CA2026631C - Method for sealing mine workings - Google Patents

Abstract

Mine workings such as concrete block stoppings are sealed under wet or humid conditions by coating them with an aqueous sealant composition comprising a water soluble alkali metal silicate, a curing agent for the alkali metal silicate and a filler which is substantially non-reactive with the alkali metal silicate. The method provides an impervious sealant coating which prevents penetration of fluids or dust through the workings.

Description

a .~.,. . -3 a' 1 j S) METHOD FOR SEALING MINING WORKINGS
This invention relates to a method for sealing mine workings such as ventilation stoppings, other seals for example explosion proof stoppings, and roadway surfaces.
It is known to use stoppings to control and direct flow of air through underground mine areas and to seal off sections of particular areas in the mine to enable the maintenance of a proper atmosphere affording the least hostile conditions under the circumstances to miners or workers in such sections or areas.
The method is particularly useful for sealing mine stoppings formed from concrete blocks, and it is in the context of that application that the method will be described.
These stoppings are usually made airtight by applying a non-porous coating or layer to the surfaces of the blocks and to the various areas of abutment.
The usual technique involves the trowelling over the surfaces and abutment areas with cementitious mortars based on Portland cement/sand powder blends mixed with water.
Such cementitious mortars are generally satisfactory to reduce or prevent unwanted airflow.
Thus, the stoppings as covered with the cementitious mortar considerably reduce the quantity of undesirable air flowing into a sealed off surface. Stoppings are G'~ ~~. ...'2 .-z ~ i .#
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for example walls or partitions used in underground room and pillar mines. They are strategically constructed to direct fresh air into areas of the mine required by law to be properly ventilated.
Conventional stoppings are constructed, for example, from hollow concrete block either dry stacked or wet laid, i.e., cemented in place. Without adequate sealing, such conventional stoppings leak large amounts of air through the porous block and especially around perimeters, where sealing is difficult. Also, these stoppings may also be of metal or other materials.
Accordingly, the elimination of leakage from stoppings is essential for safe Working. Also, the elimination of stopping leakage considerably cuts power costs for ventilation.
Cementitious mortars usually suffer from disadvantages in that they have to be mixed with water before use, they are applied by hand, and they produce a rigid coating. Silicate based sealants have been used instead of cementitious mortars because they do not suffer from these disadvantages but the silicate based sealants used hitherto will not cure under wet conditions or conditions of high humidity.
It has now been found that mine stoppings and other mine workings can be sealed under wet or humid conditions using an aqueous curable sealant composition C, ~ !~ ~ is i a r ...s V ib - 3 ' FT24 comprising an alkali metal silicate, a curing agent for the alkali metal silicate, and a substantially non-reactive filler.
According to the invention there is provided a method for sealing mine workings comprising providing (a) a water soluble alkali metal silicate, (b) a water soluble or water dispersible curing agent for the alkali metal silicate and (c) a filler which is substantially non-reactive with the alkali metal silicate, mixing components (a), (b) and (c) together with water to form a sealant composition, applying the sealant composition as a coating to the workings, and permitting the sealant composition to cure to form an impervious sealant coating.
The water soluble alkali metal silicate may be for example sodium or potassium silicate and is preferably a sodium silicate having a Si02 to Na20 mole ratio of from 2:1 to about 4:1 and a solids content in the range of 30 to 40% by weight, more preferably about 36% by weight.
The water soluble or water dispersible curing agent may be any weak acid or acid salt or one or more esters which hydrolyse to release an acid. Suitable esters include esters of polyhydric alcohols such as glycerol or ethylene glycol, for example include diacetin, triacetin, ethylene glycol monoacetate or ethylene glycol diacetate and blends of commercially available dibasic esters known as D.B.E. comprising the methyl esters of adipic, glutaric and succinic acids.

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The fillers used in the sealant should be substantially non-reactive and compatible with the water soluble silicate for long-term shelf life. Such fillers may comprise mica, clay or a fibrous material such as cellulose fibre or glass fibre.
The sealant composition may also contain a pigment such as titanium dioxide.
In order to aid dispersion of the curing agent in the sealant composition the composition may also contain a polyhydric alcohol, such as glycerol, ethylene glycol or propylene glycol with which the curing agent is predissolved in water, or an emulsifier which is premixed with the curing agent and water to produce an emulsion.
The aqueous sealant composition preferably contains 10% to 85%, more preferably 50% - 70% by weight alkali metal silicate, 0.7% to 10%, more preferatly 3.5% to 5% by weight of water soluble or water dispersible curing agent, and 2% to 50%, more preferably 35% to 40% by weight substantially non-reactive filler.
Components (a) and (c) of the sealant composition used in the method of the invention can be premixed with water to provide a ready-to-use composition of extended shelf life of at least six months and as long as one year.

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The sealant composition can readily be applied by spraying on to underground mine workings under wet conditions or under conditions of high humidity. The sealant composition will gel in approximately 15 to 30 minutes after application but the time which elapses before gelling takes place is sufficient to enable hoses through which the sealant composition has been transported to be cleaned after use before residual material in the hoses hardens.
Curing of the sealant composition will usually take place within 8 hours under normal mine conditions and air and moisture resistance properties will usually develop in about 24 hours.
The sealant compositions used in the present invention are to be contrasted with the prior art ready-made sealants which function by evaporation of water and therefore, need dry conditions before setting hard. The sealant used in the present invention is capable of setting in a predetermined time in wet, humid or dry conditions.
When the method is used to seal mine stoppings in the form of porous concrete blocks air loss through the block surfaces is prevented. Prevention of air loss is achieved when the porous blocks are coated on one or both surfaces, as well as in areas of abutment or around perimeters where sealing is difficult. Thus, with the prevention of air loss, there is a corresponding improved efficiency of ventilation equipment.

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The method of the present invention in the course of sealing also provides a valuable fireproof barrier.
The following examples will serve to illustrate the invention:-A sealant composition is prepared in two parts, part A containing components (a) and (c), and part B containing component (b) as set out below:-PART 'A' PARTS
BY WEIGHT
Sodium Silicate (Si02/Na20 = 3.22) 66 Water 23 Kaolin 4 Cellulose Fibre Titanium Dioxide Mica ~~~~~i3~

s PART 'B' PARTS
BY WEIGHT
Water Tergitol XH (Nonionic surfactant) Triacetin 62 The kaolin in the above formula is a filler that adds consistency, trowellability and thixotropy (false body) to the final product.
Part A of the above-noted example also includes cellulose fibre which is another filler.
There is also a minor amount of titanium dioxide that acts as a coloring agent so that the set coating on the stoppings has some reflectant properties.
The final component in Part A is mica which is a good film former and adds trowelability and thixotropy to the Part A mix.
In the Part B mix, the Tergitol XH is a true emulsifier for the triacetin so that it readily blends with the water.
Each of the Parts A and B are prepared separately by simply adding the various ingredients to a mixing vessel and mixing at room temperature. Sodium ' FT24 silicate is readily soluble in the water and then the outer components of Part A are added in the order shown in the above example, with sufficient mixing.
To the same effect is Part B wherein the Tergitol XH is added to the water and then the triacetin is added, with the Tergitol XH acting as an emulsifier.
In use, the Part A and Part B components are brought together in a volume ratio of 20 parts of A to 1 part of B. On a weight basis, this is 26 parts by weight of Part A to 1 part of Part B. After adequate mixing in a tank, the slurry (which is reasonably pumpable), is forced through hoses and through a spray head on to the stopping or concrete block surfaces and abutment areas in order to provide a continuous coating. This coating sets in 30 minutes where the weight ratia of Part A to Part B is 26:1 and the temperature is 70°F.
In a second blend, the ratio of Part A to Part B on a volume basis is 10:1 to 13:1 parts by weight and the setting time is 17 minutes at 70°F. In a third blend where the ratio of Part A to Part B is 17:1 on a volume basis and 22:1 on a weight basis, the set time is 23 minutes at 70°F. In the event the temperature is lowered, the set time will be longer.
The field test case histories of Example 3 further illustrate the use of varying amounts of Part A
and Part B.

- g - FT24 The fillers used in the sealant should be non-reactive and compatible with the water soluble silicate for long term shelf-life, In another embodiment of the invention Part 'A' and Part 'B' of the above Example 1 are formulated as follows:
PART °A' PARTS
BY WEIGHT
Sodium Silicate (Si02/Na20 = 3.22) 56 Water 6 Kaolin Clay 37.5 Alkali Resistant (AR) Glass Fibre 0.5 PART 'B' PARTS
BY WEIGHT
Triacetin g0 Propylene Glycol l0 It is contemplated that Part B of Example 2 can be used with Part A of Example 1 and vice versa.

(a) Blending Part 'A' with Part 'B' at a volume ratio of 20:1 results in a gel time of 22 minutes at 70°F.
(b) Blending Part 'A' with Part 'B' at a volume of ratio of 10:1 results in a gel time of 20 minutes at 70°F.
In the Part B of this example, there is no emulsifier the emulsifier being replaced by propylene glycol, Thus, there is a true solution. This is the preferred formulation. This formulation has long shelf life and stability, and added thixotropic properties in the mixed product.

FIELD TEST CASE TiISTORIES
TEST 1 Test site - Greenwich Collieries (#580 Portal) Penn. Relative Humidity 100%. Mine Temperature 65°F. (Water dripping from roof) Mine Temperature - 60°F.
A total of 400 lbs. of Part A mine sealant were blended with 18 pounds of Part B. The resulting formulation was sprayed on to both sides of a wet hollow concrete block stopping, measuring 6 foot by 16 feet. The spray unit consisted of a progressing cavity pump feeding through 50 feet of discharge hose to a spray nozzle.

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Within 50 minutes after spraying the material had set hard over the total surface of stopping which included a section on the backside subjected to running water.
TEST 2 Test Site: Beth Energy Underground Mine #81 Summersville, West Virginia The mine conditions were 100% relative humidity and 64°F. A total of 400 lbs. of Part A mine sealant were blended with 18 pounds Part B. The resulting composition was sprayed on to concrete block stoppings of dimensions 8 ft. x 20 ft. and 5~ ft. x 20 ft.
respectively. Both these were old coated stoppings, badly cracked, having been subjected to roof and floor convergence, and leaking considerable amounts of air. Within one hour of spraying the treated stoppings were set hard and no leakage of air detectable.
TEST 3 Test Site: Southern Ohio Coal Company Miegs #1 Mine, Athens, Ohio Mine Conditions - 90% + Relative Humidity Temperature 62°F
500 lbs. of formulation were sprayed at 17 to 1 volume ratio of Part A and Part B of the mine sealant system. Material applied to four stopping Wads of size 6 ft. x 18 ft., and one battery c~ax~ing station approximately 6 ft. x 12 ft. on both sides. Total elapsed time to spray all areas - 35 minutes. After 45 minutes all stoppings were set dry.
TEST 4 A test conducted by the National Concrete Masonry Association indicated that a coating of 1/8 inch thick when applied to a dry stacked block stopping provides equivalent strength compared to cement mortared concrete block.
This meets the MINE SAFETY AND HEALTH
ADMINISTRATION (MSHA) requirements for coatings applied as stopping compounds underground.
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Claims (12)

1. A method of sealing of mine stopping utilizing non-reactive fillers and optionally associated fibers, said method being useful in the sealing of mine stoppings, under wet or humid conditions, said method comprising providing an aqueous curable sealant composition having good shelf life, said composition having first and second components, said first component comprising on a total weight basis (a) from about 10 to 85% by weight an alkali metal silicate solution and (b) about 2 to about 50% of at least a one non-reactive filler, said, second component being essentially a solution on a total weight basis of from about 0.7% to about 10.0% of a water soluble or water miscible reactant for said alkaline metal silicate, bringing said two components together with sufficient mixing to form a sealing composition, applying said composition in a surface coating to said stoppings and permitting said compositions to set in a chemical reaction to initiate gel formation, said chemical reaction involving said alkali metal silicate and said water miscible reactant, while being exposed to wet or humid conditions to form an impervious sealant coating imparting structural strength and also preventing penetration of air and dust through said stoppings.

2. The method of claim 1 wherein said alkali metal silicate is sodium silicate.

3. The method of claim 2 wherein said sodium silicate has a SiO2 to M2O mole ratio of from 2:1 to about 4:1 (wherein M represents the alkali metal) and said silicate solution has a solids content in the range of 10 to 60%
by weight preferably 30 to 40% by weight.

4. The method of claim 2 wherein said reactant is triacetin.

5. The method of claim 1 wherein said reactant comprises commercially available dialkyl esters of the formula R1OOC(CH2)n,COOR2 wherein R1 and R2 may be the same or different alkyl carbon atoms of 1 to 20, preferably 1 to 6 and n is 2, 3 or 4, said ester being selected from the group consisting of dimethyl succinate, dimethyl glutarate, dimethyl adipate, glycol esters and blends thereof.

6. The method of claim 4, including an emulsifier.

7. The method of claim 1 wherein said fillers are at least kaolin clay.

8. The method of claim 1 wherein said fibers are at least cellulose fiber.

9. The method of claim 1 wherein said fillers are at least titanium dioxide.

10. The method of claim 1 wherein said fillers are at least mica.

11. The method of claim 1 wherein said fibers are at least glass fiber.

12. The method of claim 5 wherein the glycol esters are selected from the group consisting of ethylene glycol diacetate, diacetin and triacetin.