AU2009352672B2 - Geothermal grout and method of using same to install a geothermal heating system - Google Patents

Abstract

A thermally enhanced, single component, geothermal grout is composed of recycled materials including class F fly ash and cement kiln dust and is particularly useful as a grout mixture in filling a borehole in the ground for use in protecting a loop of a geothermal sytem. Additional components of the grout mixture can include a mid-range water reducer and a dry caustic material. The thermally enhanced geothermal grout can comprise a class F fly ash in a range of between approximately 50 to 80% by weight of the grout and cement kiln dust in a range of between approximately 20 to 50% by weight of the grout mixture.

Description

H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 GEOTHERMAL GROUT AND METHOD OF USING SAME TO INSTALL A GEOTHERMAL HEATING SYSTEM BACKGROUND [0001-0002] The present disclosure relates to a grout composition and methods of preparing and utilizing same. More particularly, the present disclosure relates to a novel and unique grout composition made from recycled materials which grout is thermally enhanced and usable as a geothermal material, and especially concerns a method of installing a geothermal heating system. [0003] Typically 4 bags of silica sand material is added to 1 bag of Bentonite material and is added to a water reducing admixture along with one bag of Portland cement for obtaining certain grout mixtures that are commonly used in geothermal applications such as for filling a ground, bore hole containing pipes. [0004] In a geothermal direct exchange (DX) system or a water loop in ground heat pump system, boreholes are put into the ground and commonly range from 100 to 300 feet in depth (or more), are generally 4 to 6 inches in diameter, and include a tubular "loop" which can be made of a copper or PVC material. Generally, one loop is installed for each "ton" of heating and cooling capacity for the building or facility for which the geothermal direct exchange will service. A typical installation is between 4 to 6 loops for an average sized United States household. Once the loop is installed in the ground, the borehole is closed with a grout (i.e., grout material). Approximately 95% of these bore-holes worldwide utilize a Bentonite material mixture with silica sand. The known Bentonite mixed with sand-based mixtures are difficult to maintain flowability while placing, and very difficult to pump through drilling, such as with a contractor's typical on-board mud pump. To pump a Bentonite mixed with sand-based material it requires additional pump equipment for placement of the mixed grout. Notwithstanding, many known grout materials is subject to "bridging" in the borehole (where the material bridges across the hole and there is an empty gap below and/or above the bridged material in the borehole), so laborers are accustomed to adding extra, and too much, water in an effort to make the known grout mixture more flowable. However, few laborers understand the damage that they are creating to the performance of the installed system with every ounce of extra added water - and few homeowners are aware of the resulting degraded geothermal system H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 -2 performance. [0005] Side-by-side testing was conducted of nearly all available Bentonite-based grout mixtures, as well as several other available geothermal grout products and many performance flaws to the known systems was witnessed. The most significant flaw to all bentonite/silica materials is that they all shrink, crack and separate from the loops. They particularly perform poorly in the Vadose Zone which is typically dryer elevations in the ground above the water tables. Because Bentonite does not set, the excess moisture added is absorbed into the surrounding soils and the grout material shrinks dramatically. [0006] The greater the water addition for flowability, the greater the amount of shrinkage and cracking that occurs in the Bentonite-based grout mixtures. These cracks and fissures create air gaps along surfaces of the loop, which affects the heat transfer between the loop and grout thereby effecting the temperature re-generation which is the main performance criteria for in-ground (geothermal) heat pump systems. Additionally, ground water can also fill these voids and further degrade the performance of the heat transfer - particularly near the surface (i.e., at or above the frost line in the ground). Accordingly, these known products typically require multiple components making it further complicated for installers to inventory, haul and deliver such material to the bore hole. SUMMARY [0007] According to the present invention there is provided a method of installing a geothermal heating system, comprising: creating a bore hole in ground with said bore hole being located substantially in a Vadose Zone; inserting at least one heat loop, intended to be in a heat exchange relationship with the ground, in said bore hole; preparing a dry grout mixture including class F fly ash in a range of approximately 50-80% by weight of said dry grout mixture, cement kiln dust in a range of approximately 20-50% by weight of said dry grout mixture, a mid-range water reducer at a rate of up to approximately 8 fluid ounces (approximately 236.6 millilitres) equivalent per hundredweight (50.8 kg) of dry grout mixture; and dry sodium hydroxide at a rate of up to approximately 12 dry ounces (approximately 340.2 grams) per hundredweight (50.8 kg) of H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 -3 dry grout mixture; mixing said dry grout mixture with water to provide a fluid grout mixture; filling said bore hole with said fluid grout mixture about said at least one heat loop; and allowing said fluid grout mixture to harden such that the fluid grout mixture resists shrinkage and provides a hardened grout material; wherein said hardened grout material encapsulates and provides a tight bond around said at least one heat loop to provide improved thermal conductivity between said at least one heat loop and ground in said Vadose Zone. In one embodiment, approximately seventy pounds (70 lbs) of the above dry grout mixture materials may be mixed with approximately five gallons of water to prepare a grout material that can be directly deposited in a borehole for a geothermal application. [0008] Further according to the invention there is provided a geothermal heating system installed according to the method of the invention. [0009] Other objects, advantages, and features of the present disclosure will become apparent to those persons skilled in this particular area of technology and to other persons after having been exposed to the present patent application when read in conjunction with the accompanying patent drawings. BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is a microscopic photograph of the prior art; and [0011] FIG. 2 is a microscopic photograph of Geo SuperGrout

TM

. DETAILED DESCRIPTION [0012] The present disclosure relates to a grout product that was conceived to fill the void in the marketplace for a higher performing grout product that would eliminate most of the problems associated with currently-available grout products. The term "single component grout" is intended to mean a single bag of material that can be mixed with only water to make a finished grout material. The term "Geo SuperGroutTM" as used herein means a grout material prepared in accordance with the present disclosure. [0013] In one exemplary embodiment, the grout material of the present disclosure H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 -4 fills a long-standing market need for a superior functioning borehole grout that has a higher degree of thermal conductivity, but still resists shrinkage and cracking that is prevalent in nearly all currently-available grout products. [0014] In one exemplary embodiment, the a single component grout mixture includes between 50 and 80% by weight of class "F" fly ash and between 20 and 50% by weight of Cement Kiln Dust (CKD). These raw materials are preferably pre-blended and packed into one seventy pound bag. The packaged 70 pound bags are clearly marked to add five (5) gallons of water per 70 pound bag to prepare a predetermined amount of grout material for being added to a borehole. When five gallons of water are added to each seventy pound bag, the yield of finished grout is then approximately seven gallons of liquid grout material. [0015] In one exemplary embodiment of the present disclosure, two other dry chemical components are added to the seventy pound bag of combined fly ash and CKD to aid in the performance of the grout material. [0016] The first added material is added to enhance the flowability of the mixed grout material, and is commonly known as a mid-range water reducer. The preferred mid range water reducer materials are either naphthalene or a lignosulphonate, commonly known as a "lignin". The addition rate of the dry form mid-range water reducer depends upon the physical characteristics of the fly ash component, as the particles of fly ash are typically round, hollow spheres. The addition rate of the mid-range water reducer is up to 8 fluid ounce equivalent per CWT (hundredweight) of dry grout mixture. [0017] The second dry chemical addition to the blended bagged product is used to help artificially "hydrate" the fly ash particles. It is in the form of a caustic known as sodium hydroxide. Because Class "F" fly ash has calcium oxide (CaO) under the hard, non-reactive layer of silica (SiO 2 ), the sodium hydroxide is used to perforate the shell of the fly ash particle, which opens up the calcium oxide (CaO) to hydration, thus hardening the grout when in place. The addition rate of the dry "caustic" is up to 12 dry ounces per CWT (hundredweight) of dry grout mixture. [0018] The grout material of the exemplary embodiment involves a balance of component chemistries. In particular, depending upon the source of the fly ash and the cement WO 2011/034545 PCT/US2009/057638 kiln dust (CKD) (i.e., location of manufacture), the available chemistries of those raw materials sometimes require very little sodium hydroxide, and based on the fineness and particle shape of the fly ash, it may require very little lignin (water reducer). The present disclosure includes the flexibility to determine what amounts of added mid range water reducer is needed based on the manufacturing locations of the fly ash and CKD, so when blended the performance of the resultant grout material is consistent. Accordingly, in one exemplary embodiment, while it will be extremely rare that the first and second chemical additions will ever be at zero on these components, it is statistically possible. [0019] Unlike other grouting materials in the geothermal market, the grout composition of the exemplary embodiments hydrates and hardens within 24 to 48 hours. This is very significant in counteracting the shrinkage occurring in the Vadose Zone, in reducing internal shrinkage of the grout material itself, and improves the stiffening of the material which helps secure the particles in place in the hardening grout material once it begins to hydrate in the borehole. Calcium silicate hydrate (CSH) is microscopic siliceous glass crystals that grow and surround all particles in the paste matrix. The CSH crystals act as both strength and stiffness against shrinkage pressures. As long as there is moisture available, hydration continues in perpetuity and continually reduces permeability of the grout material, as well as continuing to increase the thermal conductivity performance thereof. Because the hydrated grout material is composed of fly ash particles which are silica, the hydration product which is silica, the cement kiln dust (CKD) which is silica, and because the particle sizes are so small and numerous, the thermal conductivity is enhanced because all surfaces of non-similar shapes are touching. [00201 As previously noted, the known typical grout materials made from Bentonite/Silica Sand mixtures are flooded with water to make the jagged rough particles flow around each other. However, the more water added to these known mixtures, the more shrinkage there will be since these Bentonite/Silica Sand mixtures products typically dehydrate, rather than hydrate. The water in such Bentonite/Silica Sand mixtures is absorbed into the surrounding soil, and is most damaging in the Vadose Zone. The Vadose Zone is typically dryer than most ground soils and therefore absorbs water relatively quickly compared to other zones. The result is there will be more severe shrinkage and voids around the loops and the annular space in the borehole -5- WO 2011/034545 PCT/US2009/057638 in the Vadose Zone. A typical Bentonite/Silica Sand mixture is about 1:4 Bentonite to sand ratio. The performance of any geothermal ground system depends upon the transfer of heat from the loop to the surrounding soils and the regeneration of needed loop temperatures as the coolant or water is returned to the pump system for further compressing. When the typical Bentonite/Silica Sand mixture stops being agitated by a mixer or pump such as those used at a work site location where the grout is to be put in the borehole, they quickly settle and separate. When the typical Bentonite/Silica Sand mixture is put in the borehole and is not agitated/mixed, the water rises to the top of the borehole and the heavier Bentonite and silica sand settle at varying levels in the borehole. Accordingly, for typical Bentonite/Silica Sand grout mixtures, shrinkage takes place, and in 24 hours, there is visible evidence of significant shrinkage at the top of the borehole where, sometimes as much as 20-25% of the depth is now void. Additionally, annular shrinkage and cracking near the loops creates problems of performance as noted above. If the mixture of Bentonite and sand would reach marketed thermal conductivity of 1.0 btu/hr-ft-F using ASTM D1554, air voids only measure 0.02 btu/hr-ft-F. Air voids essentially eliminates the ability to transfer the heat from the loops to the surrounding soils. [0021] In contrast, the grout mixture of the exemplary embodiment, (e.g., the Geo SuperGroutTM) comparatively performs very well with very little shrinkage, no cracking and tight bond around the copper loops. [0022] FIG. 1 shows a microscopic photograph of the prior art, Bentonite/silica sand 1:4 ratio (at 40X). FIG. 2 shows a microscopic photograph of a grout mixture prepared according to the present disclosure (e.g., Geo SuperGrout T M (at 40X)). Notice the marble like surface with no pronounced void spacing being observable at 40 times magnification. The black specks in FIG. 2 are carbon from the fly ash. The particles are extremely small and close in around each other giving a dense impervious structure. The density and non-porosity of the grout material as observable in FIG. 2 increases over time as a result of hydration. [0023] Furthermore, the following chart shows thermal conductivity results for values generated by performing ASTM D1554 - a standard test used by all grout manufacturers. The test results shown were taken at the same age in a plastic state at 48 hours. Typically, test values -6- WO 2011/034545 PCT/US2009/057638 will rise as the grout ages; however, the grout mixture of the exemplary embodiment (Geo SuperGroutTM) is the only material stiff enough at 7 days to compare. All Bentonite mixes are still very fluid resulting in lower than promoted values. Material Result 48 hrs Geo Pro Blackhills Bentonite .57 0.40 Btu/hr-ft-F Geo Pro Blackhills Bentonite 1.0 0.55 Btu/hr-ft-F Thermex Bentonite 0.93 0.65 Btu/hr-ft-F IDP-357 Graphite/Bentonite 1.10 Btu/hr-ft-F Geo SuperGrout T M 0.80 Btu/hr-ft-F [0024] Although. the IDP-357 material in the chart above indicates it has a relatively higher thermal conductivity value, the price of IDP-357 material is approximately $90.00 per 501b. bag which makes it too costly to use in geothermal applications where a very significant amount of material is required. [0025] Also, because Geo SuperGrout T M is unlike other geothermal grouting materials and includes cementitious properties, significant amounts of additional calcium silicates are produced upon hydration and hardening of the grout material, according to the exemplary embodiment, which reduces significantly the permeability of hydraulic and non-hydraulic liquids. These silicates in the grout material of the exemplary embodiment provide a perpetual protection of the loop system from acidic soils as the silicates are effective to neutralize the surrounding acidic soil conditions. [0026] The following table describes the grout weight and solids of an grout material example according to the exemplary embodiment (Geo SuperGroutTM). SOLIDS OF FRESH GROUT: Solids by weight of slurry: 62.7% (5.0 gallons of water per 70# bag, OR .595 W/C ratio) WEIGHT PER GALLON OF FINISHED GROUT (US): Dry Mixture: 70.00 lbs Water (5 gal): 41.65 lbs Total: 111.65 lbs Yield: 7.0 Gallons Weight Per Gallon: 15.95 lbs/Gallon. -7- H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 [0027] According to one exemplary embodiment, the GEO SuperGroutTM grout material can be comprised of approximately 60% class F fly ash and approximately 40% CKD. In this formulation, no other products are introduced into the mixture. [0028] According to an another exemplary embodiment, Geo SuperGroutTM grout material can be comprised of the following components: approximately 55% class F fly ash, approximately 45% CKD, approximately 8 dry oz. of NaOH/100 lb. weight of material (where the naphthalene is in dry form which is required to obtain a proper mix for the grout material in dry form), and approximately 6 dry oz. of Naphthalene/100 lb. weight. In the exemplary embodiment, the components are in dry form and placed in 70 lb. bags for shipping and mixing/use purposes. The amount of water to be added and mixed is, in the exemplary embodiment, preferably kept constant- 5 gallons /70 lb. bag of material. However, it should be understood that different size bags and amounts of water can be prepared as may be desired in various applications. [0029] Accordingly, it should be understood that many changes, modifications, variations, and other uses and applications will become apparent to those persons skilled in this particular area of technology and to others after having been exposed to the present patent application. [0030] Any and all such changes, modifications, variations and other uses and applications which do not depart from the spirit and scope of the present disclosure are therefore covered by and embraced within the present disclosure and the patent claims set forth herein below. [0031] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and 'comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. [0032] The reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endeavour to which this specification relates.

Claims (7)

1. A method of installing a geothermal heating system, comprising: creating a bore hole in ground with said bore hole being located substantially in a Vadose Zone; inserting at least one heat loop, intended to be in a heat exchange relationship with the ground, in said bore hole; preparing a dry grout mixture including class F fly ash in a range of approximately 50-80% by weight of said dry grout mixture, cement kiln dust in a range of approximately 20-50% by weight of said dry grout mixture, a mid-range water reducer at a rate of up to approximately 8 fluid ounces (approximately 236.6 millilitres) equivalent per hundredweight (50.8 kg) of dry grout mixture; and dry sodium hydroxide at a rate of up to approximately 12 dry ounces (approximately 340.2 grams) per hundredweight (50.8 kg) of dry grout mixture; mixing said dry grout mixture with water to provide a fluid grout mixture; filling said bore hole with said fluid grout mixture about said at least one heat loop; and allowing said fluid grout mixture to harden such that the fluid grout mixture resists shrinkage and provides a hardened grout material; wherein said hardened grout material encapsulates and provides a tight bond around said at least one heat loop to provide improved thermal conductivity between said at least one heat loop and ground in said Vadose Zone.

2. The method of claim 1, wherein said mid-range water reducer comprises naphthalene.

3. The method of claim 1, wherein said mid-range water reducer comprises a lignin.

4. The method of claim 1, wherein said mid-range water reducer comprises a lignosulphonate. H:\txb\Interwoven\NRPortbl\DCC\TXB\4493973_2.doc - 8/5/15 - 10

5. The method of any one of claims 1 to 4, wherein mixing said dry grout mixture with a predetermined amount of water includes mixing approximately five gallons (approximately 18.92 litres) of water with approximately 70 pounds (approximately 31.75 kilograms) of said dry grout material.

6. A method according to claim 1 and substantially as hereinbefore described.

7. A geothermal heating system installed according to the method of any one of the preceding claims.