WO2002084207A1

WO2002084207A1 - Method of breaking or fracturing concrete

Info

Publication number: WO2002084207A1
Application number: PCT/AU2002/000460
Authority: WO
Inventors: Chris Woolford
Original assignee: Rocktek Limited
Priority date: 2001-04-11
Filing date: 2002-04-10
Publication date: 2002-10-24

Abstract

A method for breaking or fracturing concrete particularly in the form of a concrete slab (10) forming a floor in a multi-storey building. The method includes placing support beams (20) across an area (18) of the slab (10), the beams (20) being supported at its ends on portions of the slab (10) outside the area (18) and coupled at one or more locations within the area (18) to the slab (10). A through cut is formed about substantially the full perimeter (26) of the slab with a plurality of blind holes (12) drilled in area (18). Propellant is inserted into at least some of the holes (12), the propellant burning within 10-15 milliseconds of ignition and developing a gas pressure in the range of 100-150 MPa. Holes (12) are stemmed typically with a particulate settable stemming material prior to ignition of the propellant.

Description

METHOD OF BREAKING OR FRACTURING CONCRETE

Field of the Invention

The present invention relates to a method of fracturing or breaking concrete and, in particular, but not exclusively, to a method of fracturing or breaking a suspended or elevated concrete slab.

Background of the Invention

There is often a need to fracture or break concrete during large or small-scale civil construction/refurbishment or demolition. Typically this is achieved by the use of impact breakers. For small volumes or areas of concrete hand operated jackhammers may be sufficient. For larger volumes or areas tractor mounted impact rippers may be employed. While such impact breakers are of course able to fracture concrete, they do suffer from several disadvantages. Most notably, their rate of advance is particularly slow and they are not well suited to use within buildings more particularly on the second or subsequent floors of high rise buildings. This is often due to their physical size, width and weight (for tractor mounted impact rippers) which prohibits their use within buildings. Further, the vibrations caused by these devices particularly in buildings which are being repaired or refurbished rather than being demolished, may be unacceptably high.

It is also known to use explosives for fracturing or breaking concrete. However typically this is only during demolition of a structure such as a building. There are of course inherent safety problems in using explosives not the least of which are safety problems in the handling of the explosives themselves as well as the generation of flyrock which has been known to accidentally kill and injure spectators at demolition sites and damage adjoining buildings and property. A further potential problem with the use of explosives is the generation of seismic waves which can damage underground utilities and fracture walls of buildings surrounding the location of the use of the explosives. Summary of the Invention

It is an object of the present invention to provide an alternate method for breaking or fracturing concrete which attempts to alleviate at least one of the above described disadvantages in the prior art.

According to a first aspect of the present invention there is provided a method of breaking or fracturing concrete including at least the steps of:

forming a plurality of holes in said concrete; inserting a quantity of propellant in at least some of said holes, said propellant adapted to fully burn within 10 to 15 milliseconds of initiation and develop a gas pressure in the range of 100 to 150 MPa; stemming said holes containing said propellant; and, igniting said propellant.

Preferably said stemming step includes stemming said holes with a settable particulate stemming material.

Preferably said stemming step includes forming said particulate stemming material from a mixture of 8 parts sand and 1 part cement.

Preferably said stemming step includes adding sufficient water to dampen said particulate stemming material.

Preferably said dampening of said particulate stemming material includes adding water in a quantity of up to about 5% by weight of said particulate stemming material.

Preferably said inserting step includes inserting a quantity of propellant in alternating holes. Preferably said igniting step includes igniting the propellant in said holes sequentially.

According to a further aspect of the present invention there is provided a method of breaking or fracturing at least an area of a concrete slab including at least the steps of:

placing support means across said area, said support means supported at its ends on portions of said slab outside said area, and coupling said support means at one or more locations within said area to said slab; forming a through cut about substantially a full perimeter of said area; forming a plurality of blind holes in said slab within said area; inserting a quantity of propellant into at least some of said holes, said propellant adapted to fully burn within 10 to 15 milliseconds of ignition and develop a gas pressure in the range of 100-150 MPa; stemming said holes; and, igniting said propellant.

Preferably said stemming step includes stemming said holes with a settable stemming material.

Preferably said stemming step f rther includes forming said stemming material as a mixture of 8 parts sand to 1 part cement.

Preferably said step of placing said support means across said area includes placing two or more elongated beams across said area wherein opposite ends of each beam are disposed outside said area. Preferably said method further includes the step of placing a vibration damping means between said support means and said slab.

Preferably, when said concrete slab is located above a floor said method further includes a step of placing an impact dampening structure on said floor underneath said slab.

Preferably said placing, cutting, forming, inserting, stemming and igniting steps are sequentially repeated for a plurality of areas which constitute said concrete slab.

According to a further aspect of the present invention there is provided a method of breaking or fracturing concrete including at least the steps of:

forming a plurality of holes in said concrete; inserting a quantity of propellant in at least some of said holes; stemming said holes containing said propellant with a settable particulate stemming material which includes a mixture of sand and cement in the ratios of 6 to 10 parts sand and ^lA to 3 parts cement; and igniting said propellant.

Preferably said sand and cement are included in a proportion of approximately 8 parts sand and 1 part cement.

Preferably the method further includes when said concrete is in the form of a slab, placing support means across at least an area of said slab, said support means supported at its ends on portions of said slab outside said area, and coupling said support means at one or more locations within said area to said slab.

Brief Description of the Drawings

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawing in which: Figure 1 depicts a plan view of an elevated or suspended concrete slab to which an embodiment of the present method is applied;

Figure 2 is a side interior view of a portion of a building to which the present method is applied; and, Figure 3 is a view of detail A depicted in Figure 2; and,

Figure 4 is a plan view of a ground level concrete block or slab to which an embodiment of the present invention is applied.

Detailed Description of the Preferred Embodiments

Referring to Figure 4, a general and broad embodiment of the method for fracturing concrete in the form of a ground level block of concrete 10 includes forming, typically by drilling, a plurality of holes 12 in the concrete in a vertical direction from its exposed upper surface 14. The holes 12 are blind holes. Once the holes 12 have been drilled, a quantity of propellant is deposited therein. Typically the propellant is provided in cartridges. When breaking concrete, using energetic material Applicant believes it more beneficial for the energy released by the energetic material to have a higher rupturing component than a stressing component. To this end, a very fast burn rate and high pressure development is required. In particular, the propellant material ideally is of a composition which is fully burnt or consumed within 10 to 15 milliseconds of initial ignition and develops a gas pressure in the range of 100 to 150 MPa.

The propellant may not necessarily be inserted into each of the holes 12 with some of the holes acting as stress relievers to direct (and attract) fractures developed by the initiation of the propellant. This enables highly directional fracturing to occur so that selected areas of concrete can be fractured. The holes 12 which do not receive propellant may be formed as through holes rather than blind holes.

The holes containing propellant are stemmed to increase the efficiency of the propellant. The stemming may be by way of plugs hammered into the holes, use of a flowable stemming material or both. In the latter case, the flowable stemming material is inserted into the hole after the propellant with the stemming plug inserted on top of the flowable stemming material.

The propellant is then ignited causing a rapid build up of gas pressure within the holes. This gas pressure produces fracturing within the concrete 10. Ideally, the propellant material used, depth of hole 12 and stemming are arranged to facilitate the formation of a penetrating cone fracture (PCF) upon initiation of the energetic material. However, due to the nature of concrete and the thickness of block/slab to be operated on, PCF may not occur, and is not an essential requirement of this embodiment of the invention. The PCF is characterised by the formation of fractures or fracture planes which initially extend downwardly from toe of the hole in the shape of a cone and then turn upwardly toward a free surface of the material in which the hole 12 is formed. A PCF 16 is depicted in Figure 2. A further highly beneficial feature of PCF is that no or very little flyrock is generated. Further, any flyrock which does occur is of relatively low energy and travels short distances.

As mentioned above, the holes 12 which are loaded with a propellant are blind holes, however other holes which propellant is not inserted may be through holes. The blind holes preferably have a depth range of between 25% to 80% of the thickness of the concrete block 10 but, most preferably the hole depth is about 60% to 70% of block/slab thickness. Indeed a combination of holes 12 of different depth may be applied in any one particular concrete block 10. For example, referring to Figure 4, rows or lines of through holes 12T may be formed in the concrete block 10 to effectively segment the block 10 into different areas. The propellant may be ignited sequentially rather than simultaneously in all of the holes. This facilitates successive fracturing of the concrete block 10 in a controlled manner.

When particulate stemming material is used, it is preferred that this stemming material is settable. It is envisaged that a particularly suitable particulate stemming material comprises a mixture of sand and cement in a dry ratio of around 6 to 10 parts cement to a Vi to 3 parts cement with sufficient water to make the mixture damp. More preferably, the sand and cement are in the dry ratio of around 8 to 1. The particulate stemming material is tamped into the hole and allowed to set for approximately 15 to 20 minutes. The present method is particularly well suited to selectively removing portions of elevated or suspended concrete slabs as depicted in Figure 1 - 3. In this embodiment, the concrete is in the form of a slab 10, which may constitute for example the second floor in a multi storey building. In this embodiment, the method is used to remove a selected area 18 of the concrete slab 10 involves the additional steps of supporting the area 18 and cutting the slab 10 about the perimeter of the area 18.

The area 18 is supported by providing support means in the form of two I beam 20, which lie over the area 18 and having ends 22 that lie on the slab 10 outside of the area 18. The I beams 20 are connected or attached to the slab 10 within the area 18, for example by use of dyna bolts 24.

Perimeter 26 defining the area 18 is cut through the thickness of the slab 10 using a conventional diamond saw. Thus, the area 18 is substantially supported by the I beams 20. There will be a small bridge of material underlying the I beams 20 that connect the area 18 to the main body of the slab 10. However, this also can be removed if, prior to coupling the I beams 20 to the slab 10, slits or slots are cut in the perimeter 18 at locations over which the I beams 20 will extend. Thereafter, once the I beams 20 have been connected to the area 18, the remainder of the perimeter 26 can be cut in which case the hole area 18 is freely suspended by the I beams 20. An alternate method of dealing with the small bridge of material underlying the I beams 20 would be to simply cut the perimeter 26 with a diamond saw as described above while the I beams 20 are in place and thereafter drilling a blind hole near one or both intersecting points of each end of each I beam with the perimeter 26, charging the holes with a propellant, stemming the holes and subsequently igniting the propellant. This will cause propagation of cracks or fractures to occur in the underlying small bridge spanning the previously cut areas of the perimeter 26. The fractures in the small bridges act largely in the same way as a through cut formed by a diamond saw in providing vibration isolation between the area 18 and the remainder of the block 10.

A vibration damping means such as a rubber strip 28 may be placed between the I beam 20 and the slab 10 to limit the promulgation of vibrations to other areas of the slab 10 and indeed the building itself.

Holes 12 are formed in the area 18 with propellant being inserted or deposited into at least some of the holes and those holes being stemmed in the manner described above in relation to the first embodiment illustrated in Figure 4.

Prior to initiation of the propellant, advantageously a impact damping device or structure 30 can be disposed beneath the area 18. The structure 30 may be in the form of cardboard boxes or airbags or both and act to damp the impact of falling pieces of concrete onto the underlying floor.

The floor 10 illustrated in Figures 1 and 2 is generally supported by the corresponding building's support columns 32. The area 18 of floor 10 removed by this method would typically be disposed so as to not overly any of the columns 32 in order to avoid inducing structural weakness into the building.

By practicing this method either selected areas of the slab 10 can be removed or the whole slab can be removed by simply repeating the removal of adjacent smaller areas 18. Appropriate propellants for use in this method in order to produce the burn rate and gas pressure required include: AS/AP 3ON, S125 and NITRO 100.

In one embodiment of the present invention it may be preferable that a "key block" is first removed from a central portion of the area 18. This can be done by drilling a blind hold into the central portion with say 4 to 6 through holes drilled in a circle about the central blind hole. A propellant cartridge is then inserted into the blind hole, stemmed and ignited causing fractures to propagate between adjacent through holes about the central blind hole. This defines a "key block" which may either fall of its own accord by the action of gravity or, can be easily removed by one or two blows of a hammer. Thereafter, the remainder of the area 18 can be fractured outwardly of the void left by the removal of the key block toward the perimeter 26. During this process, multiple holes can be charged, stemmed and then simultaneously ignited. However in some situations it may be preferable to commence fracturing from the perimeter and then move toward the central portion of the area 18.

Embodiments of the present invention have been found to be particularly beneficial when used in relation to concrete reinforced by steel rods or mesh. In trials practicing this method, it has been discovered that fractures induced upon the initiation of the propellant tend to propagate along the reinforcing and act to separate the concrete from the reinforcing. This has been found to be of immense benefit in separating steel from concrete in demolished concrete structures thereby reducing overall demolition/waste removal charges.

Now that embodiments of the present method have been described in detail it will be apparent to those skilled in the relevant arts that numerous modifications and variations may be made without departing from the basic inventive concepts. For example, the features of the embodiment depicted in Figures 1 and 2, the support 20 as shown in the form of two parallel spaced apart I beams. However different forms of support can be provided, for example, a single beam can be provided which spans the area 18 with a plurality of transversely extending ribs coupled thereto. Selected ribs may also extend beyond the perimeter of the area 18. Further, when large elevated or suspended areas or a complete slab 10 is to be removed, the method may also include the step of providing additional support to an underlying floor. This may include erecting a plurality of support members including aero props on one or more of the underlying floors. The present embodiments have been described in relation to suspended concrete floors or slabs. However, the method can be equally applied to concrete walls.

All such modifications and variations together with others that would be obvious to a person of ordinary skill in the art are deemed to be within the scope of the present invention the nature of which is to be determined from the above description.

Claims

Claims:

1. A method of breaking or fracturing concrete including at least the steps of:

forming a plurality of holes in said concrete; inserting a quantity of propellant in at least some of said holes, said propellant adapted to fully bum within 10 to 15 milliseconds of initiation and develop a gas pressure in the range of 100 to 150 MPa; stemming said holes containing said propellant; and, igniting said propellant.

2. The method of claim 1 wherein said stemming step includes stemming said holes with a settable particulate stemming material.

3. The method of claim 2 wherein said stemming step includes forming said particulate stemming material from a mixture of 8 parts sand and 1 part cement.

4. The method of claim 3 wherein said stemming step includes adding sufficient water to dampen said particulate stemming material.

5. The method of claim 4 wherein said dampening of said particulate stemming material includes adding water in a quantity of up to about 5% by weight of said particulate stemming material.

6. The method of any one of claims 1-5 wherein said inserting step includes inserting a quantity of propellant in alternating holes.

7. The method of any one of claims 1-6 wherein said igniting step includes igniting the propellant in said holes sequentially.

8. A method of breaking or fracturing at least an area of a concrete slab including at least the steps of: placing support means across said area, said support means supported at its ends on portions of said slab outside said area, and coupling said support means at one or more locations within said area to said slab; forming a through cut about substantially a full perimeter of said area; forming a plurality of blind holes in said slab within said area; inserting a quantity of propellant into at least some of said holes, said propellant adapted to fully bum within 10 to 15 milliseconds of ignition and develop a gas pressure in the range of 100-150 Mpa; stemming said holes; and, igniting said propellant.

9. The method of claim 8 wherein said step of placing said support means across said area includes placing two or more elongated beams across said area wherein opposite ends of each beam are disposed outside said area.

10. The method of claims 8 or 9 further including the step of placing a vibration damping means between said support means and said slab.

11. The method of any one of claims 8-10 wherein when said concrete slab is located above a floor said method further includes a step of placing an impact dampening structure on said floor underneath said slab.

12. The method of any one of claims 8-11 wherein said placing, cutting, forming, inserting, stemming and igniting steps are sequentially repeated for a plurality of areas which constitute said concrete slab.

13. The method of any one of claims 8-12 wherein said stemming step includes stemming said holes with a settable stemming material.

14. The method of claim 13 wherein said stemming step further includes forming said stemming material as a mixture of 8 parts said to 1 part cement.

15. The method of claim 14 wherein said stemming step includes adding sufficient water to dampen said particulate stemming material.

16. A method of breaking or fracturing concrete including at least the steps of:

forming a plurality of holes in said concrete; inserting a quantity of propellant in at least some of said holes; stemming said holes containing said propellant with a settable particulate stemming material which includes a mixture of sand and cement in the ratios of 6 to 10 parts sand and Vz to 3 parts cement; and, igniting said propellant.

17. The method of claim 16 wherein said sand and cement are included in a proportion of approximately 8 parts sand and 1 part cement.

18. The method of claim 17 wherein said stemming step includes adding sufficient water to dampen said particulate stemming material.

19. The method of any one of claims 16-18 further including when said concrete is in the form of a slab, placing support means across at least an area of said slab, said support means supported at its ends on portions of said slab outside said area, and coupling said support means at one or more locations within said area to said slab.

20. The method of claim 19 wherein said step of placing said support means across said area includes placing two or more elongated beams across said area wherein opposite ends of each beam are disposed outside said area.

21. The method of claim 20 wherein the step of placing a vibration damping means between said support means and said slab.

22. The method of any one of claims 16-21 wherein said propellant fully bums within 10-15 milliseconds of ignition and develops a gas pressure in the range of 100- 150 MPa.