Title:
PROCESS FOR PROTECTING POROUS STRUCTURE USING NANOPARTICLES DRIVEN BY ELECTROKINETIC PULSE
Kind Code:
A1


Abstract:
A process for protecting a porous structure includes providing a treatment fluid including nanoparticles including a sealant material coated with a metal ion to a face of the porous structure, and applying a sequence of DC voltage pulses to the porous structure in a position so as to drive the nanoparticles on the face of the porous structure into the porous structure. The metal ion coating of the nanoparticle separates from the sealant material within the porous structure to close pores within the porous structure.



Inventors:
Femmer, Paul (Chesterfield, MO, US)
Application Number:
12/473196
Publication Date:
01/14/2010
Filing Date:
05/27/2009
Primary Class:
Other Classes:
204/515
International Classes:
C25D13/18; C25D13/06
View Patent Images:



Primary Examiner:
MAYEKAR, KISHOR
Attorney, Agent or Firm:
STINSON LLP (ST LOUIS, MO, US)
Claims:
What is claimed is:

1. A process for protecting a porous structure comprising: providing a treatment fluid including nanoparticles comprising a sealant material coated with a metal ion to a face of the porous structure; applying a sequence of DC voltage pulses to the porous structure in a position so as to drive the nanoparticles on the face of the porous structure into the porous structure; wherein the metal ion coating of the nanoparticle separates from the sealant material within the porous structure, the sealant material being for use in closing pores within the porous structure.

2. A process as set forth in claim 1 wherein applying a sequence of DC voltage pulses comprises applying pulses having a duration of less than about 1000 ms.

3. A process as set forth in claim 2 wherein the pulse duration is about 100 ms.

4. A process as set forth in claim 2 wherein the pulses are separated from each other by an time approximately equal to the duration of the pulse.

5. A process as set forth in claim 1 wherein applying a sequence of DC pulses comprises periodically changing the polarity of the DC pulse.

6. A process as set forth in claim 5 wherein periodically changing the polarity comprises changing the polarity of no more than about 1 out of every 5 DC voltage pulses applied to the porous structure.

7. A process as set forth in claim 5 wherein periodically changing the polarity comprises changing the polarity of no more than about 1 out of every 10 DC voltage pulses applied to the porous structure.

8. A process as set forth in claim 1 wherein providing a treatment fluid comprises providing nanoparticles having a silicate sealant material.

9. A process as set forth in claim 8 wherein providing a treatment fluid comprises providing nanoparticles having a lithium ion coating.

10. A process as set forth in claim 9 wherein providing a treatment fluid comprises providing nanoparticles having a latex sealant material.

11. A process as set forth in claim 10 wherein providing a treatment fluid comprises providing nanoparticles having a zinc ion coating.

12. A process as set forth in claim 10 further comprising, subsequent to said step of applying a sequence of DC pulses of applying electroosmosis to the porous structure to dehydrate the latex and initiate self assembly of the latex to block pores within the porous structure.

13. A process for moving nanoparticles into a concrete structure having capillary pores to treat the concrete structure, the process comprising: delivering a treatment fluid mixture of nanoparticles within a carrier liquid to an anode, the nanoparticles comprising silica colloidal nanoparticles coated with lithium; applying a sequence of DC voltage pulses to the anode to induce movement of the treatment fluid mixture from the anode toward a cathode spaced remotely from the anode so that the treatment fluid mixture flows into the capillary pores of the concrete structure, wherein lithium ions of the nanoparticles separate from the silica colloidal nanoparticles in the capillary pores of the concrete structure, wherein the separated lithium ions prevent or mitigate alkali-silica reactions (ASR) in the concrete structure and the silica colloidal nanoparticles react with free calcium hydroxides in the concrete structure to create calcium silicate hydrate (CSH).

14. A process for moving nanoparticles into a concrete structure having capillary pores to treat the concrete structure, the process comprising: delivering a treatment fluid mixture of nanoparticles within a carrier liquid to an anode, the nanoparticles comprising a polymer coated with zinc; applying a first sequence of DC voltage pulses to the anode to induce movement of the treatment fluid mixture from the anode toward a cathode spaced remotely from the anode so that the treatment fluid mixture flows into the capillary pores of the concrete structure, applying a second sequence of DC voltage pulses to drive the carrier liquid out of the concrete structure leaving the polymer coated with zinc in the capillary pores, whereby the polymer expands into pores within the concrete structure.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/056,112 filed May 27, 2008, the entirety of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to processes for protecting porous structures such as concrete from deterioration, and more particularly to a process for moving particles into the porous structure that can prevent and/or ameliorate deterioration of the porous structure.

BACKGROUND OF THE INVENTION

Structures made of materials such as concrete, brick and other cementitious construction materials are porous and therefore subject to invasion by water and other substances. Alkali silica reaction (ASR) is a degradation mechanism in cementitious materials caused by the combination of reactive siliceous aggregates, sufficient alkali and water. ASR forms a gel that expands, with addition of water, and damages concrete and mortars. In addition, reinforcing structure (e.g., rebar) within the concrete will degrade in the presence of water and other substances and causes further degradation of the overall structure.

SUMMARY OF THE INVENTION

In one aspect, a process for protecting a porous structure generally comprises providing a treatment fluid including nanoparticles comprising a sealant material coated with a metal ion to a face of the porous structure. A sequence of DC voltage pulses is applied to the porous structure in a position so as to drive the nanoparticles on the face of the porous structure into the porous structure. The metal ion coating of the nanoparticle separates from the sealant material within the porous structure, and the sealant material is used in closing pores within the porous structure.

In another aspect, a process for moving nanoparticles into a concrete structure having capillary pores to treat the concrete structure generally comprises delivering a treatment fluid mixture of nanoparticles within a carrier liquid to an anode. The nanoparticles comprise silica colloidal nanoparticles coated with lithium. A sequence of DC voltage pulses is applied to the anode to induce movement of the treatment fluid mixture from the anode toward a cathode spaced remotely from the anode so that the treatment fluid mixture flows into the capillary pores of the concrete structure. Lithium ions of the nanoparticles separate from the silica colloidal nanoparticles in the capillary pores of the concrete structure. The separated lithium ions prevent or mitigate alkali-silica reactions (ASR) in the concrete structure and the silica colloidal nanoparticles react with free calcium hydroxides in the concrete structure to create calcium silicate hydrate (CSH).

In yet another aspect, a process for moving nanoparticles into a concrete structure having capillary pores to treat the concrete structure generally comprises delivering a treatment fluid mixture of nanoparticles within a carrier liquid to an anode. The nanoparticles comprise a polymer coated with zinc. A first sequence of DC voltage pulses is applied to the anode to induce movement of the treatment fluid mixture from the anode toward a cathode spaced remotely from the anode so that the treatment fluid mixture flows into the capillary pores of the concrete structure. A second sequence of DC voltage pulses is applied to drive the carrier liquid out of the concrete structure leaving the polymer coated with zinc in the capillary pores, whereby the polymer expands into pores within the concrete structure.

Other features will be in part apparent and in part pointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a first embodiment of an electrokinetic pulse device;

FIG. 2 is a schematic of a mesh anode of the electrokinetic pulse device in FIG. 1 electrically connected to a power supply;

FIG. 3 is a schematic of a second embodiment of the electrokinetic pulse device;

FIG. 4 is a schematic of a third embodiment of the electrokinetic pulse device;

FIG. 5 is a schematic of a porous anode of the third embodiment of the electrokinetic pulse device;

FIG. 6 is a schematic of a fourth embodiment of the electrokinetic pulse device; and

FIG. 7 is a graph showing the electrokinetic pulses provided to in a process according to the present invention.

Corresponding reference characters indicate corresponding parts throughout the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to the drawings, and in particular to FIG. 1, a first embodiment of an electrokinetic pulse (EKP) device is generally indicated at 10. As explained in more detail below, the EKP device 10 is configured to move a treatment fluid mixture of charged (negatively or positively charged) nanoparticles within a carrier liquid through a porous structure 11, such as hardened concrete. Electrokinetic transport includes ionic conduction, electrophoresis, and electroosmosis. Ionic solution conductivity accounts for the overwhelming majority of conductivity measured in concrete. In an aqueous system (concrete structures generally retain some level of moisture content), ions can be induced to drift in response to an applied electronic field. Electrophoresis is characterized by the movement of a solid particle dispersed in an electrolyte under the influence of an electric field. Electroosmosis is the induced flow of water through a porous medium when an electric potential is applied across the medium.

Electro-osmosis has origins in 1809, when F. F. Reuss originally described an experiment demonstrating that water could be forced to flow through a clay-water system when an external electric field was applied to the soil. Research since then has shown that water surrounding the cations moves with them, the flow initiated by the movement of cations present in the pore fluid of a clay, or like porous media such as concrete, brick, and other cementitious construction materials.

The EKP device 10 according to one embodiment of the present invention includes an anode applicator, generally indicated at 12, and fluid delivery system, generally indicated at 14, for delivering the treatment mixture to the anode applicator. In the first embodiment, the anode applicator 12 includes an applicator housing 16 and a porous anode 18 received in the housing. The porous anode 18 may be of a generally planar, mesh construction, such as an expanded titanium mesh strip that is coated with a mixed-metal oxide catalyst. A suitable mesh anode is available from Corrpro Companies Inc., of Medina, Ohio. Other types of porous anodes do not depart from the scope of the present invention. In use, the anode 18 is positioned close to, but not in contact with the porous structure 11. In one embodiment, nonconductive spacers (not shown) may be used to locate the anode 18 relative to the porous structure 11.

In the illustrated embodiment, the mesh anode 18 is located in a distensible member, generally indicated at 19. The distensible member 19 includes a liquid impervious upper portion 20, such as a latex material, and a liquid pervious lower portion 22, such as a porous fabric or absorbent spongy material. In the illustrated embodiment, the distensible member 19 is generally cuboidal, where the upper portion 20 includes an upper face and four side faces and the lower portion 22 includes a bottom face. At least the upper portion 20 may be distended to some degree under fluid pressure. As will be explained in more detail below, the applicator housing 16 includes an open bottom through which the bottom face of the lower portion 22 contacts a surface of the porous structure to be treated. Generally, contact of the lower portion 22 with the surface of the porous structure places treatment fluid mixture on the face of the porous structure. However, the portion may be located close to, but not in contact with the face of the porous structure and still be considered to have treatment fluid mixture on the face of the porous structure. In one example, the distensible member 19 may have a length of about 4 ft (1.2 m), a depth of about 4 ft (1.2 m), and a height of about 6 in (15.2 cm), and the mesh anode 18 may have a length of about 4 ft (1.2 m), a depth of about 4 ft (1.2 m. The anode applicator 12 may have other configurations without departing from the scope of the present invention. For example, a mesh anode may be disposed between upper and lower absorbent layers so that opposite faces of the porous anode are in contact with the absorbent material.

The fluid delivery system 14 includes a treatment container 30 for holding a quantity of the treatment fluid mixture, and a pump 32 or other fluid mover for delivering the treatment fluid mixture from the treatment container to inlet(s) 33 of the anode applicator 12. In one example, the treatment container 30 may be a large volume container, and the pump 32 may be a pump that is suitable for delivering between about ⅛ L/hour and about 5 L/hour of treatment fluid mixture to the anode applicator 12. The treatment container 30 and the pump 32 may have other specifications and working capabilities without departing from the scope of the present invention. Flexible tubing 34 fluidly connects the treatment container 30 to the pump 32, and additional flexible tubing 35 connects the pump to the anode applicator 12. The components may be fluidly connected in other ways without departing from the scope of the present invention. Moreover, the treatment fluid mixture may be delivered to the anode applicator 12 in other ways without departing from the scope of the present invention.

Referring to FIGS. 1 and 2, the EKP device 10 also includes a power supply 36 that is electrically connected to a cathode 38 and the mesh anode 18 by independent electrical lead wires 39 or in other ways without departing from the scope of the present invention. The power supply 36 may be a DC or AC generator, whose output signal (e.g., voltage) is controlled by a controller 40, such as a microcontroller. In the illustrated embodiment (FIG. 2), separate lead wires 39 are connected at a center and four corners of the mesh anode 18. The controller 40 controls the power supply 36 to apply equal amounts of current to each of the five connection points of the mesh anode 18 so that current is uniformly distributed across the face of the anode during active treatment. In one example, which is explained in more detail below, the output signal from the power supply 36 may be a pulsed DC signal (e.g., voltage signage). An exemplary sequence of DC voltage pulses is illustrated in FIG. 7. In this illustrated sequence, a positive pulsed DC voltage of a selected magnitude (e.g., within a range of about 30 volts to about 50 volts) is applied for 100 ms, followed by 0 volts for 100 ms. In the illustrated embodiment, this 100 ms of positive DC voltage followed by 0 volts is repeated 9 more times for a total of 10 times. After the 10th time (an elapsed time of 2 seconds), a negative pulsed DC voltage of a selected magnitude (e.g., within a range of about −30 volts to about −50 volts) is applied, followed by 0 volts for 100 ms. Applying a negative pulsed DC voltage every 2 seconds or so prevents polarization of the cathode and anode. The illustrated sequence is repeated for up to 48 to 72 hours or more, depending on the treatment and the structure being treated.

In one example, the parameters of the output signal may be selectable by the user and implemented by the controller 40. For example, the user may be able to select the most effective voltage, amperage, pulse sequence, pulse duration, pulse shape and treatment period for a given application. In one embodiment, the duration of the electrokinetic pulses may be from about 10 ms to about 100,000 ms and the voltage range may be from about 20V to about 100V. The controller may also be configured (i.e., programmed) to automatically switch the direction of the flow of electrical current from the cathode 38 to porous anode 18 to reduce polarization of the cathode and anode. Further, the controller may be configured (i.e., programmed) to provide the user with programmable controls over the quantity, timing and duration of the mixture delivered to the anode applicator platform.

The ability to control such parameters gives the user flexibility in applying treatments from structure to structure. For example, one may want to use a higher voltage in order to move nanoparticles into the porous structure more quickly. The greater magnitude of the voltage, the greater the particle density, but the more concrete damage is likely. Also, for example, changing pulse duration from a typical 1 to 6 seconds each, to only 100 milliseconds each will drive the nanoparticles deeper because the faster the pulses, the greater the depth penetration of nanoparticles. Moreover, different durations of negative pulses (reversed polarity—anodes become cathodes, cathodes become anodes) to try to get more positive pulses sandwiched in between two negative pulses may be advantageous in some applications because it is believed that increasing the total percentage of positive vs. negative pulses in one sequence will increase the amount of nanoparticles that can be migrated into the porous structure. However, it is also believed that the lower the percentage of negative pulses in a repeating sequence, the greater risk of polarizing the electrodes (anodes and cathodes).

Referring to FIG. 4, a second embodiment of an anode of the EKP device 10 is generally indicated 118. The anode 118 comprises at least one porous anode tube in place of the porous anode 18 and absorbent layers 22, 24. The porous anode tube(s) 118 may be embedded in the porous structure 11. The porous anode tube 118 is in fluid communication with the fluid delivery system 14 for receiving the treatment fluid mixture from the container 30. The anode tube 118 may include a plurality of openings 120 to allow movement of the treatment mixture out of the tube and toward the cathode during treatment.

In the embodiment illustrated in FIGS. 1 and 4, the cathode 38 comprises a metal object or an interconnected series of metal objects that are inserted into the porous structure 11 to be treated. For example, hole(s) may be drilled into the porous structure 11 and the cathode(s) 38 may be inserted therein. In another example (FIG. 3), a metal reinforcement component 42 (e.g., steel rebar) embedded in the porous structure may be used as the cathode. Referring to FIGS. 5 and 6, in yet another example, the cathode 38 may comprise one or more metal saturation tubes 44 inserted into soil S (i.e., earth) adjacent the porous structure 11. The saturation tube 44 includes openings 45 or are otherwise porous for delivering fluid outward into the soil. For example, the saturation tubes 44 may be made from copper, and may have a diameter of between 0.5 in and 1.0 in. In this illustrated embodiment (FIGS. 5 and 6), flexible tubing 46 fluidly connects the metal saturation tube(s) 44 to a container 48 comprising an electrically conductive fluid (e.g., an electrolyte solution). A pump 50 delivers the electrically conductive fluid into the metal saturation tube(s). The delivered fluid flows through the openings 45 in the metal saturation tube(s) 44 and saturates the area surrounding the metal saturation tube. The saturated area effectively becomes cathodic to increase the size, uniformity and coverage of the cathode surface area so as to provide an effective ratio of cathode surface area to anode surface area. The cathode(s) 38 may be of other types and configurations without departing from the scope of the present invention. In general, the cathode(s) 38 would be placed on the opposite side of the porous structure 11 (from the anode 18). The cathode 38 may be in direct contact with the porous structure (e.g., embedded in the porous structure) or may be next to the porous structure in a porous media. As one example, if the porous structure is reinforced with steel, the reinforcing structure may be used as the cathode. Preferably, the cathode 38 is wet with water or compatible electrolyte solution to maintain uniform cathodic polarity on the opposite side of the anode 18.

In the embodiment of FIGS. 5 and 6, the porous structure 11 has a vertical orientation. Thus, the applicator housings 16 are particularly configured to prevent escape of the treatment fluid mixture down the face of the structure. For example a nonconductive seal or dam is placed at the circumference of the housing to retain the treatment fluid mixture.

In one embodiment (FIG. 3), circuitry minimizes stray current corrosion of steel reinforcement 42 (e.g., rebar) and metal penetrations during active treatments. This circuitry divides the negative potential between the protected steel and the cathode by means of real-time feedback from embedded half-cells. Programmed power supply circuitry provides an electrical path for stray current on steel reinforcement to return to the power supply. If the corrosion potential of the steel reinforcement increases during the treatment, the controller may be programmed to provide additional cathodic protection (negative potential) to the reinforcement.

Using any one of the embodiments described above or other embodiments, in use the EKP device 10 induces, by electro-osmosis, movement of the treatment fluid mixture from the porous anode 18 toward the cathode 38. The anode applicator 12 is placed on the surface of the porous structure to be treated so that the anode 18 is generally opposing the surface and the lower absorbent layer 22, through the open bottom of the applicator housing 16, is in contact with the surface. The treatment fluid mixture is delivered to the anode 18 and the controller 40 supplies the anode with a selected output signal from the power supply 38 so that the treatment fluid mixture travels through capillaries and pores in the surface of the porous structure and into the porous structure toward the cathode 38.

In one example (FIG. 6), a plurality of EKP device 10 may be interconnected to concurrently treat large areas of a single porous structure such as roadways, bridge decks, and sea walls. For example, the EKP device 10 may be mobile including, but not limited to, rolling applicators similar to flat-bed trailers. In one embodiment, the EKP devices 10 may be synchronized so that all anode applicators and tubes involved in a multi-applicator treatment of a single structure are synchronized.

There are numerous treatments that can be applied to the porous structure 11 using the EKP device 10, 110. In one example, the treatment fluid mixture may comprise coated nanoparticles in a carrier liquid. The coated nanoparticles in the carrier liquid are moved into and through the porous structure using a pulsed-DC output signal (i.e., pulsed DC voltage) from the power supply 38. In one exemplary treatment, the coated nanoparticles may comprise nanoparticles of silicate coated with lithium (i.e., lithium-coated silicate) mono-dispersed in water. For example, the lithium-coated silicate may be amorphous, silica colloidal nanoparticles that are encapsulated with lithium that is held on the surface of the silica by an ionic bond. The treatment mixture may include lithium-coated silicate nanoparticles of differing sizes. For example, the nanoparticles may have diameters ranging from about 10 nm to 100 nm, and more preferably from about 30 nm to about 60 nm. It will be understood that the appropriate sizes will depend upon the nature of the porous material and in particular the size of the pores in that material. Moreover, different sized particles may be used in the same treatment fluid mixture. Smaller sizes may more completely fill pores, but larger sizes will complete the job more rapidly. In one example a mixture of 30 nm and 60 nm particles may be used in the treatment fluid mixture.

The sequence of pulsed DC voltages illustrated in FIG. 7 and described above may be utilized in this example to drive the lithium-coated silicate into the porous structure 11. As the lithium-coated silicate are being driven into the porous structure 11, it is believed that lithium ions (broadly, “metal ions”) separate from the silicate particles, whereupon the lithium ions prevent or mitigate ASR gel expansions in the concrete and the silicate (broadly, “a sealant material”) reacts with free calcium hydroxides to create precipitates including calcium silicate hydrate (CSH), which fills the pores and capillaries, and helps prevent chlorides from reentering the treated area. It is also believed that the distribution of the lithium-coated silicate nanoparticles within hardened concrete, or other porous structure, will prevent or mitigate rebar corrosion and sulphate attack in the concrete.

In another exemplary treatment, the coated nanoparticles in the carrier liquid may comprise coated latex nanoparticles, such as zinc-coated latex nanoparticles, mono-dispersed in water. The latex may be more broadly considered a polymer and still more generally a “sealant material.” For example, the zinc-coated latex nanoparticles may be latex colloidal nanoparticles encapsulated with zinc that is held on the surface of the colloidal nanoparticles by an ionic bond. The treatment mixture may include zinc-coated latex nanoparticles of differing sizes. For example, the nanoparticles may have diameters ranging from about 30 nm to about 60 nm

In a first step of this treatment using zinc-coated latex nanoparticles, the porous structure 11 is dehydrated using the EKP device 10. A first sequence of pulsed-DC electrical signals (e.g., voltages) is applied to drive water is driven out of structure 11 by electro-osmosis. The first sequence of pulsed-DC electrical signals may be a conventional sequence as known in the art. After dehydrating the porous structure 11, the zinc-coated latex particles are moved into the hardened concrete, or other porous structure, using a second sequence of pulsed-DC electrical signals (e.g., voltages) from the power supply 38, as controlled by the controller 40, to create a second pulsating electrokinetic field between the anode 18 and the cathode 38. The sequence of pulsed DC voltages illustrated in FIG. 7 and described above may be utilized in this example to drive the coated latex particles into the porous structure 11.

Typically, although not necessarily, there is a delay following driving the zinc-coated latex nanoparticles into the hardened concrete. Subsequently, a second dehydration step by electroosmosis is carried out. The operation may be substantially the same as the first electroosmosis step. The second electroosmosis step drives water out of the latex causing the polymer in the latex to self assemble. In other words the polymer expands out in tendrils into pores in the hardened concrete, thereby sealing the pores.

The treatments may last anywhere from several hours to several months depending on the concentration and depth of penetration of the treatment fluid mixture desired. In the case of lithium coated silicates, once the electrokinetic field is removed, the lithium is allowed to react with the ASR gel to prevent gel expansion. The silicate particles will then react with the free calcium hydroxide and form calcium silicate hydrate compounds that densify and strengthen concrete while also effectively reducing the available alkali in the cementitious matrix. In the case of zinc-coated latex nanoparticles, zinc separates from the latex inside the porous structure and plates on any steel (e.g., rebar) in the porous structure. This protects the steel against corrosion. The latex free of its zinc coating is operable to close pores within the porous material.

With any of the above treatments or other treatments using the EKP device, probe sensors can be used to provide real-time feedback to the power supply indicating the ratio of lithium to potassium and sodium, the ratio of hydroxyl ions to chloride ions, and permeability changes. After the desired ratios are achieved, the user is notified automatically by an electronic display connected to the power supply that treatment for that particular area is successful. The electrodes are removed from the structure, and repairs are made to any anode and/or cathode holes.

Moreover, in one embodiment the EKP device may include a system for self-monitoring (i) the ratio of lithium to potassium and sodium ions so as to determine effectiveness of the alkali-silica reaction (“ASR”) treatment, (ii) the ratio of chloride to hydroxyl ions so as to determine the effectiveness of the corrosion treatment, and (iii) the moisture transmission rates within the concrete or other material so as to determine the effectiveness of the permeability reduction treatment, and (iv) the uniformity of current distribution across the face of each anode or cathode applicator, so as to determine the effectiveness of each applicator for its intended use.

Moreover, during treatment sufficient quantities of conductive fluids may be introduced into the surrounding permeable media, saturating said media with those fluids, embedding cathode in said saturated media, and using said saturated media as a wide-coverage cathode similar in size to the surface area of the anode to ensure that the coated particles and/or latex spheres are distributed throughout the treated structure.

When introducing elements of the present invention or the preferred embodiment(s) thereof, the articles “a”, “an”, “the” and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

As various changes could be made in the above constructions, products, and methods without departing from the scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.