Sustainable two-component annular grout composition and method for use with a tunnel-boring machine

Abstract

A method and composition are provided for backfilling the annular gap created as a tunnel boring machine advances through the ground. The fill material is comprised of two components that are combined and mixed together just prior to entering the annular gap. The first component is non-cement slurry consisting of a fluidized bed combustion ash such as coal ash. The second component consists of an alkali silicate such as sodium silicate. Additionally, ordinary Portland cement and/or metakaolin can be added to the grout composition.

Claims

1. A grout composition for filling a tunnel annulus comprising: a. a slurry of fluidized bed combustion ash; and b. an aqueous alkali metal silicate, wherein the ratio of aqueous alkali material metal silicate to fluidized bed combustion ash is in the range of 0.2 to 0.55.

2. The grout composition of claim 1, wherein said aqueous alkali metal silicate is at least one of sodium silicate and potassium silicate.

3. The grout composition of claim 2, wherein said aqueous alkali metal silicate is sodium silicate and the concentration of said sodium silicate ranges from 5-14 wt % of the total grout composition.

4. The grout composition of claim 1, wherein said fluidized bed combustion ash includes calcium hydroxide.

5. The grout composition of claim 1 further comprising ordinary Portland cement.

6. The grout composition of claim 1 further comprising metakaolin or ground granulated blast furnace slag.

7. The grout composition of claim 1, wherein said slurry of fluidized bed combustion ash further includes bentonite, the ratio of bentonite to fluidized bed combustion ash being less than 0.05.

8. A method of grouting a tunnel annulus comprising the steps of: a. mixing a slurry of fluidized bed combustion ash and an aqueous alkali metal silicate; and b. immediately applying said mixture into said tunnel annulus, wherein the ratio of aqueous alkali material metal silicate to fluidized bed combustion ash is in the range of 0.2 to 0.55.

9. The method of claim 8, wherein said aqueous alkali metal silicate is at least one of sodium silicate and potassium silicate.

10. The method of claim 9, wherein said aqueous alkali metal silicate is sodium silicate and the concentration of said sodium silicate ranges from 5-14 wt % of the total grout composition.

11. The method of claim 8, wherein said fluidized bed combustion ash includes calcium hydroxide.

12. The method of claim 8, wherein said slurry further includes ordinary Portland cement.

13. The method of claim 8, wherein said slurry further includes metakaolin or ground granulated blast furnace slag.

14. The method of claim 8, wherein said slurry of fluidized bed combustion ash further includes bentonite, the ratio of bentonite to fluidized bed combustion ash being less than 0.05.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic representation of a tunnel boring machine and the annulus created thereby.

DETAILED DESCRIPTION OF THE INVENTION

(2) While the present invention will be described with reference to the following ingredients, it will be understood by those skilled in the prior art that various changes may be made and equivalents may be substituted without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. It is therefore intended that the present invention not be limited to the particular embodiments disclosed as the best mode contemplated for carrying this invention, but that the invention will include all embodiments and legal equivalents thereof which are within the scope of the appended claims.

(3) The present invention provides a method and composition for backfilling the annular gap surrounding a tunnel produced by a tunnel boring machine. Fluidized bed coal ash that can be used for the compositions and methods for this invention are generated from the burning of coal and/or biomass or waste. The preferred fluidized bed coal ash is crystalline and contains at least 10% calcium oxide. These fluidized bed coal ashes are commercially available in large quantities as by-product from power generation. It is apparent that other types of fluidized bed ash generated from other sources such as agricultural waste or wood can be potential sources of material.

(4) The fluidized bed coal ash is made into slurry using water. Bentonite can be added to the water to improve suspension properties and prevent solids from settling. Bentonite is typically used with cement-based grouts for improved rheology characteristics. The option exists to use other suspension agents or a combination of these suspension agents with bentonite. Examples of suitable suspension agents include polysaccharide-type viscosifiers such as guar gum, welan gum or xanthan gum, as well as other commonly used synthetic viscosifiers such as polyacrylates. The slurry properties can be further improved via the addition of certain admixtures such as retarders and dispersants. These type of admixtures are commonly used in cement-based grouts to improve performance.

(5) The slurry is set using a water-soluble alkali silicate. Soluble silicates are produced with varying degrees of alkalinity as measured by the ratio of SiO.sub.2 to Me.sub.2O where Me is the alkali metal and is most commonly sodium or potassium. Table 1 lists several grades of alkali silicate made by PQ Corporation that can be used for this application. Generally, sodium silicate is the preferred form of alkali silicate for reasons of cost. For cost and to reduce hazardous exposure to high alkalinity, higher ratio sodium silicates have the advantage over low ratio silicates. For geopolymers, the preferred sodium silicate is a low ratio sodium and/or a higher ratio sodium silicate that is combined with sodium or potassium hydroxide.

(6) TABLE-US-00001 TABLE 1 PQ Corporation SiO.sub.2/ Product Name Me.sub.2O % SiO.sub.2 % Me.sub.2O % Solids Potassium Silicates KASIL ® 1 2.5 20.8 8.3 29.1 Liquid KASIL ® 6 2.1 26.5 12.65 39.15 Liquid EcoDrill ® K45 3.0 18.0 6.0 24.0 Liquid KASOLV ® 16 1.6 52.8 32.5 85.3 Hydrous powder KASIL ® SS 2.5 71.0 28.4 99.4 Ground Glass BW ™ 50 1.60 26.2 16.75 42.55 Liquid BJ ™ 120 1.80 23.7 13.15 36.85 Liquid D ™ 2.00 29.4 14.7 44.1 Liquid RU ™ 2.40 33.0 13.9 47.1 Liquid M ® 2.58 32.1 12.4 44.5 Liquid K ® 2.88 31.7 11.0 42.7 Liquid N ® 3.22 28.7 8.9 37.6 Liquid N38 ® 3.22 26.4 8.2 34.6 Liquid EcoDrill S45 Liquid SS ® 20 3.22 75.0 23.3 99.2 Ground glass G ® 3.22 61.8 19.2 Hydrous powder GD ® 2.00 54.0 27.0 Hydrous Powder Metso Beads ® 1.00 47.0 51.0 Granule 2048 Other Silicates Lithisil ® 25 8.2 20.5 2.5 23.0 Liquid lithium silicate EcoDrill ® 1.7 27.9 16.2 45.7 Aqueous AAAS alkali alumino silicate

EXAMPLE 1

(7) A fluidized bed coal slurry is compared against similar formulated slurries using a range of aluminosilicate powder sources set forth in Table 2 below. The class F and C fly ash meet ASTM C618 requirements for use in “Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete” and ground granulated blast furnace slag conforms to ASTM C989, “Standard Specification for Slag Cement for Use in Concrete and Mortar”.

(8) TABLE-US-00002 TABLE 2 Weight Component A Aluminosilicate powder* 460 g Bentonite 10 g Water 750 g Retarder 5 g Component B N ®38 Sodium Silicate 200 g *fluidized bed coal ash, Class C fly ash, Class F fly ash, Ground blast furnace slag, Pumice, Metakaolin

(9) The first set of tests evaluates initial slurry viscosity and then viscosity at 24 hrs using ASTM D6910 (Marsh® Funnel). Later examples determined “Marsh seconds” using a Coulette rheometer and measuring the viscosity at a shear rate of 1000 s.sup.−1. The viscosity reading is converted to “Marsh seconds” using the indicated equation
Marsh seconds=viscosity/slurry density+25
To measure the tendency of slurry to settle solids and segregate (i.e. bleed), the slurries are tested using ASTM C940.

(10) The slurry is mixed with N38® grade of sodium silicate, a widely used grade of sodium silicate for cement based grouts. The concentration of the sodium silicate can range from approximately 5% to 20% weight to weight of hardened material. Gel times are measured by rapidly stirring the mix and recording the time when the mixture rapidly develops viscosity. Compressive strength is measured according to ASTM C109.

(11) The results of these tests are presented in Table 3 below.

(12) TABLE-US-00003 TABLE 3 Typical Fluidized Class C Class F Ground Blast Test Values Bed Coal Ash Fly Ash Fly Ash Furnace Slag Pumice Metakaolin Flow - (slurry A) initial <60 s 38 s 34 s 32 s 34 s 34 s 34 s 24 hr 67 s 34 s 34 s 34 s 35 s 36 s Bleed <10%  1 hr  3.1%  3.8% 16.3%  3.1% ~25% 10.6% 24 hrs 10.0% 28.8% 38.8% 30.0% 53.8% 31.9% Gel Time 8-60 s 36 s >60 min >60 min >60 min >60 min 18 s Compressive Strength  1 hr (24 hr >0.15 MPa 0.28 MPa 0 0 0 0 0.0064 MPa slurry)  1 day >0.7 MPa 1.14 MPa Soft gel Soft gel Soft gel Settled 0.24 MPa

(13) The results of this experiment show that the use of fluidized bed coal ash provides a slurry with properties similar to a cement-based slurry currently used by industry. When the slurry is combined with sodium silicate, it provides the required set time and compressive strength. The results also indicate that this is unique to fluidized bed coal combustion ash. In contrast to ground granulated blast furnace slag the fluidized bed coal ash had a significantly lower level of CaO.

EXAMPLE 2

(14) Using a different source of fluidized bed coal ash, Component “A” was formulated according to Example 1 and set forth in Table 2 above.

(15) Component “B’ was changed to evaluate the impact of different sources of alkali on the setting and material properties when combined with Component “A”. Example 2 compares the commonly used N®38 grade of sodium silicate with 8 M NaOH, 2.64 M NaOH, 1:1 mix of N®38, and a 1:1 mix by weight of 8 M NaOH and 2.64 M NaOH mixed with N®38 sodium silicate. The molarity of 2.64 NaOH was selected to closely match the Na.sub.2O level present in N®38 sodium silicate.

(16) Example 2 demonstrates suitable gel times and compressive strength properties can only be achieved using sodium silicate vs. sodium hydroxide or a mixture of sodium silicate and sodium hydroxide.

(17) TABLE-US-00004 TABLE 4 1:1 1:1 8M 2.64M N38:8M N38:2.64M Run Control NaOH NaOH NaOH NaOH Component A Fluidized 460 g 460 g 460 g 460 g 460 g Bed Coal Ash (g) Water (g) 750 g 750 g 750 g 750 g 750 g Retarder(g) 5 g 5 g 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g 10 g 10 g Component B N ®38 200 g 0 g 0 g 100 g 100 g sodium silicate   8M NaOH 0 g 200 g 0 g 100 g 0 g 2.64M NaOH 0 g 0 g 200 g 0 g 100 g Gel time 39 s >1 hr >1 hr- ~6′:50″ ~12′:30″ Not a Not a sharp set sharp set Compressive strength Str @ 1 hour 0.27 MPa 0 MPa 0 MPa 0 MPa 0 MPa Str @ 1 Day 0 MPa 0 MPa 0.02 MPa 0.01 MPa

EXAMPLE 3

(18) Depending on the end-user there will be a need to customize properties such as gel times and compressive strength. Example 3 demonstrates that minor additions of calcium hydroxide, calcium sulfate dihydrate (gypsum) or ordinary Portland cement. Other sources of aluminosilicate such as ground granulated blast furnace slag and metakaolin may be added to the blend with no adverse effect. The incorporation of these additives can also be used to adjust for the variable nature of fluidized bed combustion ash. In the case of gypsum it was noted that it had a thinning effect on viscosity. Ordinary Portland cement can be incorporated as a minor component to shorten gelation times and further improve compressive strength.

(19) Tables 5a and 5b look at the impact soluble sources of calcium, ordinary Portland cement (OPC) and metakaolin and ground granulated blast furnace slag (GGBFS) on slurry properties, such as gelation time and compressive strength. These materials were added at a concentration of 2.17% and 5% on a weight to weight basis with cement.

(20) TABLE-US-00005 TABLE 5a Run Control Lime Gypsum OPC Metakolin GGBFS Component A Fluidized Bed 460 g 450 g 450 g 450 g 450 g 450 g Coal Ash (g) Ca(OH).sub.2 (g) 0 g 10 g 0 g 0 g 0 g 0 g Gypsum 0 g 0 g 10 g 0 g 0 g 0 g OPC 0 g 0 0 10 g 0 0 Metakaolin 0 g 0 0 0 10 g 0 Ground granulated 0 g 0 0 0 0 10 g blast furnace slag Water (g) 750 g 750 g 750 g 750 g 750 g 750 g Retarder(g) 5 g 5 g 5 g 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g 10 g 10 g 10 g Component B N ®38 sodium 200 g 200 g 200 g 200 g 200 g 200 g silicate Gel time 34 s 18 s 21 s 27 s 29 s 34 s Viscosity Initial viscosity 40 s 41 s 36 s 40 s 40 s 39 s  1 day viscosity 78 s 87 s 49 s 86 s 84 s 81 s Bleed  1 hour 1.1% 1.1%   2% 1.6 s 1.4 s 1.2 s 24 hour 2.1% 1.9% 12.2% 2.5 s 2.2 s 2.6 s Compressive strength Str @ 1 hour 0.17 MPa 0.25 MPa 0.18 MPa 0.20 MPa 0.17 MPa 0.15 MPa Str @ 1 Day 0.81 MPa 0.78 MPa 0.84 MPa 0.93 MPa 0.93 MPa 1.11 MPa

(21) TABLE-US-00006 TABLE 5b Run Control Gypsum Cement Metakaolin Slag Component A Fluidized 460 g 437 g 437 g 437 g 437 g bed coal ash (g) Gypsum 0 23 g 0 0 0 Cement 0 0 23 g 0 0 Metakaolin 0 0 0 23 g 0 Slag (Seattle) 0 0 0 0 23 g Water (g) 750 g 750 g 750 g 750 g 750 g Retarder (g) 5 g 5 g 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g 10 g 10 g Component B N ®38 200 g 200 g 200 g 200 g 200 g sodium silicate Gel time 34 s 16 s 28 s 30 s 32 s Viscosity Initial 37 s 41 s 41 s 41 s viscosity (s)  1 day 51 s 82 s 83 s 81 s viscosity (s) Bleed  1 hour   .sup. 1.6%   .sup. 1.1%   .sup. 1.5%   1% 24 hour  .sup. 12.1%   .sup. 1.9%   .sup. 1.4% 2.3% Compressive strength Str @ 1 hour 0.21 MPa 0.23 MPa 0.25 MPa 0.18 MPa 0.17 MPa Str @ 1 Day 0.96 MPa 1.14 MPa 1.25 MPa 0.99 MPa

EXAMPLE 4

(22) For tunnels that require higher compressive strength values and/or shorter gelation times can be achieved by the addition of Portland cement to the slurry mix. Slurry properties, gel times and compressive values are still in line with cement-based grouts. The addition of ordinary Portland cement is still a minority of the solid component “A”. Example 4 shows that similar loadings of ordinary Portland cement in a slurry composed of ground granulated blast furnace slag or Metakaolin did not yield a product with acceptable 1 hour and 1 day compressive strength. In the case of the metakaolin slurry, it gelled after 24 hours and the ground granulated blast furnace slag had unacceptably high level of bleed.

(23) TABLE-US-00007 TABLE 6 Fluidized Bed Coal Metakaolin + Slag + Control Ash + OPC OPC OPC Component A Fluidized 460 g 345 g 0 0 bed coal ash C (g) Metakaolin 0 0 345 g 0 Slag 0 0 0 345 g OPC 0 115 g 115 g 115 g Water (g) 750 g 750 g 750 g 750 g Retarder (g) 5 g 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g 10 g Component B N ®38 200 g 200 g 200 g 200 g sodium silicate Gel time 41 s 27 s 84 s 19 s Viscosity Initial 36 s 37 s 39 s 33  viscosity  2 day 66 s 56 s gel 39 s viscosity Bleed  1 hour   .sup. 1.2%   .sup. 1.6% <1%   .sup. 4.9% 48 hour   .sup. 6.9%  .sup. 13.2% <1%  .sup. 23.8% Compressive strength Str @ 1 hour 0.16 MPa 0.36 MPa 0.02 MPa 0.02 MPa Str @ 1 Day 0.93 MPa 1.32 MPa 0.05 MPa 0.57 MPa

EXAMPLE 5

(24) Example 5 demonstrates that gel times can also be controlled by adjusting the volume of sodium silicate added to the slurry of fluidized bed coal combustion ash as a slurry of fluidized bed coal combustion ash blended with ordinary Portland cement.

(25) TABLE-US-00008 TABLE 7a 5 wt % 7.5 wt % 14 wt % 19.7 wt % silicate silicate silicate silicate Run dosage dosage dosage dosage Component A Fluidized 460 g 460 g 460 g 460 g Bed Coal Ash (g) OPC 0 0 0 0 Water (g) 750 g 750 g 750 g 750 g Retarder (g) 5 g 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g 10 g Component B N ®38 68 g 100 g 200 g 300 g Sodium Silicate Gel time 4 s 13 s 37 s 52 s

(26) TABLE-US-00009 TABLE 7b 7.5 wt % 14 wt % 19.7 wt % silicate silicate silicate Run dosage dosage dosage Component A Fluidized Bed 345 g 345 g 345 g Combustion Ash (g) OPC 115 g 115 g 115 g Water (g) 750 g 750 g 750 g Retarder (g) 5 g 5 g 5 g Bentonite (g) 10 g 10 g 10 g Component B N ® 38 100 g 200 g 300 g sodium silicate Gel time 6 s 25 s 36 s

(27) The annular grout of the present invention is used in connection with a tunnel boring machine. The properties of the grout such as strength at one hour and gel time are important characteristics for such a grout. There is a need for a quick gel time and relatively high strength at one hour to enable the progress of the tunnel boring machine in the tunneling process to proceed at a commercially acceptable rate.

(28) Although the description above contains certain specificities, they should not be interpreted as limitations to the scope of the invention, but as an example of a preferred embodiment of the same. Therefore, the scope of the present invention must not be determined by the embodiments illustrated, but by the attached set of claims and its legal equivalents.