Patent Application
20190194882
The present invention relates to the field of pavement structure removal. More specifically, the present invention relates to the field of plasma blasting to remove pavement structures.
The field of removing pavement structures generally comprises conventional jackhammering. Specifically, whether for mining or civil construction, the pavement structure excavation process generally includes mechanical fracturing and grinding as the primary mechanism for breaking up the pavement. Jackhammering is inefficient, loud, and can cause physical damage to the operator. Mechanical grinding is sometimes used for asphalt, but does not work well for removing concrete surfaces. A better solution to this problem is needed.
An alternate method of surface processing for the excavation of hard rock incorporates the use of electrically powered plasma blasting. In this method, a capacitor bank is charged over a relatively long period of time at a low current, and then discharged in a very short pulse at a very high current into a blasting probe comprised of two or more electrodes immersed in an incompressible fluid media. The fluid media is in direct or indirect contact with the pavement to be fractured.
Previous plasma blasting probes suffered from difficulties in reusability due to the lack of control of the dynamics of the plasma spark. This lack of control also prevented the aiming of the shock waves from the blast into a desired direction.
The present invention, eliminates the issues articulated above as well as other issues with the currently known products.
A pavement structure removal method is described that first uses two saws to cut two slits in a pavement structure to separate a working area from the rest of the pavement, and then drilling boreholes in the pavement in between the two slits, filling the boreholes with incompressible fluid (water, for example), inserting plasma blast probes in the boreholes, and blasting the pavement using the plasma blast probes. The fractured pavement is then removed using conventional methods, such as grinding, shoveling, or excavating.
A method for fracturing pavement is described herein. The method is made up of the steps of drilling a borehole in the pavement using a drill and removing the drill. The method als includes the steps of inserting a plasma blast probe into the borehole, where the blast probe is designed to focus the blast horizontally and slightly upwards by locating a gap between a plurality of electrodes low in the blast probe, initiating a plasma blast in the plasma blast probe by creating a plasma spark between the electrodes, and removing the plasma blast probe from the borehole.
In some embodiments, the method also include the step of vacuuming pavement debris from the borehole before inserting the plasma blast probe. It could also include the step of flushing pavement debris from the borehole with water before inserting the plasma blast probe. The method could also include cutting the pavement with a saw. In some embodiments, there are a plurality of drills and plasma probes drilling and blasting simultaneously. In some cases the drill and plasma probe are mounted on a platform. The method could also include the steps of moving the platform and repeating the method at a new location. Alternatively, the method could include drilling one borehole and inserting the blast probe in a second borehole simultaneously. In some embodiments, the steps also include filling the borehole with blast media. The plasma blast probe could include a housing in the shape of a cylinder.
An apparatus for fracturing pavement is described below. The apparatus is made up of a platform mounted on a plurality of wheels, where the wheels are in contact with the pavement, a power source, and a drill electrically connected to the power source and mechanically mounted on the platform such that the drill can drill a borehole to and a bottom surface of the pavement. The apparatus also includes a plasma blast probe, mounted on the platform such that the plasma blast probe can be inserted in a borehole to the bottom surface of the pavement, a power storage device, electrically connected to the power source and mechanically mounted on the platform and connected to the plasma blast probe, and a plurality of electrodes mounted inside of the plasma blast probe and electrically connected to the power storage device.
In some embodiments, the drill has a carbide drill bit. The apparatus could also include a saw electrically connected to the power source and mechanically connected to the platform such that the saw can cut the pavement from a top surface to the bottom surface. The saw could have a diamond tipped saw blade. The platform could be attached to a motorized vehicle. The platform could have a plurality of drills and plasma blast probes mounted on it. The apparatus could also include an air compressor electrically connected to the power source and mechanically connected to the platform wherein the air compressor can force compressed air into the borehole. The apparatus could also include a special purpose controller electrically connected to the power source and to the plasma blast probe to control characteristics of the plasma blast. The special purpose controller could be electrically connected to the drill to control a depth of the borehole. The apparatus could also include a pump electrically connected to the power source and mechanically mounted on the platform and controlled by the special purpose controller to pump blast media into the borehole.
In some embodiments, the plasma blasting system 100 comprises a power supply 106, an electrical storage unit 108, a voltage protection device 110, a high voltage switch 112, a transmission line 114, a cable 116, a blasting probe 118 and a blasting media 104. In some embodiments, the plasma blasting system 100 comprises any number of blasting probes and corresponding blasting media. The power supply 106 comprises any electrical power supply capable of supplying a sufficient voltage to the electrical storage unit 108. The electrical storage unit 108 comprises a capacitor bank or any other suitable electrical storage means. The voltage protection device 110 comprises a crowbar circuit, with voltage-reversal protection means as is well known in the art. The high voltage switch 112 comprises a spark gap, an ignitron, a solid state switch, or any other switch capable of handling high voltages and high currents. In some embodiments, the transmission line 114 and cable 116 comprise a coaxial cable. Alternatively, the transmission line 114 and cable 116 comprises any transmission cable capable of adequately transmitting the pulsed electrical power.
In some embodiments, the power supply 106 couples to the voltage protection device 110 and the electrical storage unit 108 via the power line 140 such that the power supply 106 is able to supply power to the electrical storage unit 108 through the power line 140 and the voltage protection device 110 is able to prevent voltage reversal from harming the system. In some embodiments, the power supply 106, voltage protection device 110 and electric storage unit 108 also couple to the high voltage switch 112 via the transmission line 114 such that the switch 112 is able to receive a specified voltage/current from the electric storage unit 108. The switch 112 then couples to the cable 116 which couples to the blasting probe 118 each that the switch 112 is able to selectively allow the specified voltage/amperage received from the electric storage unit 108 to be transmitted through the line 116 to the blasting probe 118.
The adjustment unit 120 comprises any suitable probe tip adjustment means as are well known in the art. Further, the adjustment unit 120 couples to the adjustable tip 130 such that the adjustment unit 120 is able to selectively adjust/move the adjustable tip 130 axially away from or towards the end of the ground electrode 124, thereby adjusting the electrode gap 132. In some embodiments, the adjustment unit 120 adjusts/moves the adjustable tip 130 automatically. The term “electrode gap” is defined as the distance between the high voltage and ground electrode 126, 124 through the blasting media 104. Thus, by moving the adjustable tip 130 axially in or out in relation to the end of the ground electrode 124, the adjustment unit 120 is able to adjust the power of the blasting probe 118. As a result, a change in the distance separating the electrodes 124, 126 in the blasting probe 118 is able to be used to vary the electrical power deposited into the solid 102 to be broken or fractured. Accordingly, by allowing more refined control over the electrode gap 132 via the adjustable tip 130, better control over the blasting and breakage yield is able to be obtained.
Another embodiment, as shown in
In one embodiment, water is used as the blasting media 104. The water could be poured down the borehole 122 before or after the probe 118 is inserted in the borehole 122. In some embodiments, such as horizontal boreholes 122 or bore holes 122 that extend upward, the blasting media 104 could be contained in a balloon or could be forced under pressure into the borehole 122 with the probe 118.
As shown in
The method and operation 400 of the plasma blasting system 100 will now be discussed in conjunction with a flow chart illustrated in
During the first microseconds of the electrical breakdown, the blasting media 104 is subjected to a sudden increase in temperature (e.g. about 5000 to 10,000° C. or more) due to a plasma channel formed between the electrodes 124, 126, which is confined in the borehole 122 and not able to dissipate. The heat generated vaporizes or reacts with part of the blasting media 104, depending on if the blasting media 104 comprises a liquid or a solid respectively, creating a steep pressure rise confined in the borehole 122. Because the discharge is very brief, a blast wave comprising a layer of compressed water vapor (or other vaporized blasting media 104) is formed in front of the vapor containing most of the energy from the discharge. It is this blast wave that then applies force to the inner walls of the borehole 122 and ultimately breaks or fractures the solid 102. Specifically, when the pressure expressed by the wave front (which is able to reach up to 2.5 GPa or more), exceeds the tensile strength of the solid 102, fracture is expected. Thus, the blasting ability depends on the tensile strength of the solid 102 where the plasma blasting probe 118 is placed, and on the intensity of the pressure formed. The plasma blasting system 100 described herein is able to provide pressures well above the tensile strengths of common rocks (e.g. granite=10-20 MPa, tuff=1-4 MPa, and concrete=7 MPa). Thus, the major cause of the fracturing or breaking of the solid 102 is the impact of this compressed water shock wave front which is comparable to one resulting from a high-energy chemical explosive (e.g., dynamite).
As the reaction continues, the blast wave begins propagating outward toward regions with lower atmospheric pressure. As the wave propagates, the pressure of the blast wave front falls with increasing distance. This finally leads to cooling of the gasses and a reversal of flow as a low-pressure region is created behind the wave front, resulting in equilibrium.
If the blasting media 104 comprises a thixotropic fluid as discussed above, when the pulsed discharge vaporizes part of the fluid, the other part rheologically reacts by instantaneously increasing in viscosity, due to being subjected to the force of the vaporized wave front, such that outer part of the fluid acts solid like. This now high viscosity thixotropic fluid thereby seals the borehole 122 where the blasting probe 118 is inserted. Simultaneously, when the plasma blasting system 100 is discharged, and cracks or fractures begin to form in the solid 102, this newly high viscosity thixotropic fluid temporarily seals them thereby allowing for a longer time of confinement of the plasma. Thus, the vapors are prevented from escaping before building up a blast wave with sufficient pressure. This increase in pressure makes the blasting process 400 described herein more efficient, resulting in a more dramatic breakage effect on the solid 102 using the same or less energy compared to traditional plasma blasting techniques when water or other non-thixotropic media are used.
Similarly, if the blasting media 104 comprises an ER fluid as discussed above, when the pulsed discharge vaporizes part of the fluid, a strong electrical field is formed instantaneously increasing the non-vaporized fluid in viscosity such that it acts solid like. Similar to above, this now high viscosity ER fluid thereby seals the borehole 122 where the blasting probe 118 is inserted. Simultaneously, when the plasma blasting system 100 is discharged, and cracks or fractures begin to form in the solid 102, this newly high viscosity ER fluid temporarily seals them thereby allowing for a longer time of confinement of the plasma. Thus, again the vapors are prevented from escaping before building up a blast wave with sufficient pressure.
During testing, the blast probe of the blasting system described herein was inserted into solids comprising either concrete or granite with cast or drilled boreholes having a one inch diameter. A capacitor bank system was used for the electrical storage unit and was charged at a low current and then discharged at a high current via the high voltage switch 112. Peak power achieved was measured in gigawatts. Pulse rise times were around 10-20 μsec and pulse lengths were on the order of 50-100 μsec. The system was able to produce pressures of up to 2.5 GPa and break concrete and granite blocks with masses of more than 850 kg with one discharge.
The probe connector 501 is mechanically connected to the shaft connector 502 with screws, welds, or other mechanical connections. The shaft connector 502 is connected to the probe shaft 503. The connection to the probe shaft 503 could be through male threads on the top of the probe shaft 503 and female threads on the shaft connector 502. Alternately, the shaft connector 502 could include a set screw on through the side to keep the shaft 503 connected to the shaft connector 502. The shaft connector 502 could be a donut shape and made of stainless steel, copper, aluminum, or another conductive material. Electrically, the shaft connector 502 is connected to the ground side of the cable 116. An insulated wire from the probe connector 501 to the high voltage electrode 602 passes through the center of the shaft connector 502. For a 2 inch borehole 122, the shaft connector could be about 1.75 inches in diameter.
The shaft 503 is a hollow shaft that may be threaded 507 at one (or both) ends. The shaft 503 made of stainless steel, copper, aluminum, or another conductive material. Electrically, the shaft 503 is connected to the ground side of the cable 116 through the shaft connector 502. An insulated wire from the probe connector 501 to the high voltage electrode 602 passes through the center of the shaft 503. Mechanically, the shaft 503 is connected to the shaft connector 502 as described above. At the other end, the shaft 503 is connected to the cage 506 through the threaded bolt 508 into the shafts threads 507, or through another mechanical connection (welding, set screws, etc). The shaft 503 may be circular and 1.5 inches in diameter in a 2 inch borehole 122 application. The shaft may be 40 inches long, in one embodiment. At several intervals in the shaft, blast force inhibitors 504a, 504b, 504c may be placed to inhibit the escape of blast wave and the blasting media 104 during the blast. The blast force inhibitors 504a, 504b, 504c may be made of the same material as the shaft 503 and may be welded to the shaft, machined into the shaft, slip fitted onto the shaft or connected with set screws. The inhibitors 504a, 504b, 504c could be shaped as a donut.
The shaft 503 connects to the cage 506 through a threaded bolt 508 that threads into the shaft's threads 507. This allows adjustment of the positioning of the cage 506 and the blast. Other methods of connecting the cage 503 to the shaft 506 could be used without deviating from the invention (for example, a set screw or welding). The cage 506 may be circular and may be 1.75 inches in diameter. The cage 506 may be 4-6 inches long, and may include 4-8 holes 604 in the side to allow the blast to impact the side of the blast hole 122. These holes 604 may be 2-4 inches high and may be 0.5-1 inch wide, with 0.2-0.4 inch pillars in the cage 506 attaching the bottom of the cage 506 to the top. The cage 506 could be made of high strength steel, carbon steel, copper, titanium, tungsten, aluminum, cast iron, or similar materials of sufficient strength to withstand the blast. Electrically, the cage 506 is part of the ground circuit from the shaft 503 to the ground electrode 601.
In an alternative embodiment, a single blast cage could be made of weaker materials, such as plastic, with a wire connected from the shaft to the ground electrode 601 at the bottom of the cage 506.
The details of the cage 506 can be viewed in
The wire that runs down the shaft 503, as connected to the cable 116 at the probe connector 501, is electrically connected to the high voltage electrode 602. A dielectric separator 603 keeps the electricity from coming in contact with the cage 506. Instead, when the power is applied, a spark is formed between the high voltage electrode 602 and the ground electrode 601. In order to prevent the spark from forming between the high voltage electrode 602 and the cage 506, the distance between the high voltage electrode 602 and the ground electrode 601 must be less than the distance from the high voltage electrode 602 and the cage 506 walls. The two electrodes 601, 602 are on the same axis with the tips opposing each other. If the cage is 1.75 inches in diameter, the cage 506 walls will be about 0.8 inches from the high voltage electrode 602, so the distance between the high voltage electrode 602 and the ground electrode 601 should be less than 0.7 inches. In another embodiment, an insulator could be added inside the cage to prevent sparks between the electrode 602 and the cage when the distance between the high voltage electrode 602 and the ground electrode 601 is larger.
This cage 506 design creates a mostly cylindrical shock wave with the force applied to the sides of the borehole 122. In another embodiment, additional metal or plastic cone-shaped elements may be inserted around lower 601 and upper electrodes 602 to direct a shock wave outside the probe and to reduce axial forces inside the cage.
In one embodiment, a balloon filled with water could be inserted in the cage 506 or the cage 506 could be enclosed in a water filled balloon to keep the water around the electrodes 601, 602 in a horizontal or upside down application.
The method of and apparatus for plasma blasting described herein has numerous advantages. Specifically, by adjusting the blasting probe's tip and thereby the electrode gap, the plasma blasting system is able to provide better control over the power deposited into the specimen to be broken. Consequently, the power used is able to be adjusted according to the size and tensile strength of the solid to be broken instead of using the same amount of power regardless of the solid to be broken. Furthermore, the system efficiency is also increased by using a thixotropic or reactive materials (RM) blasting media in the plasma blasting system. Specifically, the thixotropic or RM properties of the blasting media maximize the amount of force applied to the solid relative to the energy input into the system by not allowing the energy to easily escape the borehole as described above and to add energy from the RM reaction. Moreover, because the thixotropic or RM blasting media is inert, it is safer than the use of combustible chemicals and/or explosives. As a result, the plasma blasting system is more efficient in terms of energy, safer in terms of its inert qualities, and requires smaller components thereby dramatically decreasing the cost of operation.
Accordingly, for the mining and civil construction industries this will represent more volume of rock breakage per blast at lower cost with better control. For the public works construction around populated areas this represents less vibration, reduced noise and little to no flying rock produced. For the space exploration industry where chemical explosives are a big concern, the use of this inert blasting media is an excellent alternative. Overall, the method of and apparatus for plasma blasting described herein provides an effective reduction in cost per blast and a higher volume breakage yield of a solid substance while being safe, environmentally friendly and providing better control.
The above plasma blasting probes can be very useful in the removal of pavement, especially rigid pavement such as Portland cement concrete. Because the concrete is rigid and hard, it is difficult to break using traditional methods such as jackhammers or grinding machines. Grinding machines are often used for flexible pavement such as hot mix asphalt, but the grinding machines are less effective with rigid pavement. Jackhammers are often used to break up the rigid concrete, but this is labor intensive, and can be harmful to the workers. Another method for the removal of pavement is to cut the concrete into large blocks that are lifted intact into trucks for removal. But block removal does not work if the concrete has deteriorated. Furthermore, block removal leaves huge blocks of concrete that need to be broken up at a later time.
The platform 701 could be the width of a lane of road for applications where the pavement is on a roadway. However, other sizes could be used without departing from the invention.
In one embodiment, the platform 701 is mounted on two wheels 703a, 703b. This allows the hitch 706a, 706b to maintain level over various surface conditions. It also allows the hitch 706a, 706b to vary the level of the saws 702a, 702b. In another embodiment, the apparatus 700 is mounted on four (or more) wheels. This embodiment could include a leveling apparatuses on the platform 701 to assure that the platform 701 is level. This embodiment might include accelerometers at the corners of the platform 701 and a controller to direct the leveling apparatuses.
The platform 701 may have saws 702a, 702b on either side for cutting the pavement at the edge of the area to cut. In another embodiment, the saws 702a, 702b could be mounted of such that the saws 702a, 702b could be moved to any distance apart, perhaps by mounting the saws 702a, 702b on the front of the platform 701 on a rail. Saws 702a, 702b could be diamond saws, carbide saws, of any other type of saw suitable for cutting pavement. In many embodiments, water is used to cool the saws 702a, 702b and to minimize the dust from the cutting. The saws 702a, 702b are powered by the power source 106 through the wire harness 707.
The platform 701 also has a variable number of drills 704a-i mounted on the platform. These drills receive their power from the power source 106 through a wiring harness 707. In some embodiments, each drill can be turned on or off separately so that any width of pavement can be removed. For instance, in the moveable saw embodiment above, the saws 702a, 702b could be moved in and four drills 704a-i activated to use the apparatus 700 to remove a smaller section of pavement. The drills 704a-i could be located 1 foot apart in some embodiments and could drill 1 inch holes. The holes could be drilled about 60% of the way into the pavement. The drills 704a-i could be diamond tipped drills, carbide tipped, or other material suitable for drilling pavement. The drills 704a-i could create a core for removal or could break up the material as it drills. In many embodiments, water is used to cool the drills 704a-i and to minimize the dust from the drilling.
In addition to powering the drills and the saws, the power source 106 supplies power to the power storage device 108 through the wire harness 707.
There are also a various number of plasma blast probes 705a-i mounted on the platform, one each behind and in line with the drills 704a-i. After the drills 704a-i create the boreholes in the pavement, the platform is moved forward and the plasma blast probes 705a-i are inserted in the boreholes. The energy stored in the power storage device 108 is then discharged through the cable 116 into the probes to create a plasma blast in the borehole, breaking up the pavement. The plasma blast probes 705a-i are described above, although the design may be modified to maximize the blast waves in a symmetrical, horizontal direction. The distance between the drills and the plasma blast probes could be 1 foot in some embodiments.
In many applications, the energy from the blast needs to be focused on the horizontal directions, and the forces going down minimized. This could be done by designing the probe 500, 705a-i to create the plasma blast low in the cage 506 by making the gap in between the electrodes 601,602 low in the cage 506. The cage 506 then protects the surface below the probes 500, 705a-i and focuses the energy horizontally and slightly upward. Alternately, a metal cone could be placed at the bottom of the borehole to reflect the shock waves going downward back up.
The apparatus 700 could vary the depths of the boreholes, the width of the boreholes, the distance between the boreholes, the distance between the drills 704a-i and the probes 705a-i, the energy used in the blasts, and the distance between the electrodes 601,602 to manage the precision of the pavement removal and to account for various strengths and characteristics of the pavement. Typically, the pavement is about 12 inches thick, and care must be taken not to damage the compacted gravel underside of the concrete roadway. Other applications could consist of airport runways or bridge decking.
In one embodiment, the drills 704a-i and the probes 705a-i could be mounted on such that when the drills 704a-i finish drilling, they are removed from the boreholes and the probes 705a-i are inserted and blast before the platform 701 moves.
In another embodiment, the drills 704a-i and probes 705a-i are mounted such that the boreholes are drilled horizontally into the side pavement. The cage 506 on the probes 705a-i could be designed to focus the blast up and to the sides, protecting the under-pavement and loosening the pavement above the horizontal borehole.
In still another embodiment, the drill bits could be designed to also incorporate a plasma blast probe, so that the drilling and blasting are performed without removing the drill bit/blast probe. In this embodiment, the drill bit is on the bottom of the probe, and cuts the pavement until the blast probe is at the proper depth. Then the probe initiates the plasma blast. To prevent the drilling debris from blocking the electrodes, a plastic sleeve may need to surround the blast chamber. Alternatively, a suction mechanism could be used to remove the drilling debris.
In one embodiment, the functionality of the drills 704a-i could be combined with the plasma blast probe 705a-i. In this embodiment, the probe shown in
A special purpose controller 707 is also located on the platform 701. The special purpose controller 707 is shielded to protect the controller from electrical, magnetic, and mechanical interference from the plasma blasts. The controller 707 could include a special purpose microprocessor, memory, a mass storage device (hard disk, CD or solid state drive), IO interfaces to the probes 705a-i and the drills 704a-i, power conditioning equipment, a Bluetooth interface, a network interfaces (could be WiFi, Cellular, wired Ethernet, or similar).
The controller 707 could operate algorithms to control the separation of the electrodes in the probe 705a-i and the amount of energy (varying voltages and/or the number of capacitors) sent to the probe to create the spark/plasma blast. In addition, the controller 707 could control length of time that the spark is present and the timing of one or more plasma blasts if multiple blasts are desired. By controlling these factors the characteristics of the plasma blast can be controlled with precision. In addition, the controller 707 could determine how deep the drills make the boreholes and the depth where plasma blast probe is located when the blast is initiated.
The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be readily apparent to one skilled in the art that other various modifications may be made in the embodiment chosen for illustration without departing from the spirit and scope of the invention as defined by the claims.
The foregoing devices and operations, including their implementation, will be familiar to, and understood by, those having ordinary skill in the art.
The above description of the embodiments, alternative embodiments, and specific examples, are given by way of illustration and should not be viewed as limiting. Further, many changes and modifications within the scope of the present embodiments may be made without departing from the spirit thereof, and the present invention includes such changes and modifications.
This provisional application draws from US Pat. No. 8,628,146, filed by Martin Baltazar-Lopez and Steve Best, issued on Jan. 14, 2010, entitled “Method of and apparatus for plasma blasting”. The entire patent incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62652076 | Apr 2018 | US |
