SUGGESTED SPECIFICATIONS
Grouting Materials for Ground-Loop Heat Exchangers on Closed-Loop Ground Source Heat Pump Systems

THERMALLY ENHANCED BENTONITE GROUT

PART 1 - GENERAL

Thermally-enhanced bentonite grout shall be used to seal and backfill each geothermal bore of the closed-loop ground heat exchanger to ensure proper thermal contact with the earth and to ensure the environmental integrity of each bore. The bentonite base plus thermal enhancement additive; hereafter referred to as the grouting material, shall remain in a plastic state (moldable) throughout the life of the system and shall not generate heat during the hydration process.

The thermal enhancement additive shall be a graphite-based material, high grade silica sand or a combination thereof. If a graphite-based material is selected, it shall be supplied by the grout manufacturer. If high grade silica sand is selected, it shall have a particle distribution and silica dioxide content that has been specified and approved by the grout manufacturer.

No other backfill material shall be accepted.

Manufacturer's published product submittal information sheet(s) shall be submitted with the bid package. Submittals shall include mixing instructions, minimum thermal conductivity performance, maximum permeability, total percent solids, percent active solids, grout weight and unit yield along with verification of the required listing(s).

The grouting material shall be certified and listed according to NSF (National Sanitation Foundation International) to ANSI/NSF Standard 60, "Drinking Water Treatment Chemicals - Health Effects".

Grouting material shall consist of a bentonite base and a thermal enhancement additive. The bentonite base shall be one of the Thermal Grout products supplied by GeoPro, Inc. or a pre-approved equivalent. The thermal enhancement additive shall be either PowerTEC or PowerTECx supplied by GeoPro, Inc. or a high grade silica sand supplied by or pre-approved by the manufacturer of the bentonite base material. Approved suppliers for these materials are GeoPro, Inc. or pre-approved equivalent.

The thermal conductivity of the grouting material must be NaN Btu/hr-ft-°F or greater as determined when tested in accordance to ASTM D-5334, "Standard Test Method for Determination of Thermal Conductivity of Soils and Soft Rock by Thermal Needle Probe Procedure" per International Ground Source Heat Pump Association (IGSHPA) Standard 2B.3.2.1.

Upon request, supplier must be able to produce independent, third party verification of the grouting material's ability to achieve the specified thermal conductivity. The independent company verifying the thermal conductivity of the grouting material shall have a minimum of 5 years of experience in measuring thermal conductivity using the methods outlined in ASTM D-5334.  Date of independent verification testing and reporting shall be no more than three (3) years prior to the date of request from the engineer.

The grout mixture shall have a maximum permeability rate of 1.0 x 10-7 cm/s as determined by ASTM D-5084, "Measurement of Hydraulic Conductivity of Saturated Porous Materials using a Flexible Wall Permeameter, Method C - test with increasing tailwater level", per IGSHPA Standard 2B.3.3, with a 5 psi confinement pressure (to simulate an approximate sample depth of 5 ft).

The reported permeability shall be verified by an independent, lab certified by AMRL (American Association of State Highway & Transportation Officials, Materials Reference Laboratory) and validated by the US Army Corps of Engineers to perform ASTM D-5084 at the time of verification as per IGSHPA Standard 2B.3.4.1. A copy of the report shall be supplied upon request from the engineer. Credentials of the independent laboratory shall also be supplied upon request from the engineer.

Within 4 hours of being pressure pumped in the bore annulus, the installed material will have the consistency of moldable putty.

The bentonite component and thermal enhancement additives of the grouting mix shall be manufactured and packaged such that they are ready for field mixing prior to delivery to the job site. Bulk materials that require on site handling such as grinding, sieving, drying or other processing prior to being mixable will not be accepted.

The grouting material shall be mixed according to manufacturer's written instructions as provided on manufacturer’s product submittal.

Grout material shall be pressure pumped through a one (1) inch, one and one-quarter (1-1/4) inch or a one and one-half (1-1/2) inch nominal diameter tremie pipe and placed in the bore column from the bottom to the top (or from end to end in horizontally-bored applications). Grouting process shall conform to the manufacturer's instructions and "Grouting for Vertical Geothermal Heat Pump Systems -- Engineering Design and Field Procedures Manual", as published by the IGSHPA, Oklahoma State University (OSU), 2000. The grout column shall be brought to ground level to ensure complete fill of the bore annulus.

3.3 INSPECTION

Settling may occur after initial placement of the grout material. The contractor shall monitor each borehole for a period of 24-48 hours and continue adding grout as required.

During installation, regular verification of the grout mixture shall be carried out through sampling. All grout samples shall be collected in the field per manufacturer guidelines.

At minimum, the collection of three samples is required for this project. Samples shall be taken once at the beginning of the project, once at approximately one-third to completion, and finally at approximately two-thirds to completion. Once collected, the samples shall be sent to the manufacturer, or to an independent lab for testing in accordance with ASTM D-5334 to measure thermal conductivity and verify that it meets minimum requirements.

In the event that the analyses indicate a thermal conductivity value below the minimum specified value, corrective action shall be taken to increase thermal conductivity to the minimum specified requirement. A written report will be submitted defining corrective action taken.