionally, the critical moisture level is used as a specifying point. Critical moisture level is the intercept of the two distinct slopes in a dryout curve.
CJTherm is available in both high strength and low strength blends.
Conduit Buoyancy Considerations
Carrier buoyancy is a function of the grout density. Thermal grouts are inherently heavy, due to their high silica content and nominal air content.
Buoyancy management is typically done with water filling and designing conduit bundles tolerant of some uplift. Designing conduit systems tolerant of uplift during grouting is critical.
Relative Grouting Pressures
CJGeo's thermal grout mixtures are designed with flow cone times of less than 45 seconds. This very high fluidity, but with very low water:cement ratios ensures stability during placement, and very low placement pressures. Placement pressures during thermal grouting operations are typically measured with in-annulus pressure/thermistor cells. As distance and head increase, pressure increases. This pressure can be managed by installing multiple sacrificial injection lines in the annulus.
CJTherm Generation
CJGeo's CJTherm materials are available in a number of ways. Low thermal resistivity, low heat of hydration, high fluidity and dimensional stability are all highly dependent on aggregate source & composition. Depend on where your project is, CJGeo can manufacture and install CJTherm through the following channels/formats:
- ready mix - in some markets, aggregate available through the ready mix supply chain is suitable for thermal grouting
- bulk pneumatic - CJGeo can ship bulk pneumatic thermal grout throughout the United States
- super sack - CJGeo can ship super sacked thermal grout throughout the United States
If not working in an area where ready mix produces have access to suitable aggregate, CJGeo uses specialized on-site batching equipment to mix and place the CJTherm onsite.
Speak With An Expert
Facing a thermal grouting challenge? CJGeo consults on and performs thermal grouting throughout the United States.
Kirk Roberts | Principal, Strategic Projects | 804-396-4845.
