METHOD FOR MAKING A CONCRETE BLOCK

METHODE DE FABRICATION D'UN BLOC DE BETON

English Abstract

ABSTRACT
A method for making metal fiber reinforced concrete
block which comprises forming a mix of aggregates to which
metal fibers and the cement are added. Water is added to the
mix to form a mixture which is poured into a mold having two
parallel spaced apart surfaces. A stripper is advanced through
the mold and frictionally engages the inner surfaces of the two
parallel walls and removes the concrete block.

Claims

The embodiments of the invention in which an exclu-
sive property or privilege is claimed are defined as follows:

1. A method for making metal fiber reinforced
concrete block having a pair of opposite parallel surfaces in
which the deviation from parallel throughout the spacing of the
surfaces is not greater than plus or minus 0.032 inches and
when installed in a crib configuration the crib develops 3,000
PSI compressive strength comprising:
a. providing a mold having two parallel, aligned,
spaced apart inner face walls wherein the
deviation from the parallel alignment of the
inner face walls of the mold is not greater than
plus or minus 0.032 inches;
b. providing a mix as follows:
(1) commencing with aggregates;
(2) adding metal fibers to the aggregate and
mixing them with the aggregates; and
(3) then adding cement to the aggregates and
metal fibers:
c. adding water to the mix and forming a mixture;
d. filling a mold with the mixture and compacting it
in the mold to form the concrete block; and
e. advancing a stripper means through the mold
wherein the stripper means frictionally engages
the inner surfaces of the two parallel walls and
removes the concrete block from the mold.

2. A method as recited in claim 1 wherein the
aggregates include:
a. sand having a fineness modulus in a range of 2.75
to 3.00 and which is between 30% and 60% by


- 5 -


weight of the mix; and
b. gravel which is between 25% to 50% by weight of
the mix.

3. A method as recited in claim 1 wherein the
aggregates include:
a. sand having a fineness modulus in a range of 2.75
to 3.00 and which is between 30% and 60% by
weight of the mix; and
b. gravel 1/2 inch by 1/8 inch which is between 25%
to 50% by weight of the mix.

4. A method as recited in claim 1 wherein the
aggregates include:
a. sand having a fineness modulus in a range of 2.75
to 3.00 and which is 44% by weight of the mix;
and
b. gravel which is 36.7% by weight of the mix.

5. A method as recited in claim 1 wherein the metal
fibers are in the range of 0.787 inches to 1.9685 inches in
length and the fibers are between 1% to 4% by weight of the
mix.

6. A method as recited in claim 1 wherein the metal
fibers are in the range of 0.787 inches to 1.9685 inches in
length and the fibers are 1.96% by weight of the mix.



7. A method as recited in claim 1 wherein the metal
fibers are discretely added to the aggregates before the cement
is added to the mix.


- 6 -


8. A method as recited in claim 1 wherein the cement
is type III and between 10% to 16% by weight of the mix.


9. A method as recited in claim 1 wherein the cement
is type III and is 14.8% by weight of the mix.

10. A method as recited in claim 1 including adding
fly ash to the mix which is between 1% to 5% of the weight of
the mix.


11. A method as recited in claim 1 including adding
fly ash to the mix which is 2.4% by weight of the mix.

12. A method as recited in claim 1 including adding a
plasticizer to the mix.

13. A method as recited in claim 1 including adding a
plasticizer to the mix at a rate of 1.75 ounces per 100 pounds
of cement.

14. A method as recited in claim 1 including filling
the mold with the mixture and compacting it in the mold to form
the concrete block, the filling and compacting is accomplished
in a time period of not less than two seconds.

15. A method as recited in claim 1 including allowing
the block which is removed from the mold to set for 1 to 4
hours.

16. A method as recited in claim 1 including applying
steam heat to the block after it is removed from the mold at a
rate of increase of 60° F. per hour until a range of 120°F. to
190° F. is reached and then continuing to apply the stream for
10 hours.


-7-


17. A method as recited in claim 1 including applying
dry heat to the block at 180° F. for 22 hours.

18. A method as recited in claim 1 including removing
heat from the block at a rate of 50° F. per hour.

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Description

The invention relates to a method for making metal
fiber reinforced concrete blocks used for cribbing for mine
roof support systems.
PROBLEM
The mining industry searched for material to replace
conventional wood cribbing to maintain positive roof support
and at the same time reduce the cost of the support system.
Wood has a compressive strength of 500 PSI. The requirements
of the material to replace the wood is that it must: have
greater compressive strength; use less space to obtain greater
support capacity; be non-flammable; be non-biodegradable; avoid
adding to methane generation; be easier to handle and install;
have an indefinite storage lie; and have lower installation
time. To meet these requirements a concrete block was prepared
by the Bureau of Mines. Cribbing made of such block is able to
take slack in the mine roof thereby greatly reducing the roof-
to-floor closure without failure.
Cribs constructed of concrete blocks are cross
stacked without mortar in square or rectangular columns similar
to wooden cribs. The first layer of cribbing is leveled by
locally excavating the floor. The crib is erected to
distribute the load evenly. The outer physical dimensions of
every block must have their contacting surfaces uniform to
prevent stress points from buildiny within any block which
would cause crumbling. Blocks can be made by hand which could
maintain this uniformly however, this would make the cost
prohibitive and limit supply.
The inventors developed a method of making the block
which can be used to mass produce the block and which gives the
necessary compressive strength and unlEormity o the critical

surfaces of the block.
SUMMARY OF THE INVENTION
The invention provides a method for making metal
fiber reinforced concrete block having a pair of opposite
parallel surfaces in which the deviation from parallel through-
out the spacing of the surfaces is not grea-ter than plus or
minus 0.032 inches and when installed in a crib configuration
the crib develops 3,000 PSI compressive streng-th comprising:
a. providing a mold having two parallel, aligned,
spaced apart inner face walls wherein -the deviation from the
parallel alignment of the inner face walls of the mold is not
greater than plus or minus 0.032 inches;
b. providing a mix as follows:
(1) commencing with aggregates;
(2) adding metal fibers to the aggregate and
mixing them with the aggregates; and
(3) then adding cement to the aggrega-tes and
metal fibers;
c. adding water to the mix and forming a mix-ture;
d. filling a mold with the mix-ture and compac-ting it
in the mold -to form the concrete block; and
e. advancing a stripper means through the mold
wherein the stripper means frictionally engages the inner sur-
faces of the two parallel walls and removes the concre-te block
from the mold.
The invention will further be described,by way of
example only, with reference to the accompanying drawing which
shows a perspective view of a mold with a corresponding stripper
member for removing a concrete block from the mold.
The figure shows a mold 10 which has two parallel,
aligned and spaced apart inner face walls 12 and 14 which are
23 inches long and 7 5/8 inches high. The end walls 16 and 18

5~5

are 3 5/8 inches wide inside. The mold 10, therefore, produces
a block 23 inches x 7 5/8 x 3 5/8. The blocks are stacked in
such a manner that the planar dimensions oE 23 inches x 7 5/8
lay flat, one on top of the other. It is -therefore important
that the surface defined by the 23 inches x 7 5/8 inches be
flat and uniform to avoid any irregularities. It is also
important that the thickness of the block, namely the 3 5/8
inches, remain constant to achieve uniformity. To achieve -the
uniform -thickness of the block the deviation from parallel
-throughout the spacing of the walls 12 and 14 should not be
greater than plus or minus 0.032 inches and preferably should
be not more than 0.010 inches.
In making the concrete block a mix is made using:
river sand having a fineness modulus in a range of 2.75 to 3.00
and which is in a weight range of between 30% to 60% by weight
of the entire mix preferably 44% by weight of the mix; river
gravel which is 1/2 inch x 1/8 inch and 25% to 50% by weight of
the entire mix and preferably 36.7% by weight of the mix. These
aggregates are designated as A.S.T.M. C-33. The mix also con-

tains metal fibers which range in length between 20 mm. -to
50 mm. (or 0.7874 inches to 1.9685 inches) with a diameter of




2a.

~2~ 5~

0.50 mm. to 0.80 mm. (or 0.02 inches to 0.03 inches). The
fibers form between 1% to 4% by weight oE the mix and
preferably 1.95% by weight of the mix. These fibers are sold
by Bekaert Steel Wire Corporation, Niles, Illinois under the
mark DRAMIX. It is important to add these fibers discretely by
separating them while adding them to the aggregates and mixing
them before any cement is added. If the cement is added before
or simultaneously with the metal fibers the proper dispersion
of the fibers will not take place. Cement is then added and
forms part of the mix. The cement comprises between 10% to 16
by weight of the mix and peferrably 14.8~ by weight of the
mix. The cement is identified as A~S~ToM~ Type III C-150. Fly
ash is added and forms part of the mix which is l to 5% by
weight of the mix and preferably 2.4~ by weight of the mix.
plasticizer which forms part of the mix is added at a rate of
1.75 ounces per 100 pounds of cement.
Water is added to the mix to form a mixture which i5
poured into the mold 10. The mold 10 is filled and compacted
over a time period not less than two seconds to achieve proper
compaction.
A stripper means 20 having longitudinal faces 22 and
24 frictionally engages the inner surfaces 14 and 12
respectively and removes the cement block. This frictional
engagement is necessary to achieve a uniformity of the
corresponding block faces which are formed by walls 12 and 14
and avoid any protuding fibers on the surface.
After the block is removed from the mold it should
sex between 1 to 4 hours and then steam heat is applied a-t a
rate of increase of 60 F. per hour until a range of 120 F~ to
190 F. is reached. After the desired ternperature is reached
x r r k



~25~85

the steam heat ;s maintained for 10 hours. Then dry heat at
180~ F. is applied for 22 hours. Heat is then removed from the
block at a rate of 50 F. per hour.
This results in a block which has an individual
compressive strength of 5,200 PSI and when installed in a crib
configuration develops 3,000 PSI compressive strength. Each
block weighs approximately 50 pounds and has post-failure
toughness and will not easily crumble.