US3618520A

US3618520A - Method of cracking concrete

Info

Publication number: US3618520A
Application number: US796445A
Authority: US
Inventors: Masafumi Hamasaki; Noriaki Nakashima
Original assignee: Asahi Chemical Industry Co Ltd
Current assignee: Asahi Kasei Corp; Asahi Chemical Industry Co Ltd
Priority date: 1969-02-04
Filing date: 1969-02-04
Publication date: 1971-11-09
Anticipated expiration: 1988-11-09

Abstract

Method of cracking concrete particularly useful for removing obsolete or unnecessary concrete structures in urban area which comprises drilling a borehole in concrete, filling thus drilled hole with a combustible composition mainly comprising a metallic reducing agent and an oxidizer, tamping thus filled borehole securely and igniting said combustible composition to crack the concrete.

Description

United States Patent 282,061 7/1883 Dennett Inventors Appl. No.

Filed Patented Assignee Masafumi Hamasaki;

Noriaki Nakashima, both of Nobeoka-shi, Japan Feb. 4, 1969 Nov. 9, 1971 Asahi Kasei Kogyo Kabushiki Kaisha Osaka, Japan METHOD OF CRACKING CONCRETE 5 Claims, 5 Drawing Figs.

U.S. C1 102/23 Int. Cl F42d 1/08 Field of Search... 102/22-24; l49/37;299/12, 13

References Cited UNITED STATES PATENTS 2,911,046 11/1959 Yahn 3,050,409 8/1962 Bayer 3,150,020 9/1964 Kilmer 3,297,503 l/l967 Hoffmann FOREIGN PATENTS 945,934 l/1964 Great Britain Primary Examiner- Verlin R. Pendegrass AttorneyRobert D. Flynn ABSTRACT: Method of cracking concrete particularly useful for removing obsolete or unnecessary concrete structures in urban area which comprises drilling a borehole in concrete, filling thus drilled hole with a combustible composition mainly comprising a metallic reducing agent and an oxidizer. tamping thus filled borehole securely and igniting said combustible composition to crack the concrete.

PATENTEU NOV 9 I97! SHEET 1 OF 2 FIG! FIG. 2

METHOD OF CRACKING CONCRETE BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a method of cracking concrete, more particularly, to a method of cracking concrete utilizing a combustible composition.

2. Description of the Prior Art 0.5 1.5

Heretofore, as crushing means for removing obsolete or unnecessary concrete structures, there have been known mechanical means using a breaker, pick, jackhammer, wedge, etc. and blasting means employing explosives.

However, among these known methods, the mechanical method is usually inefficient, while the blasting method is accompanied by inconveniences in creating big blasting sounds and scattering concrete pieces at the time of blasting which are hardly preventable, and requires much cost. Thus, the adoption of the blasting means has been greatly restricted by environmental conditions, notwithstanding the high efficiency afforded thereby. Hence, the crushing of concrete in urban or populated area, or places involving dangerous objects in the vicinities is still relied on the inefficient mechanical means mentioned above.

SUMMARY OF THE INVENTION It is, therefore, an object of this invention to provide a method of cracking concrete, which may be employed safely and efficiently in such places as mentioned above.

The object may be accomplished by the method of this invention which comprises drilling a borehole in concrete, filling thus-drilled hole with a combustible composition having a relatively high heat of reaction and affording reaction products mostly of solid at normal temperature free from detonation, said composition being mainly composed of a metallic reducing agent and an oxidizer, instead of explosives employed heretofore, tamping thus filled bore hole and igniting said combustible composition.

The combustible composition used in this invention mainly comprises a mixture consisting of 10-60 parts by weight of a reducing agent of at least a member selected from the group consisting of powders of zirconium, magnesium, silicon, aluminum, aluminum-magnesium alloy and boron, and 90-40 parts by weight of an oxidizer of at least a member selected from the group consisting of potassium perchlorate, potassium chlorate, potassium nitrate, barium nitrate, barium peroxide, lead tetroxide and lead mono-oxide. The combustible composition having the mixing proportion other than the range specified above shows poor combustibility and the required high temperature reaction does not take place due to interrupted combustion. Moreover, the combustion is not started easily with an electric squib.

In actual practice, the combustible composition of this invention is used by granulating the same employing a suitable binder. Normally, l-l parts by weight of rubber, synthetic rubber or synthetic resin per 100 parts by weight of the total sum of the reducing agent and oxidizer is used as a binder.

Presumable reaction equations, heats of reaction and actually measured combustion rates of typical combustible compositions are as follows:

The combustible composition of this type has the following three characteristics in its combustion.

l Small amounts of gases are produced.

2. Relatively high temperature is generated due to the heat of reaction.

3. The combustion rate is slow so that no detonation occurs.

Now, when the combustible composition is filled into a borehole drilled in concrete and tamping is effected followed by igniting, an impact accompanied by a rapid exothermic reaction and a rapid expansion of the reaction products due to gasification thereof by a high heat of reaction create instantaneously innumerable cracks in the concrete.

However, the gasified reaction products are brought under an unconfined condition when the concrete is cracked and the pressures and temperatures are rapidly decreased so that they are immediately condensed to resume their inherent solidities.

Thus, there is no longer a force enough to further crush the cracked concrete into smaller pieces and scatter them therearound. In this instance, since the combustion rate of the combustible composition used in this invention is slow, unlike explosives used heretofore, the tamping of the combustible composition must be secure and rigid.

With conventional tamping by way of sand, clay or water followed heretofore, there is afforded only a poor sealing strength and the tamping is blown out before concrete is cracked so that the contemplated object of this invention may not be accomplished. Although it is difficult to specify exactly the necessary tamping strength since the same is dependent upon the strength of concrete to be cracked, the length of burden thereof and depth of the bore hole, normally, there is required the tamping strength at least 50 percent of the strength of concrete at the minimum burden.

It is also difficult to specify exactly the amount of the combustible composition to be used since the same is dependent upon the strength of concrete to be cracked, structure, length of the minimum burden, number of free surface, reinforcing condition, etc., but, normally, the amount to be used per l m." of concrete is 20-40 g. for nonreinforced concrete and 50-70 g. for iron-bar-reinforced concrete.

In carrying out a secure tamping quickly, it is preferable to use a cement paste, mortar cement or concrete mixed with a quick-setting agent or a quick-setting cement as a tamping material.

The quick-setting cement or quick-setting agent referred to above comprises calcium chloride, water glass, sodium carbonate, hydrosilicofluorate or other inorganic high molecular weight materials and is commercially available as an additive for quick-setting and waterproofing of cement.

The quick-setting cement has characteristics in its high affinity and bonding strength with concrete, short solidifying time required and high strength. Thus, when tamping is carried out using the quick-setting cement, the so-called blownout shot phenomenon in which the tamping area is destroyed before concrete is cracked, never occurs.

In carrying out the tamping in the method of this invention, cement materials such as conventional cement paste, mortar cement or concrete, a plastic or resin concrete, and an epoxy or alkali-amide plastics, other than the quick-setting cement mentioned above, may be conveniently employed.

BRIEF DESCRIPTION OF THE DRAWING Now, the preferred embodiments of the present invention will be explained more in detail by referring to the accompanying drawings in which;

FIG. 1 shows a cross-sectional view of a cartridge used in this invention;

FIG. 2 illustrates cross-sectional views of the basic arrangements followed in the method of this invention;

FIGS. 3, 4 and 5 show elevational views of typical applications of the method of this invention to various concrete bodies.

Referring to the FIG. 1, a cartridge used in this invention comprises a closed end cylindrical body 1, e.g. made of plastics, having a hollow 2 at the bottom, directed toward inside the cylindrical body, into which an electric squib is inserted. The closed end cylindrical body 1 is filled with a combustible composition 4 and the upper end-opening thereof is sealed by a plate 3. The electrical squib 5 is easily inserted into the hollow 2 of the cartridge in the working site.

Thus, the use of the cartridge brings about an advantage in permitting easy insertion of the electric squib 5 and the subsequent loading into a borehole.

FIG. 2 illustrates a couple of basic arrangements in the method of this invention. First, a borehole 7 is drilled into a concrete body 6, then, into the borehole 7 thus drilled is inserted a cartridge 1 provided with an electric squib 5 and the remaining void of the borehole is filled by tamping.

In this instance, the length of borehole to be drilled is preferably about two-thirds of the thickness of concrete body to be cracked. Since the length of burden with respect to the borehole length varies depending on the concrete body to be cracked, for effectively cracking the concrete body, it is advisable that the amounts of combustible compositions employed be suitably adjusted. Thus, at times, there may be used a plurality of cartridges in one cracking operation.

In tamping the borehole, a high-strength tamping agent 8 such as a cement mortar in admixture with an accelerator is required. However, when the borehole length is long, i.e. the tamping length is long, as shown in FIG. 2 (B), about lower half of the tamping void may be filled with sand 9 in obtaining the required tamping effect. By carrying out the blasting with the tamping operation as described above, a concrete body may be effectively cracked without experiencing the blown out shot.

FIGS. 3, 4 and 5 illustrate some embodiments of the basic arrangements shown in FIG. 2.

When a plurality of cartridges are ignited altogether at the same time for cracking a concrete body having a thickness of about 0.5 rn. to about 1.5 rn., there are drilled

boreholes

7a and 7b, taking about 0.5 rn. of length of burden from both ends of the concrete body 6, at positions as shown in FIG. 3. Between the

boreholes

7a and 7b are drilled boreholes 7c, 7d and 7e at a distance of about 0.4-0.5 m. from each other.

When there are drilled many boreholes of a plurality of rows, it is preferable that boreholes of the first row are first blasted, then proceed to the next row and so forth.

The length of borehole which can be drilled practically and efficiently normally ranges about 0.7-0.9 rn. Thus, the maximum thickness of a concrete body that can be cracked by a single blasting is nonnally about 1.5 m. Accordingly, when a concrete body to be cracked has a thickness of more than 1.5 m., it is preferable that the blasting operations be carried out in a stepwise fashion as shown in FIG. 4.

For cracking a concrete body of a pillar shape, a borehole or holes may be drilled with an inclination of less than 45 with respect to the axis of the pillar-shaped body as shown in FIG. 5 for facilitating the tamping operation and preventing the tamping agent from flowing out of the borehole and there can be obtained a satisfactory tamping effect.

By the cracking of concrete according to this invention, the crushing and removing operations can be carried out quite ef ficiently as compared with the operation relied solely on mechanical means followed heretofore.

On the other hand, by the use of the combustible composition adopted in this invention, there is no fear of scattering concrete pieces as in the conventional blasting means followed heretofore thus the operation of removing unnecessary concrete structures from urban or populated area can be carried out safely. In addition, the combustible composition has no detonating property so that it can be handled quite safely free from any hazardous explosion.

DESCRIPTION OF PREFERRED EMBODIMENTS The following examples will serve to illustrate this invention more fully. It should not be construed, however, that these examples restrict this invention as they are given merely by way of illustration.

EXAMPLE I In an iron-bar-reinforced concrete block was drilled a borehole in a depth of 0.8 m. with a length of burden of0.5 m. Into the borehole thus drilled were filled 60 g. of a combustible composition consisting of 40 parts by weight of aluminum, 60 parts by weight of potassium perchlorate and 4 parts by weight of rubber chloride. The combustible composition was provided with an electric squib.

The tamping of the drilled borehole was carried out by employing a cement paste obtained by mixing and kneading 200 g. of an expansive quick-setting cement, Basetop P (trade name, a product of Taiho Industrial Co., Ltd., Japan) with a suitable amount of water.

After the tamping was solidified, the electric squib was ignited using a blasting machine and the composition was combusted.

As a result, no leaking of gas nor blown-out shot was observed at the tamping area and there were created enough cracks in the concrete to crush the same. No scattering of concrete pieces at the time of combustion.

EXAMPLE 2 In a nonreinforced concrete block was drilled a borehole in a depth of 0.8 m. with a length of burden of 0.5 m. Into the borehole thus drilled were filled 40 g. of a combustible composition consisting of 40 parts by weight of aluminum, 60 parts by weight of potassium chlorate and 4 parts by weight of rubber chloride together with an electric squib. The tamping of the borehole was carried out by employing a mixture consisting of a part by weight of cement, a part by weight of sand and 0.5 part by weight of a quick-setting agent, MAGNA NO. 1 LIQUID (trade name, a product of Magna Industries, Co., Ltd., Japan).

After the tamping was solidified, the composition was ignited and the concrete was satisfactorily cracked with no blown-out shot nor scattering of concrete pieces.

EXAMPLE 3 In a nonreinforced concrete block was drilled a borehole in a depth of 0.7 m. with a length of burden of 0.4 rn. Into the borehole thus drilled were filled 50 g. of a combustible composition consisting of 40 parts by weight of magnesium, 60 parts by weight of barium peroxide and 4 parts by weight of rubber chloride, together with an electric squib. The tamping of the borehole was carried out by employing a concrete consisting of a part by weight of cement, a part by weight of sand and a part by weight of gravel of small diameters.

As a result of combustion, there were created cracks in the concrete without blown-out shot nor scattering of concrete pieces.

EXAMPLE 4 In a nonreinforced concrete block was drilled a borehole in a depth of 0.8 m. with a length of burden of 0.5 rn. Into the borehole thus drilled were filled a combustible composition consisting of 20 parts by weight of aluminum, 20 parts by weight of magnesium, 60 parts by weight of potassium nitrate and 4 parts by weight of rubber chloride, together with an electric squib. The tamping of the borehole was done by using a resin concrete.

As a result of combustion, the concrete was satisfactorily cracked without blown-out shot nor scattering of concrete pieces.

EXAMPLE 5 In an iron-bar-reinforced concrete block was drilled a borehole in a depth of 0.8 m. with a length of burden of 0.5 m. Into the borehole thus drilled were filled 50 g. of a combustible composition consisting of 40 parts by weight of a powder of aluminum-magnesium alloy, 60 parts by weight of potassium perchlorate and 4 parts by weight of rubber chloride, together with an electric squib. The tamping was carried out by using an epoxy resin mixed with a small amount of hardening agent.

As a result of combustion, the concrete was satisfactorily cracked without observing blown-out shot nor scattering of concrete pieces.

We claim:

1. A method of cracking concrete which comprises the sequential steps of drilling a borehole in concrete to be cracked, loading a combustible composition into the borehole, said composition being combustible free from detonation in confinement with evolution of gasified reaction products which are mostly solid at normal temperature and a high heat of reaction sufficient to gasify the reaction products, and comprising -60 parts by weight of a metallic reducing agent and 90-0 parts by weight of an oxidizer, tamping the borehole with a quick-setting cement with a sealing strength at least 50 percent of the strength of the concrete to be cracked at the minimum burden, and igniting the combustible composition.

2. A method according to claim 1, wherein said combustible composition comprises a metallic reducing agent of at least a member selected from the group consisting of a powder of zirconium, magnesium, silicon, aluminum, aluminum-magnesium alloy and boron, and an oxidizer of at least a member selected from the group consisting of potassium chlorate, potassium perchlorate, potassium nitrate, barium nitrate, barium peroxide, lead tetroxide and lead mono-oxide.

3. A method according to claim 1, wherein said combustible composition is encased in a plastic container.

4. A method according to claim 3, wherein said plastic container comprises a cylindrical tube opened at one end and closed at its other end with a bottom member having a hollow for inserting an electric squib therethrough into the cylindrical tube, and a member for sealing the open end of the cylindrical tube.

5. A method according to claim 1, wherein said borehole is tamped with a member selected from the group consisting of cement, cement mortar and concrete into which a quicksetting agent is incorporated.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO, 3518' 520 Dated November 9, 1971 Inventor(s) MASAFUMI HAMASAKI et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 9 "0.5 1.5" should be deleted.

Column 5, line 24 "90-0" should read "90-40".

Signed an sealed this 2nd day of May 1972.

(SEAL) Attest:

EDWARD ILFLEICHER TR. ROBERT GOTTSGHALK Attesting Officer Commissioner of Patents )RM P0-1050(10-69 USCOMM-DC 60376-7 69 fi v.5 GOVERNMENT PR NTING OFFICE 19'! 0-356-384

Claims

1. A method of cracking concrete which comprises the sequential steps of drilling a borehole in concrete to be cracked, loading a combustible composition into the borehole, said composition being combustible free from detonation in confinement with evolution of gasified reaction products which are mostly solid at normal temperature and a high heat of reaction sufficient to gasify the reaction products, and comprising 10-60 parts by weight of a metallic reducing agent and 90-40 parts by weight of an oxidizer, tamping the borehole with a quick-setting cement with a sealing strength at least 50 percent of the strength of the concrete to be cracked at the minimum burden, and igniting the combustible composition.

5. A method according to claim 1, wherein said borehole is tamped with a member selected from the group consisting of cement, cement mortar and concrete into which a quick-setting agent is incorporated.