US3587964A - Protective course for bridge deck - Google Patents

Abstract

A PROTECTIVE COURSE FOR A RAILROAD BRIDGE DECK TO BE INTERPOSED BETWEEN A MEMBRANE AT THE DECK SURFACE AND BALLAST ROCK THEREABOVE. THE COURSE IS FORMED AS TWO LAYERS OF SHEETING OF MODULAR SIZE ARRANGED IN AN ALTERNATING PATTERN SO THAT THE JOINTS OF ONE LAYER OFFSET THE JOINTS OF THE OTHER LAYER. EACH SHEET, RECTANGULAR IS FORM, IS A SANDWICHLIKE CONSTRUCTION INCLUDING A CORE SO ASPHALT AND LIMESTONE PARTICLES BETWEEN REINFORCING COVERS OF FELT WEB SATURATED WITH ASPHALT AND COATED WITH ASPHALT.

Description

United States Patent [mentor Dale J. ('ork Elgin, Ill. Appl. No. 817.338 Filed Apr. 18, 1969 Patented June 28,1971 Assignee W. R. Meadows, Inc.

Elgin, Ill.

PROTECTIVE COURSE FOR BRIDGE DECK 9 Claims, 8 Drawing Figs.

Int. Cl EOIb 2/00, EOlc 3/00 Field oi'Search 238/],2;

{56] References Cited UNlTED STATES PATENTS 1,193,843 8/1916 Symmes 94/3 1,552,852 9/1925 lnnes 94/3 2,420,833 5/1947 Monroe..... 94/4 2,742,829 4/1951 Bagby 94/4 Primary ExaminerArthur L. La Point Assistant Examiner Richard A. Bertsch Attorney-Van Valkenburgh & Lowe ABSTRACT: A protective course for a railroad bridge deck to be interposed between a membrane at the deck surface and ballast rock thereabove. The course is formed as two layers of sheeting of modular size arranged in an alternating pattern so that the joints of one layer offset the joints of the other layer. Each sheet, rectangular in form, is a sandwichlike construction including a core 0s asphalt and limestone particles between reinforcing covers of felt web saturated with asphalt and coated with asphalt.

PATENTED JUN28 Mi 3 587 964 sum 1 or 2 Fig. 5

INVENTOR. Dale J. Cork ATTORNEYS PATENTED Juuzs 1971 3587964 sum 2 0F 2 33 30 H h g 6 as 34 I" 1. i V l l l 52 fig Q g I M as T 1N TOR.

Dale J. C

ATTORNEYS Fig. a um WM /g PROTECTIVE COURSE FOR BRIDGE DECK The present invention relates to the placement of a waterproof membrance upon the deck of a railroad bridge, and more particularly to the use of a protective cover, commonly called a protection course, of material to be placed upon the membrane to protect the membrance from being cut by the ballast rock thereabove.

It has been found advantageous to provide for continuous deck surfaces on railroad bridges, instead of using open trestle types. This permits ballast to be placed upon the deck to better support the ties and rails. However, one problem which has developed by changing the type of bridge structure, relates to the accumulation and retention of moisture upon the bridge decks, not only from rain and snow, but also from the trains passing over the bridge. Supplementing this moisture accumulations, there is an accumulation of substances dropped from passing trains, especially brine, which is of a deleterious nature when wet. Over a period of a few years, this moisture and substances such as brine drippings can corrode or otherwise damage a bridge structure excessively and such damage will occur whether the bridge is a steel or reinforced concrete structure. Accordingly, the accepted standards of railroad bridge construction require the installation of a moistureproof membrane upon the bridge deck before the ballast is placed thereon to support the'ties and rails. Thus, water accumulating on the bridge will either subsequently evaporate or be discharged from the deck through drains provided for that purpose wetting the structural members of the bridge deck.

Initially, this protection course was provided as extruded planks of an asphaltic material approximately 1 foot wide, 1%.inches thick and of various lengths suitable for handling. The planks and layers of asphalt felt were placed upon the bridge deck and hot mopped with asphalt to form a comparatively heavy monolithic membrane. One disadvantage of such a membrane was the tendency to crack at the joints under the vibration imposed by trains passing over the bridge, especially in extremely cold weather. Therefore, sheets of pliable, rubberlike, synthetic resin has substantially replaced the asphalt plank-hot mop construction as the moisture barrier membrane. Butyl rubber has been found to be the preferable material for this purpose. One advantage in the use of butyl rubber resides in the fact that sheets are easily welded together and it is now a common practice to use a continuous l/I6-inch-thick layer of butyl rubber to serve as the membrane for the deck of a railroad bridge.

However, butyl rubber and any other type of synthetic resin sheet or other conventional waterproofing layer must be protected because the ballast rock will have to withstand heavy loads and be subjected to intense vibration as trains cross the bridge. Without a'protective cover, the sharp edges and corners of the rock would quickly cut through the rubber membrane to render it useless. Accordingly, the practice has been to cover the butyl rubber with a layer of asphalt planks to serve as a protective course for the membrane.

The use of asphalt planks to cover and protect the butyl rubber membrane has not proven satisfactory. The common practice is to hot mop these planks to seal the cracks between then and this is necessary to fully protect the membrane from the action of dust and fine particles which would otherwise sift through cracks and onto the membrane. The planks are quite heavy and expensive. Also, the mopped asphalt planks produce a solid, inelastic layer which will not move or yield without cracking, but a protective course on a railroad bridge is subjected to and must be flexible. Moreover, there always exists the further possibility that the hot asphalt flowing through joints between the planks will affect the quality of the butyl rubber used as the protection layer. As a result of these unsatisfactory features, the railroads have now removed from their specifications any hot mopped application wherein a protective course is to be applied of butyl rubber.

The present invention was conceived and developed with such and other considerations in view and comprises, in essence, a protective course to cover the butyl rubber membrane on a bridge deck which consists of at least two layers of prepared asphalt sheets of a dense, asphaltic construction uniquely compounded to combine the qualities of toughness, resistance to rock penetration and the ability to withstand vibration without cracking, especially at low temperature. The sheets are proportioned as easily handled modular units to permit them to be applied to the bridge deck, with the two layers being in a staggered manner and in an arrangement which produces a weatherproofed construction without the need of applying hot asphalt to the same.

It follows that an object of the invention is to provide a novel and improved sheeting material for the protective course for bridge decks adapted to overly a membrane of butyl rubber or similar water-resistant material.

Another object of the invention .is to provide a novel and improved protective course for overlaying the membrane of a bridge deck which is a tough, weather-resistant construction adapted to effectively resist the cutting and penetrating action of sharp ballast rock when the rock is under the influence of the vibration and pressure caused by heavy trains crossing a bridge.

Another object of the invention is to provide a novel and improved protective course for overlaying a bridge deck membrane which is formed of a material having sufficient ductility to yieldably receive and seat the ballast rock into the surface of the course, but at the same time resist any excessive penetration of any rock, and which will also retain the desirable qualities of limited ductility in extremely cold weather, sufficient to resist any tendency of cracking or breakdown due to vibration imparted to the ballast by passing trains.

A further object of the invention is to provide a novel and improved multilayer protective course for a railroad bridge which willeffectively prevent dust particles and the like in the ballast from sifting downwardly through any joint or crack to contact the membrane therebelow.

Another object of the invention is to provide a novel and improved, multilayer protective course for a railroad bridge which may be quickly applied with a minimum of labor and with the layers being in a staggered arrangement to fully protect a membrane therebelow.

Other objects of the invention are to provide a protective course for a bridge deck membrane which has a low initial cost, a long life and which will effectively increase the useful life of the membrane it covers and the useful life of the bridge structure itself.

With the foregoing and other objects in view, the present invention comprises certain constructions, combinations and arrangements of parts and elements, and steps and sequences, as hereinafter described, defined in the appended claims, and illustrated in preferred embodiment by the accompanying drawing in which:

FIG. 1 is a transverse sectional view of a bridge deck of a type wherein the invention, the improved protective course, is applied to protect the deck membrane from the ballast thereabove.

FIG. 2 is a fragmentary sectional portion as taken from the indicated line 2-2 at FIG. 1, but on an enlarged scale.

FIG. 3 is a fragmentary sectional portion as takenfrom the indicated line 3-3 at FIG. 2, but on a further enlarged scale.

FIG. 4 is a perspective view of a single, modular sheet of protective course material.

FIG. 5 is a fragmentary sectional portion of the sheet shown at FIG. 4, as from the indicated line'5-5 at FIG. 4, but on a greatly enlarged scale to indicate in a somewhat diagrammatic manner the construction of this sheet.

FIG. 6 is a perspective view of a portion of a bridge deck, commencing with a transverse section similar to FIG. 1, and illustrating the materials upon the bridge deck as being removed in a sequence to better show the layering of the membrane upon the deck and the protective course structure thereabove.

FIG. 7 is a fragmentary sectional portion as taken along a joint, as at the indicated line 7-7 at'FlG. 6, but on a greatly enlarged scale, the figure being somewhat diagrammatic to illustrate the accumulation of fines upon the surface of the sheet and the manner in which the multilayer protective course completely prevents the migration of such lines to the membrane as through a joint after the ballast is in place.

FIG. 8 is a diagrammatic line view to represent an apparatus suitable for the manufacture of the improved protective course sheets.

Referring more particularly to the drawing, FIG. 1 is illustrative of a typical railroad bridge structure S having a continuous deck D illustrated as being of reinforced concrete, although this deck may also be of structural steel members and steel plates. The bridge deck is generally formed with a flat surface whereon a membrane M, of butyl rubber or like material, is placed to protect the same from the effects of moisture. A layer of felt, not shown, may be placed upon the deck to provide a surface for the membrane if this is considered desirable. The butyl rubber, as commonly used for a membrane, is provided as a l/16-inch sheet, and there will necessarily be joints in the membrane since a single sheet, sufficiently largefor a bridge deck, cannot ordinarily be provided. However, these joints can be easily and effectively cemented together to produce a continuous, waterproof sheet or membrane.

The improved course P, hereinafter described in detail, is placed upon the membrane M to prevent it from being cut by ballast rock. The ballast B, which may be of crushed rock or slag depending upon the material available, is then placed upon the protective course and shaped and tamped to properly receive railroad ties T. To complete the structure, rails R are spiked to the ties. In order to retain ballast B upon this bridge deck, precast concrete curbs C are secured along each side of the deck by placing them directly upon the membrane M. Thus, the materials placed upon the bridge combine with the membrane to provide a sandwichlike construction, including the membrane, the improved protective course P and the ballast.

The protective course which overlies the membrane is formed as two layers of substantially rigid sheets 20, of a filledasphalt composition, having a selected thickness and a blend of materials capable of yielding somewhat to receive and seat the sharp points of ballast rock, but preventing any substantial penetration of such rock through the course to cut into the membrane.

The American Association of Railroads conducted tests on a number of types of proposed protective courses. The tests included subjecting a sample section of a proposed material, covered with ballast, to a load and to vibration. The vibration test, which thus simulated the effect of movement of a train across a bridge, was extended for a period which would approximate the vibration expected to be encountered over a 40-year life expectancy of a bridge. in tests concerning the improved material hereinafter disclosed, it was established that the maximum penetration of sharp rocks into the material was approximately three-eighths inch. Hence, for a design criterion, and to provide a realistic safety factor, the thickness of each sheet of the improved, two-layer protective course was established as three-eighths inch to cope with conditions which could be encountered in the field as suggested by the Association's tests. That is, in using the improved, two-layer protection course, the penetration of rock will be only into the top sheet 20 and with the bottom sheet fully protecting the membrane thereunder.

The improved sheet 20, as illustrated at FIG. 4, is rectangular and preferably 4 feet by 8 feet in size, to provide a modular unit, of a size and weight suitable for easy transportation and handling. This sheet is formed as a five-layer member, as illustrated at H0. 5, including a core 21 of a selected blend of asphalt and limestone particles, a reinforcing cover 22 of asphalt saturated felt at each side of this core and protective coating 23 at each other side of the felt. In addition, one side of the sheet has amica coating, forming a separator to permit the sheets to be stacked and stored without the danger of one sheet welding to an adjacent sheet while being so stored.

Asphalt and limestone particles are blended to form the core 21, with the asphalt forming the matrix of the blend to impart increased density and enhanced stiffness and body'to the core. Fine limestone particles, those which would pass a screen, can be used to permit the use of a somewhat softer asphalt than would be otherwise possible which would be desirable where the material is subjected to extreme cold weather. The important aspect to the invention, however, resides in the fact that the bulk of the limestone particles in this core 21 are of a selected size range which is much too large to constitute a dust of the type ordinarily used to stiffen an asphalt. The particles constitute instead, an aggregate bound in the asphalt matrix which will permit points of ballast rock to penetrate a short distance into the core to secure a good seating position as in the manner illustrated at FIG. 3. The aggregate will then resist further penetration and will support the ballast rock.

The core asphalt is preferably an airblown type having a softening point temperature in the range of 200--250 F. and preferably, in the range of 225-235 F. (Ring and Ball Test Method ASTM E28) and a-penetration in the range of 10 -30 at 77 F. and preferably, in the range of 16-21 at 77 F. (ASTM D-S Although an airblown asphalt having the preferred softening point and penetration properties is desirable for this core asphalt, it is to be recognized that somewhat softer asphalts can be used for the purpose at hand when they are rendered equivalent to the preferred material by blending with mineral fillers such as clay or fine limestone dust.

A preferred sizing of limestone particles to be blended with the asphalt to form the core 21 is a follows:

100 percent passing a four-mesh screen 25-40 percent passing a l6-mesh screen 5-15 percent passing a SO-mesh screen 2-5 passing a 100-mesh screen This sizing of limestone particles is not entirely critical for some particles could be large enough to be retained on a four-mesh screen although this would not be desirable. Also, the sizing of smaller particles could be varied somewhat so long as the particles would produce an aggregatelike structure within the core. It is to be recognized that while limestone particles are preferred as an aggregate in this core, the particles could be of rock such as silica, or other types, which would function in a manner fully equivalent to that of the limestone particles. In any event, the particles selected bond to the asphalt and in preparing the particles, various agents may be used to assure this bonding.

The proportions of asphalt to limestone particles found to be suitable can also be varied. The asphalt content may vary from a maximum of 75 percent to a minimum of 25 percent, by weight, and conversely, the limestone particles may vary from a minimum of 25 percent to a maximum of 75 percent, by weight. Using the preferred type of asphalt as indicated above, it was found that a suitable and preferred blend for the core material used 50 to 60 percent asphalt, by weight. The reinforcing covers 22 are conventional raw felt webs saturated with asphalt. However, the amount of asphalt used to saturate a felt web is substantially more than that commonly used. Instead of a conventional saturation of 12-130 percent of asphalt, by weight, the amount is substantially greater than normal, and in the range of -160 percent and preferably as much as percent asphalt, by weight. This higher saturation minimizes the presence of voids within each felt web and produces a tougher and stronger layer which will bond tightly to the core.

Raw felt webs are commonly available and may be provided in various weights and thicknesses. Although weights and thicknesses are not critical, a lighter web which may be used is prepared from a felt which weights 21 pounds per 480 square feet before saturation and is commonly called a 9-pound felt, per 100 square feet, after saturation. Another weight of web which is preferred as a reinforcing cover 22, is prepared from a felt which weights 27 pounds per 480 square feet before saturation and is commonly called a 15-pound felt, per 100 square feet, after saturation. These weights are somewhat approximate depending upon the degree of saturation. Also, the thicknesses of the saturated webs will vary from a minimum thickness of approximately one thirty-second inch to a thickness of one-sixteenth inch, the heavier felt being preferred to stiffen the sheet so that it may be easily handled in the field and at the same time provide for a tougher surface on the sheet 20. The asphalt used to saturate the felts is not critical and may be a blown asphalt having a 135 1 70 F. softening point and a 30-50 penetration at 77 F.

The protective coating 23 at each side of the sheet serves several functions. This asphalt is preferably the same as the asphalt in the core 21 and is applied onto the felt covers 22 while it is quite hot and while the felt covers are also hot to better soak the coating asphalt into the felt covers. it was found to be desirable to roll this coating 23 upon the felt in a conventional manner and not to finish the coating surface further, but to leave the final surface somewhat mottled or stippled from the effect of rolling. It was found that this slightly irregular surface provided for better contact with rock. The weather coating 23 allows penetration of the ballast rock and a locking and seating of this rock into place. Also, the rough surface 23 provides a better gripping of an upper sheet with a lower sheet when the protective course is placed upon a bridge.

FIG. 8 indicates in a diagrammatic manner, an apparatus for one mode of manufacturing the sheets. A roll of felt 30 is mounted above and a second roll 31 is mounted below the feeder 32 of a pugmill 33. The asphalt and lime dust are blended in the pugmill and this hot blend is extruded from the mill and is extended between the felt webs 30 and 31 as they move through the apparatus. These webs and core material next move between sizing rolls 34 which form a sandwiched web 35 and establishes the thickness of the final sheets 20. Thence, as the material continues its movement through the apparatus, the sandwiched web 35 is subjected to rolls 35 which apply the outer surface coating onto the felt covers 22 to produce the coating 23. The web 35 is then cooled and mica is applied to the upper surface thereof as from a dispenser 37. Finally, the web 35 is trimmed and cut as by a shears 38, to fonn the sheets 20. The sheets 20 are then ready for storage and for transportation to the point where they will be used.

The application of these rectangular module sheets, preferably 4 feet by 8 feet in size, is illustrated specifically at FIGS. 6 and 7. The bridge deck D is first prepared to receive butyl rubber membrane M. It may be merely cleaned of dirt and rock particles or it may be covered with asphalt of asphalt-saturated felt, if desired, since the butyl rubber mem' brane is not reactive with asphalt. Once the membrane M is layed, all of the joints in the membrane material are welded together as by heat or by solvent processes. Next, the lower, first layer of the protection course is placed upon the bridge deck, preferably with the longitudinal dimension of the sheets extending longitudinally with respect to the bridge. A number of these sheets 20 are abutted together in rows and tiers to form a continuous pad on the bridge, commencing by laying a first row 40 alongside a bridge curb C at one side of the deck. This is a quick, simple, manual operation and sheets 20 need be cut to size only at a final row 41 to fit against the opposite curb C, as illustrated at FIG. 6. The sheets forming the lower layer are preferably placed with the faces having the mica coating turned downward and against the butyl rubber membrane, and with a comparatively fresh asphalt surface facing upwardly. Preliminary to the laying of the second layer of the protective course upon the bridge, rectangular pads 42 of a resin such as polyvinyl chloride and having a thickness of approximately 20 mils, are placed at the center points of each joint reach as illustrated in full lines and in broken lines at P16. 6.

The second, upper layer of sheets S is then placed upon the first layer in a staggered manner with the first row 43 of this upper layer being only of half width. Accordingly, the joints of this second course lie halfway between the joints of the first course, and the pads are located at the crossover points of the joints of the upper and the lower courses. As indicated, the final row 44 of this upper layer is cut wide enough to fill the gap next to the opposite curb C. preferably, this upper layer is placed upon the lower layer with the comparatively fresh asphalt surfaces facing downwardly and with the mica-coated faces facing upwardly. Accordingly, the sheets will, over a time period, weld together into a practically unitary pad which is quite resistant to moisture.

The bridge deck thus prepared is then ready for ballast and for completion, by placing ties and rails upon the ballast. No further attention need be given the membrane and protective course for many years. There will be a tendency for dust from the ballast rock and from the air to settle through the rock and onto the top of the protection course to form a layer 50, FIG. 7. This dust can very well have chemically active substances which could adversely affect the membrane if such substances were permitted to settle upon and to contact the membrane M over a long period of time. However, when settling upon the protection course and upon the chemically inert asphalt cover 22, the same substances will congeal as the layer 50 and become a hard, resistant crust which actually further protects the surface of the protection course.

The pads 42 prevent this dust from sifting through cracks between the sheets 20 of the lower layer. As illustrated at FIG. 7, this dust will not only form the layer 50 on top of the protection course, but particles will sift between the cracks of the sheets 20 of the upper course as indicated at 51. However, the pads 42 will prevent further downward movement of this dust.

I have now described my invention in considerable detail. However, it is obvious that others skilled in the art can build and devise alternate and equivalent constructions which are nevertheless within the spirit and scope of my invention.

1 claim:

1. ln the combination with a railroad bridge deck having a waterproof, plastic membrane thereon, a protective course upon the membrane and ballast rock upon the protective course to support ties and rails, wherein the protective course comprises:

a bottom layer of a plurality of flat sheetsabutted together at contacting ends to form a continuous layer of uniform thickness;

a top layer of a plurality of flat sheets abutted together at contacting ends to form a continuous layer of uniform thickness; and

wherein the sheets of each layer are a sandwichlike construction having: a core of asphalt matrix and rock particles with the rock particles constituting between 25 percent and 75 percent by weight, of the core, a reinforcing cover saturated with asphalt at each side of the core, and an asphaltic protective coating over each side of the cover.

2. ln the organization set forth in claim 1, wherein the said asphalt matrix material has a softening point temperature between 200 and 250 F. and a penetration, at 77 F., between 10 and 30 and wherein the aforesaid asphalt constitutes between 25 and 75 percent, by weight, of the core material.

3. In the organization set forth in claim 1, wherein said asphalt matrix has a softening point temperature between 225 F. and a penetration, at 77 F., between 10 and 30 and wherein said asphalt constitutes between 50 and 60 percent,

by weight, of the core material.

4. In the organization set forth in claim 1, wherein said particles constitute between 25 and 75 percent of the aforesaid core material and consist of a blend passing a four mesh screen.

5. in the organization set forth in claim 4, wherein said particles are limestone.

6. in the organization set forth in claim 1, wherein each layer is formed as an array of sheets abutted together end to end to provide an uninterrupted top and bottom surface in the layer with the sheets of one layer being staggered with respect to the sheets of the other layer to prevent the joints of one layer from being in registration and alignment with the joints of the other layer; and

pads between the layers at points where the joints cross.

7. In the organization set-forth in claim 1, wherein each layer is formed as an array of substantially rectangular sheets abutted together end to end to provide an uninterrupted top and bottom surface in the layer with the sheets of one layer being staggered with respect to the sheets of the other layer to prevent the joints of one layer from being in registration and alignment with the joints of the other layer.

8. In the organization set forth in claim 7, including pads of a thin, impermeable material between the layers where a joint of one layer crosses the joint of the other.

9. In the combination with a railroad bridge deck having a waterproof, plastic membrane thereon, a protective course blend wherein percent pass a four-mesh screen, 25-

40 percent pass a 16 mesh screen, 5-15 percent pass a 50 mesh screen and 2-5 percent pass a 100 mesh screen.

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