EP2310572A1

EP2310572A1 - Machine and method for laying of a second concrete slab of a sleeperless rail-bed

Info

Publication number: EP2310572A1
Application number: EP09787459A
Authority: EP
Inventors: Shachar Nave; Dan Tamir
Original assignee: ASHTROM GROUP Ltd
Current assignee: ASHTROM GROUP Ltd
Priority date: 2008-07-08
Filing date: 2009-07-08
Publication date: 2011-04-20
Also published as: CN102131983A; WO2010004559A1; US20110227241A1

Abstract

A slip-form machine (220) for laying of a second concrete slab (120) of a sleeperless rail-bed including a locomotion mechanism (222, 232) adapted to provide axial translation of the machine along a first slab (110); a slip-form (370) adapted to receive concrete exiting a discharge port (336) via a rearward exit (340) and form an uncured second concrete slab (120) during the axial translation; and a height adjustment mechanism (360) operable to adjust a height of a cover (350) of a forward exit (338) with respect to the first concrete slab (110).

Description

TITLE: MACHINE AND METHOD FOR LAYING OF A SECOND

CONCRETE SLAB OF A SLEEPERLESS RAIL-BED

FIELD OF THE INVENTION

This invention relates to slip-form paving machinery adapted for laying rail beds for trains. BACKGROUND OF THE INVENTION

Historically, rail beds consisted of two parallel steel rails, laid on cross ties (or sleepers; typically wood) embedded in ballast. Metal rails are then fastened to the ties with rail spikes, lag screws or clips.

The ballast was usually a bed of coarse stone chippings which provided resilience, limited flexibility, and drainage.

In many cases, a baseplate is used between the rail and cross ties, to distribute the load of the rail over a larger area. Spikes can be driven through a hole in the baseplate to hold the rail, or baseplates can be spiked or screwed to the cross tie (sleeper) and the rails clipped to the baseplate.

More recently steel rails have been laid onto a concrete slab (a slab track). When tracks are applied to concrete without using conventional sleepers (ties) or track ballast, the resultant rail bed is called a "sleeperless track". Although construction cost of sleeperless tracks is higher than conventional tracks, lower maintenance costs are anticipated to offset the higher initial construction cost.

US patent 7,325,316 describes a device for inserting elements into the ground in order to carry out works including a positioning mechanism. An exemplary device described in this patent is marketed by Alstom Transport S. A. (Levallois-Perret, France) as part of the "Appitrack" system and can be used to inset baseplates into a concrete slab of a sleeperless track provided by a slip-form paving machine. Numerous slip-form paving machines and methods have been previously described. The following list is representative, but nor exhaustive: US patents 6,872,028; 6,878,315; 6,926,851; 6,962,490; 6,969,476; 6,998,075; 7,004,737; 7,108,4491; describe slip-form machines and/or methods.

SUMMARY OF THE INVENTION

A broad aspect of the invention relates to automation of the process of laying rail beds for trains and/or trams. In some exemplary embodiments of the invention, 100, 125, 150, 175, 200, 225, 250 or 300 M/day of rail beds can be installed. In some exemplary embodiments of the invention, concurrent use of a slip-form paving machine and a base insertion machine contributes to increased efficiency. Optionally, the paving machine and a base plate inserter are subject to coordinated control. In some exemplary embodiments of the invention, the rail beds are laid in a previously prepared pavement (e.g. concrete or asphalt). Optionally, a wax layer is provided between the pavement and the rail bed.

One aspect of some exemplary embodiments of the invention relates to applying a positive pressure to force concrete backwards into a slip-form. In some exemplary embodiments of the invention, the positive pressure is created by closing a frontward facing portion of an exit port of a slip-form paving machine. Optionally, a level of concrete in a loading funnel of the paving machine contributes to a magnitude of the positive pressure. Optionally, reducing changes in concrete level in the loading funnel contributes to smoothness of a layer of concrete applied by the paving machine.

In some exemplary embodiments of the invention, a degree of closing of the frontward facing portion of the exit port is variable. Optionally, variability is achieved with a movable shutter, for example a shutter controlled by a hydraulic mechanism. In some exemplary embodiments of the invention, the frontward facing portion of the exit port is partially opened in anticipation of an obstacle in a path of the paving machine.

One aspect of some embodiments of the invention relates to dragging a flexible sheet from a slip-form paving machine. In some exemplary embodiments of the invention, a sprinkler apparatus is deployed to wet the sheet and/or uncured concrete emanating from an exit port of the slip-form machine. Optionally, sprinkling water on the concrete contributes to temperature control and/or smoothes the concrete. In some exemplary embodiments of the invention, formulations used in a paving machine provide an on-site slump value not exceeding 4cm.

According to some exemplary embodiments of the invention, there is provided a slip-form machine for laying of a second concrete slab of a sleeperless rail-bed. The machine includes: a locomotion mechanism adapted to provide axial translation of the machine along a first slab; a concrete feeder having an intake port and a discharge port, the discharge port includes a forward exit facing in a direction of the axial translation and a rearward exit; a slip-form adapted to receive concrete exiting the discharge port via the rearward exit and form an uncured second concrete slab during the axial translation; and a height adjustment mechanism operable to adjust a height of a cover of the forward exit with respect to the first concrete slab.

Optionally, the machine includes a feeder regulator adapted to maintain a height of concrete in the concrete feeder within predetermined limits.

Optionally, the machine includes a pressure regulator adapted to maintain a hydrostatic pressure of concrete in the rearward exit within predetermined limits. Optionally, the machine includes a mounting bracket adapted to drag a flexible sheet over an upper surface of the uncured second concrete slab.

Optionally, the mounting bracket is provided as a horizontal bar. Optionally, an aspect ratio (width to height) of the slip form is at least 10. According to some exemplary embodiments of the invention, there is provided amethod of paving a second concrete slab of a sleeperless rail-bed. The method includes: causing a slip-form machine to axially translate along a first slab; feeding concrete into a concrete feeder having an intake port and a discharge port, the discharge port includes a forward exit facing in a direction of the axial translation and a rearward exit; adjusting a height of a cover at least partially covering the forward exit with respect to the first concrete slab so that concrete exits the discharge port via the rearward exit and fills a slip-form positioned behind the rearward exit. Optionally, the method includes regulating a height of concrete in the concrete feeder.

Optionally, the method includes regulating a height of concrete in the concrete feeder. Optionally, the method includes regulating a hydrostatic pressure of concrete in the rearward exit.

Optionally, the method includes attaching a flexible sheet to the slip-form machine and dragging the flexible sheet over an upper surface of an uncured second concrete slab formed by the slip form machine. Optionally, the attaching includes attaching to a mounting bracket.

Optionally, the mounting bracket is provided as a horizontal bar.

Optionally, an aspect ratio (width to height) of the slip form is at least 10.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although suitable methods and materials are described below, methods and materials similar or equivalent to those described herein can be used in the practice of the present invention, hi case of conflict, the patent specification, including definitions, will control. All materials, methods, and examples are illustrative only and are not intended to be limiting. As used herein, the terms "comprising" and "including" or grammatical variants thereof are to be taken as specifying inclusion of the stated features, integers, actions or components without precluding the addition of one or more additional features, integers, actions, components or groups thereof. This term is broader than, and includes the terms "consisting of and "consisting essentially of as defined by the Manual of Patent Examination Procedure of the United States Patent and Trademark Office.

For purposes of this specification and the accompanying claims, the term "slump" refers to a measure of a degree of plasticity of a fresh batch of concrete indicated by the Concrete Slump Test (ASTM C 143 and/or EN 12350-2 test standards). Briefly, slump is measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non- absorptive surface and filled in three layers of equal volume, with each layer being tamped with a steel rod in order to consolidate the layer. When the Abrams cone is carefully lifted off, the enclosed sample slumps due to gravity. Slump is expressed as a linear distance between a height of the Abrams cone and the height of the sample after the cone is removed. Slump is typically measured in the middle of a poring (e.g after 3 cubic meters have been disopensed from a 6 cubic meter mixer. Optionally, an addiotional slump test is performed at a beginning of a pour. The phrase "consisting essentially of or grammatical variants thereof when used herein are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof but only if the additional features, integers, steps, components or groups thereof do not materially alter the basic and novel characteristics of the claimed composition, device or method.

The term "method" refers to manners, means, techniques and procedures for accomplishing a given task including, but not limited to, those manners, means, techniques and procedures either known to, or readily developed from known manners, means, techniques and procedures by practitioners of engineering and/or computer science.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to understand the invention and to see how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying figures. In the figures, identical and similar structures, elements or parts thereof that appear in more than one figure are generally labeled with the same or similar references in the figures in which they appear. Dimensions of components and features shown in the figures are chosen primarily for convenience and clarity of presentation and are not necessarily to scale. The attached figures are: Fig. 1 is schematic representation of a transverse cross section of a sleeperless rail bed;

Fig. 2 is schematic representation of a side view of a system for preparation of a sleeperless rail bed including a slip-form paving machine and a base plate inserter;

Fig. 3A is schematic representation of a lateral cross section of a slip-form paving machine according to an exemplary embodiment of the invention;

Fig. 3B is an enlarged schematic representation of the area indicated as 221 in Fig. 3A; and Fig. 4 is a simplified flow diagram of a method according to an exemplary embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the invention relate to machinery and methods for laying sleeperless rail beds.

Specifically, some embodiments of the invention can be used to increase a rate at which rail beds are installed and/or reduce an amount of undesired cracking in a concrete slab of the rail beds and/or reduce fluctuations in upper surface height of an upper slab (e.g. relative to a lower support slab and/or in absolute terms). The principles and operation of machinery and/or methods according to exemplary embodiments of the invention may be better understood with reference to the drawings and accompanying descriptions.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details set forth in the following description or exemplified by the Examples. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. Overview Fig. 1 is a transverse cross section of a sleeperless rail bed 100. Rail bed 100 can be constructed using either "top-down" technology or slip-form technology. Exemplary embodiments of the invention described in this application are presented in the context of slip-form technology.

In both technologies, the finished rail bed 100 includes a first concrete slab 110 which serves as a support foundation. A second concrete slab 120 is laid on top of the first slab and base plates 130 are attached to an upper surface thereof. Typically, the base plates are installed in pairs at similar axial positions along second slab 120. A distance between two base plates 130 in a pair determines a distance between rails 140 which are subsequently attached thereto. In Fig 1, two second slabs 120 are depicted on a common first slab 110. Optionally, three or four or more second slabs 120 can be provided on a common first slab 110, for example in a train station.

In general, thicknesses of slabs 110 and 120 and their widths can be adjusted in anticipation of projected weight loads and/or in consideration of geologic and/or soil conditions below slab 110. Similarly, lateral and/or axial distances between base plates 130 can be adjusted in anticipation of expected use.

For example, rails for different types of urban transport systems may be spaced to accommodate cars with a width of 2.5, 2.7 or 3.2 M or lesser or intermediate or greater values. In general, wider rail cars are suited for higher speed travel and/or larger payloads.

Fig. 2 is a side view of a system 200 for preparation of a sleeperless rail bed of the general type indicated in Fig. 1 including a slip-form paving machine 220 and a base plate inserter 230. First concrete slab 110 can be laid using either slip-form technology or conventional "constructed form" technology. The large arrow indicates a direction of travel of slip-form paving machine 220 and base plate inserter 230 which are propelled by locomotion means 222 and 232 respectively. The locomotion means may be, for example metal treads of the type commonly employed on tanks and bulldozers and/or tires. The locomotion means are typically, but not always, powered by internal combustion engines.

During operation of system 200, slip-form machine 220 axially translates itself (leftward in the figure) along first slab 110 by locomotion means 222 and concurrently paves second slab 120 onto an upper surface thereof. Because second slab 110 will support base plates 130 which support rails 140 (see Fig. 1), an upper surface of slab 120 must be engineered within close tolerances so that it is flat in both transverse and axial dimensions.

In the depicted embodiment, base plate inserter 230 axially translates itself (leftward in the figure) along first slab 110 by locomotion means 232 and concurrently inserts base plates 130 in an upper surface of second slab 120. Any deviation of second slab 120 from engineering tolerances can cause cracking of the second slab and/or unacceptable bending of rails 140 when they are affixed to base plates 130. Exemplary modified slip-form machine

Some exemplary embodiments relate to mechanical modifications of slip form machine 220. Optionally, these modification reduce cracking of slab 120 and/or improve adherence to engineering tolerances.

Fig. 3A is a schematic representation of a lateral cross section of slip-form paving 220 machine according to an exemplary embodiment of the invention through line A-A of Fig. 2. In the depicted exemplary embodiment, a housing, frame or chassis 320 indicated generally as a rectangle physically which connects components of machine 220. Depicted exemplary slip-form machine 220 is adapted for laying second concrete slab 120 of sleeperless rail-bed 100. Depicted machine 220 includes a locomotion mechanism 222 adapted to provide axial translation of the machine along first concrete slab 110 as described hereinabove with regard to Fig. 2. For clarity, mechanism 222 is omitted from Fig. 3.

Depicted machine 220 also includes a concrete feeder 330 having an intake port 332 and a discharge port 336. Discharge port 336 has a forward exit 338 facing in the direction of axial translation and a rearward exit 340. Depicted machine 220 includes a slip-form 370 adapted to receive concrete 334 exiting discharge port 336 via rearward exit 340. Concrete 334 forms an uncured second concrete slab 120 as machine 220 continues axial translation along first slab 110.

In the figure, a cover 350 covers forward exit 338. In some exemplary embodiments of the invention, cover 350 is operably connected to a height adjustment mechanism operable to adjust a height of cover 350 with respect to an upper surface 310 of first concrete slab 110. The height adjustment mechanism is represented schematically as controller 360. Optionally, controller 360 includes electronic and/or hydraulic and/or mechanical components which move cover 350 in response to an input signal. Optionally, the input signal is provided manually (e.g. via a lever or button) or automatically (e.g. via a sensor, not pictured).

Fig. 3 B schematically depicts inset 221 in greater detail. According to the depicted exemplary embodiment, cover 350 includes a stationary element 350 which supports a movable element 351. Movable element 351 is optionally raised and lowered relative to upper surface 310 of the first slab, for example in response to a control signal from controller 360 (Fig. 3A). In the depicted exemplary embodiment, stationary element 350 extends downwards to the level of upper surface 311 of second slab 120. According to various exemplary embodiments of the invention, movable element 351 can have different ranges of motion relative to a lower edge of stationary element 350 and/or upper surface 310 of the first slab. Exemplary dimensions are described below. Optionally, machine 220 includes a feeder regulator adapted to maintain a height

(h) of concrete 334 in concrete feeder 334 within predetermined limits. The feeder regulator optionally relies upon adjusting a height of cover 350 via controller 350 and/or controlling a flow rate of incoming concrete 394 from mouth 392 of a concrete pump 390. Optionally, the feeder regulator is manually operable (e.g. via a lever or button) or automatic (e.g. responsive to an output signal from a pressure sensor installed at 380).

Numeral 380 schematically represents a vibrator provided to remove air from concrete 334 as it flows through feeder 330. Although one vibrator 380 is depicted for clarity, a larger number are typically employed. Optionally, 4, 6, 8, 12 or 16 vibrators are employed. In some exemplary embodiments of the invention, the number of vibrators employed varies with cross sectional area of feeder 330 and/or with a height of mouth 392 of pump 390 and/or with concrete composition.

Optionally, machine 220 includes a pressure regulator adapted to maintain a hydrostatic pressure of concrete 334 in rearward exit 340 within predetermined limits.

In some exemplary embodiments of the invention, the pressure regulator works by controlling h and/or a degree of opening of cover 350.

In some exemplary embodiments of the invention, a degree of deviation from flatness of upper surface 311 in the axial and/or transverse dimensions is reduced by controlling height of concrete 334 in feeder 330 and/or a degree of opening of cover 350 and/or hydrostatic pressure in rearward exit 340.

Additional Exemplary modifications to slip-form machines

Referring still to Fig. 3 A, a degree of deviation from flatness of upper surface

311 is alternatively or additionally reduced by dragging a flexible sheet 380 behind machine 220 along upper surface 311 of second slab 120. hi the depicted exemplary embodiment, a mounting bracket 382 is adapted to drag flexible 380. Optionally, a specer bar 384 holds bracket 384 at a desired distance from housing 320. Optionally, mounting bracket 384 is provided as a horizontal bar, optionally transverse to upper surface 311 of second slab 120. Exemplary methods

Fig. 4 is a simplified flow diagram 400 of a method of laying a second slab of a sleeperless rail-bed according to exemplary embodiments of the invention. According to depicted exemplary method 400 a slip-form machine is caused 410 to axially translate along a first concrete slab. Concurrently concrete is fed 420 concrete into a concrete feeder having an intake port and a discharge port. As described above, the discharge port includes a forward exit facing in a direction of the axial translation and a rearward exit. In some exemplary embodiments of the invention, method 400 includes at least partially covering 430 the forward exit so that concrete exits the discharge port via the rearward exit with sufficient pressure to fill a slip-form positioned behind the rearward exit. Alternatively or additionally, method 400 includes adjusting 440 a height of a cover of the forward exit with respect to the first concrete slab. The height can be adjusted, for example, by controller 360 as described above.

Alternatively or additionally, method 400 includes regulating 460 a height h (Fig. 3A) of concrete in the concrete feeder. Optionally, regulating 460 is at least partially achieved by adjusting 440.

In some exemplary embodiments of the invention, method 400 includes regulating 450 a hydrostatic pressure of concrete in the rearward exit. Optionally, adjusting 440 and/or regulating 460 contribute to regulating 450.

Alternatively or additionally, method 400 includes attaching 470 a flexible sheet to the slip-form machine and dragging 480 the flexible sheet over an upper surface of the uncured second concrete slab. Optionally, attaching includes attaching to a mounting bracket, optionally provided as a horizontal bar. Exemplary commercially available components

Concrete pumps suitable to provide concrete 394 to feeder 330 are commercially available from, for example, Schwing America Inc. (St. Paul MN, USA). One of ordinary skill in the art will be able to incorporate commercially available concrete pumps into the context of the invention without undue experimentation.

Slip-form paving equipment as depicted in Fig. 2 is available commercially, for example from HEM (Grundy Center Iowa; USA) and from Caterpillar (Peoria Illinois, USA). One of ordinary skill in the art will be able to modify commercially available equipment with cover 350 AP controller 360 and/or mounting bracket 382 and/or spacer bar 384 using the above description as a guide and implementing routine calibration.

Hydraulic actuators suitable for use in controller 360 according to some exemplary embodiments of the invention are available from, for example, TYCO/flow control (Bridgeport NJ, USA). One of ordinary skill in the art will be able to select a suitable commercially available actuator and incorporate it into the context of the invention without undue experimentation. Various types of electronic actuators and/or sensors suitable for use in described exemplary embodiments of the invention are available from, for example, MPC Products Corporation (Skokie IL, USA). One of ordinary skill in the art will be able to select a suitable commercially available actuator and/or sensor incorporate it into the context of the invention without undue experimentation. Exemplary tolerances and dimensions

In some exemplary embodiments of the invention, cracking of upper surface 311 of second slab 120 is reduced by controlling a degree of flatness thereof. Alternatively or additionally, stress upon and/or bending of rails 140 is reduced by controlling a degree of flatness of upper surface 311 of second slab 120. Optionally, height of upper surface 311 is restricted to + 7, 5, 3, 2 or 1 mm of a planned absolute height for the same location (or lesser or intermediate values) of transverse width (Fig. 1).

In some exemplary embodiments of the invention, stationary element 350 extends downwards to a height above upper surface 310 of the first slab equivalent to a thickness of the second slab. Optionally, stationary element 350 extends downwards to a greater degree. In some exemplary embodiments of the invention, an increased degree of downward extension enables element 350 to impart a greater degree of support to element 351 against pressure of concrete at frontward facing exit 338.

In various exemplary embodiments of the invention, movable element 351 has different ranges of motion such as, for example, 5, 10, 15 or 20 cm or intermediate values. Optionally, the range of motion is about 15 cm. In some exemplary embodiments of the invention, movable element 351 is configured to descend about 15 cm below a bottom edge of stationary element 350. Optionally, this provides a clearance of about

8cm with respect to upper surface 310 of the first slab. In some exemplary embodiments of the invention, a degree of clearance provided for movable element 351 varies with one or more of concrete composition (e.g. softness) and/or variability of terrain.

According to some exemplary embodiments of the invention, movable element 351 and stationary element 350 are constructed of rigid materials (e.g. steel). Optionally movable element 351 and stationary element 350 are characterized by a thickness of 10, 12, 15, 15 or 20 mm.

According to various exemplary embodiments of the invention, a second slab of 1500, 1750, 2000, 2250, 2500, 2750 or 3000 mm (or intermediate widths) is desired to accommodate a track width dictated by selected rolling stock. Optionally, a single slip form paving machine can be fitted with forms of different widths in accord with the demands of a specific paving job. Similarly, widths of movable element 351 and/or stationary element 350 can be adjusted as need to conform to relevant forms.

A desired thickness of second slab 120 can vary with ground type and/or anticipated load demands. In an exemplary urban light rail application where the ground is primarily bedrock, a slab thickness of 23 cm has been selected as suitable. Optionally, softer ground contributes to increased slab thickness. Optionally, slab height is subject to a tolerance of ± 5mm or less.

According to various exemplary embodiments of the invention, a distance between base plates 130 can be 600, 650, 700, 750, 800, 850 or 900 mm or intermediate or greater values. Optionally, base plate spacing varies with one or more of slab thicklness, anticipated loads and ground type.

In some exemplary embodiments of the invention, second slab 120 is characterized by an aspect ratio (width to height) of 50, 40, 150, 20, 12, 11, 10, or 8 or intermediate values. Optionally, the aspect ratio is about 10.9.

It is expected that during the life of this patent many slip-form paving machines, base plate application machines and types of base plates will be developed and the scope of the invention is intended to include all such new technologies a priori. As used herein the term "about" refers to ± 10 %. Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims. Specifically, a variety of numerical indicators have been utilized. It should be understood that these numerical indicators could vary even further based upon a variety of engineering principles, materials, intended use and designs incorporated into the invention. Additionally, components and/or actions ascribed to exemplary embodiments of the invention and depicted as a single unit may be divided into subunits. Conversely, components and/or actions ascribed to exemplary embodiments of the invention and depicted as sub-units/individual actions may be combined into a single unit/action with the described/depicted function. Alternatively, or additionally, features used to describe a method can be used to characterize an apparatus and features used to describe an apparatus can be used to characterize a method.

It should be further understood that the individual features described hereinabove can be combined in all possible combinations and sub-combinations to produce additional embodiments of the invention. The examples given above are exemplary in nature and are not intended to limit the scope of the invention which is defined solely by the following claims.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. The terms "include", and "have" and their conjugates as used herein mean

"including but not necessarily limited to".

Additional objects, advantages, and novel features of the present invention will become apparent to one ordinarily skilled in the art upon examination of the following example, which is not intended to be limiting. Additionally, each of the various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below finds experimental support in the following examples.

EXAMPLE

Reference is now made to the following example, which together with the above descriptions, illustrates the invention in a non limiting fashion.

Seasonal changes in formulation

During testing in Jerusalem (Israel), it became apparent that seasonal climatic changes influenced performance of the Appitrack system adversely. In order to offset the adverse influence of seasonal climatic changes, separate summer and winter formulations for concrete were developed.

Table 1 summarizes the relative amounts of ingredients for summer and winter formulations in comparison to typical concrete formulations for manual application. In addition, Table 1 shows slump data, tensile strength and compression strength data where available.

Results presented in table 1 indicate that decreasing average slump at plant from 15 cm (manual formulation) to 6 cm (summer and winter formulations) did not adversely affect compression strength at 28 days.

This example, together with performance data gathered in the field, indicate that increasing plasticity of concrete contributes to a reduction in cracking around base plates while allowing track installation to proceed at an increased rate.

Table 1: Exemplary concrete formulations

Claims

CLAIMS:

1. A slip-form machine for laying of a second concrete slab of a sleeperless rail-bed, the machine comprising: a locomotion mechanism adapted to provide axial translation of the machine along a first slab; a concrete feeder having an intake port and a discharge port, said discharge port comprising a forward exit facing in a direction of said axial translation and a rearward exit; a slip-form adapted to receive concrete exiting said discharge port via said rearward exit and form an uncured second concrete slab during said axial translation; and a height adjustment mechanism operable to adjust a height of a cover of said forward exit with respect to said first concrete slab.

2. A machine according to claim 1, comprising a feeder regulator adapted to maintain a height of concrete in said concrete feeder within predetermined limits.

3. A machine according to claim 1 or 2, comprising a pressure regulator adapted to maintain a hydrostatic pressure of concrete in said rearward exit within predetermined limits.

4. A machine according to any of claims 1-3, comprising a mounting bracket adapted to drag a flexible sheet over an upper surface of said uncured second concrete slab.

5. A machine according to claim 4, wherein said mounting bracket is provided as a horizontal bar.

6. A machine according to any of claims 1-5, wherein an aspect ratio (width to height) of said slip form is at least 10.

7. A method of paving a second concrete slab of a sleeperless rail-bed, the method comprising: causing a slip-form machine to axially translate along a first slab; feeding concrete into a concrete feeder having an intake port and a discharge port, said discharge port comprising a forward exit facing in a direction of said axial translation and a rearward exit; adjusting a height of a cover at least partially covering said forward exit with respect to said first concrete slab so that concrete exits said discharge port via said rearward exit and fills a slip-form positioned behind said rearward exit.

8. A method according to claim 7, comprising regulating a height of concrete in said concrete feeder.

9. A method according to claim 7 or 8, comprising regulating a hydrostatic pressure of concrete in said rearward exit.

10. A method according to any of claims 7-9, comprising attaching a flexible sheet to said slip-form machine and dragging said flexible sheet over an upper surface of an uncured second concrete slab formed by said slip form machine.

11. A method according to claim 10, wherein said attaching comprises attaching to a mounting bracket.

12. A method according to claim 11, wherein said mounting bracket is provided as a horizontal bar.

13. A method according to any of claims 7-12, wherein an aspect ratio (width to height) of said slip form is at least 10.