GB2139547A

GB2139547A - Method for making concrete blocks

Info

Publication number: GB2139547A
Application number: GB08312641A
Authority: GB
Inventors: William L Harbaugh; Raymond S Smetana
Original assignee: Burrell Construction and Supply Co
Current assignee: Burrell Construction and Supply Co
Priority date: 1983-05-07
Filing date: 1983-05-07
Publication date: 1984-11-14
Also published as: GB8312641D0; GB2139547B

Abstract

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

Description

SPECIFICATION Method for Making Concrete Blocks The invention relates to methods for making metal fibre reinforced concrete blocks used especially but not exclusively for cribbing for mine roof support systems.

According to the invention there is provided a method for making a metal fibre reinforced concrete block having a pair of opposite substantially parallel surfaces which method includes: a. filling a mould having two parallel, aligned spaced apart inner face walls wherein the deviation from the parallel alignment of the inner face walls of the mould is not greater than plus or minus 0.032 inches with a mixture of water and a mix prepared by (1) commencing with aggregates; (2) adding metal fibres to the aggregate and mixing them with the aggregates; and (3) adding cement to the aggregates and metal fibres and compacting the mixture in the mould to form the concrete block; and b. advancing a stripper means through the mould wherein the stripper means frictionally engages the inner face walls and removes the concrete block from the mould.Optional and preferred features are described in the claims and description with reference to the drawing.

The concrete block produced can have a considerable compressive strength; greater support capacity for a given volume of support material, be non-flammable, non-biodegradable, generate no methane, be easy to handle and install, and have a long storage life and short installation time.

The blocks permit siack in the mine roof to be taken, reducing the roof-to-floor closure.

Cribs constructed of the concrete blocks of the invention can be cross stacked without mortar in square or rectangular columns similar to wooden cribs. The first layer of the cribbing can be levelled by locally excavating the floor. The crib can be erected to distribute the load evenly. The outer physical dimensions of every block should have uniform contacting surfaces uniform to prevent stress points from building up within any block which can give rise to crumbling.

The method of making the block permits the block to be mass produced giving a high compressive strength and uniformity of the critical surfaces of the block.

Drawings The figure shows a perspective view of a mould with a corresponding stripper member for removing a concrete block from the mould.

Description with Reference to the Drawing The figure shows a mould 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 (1 inch=2.54 mm). The end walls 16 and 1 8 are 3 5/8 inches wide inside. The mould 10, therefore, produces a block of 23 inchesx 7 5/8x3 5/8. The blocks are stacked in such a manner that the planar dimensions of 23 inchesx7 5/8 lay flat, one on top of the other. The surface defined by the 23 inchesx7 5/8 inches should be flat and uniform avoiding any irregularities. The thickness of the block, namely the 3 5/8 inches, should 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 not be 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 from 2.75 to 3.00 and which is in a weight range of from 30% to 60% by weight of the entire mix preferably 44% by weight of the mix; river gravel which is 1/2 inchxl/8 inch and from 25% to 50% by weight of the entire mix and preferably 36.7% by weight of the mix. These aggregate are designated as A.S.T.M. C-33. The mix also contains metal fibres which range in length from 20 mm to 50 mm. (or 0.7874 inches to 1.9685 inches) with a diameter of from 0.50 mm to 0.80 mm (or 0.02 inches to 0.03 inches).

The fibres form from 1% to 4% by weight of the mix and preferably 1.96% by weight of the mix.

Suitable fibres are sold by Bekaert Steel Wire Corporation, Niles, Illinois under the mark DRAM IX. These fibres should be added 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 fibres the proper dispersion of the fibres may not take place.

Cement is then added and forms part of the mix.

The cement comprises from 10% to 1 6% by weight of the mix and preferably 14.8% by weight of the mix. The cement is identified as A.S.T.M.

Type III C-1 50. Fly ash is added and forms part of the mix which is from 1% to 5% by weight of the mix and preferably 2.4% by weight of the mix. A plasticizer which forms part of the mix is added at a rate of 1.75 ounces (one ounce=28.35 g) per 100 pounds (1 pound=0.4536 kg) of cement.

Water is added to the mix to form a mixture which is poured into the mould 10. The mould 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 fibres on the surface.

After the block is removed from the mould it may be set from 1 to 4 hours and then steam heat be applied at a rate of increase of 600F. per hour until a range of from 1200F. to 1 900F. is reached.

After the desired temperature is reached the steam heat is maintained for 10 hours. Then dry heat at 1800 F. is applied for 22 hours. Heat is then removed from the block at a rate of 500 F.

per hour.

This result in a block which has an individual compressive strength of 5,200 PSI (one pound per square inch=6897 Pascal) 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.

Claims

1. A method for making a metal fibre reinforced concrete block having a pair of opposite substantially parallel surfaces which method includes: a. filling a mould having two parallel, aligned, spaced apart inner face walls wherein the deviation from the parallel alignment of the inner face walls of the mould is not greater than plus or minus 0.032 inches with a mixture of water and a mix prepared by (1) commencing with aggregates; (2) adding metal fibres to the aggregate and mixing them with the aggregates; and (3) adding cement to the aggregates and metal fibres and compacting the mixture in the mould to form the concrete block; and b. advancing a stripper means through the mould wherein the stripper means frictionally engages the inner face walls and removes the concrete block from the mould.

2. A method according to claim 1 in which the aggregates used in preparing the mix include: a. sand having a fineness modulus in a range from 2.75 to 3.00 and which is from 30% and 60% by weight of the mix; and b. gravel which is from 25% to 50% by weight of the mix.

3. A method according to claim 2 in which the gravel is 1/2 inch by 1/8 inch.

4. A method according to any of the preceding claims in which the aggregates used in the mix include: a. sand having a fineness modulus in a range of from 2.75 to 3.00 and which is substantially 44% by weight of the mix; and b. gravel which is substantially 36.7% by weight of the mix.

5. A method according to any of the preceding claims in which the metal fibres used in preparing the mix are in the range of from 0.787 inches to

1.9685 inches in length and the fibres are from 1% to 4% by weight of the mix.

6. A method according to claim 5 in which the metal fibres are substantially 1.96% by weight of the mix.

7. A method according to any of the preceding claims in which the mix is prepared by adding the metal fibres discretely to the aggregates before the cement is added to the mix.

8. A method according to any of the preceding claims in which the mix is prepared using type III cement forming from 10% to 16% by weight of the mix.

9. A method according to claim 8 in which the cement used in the mix is substantially 14.8 by weight of the mix.

10. A method according to any of the preceding claims in which the mix prepared also has added to it fly ash at a level of from 1% to 5% by weight of the mix.

11. A method according to any of the preceding claims in which the fly ash is substantially 2.48% by weight of the mix.

12. A method according to any of the preceding claims in which plasticizer is added to the mix.

1 3. A method according to claim 12 in which the mix includes added plasticizer at a level of substantially 1.75 ounces per 100 pounds of cement.

14. A method according to any of the preceding claims in which the mould is filled with the mixture and the mixture is compacted in the mould to form the concrete block in a time period of not less than two seconds.

1 5. A method according to any of the preceding claims which includes allowing the block which is removed from the mould to set from 1 to 4 hours.

16. A method according to any of the preceding claims which includes applying steam heat to a block after it has been removed from the mould at a rate of increase of substantially 600 F.

per hour until a range of from 1200F. to 1 900F. is reached and then continuing to apply the steam for substantially 10 hours.

17. A method according to any of the preceding claims which includes applying dry heat to the block at substantially 1800 F. for substantially 22 hours.

1 8. A method according to any of the preceding claims which includes removing heat from the block at a rate of substantially 500 F. per hour.

1 9. A method for making a metal fibre reinforced concrete block substantially as described by reference to the drawing.

20. A concrete block produced by a method according to any of the preceding claims.