GB2231902A - Rail tie formed of abrasion-resistant concrete composition - Google Patents

Abstract

Concrete rail ties are resistant to erosion if an abrasion resistant composition is located in a recess of the tie in the rail seat locations. A suitable novel composition comprises primary abrasion resistant aluminium oxide particles of uniform size and secondary particles of aluminium oxide of a uniform size equal to the voids formed between closely packed primary particles. A finer material such as silica flour is also used and the particles are bound together with an epoxy resin.

Description

ABRASION RESISTANT RAIL SEAT This invention relates to improvements in rail fastening systems where the rails are elastically fastened to rail ties. In particular, this invention relates to rail fastening systems utilising concrete rail ties.

Conventionally, rails are held to rail ties by rail clips or fasteners which bear down on the rail flange. The elastomeric material such as rubber, polyurethane, ethyl vinyl acetate or high density polyethylene insulate the rail from the rail ties.

This pad has a field side on the outer side of the rail and a gauge side on the inner side of each rail.

Concrete rail ties have been found to be prone to wear particularly in sandy and wet locations or on steep grades where the locomotives use sand for traction. This invention is particularly predicated on discovering the cause of this wear. As each loaded bogey passes over the tie, the rail pad deflects vertically and thus acts as a shock absorber. However, due to the poisons ratio of the material used, the pad must also deflect horizontally which means that every vertical load pulse causes the pad face to slide horizontally over the concrete ties.

In normal use this causes slight wear to the pad and practically no wear to the concrete face. However, in the presence of sand particles the grains of sand cut into the cement paste in the mortar causing abrasion to the concrete paste and mortar which shorten-the working life of the concrete rail tie.

The problem is made worse by the presence of water which carries the sand particles under the pad and since the tie face is not absolutely flat, any microscopic gap between the tie and the rail pad is filled with water which is expelled when the load is applied to the pad. This pumping and jetting action of the water causes wear to the concrete mortar and in addition acts as a distribution method for the sand particles which further aggravate the problem.

It is an object of this invention to overcome this difficulty with rail clamping systems on concrete ties.

To this end the present invention provides a convenient means to apply to an abrasion resistant material, conveniently a cement grout to the rail seat face.

In one embodiment of the present invention there is provided a method preparing a concrete rail tie, said method comprising the steps of providing a rail tie with at least one depression in an upper surface between fastening positions for a rail, and filling the depression with an abrasion resistant material. Conveniently, the abrasion resistant material is flowable during filling into the depression but sets therein to provide a hard abrasion resistant upper surface. Preferably, the abrasion resistant upper surface is substantially flat and no higher than surrounding surfaces of the concrete rail tie.

In accordance with a second aspect of the present invention there is provided a concrete rail tie having an upper surface to support one or more rails, said upper surface having at least one depression located between rail fastening positions with said depression containing an abrasion resistant material. Conveniently, the abrasion resistant material has an upper surface substantially co-planar with surrounding surfaces of the concrete rail tie.

It is known that abrasion resistant cement grouts are available which will greatly exceed the abrasion resistance of normal concrete. One of these such materials is epoxy resins and hardener carrying a silica filler.

It is desirable for other reasons that the rail seat area is as flat as possible and having a minimum amount of wind relative to the rail seat at the opposite end of the ties. This means it is not practical to trowel the special grout onto the surface of the rail seat since the finished face would not be accurate enough.

It would also be costly and inconvenient to place the abrasive material in the tie casting mould at the time of casting the tie.

This invention shows how to apply the abrasive resistant mortar to the rail seat in a convenient and accurate manner.

This is done by casting a shallow recess in the rail at the time the tie is manufactured then, at a later date, the abrasive resistant grout is applied to the recess which can then be easily screeded flat using the edges of the recess as the reference guide for the screed.

Suitable abrasive resistant cement mortars can be selected which not only have exceptional resistance to abrasion but also will bond securely to the recess forming an integral part of the finished tie.

In a second aspect this invention provides an improved abrasive resistant cement composition which can be used to form rail ties, to repair rail ties or to provide abrasion resistant portions on rail ties in the locations of rail seats where abrasion due to particles and water jetting occurs.

To this end the invention provides a cement composition comprising: a) a primary abrasion resistant particulate material of approximately uniform particle size b) a secondary abrasion resistant particulate material of approximately uniform particle size which is equivalent to the voids formed when the primary abrasion resistant material is closely packed together, and c) a binder for said primary and secondary materials Basically, more or less uniform grains of some abrasion resistant mineral such as aluminium oxide are selected, and when these are placed together more. or less uniform voids are formed between each grain, and a secondary grain size is selected to fit into these voids.

This then produces a very high density mineral mixture with very small voids between grains and a fine powder may then be selected as the final seal between grains.

A high strength low viscosity bender such as an epoxy resin and hardener mixture is then added to the minerals and thoroughly mixed to form a very stiff paste.

The paste is then applied smoothly to the areas prone to abrasion and allowed to cure.

This material gives excellent resistance to the type of abrasion found on concrete ties apparently because the voids between the grains which are filled with the epoxy matrixes are so small that the abrading sand and water particles cannot easily pass beyond the mechanical barrier provided by the abrasion resistant compound.

In effect, each abrasion resistant particle is firmly held by the epoxy at the back of the particle and so the front part acts as the abrasion barrier while the back is the anchor and the invading abrasion particles cannot pass behind to remove the epoxy acting as the support.

In a preferred embodiment aluminium oxide of about 560 microns is used and a secondary grain size about 1/8 of this is sufficient to fill the intermediate voids (about 70 microns). Other abrasion resistant materials such as carborundum can be used.

The correct ratio by volume of these two minerals can be found by placing a known volume of the primary particles in a container and then adding the secondary particles and stirring progressively. The secondary particles then dissolve in the primary particles with little or no increase in volume until the mixture becomes saturated which is then the ideal ratio. However, in practice it has been found to be desirable to use a ratio which gives a volume increase of, from 5 to 15%.

A small amount of very fine silica flour is then added as the final sealant.

Example A typical mixture is as follows: 100 Parts by volume of 560 microns aluminium oxide 40 Parts by volume 70 microns aluminium oxide 15 Parts by volume of silica flour A preferred embodiment is disclosed in figures 1 and 2 annexed hereto. Figure 1 is a plan view of a rail tie and figure 2 is a cross sectional view taken along line BB of figure 1.

As is apparent in the drawings, the recess or depression 11 in the rail tie 10, may cover the whole rail seat area and extend slightly past the shoulders as in figure 1 or alternatively it may only cover the rail seat area between the shoulders. Another possibility is for the recess to be divided in two covering the field and gauge sides of the seat but not the central part since the main abrasion usually occurs at the field or gauge edges. The recess 11 is filled with the abrasion resistant cement 12 disclosed in the above example to provide a flat upper surface 13 coplanar with the upper surface of the tie 10.

As mentioned above the preferred cement composition of this invention can be used to form new ties or repair eroded rail ties. It can be seen from the above that this invention provides a unique solution to overcome erosion of rail ties.

Claims (6)

THE CLAIMS DEFINING TEE INVENTION ARE AS FOLLOWS:

1. A rail seat comprising a rail, a rail tie and a resistant rail pad interposed between the rail and the rail tie, said rail being fastened to said rail tie by spring clamps, wherein at least the portion of the rail tie lying below and adjacent to the rail seat is formed of an abrasion resistant concrete.

2. A rail seat as claimed in claim 1, wherein the rail tie incorporates a recess below the rail seat filled with said abrasion resistant material.

3. An abrasion resistant concrete composition comprising: a) primary abrasion resistant particles b) secondary abrasion resistant particles selected to fill the voids between the closely packed primary particles, and c) a binder

4. A composition as claimed in claim 3 wherein the secondary particles are sufficient to provide a 5 to 15% increase in volume of the mixture when well mixed compared to the volume of the primary particles above.

5. A composition as claimed in claim 3 or 4 wherein aluminium oxide particles are used.

6. A composition as claimed in claim 5 wherein silica flour is also added to the particulate mixture.