Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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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
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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
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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:-
EXAMPLE 1
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
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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
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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.
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The fillers used in the sealant should be non-
reactive and compatible with the water soluble silicate
for long term shelf-life,
EXAMPLE 2
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.
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(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.
EXAMPLE 3
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
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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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