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Aggregates are the most commonly used construction materials in the UK. They are widely distributed with a huge range of potential sources, whilst remaining a low cost product; they contribute huge expenditure to the construction industry due to the sheer volume of their use. They are essential for constructing and maintaining what is the physical framework, buildings and infrastructure of which our society depends.
A typical definition of aggregates is a hard, granular material suitable for use on their own or mixed with cement, lime or other bituminous binder in the construction industry. Their applications comprise of, but are not limited to, concrete, mortar, road stone, asphalt, drainage courses and railway ballast.
This report will be focusing on aggregate and its manufacture for use as railway ballast, offering a critical assessment of source material, and intimate testing methods used in order to grade the aggregate fit for use. All ballast used on the UK Railway is required to be graded and tested in accordance with a document of specification “Railtrack Line Specification RT/CE/S/006 Issue 3, 2000” with the use of applicable British Standards set out for the sampling and testing of aggregates. Key points to be reviewed in the following test are;
Ballast testing as specified in Railtrack Line Specification (RT/CE/S/006 Issue 3, 2000)
[Railway Track Ballast & Granite]
Track Ballast is usually formed of very strong crushed rock, such as igneous granite, and is required for many reasons including;
To facilitate surface water drainage and prevent ballast attrition.
The large voids in ballast substructure provide “immediate” drainage for rain fall and surface water on the track, preventing it pooling around the sleepers and avoiding damaging rot. The large voids in ballast also provide a good storage space for silt, which is a natural by-product of granite degradation, prolonging its life. Coupled with its strong weather resistance, it means the replacement and upkeep of track ballast is kept to a minimum.
To distribute load from sleepers, rails and rail traffic.
To maintain track alignment ballast needs to resist vertical, lateral and
longitudinal forces. Without ballast, the tracks and sleepers (which support rails) would be subject to movement and the track structure could fail.
To prevent or hinder the growth of vegetation that may disrupt the underlying structure of the track.
As mentioned above ballast nowadays tends to be igneous granite, preferred because of its high strength and slow degradation qualities. Granite is part of the Plutonic family of igneous rocks and its constituents include feldspar (responsible for its colouring), quartz (responsible for its high weather resistance and high mineral hardness) and mica (Construction Materials Manual, Hegger et al, 2006). A majority of granite used in the UK for Rail Construction is Strontian Granite, quarried from the Glensanda Quarry in the Scottish Highlands. In this report, the provision of Strontian Granite from Glensanda will be focused on, however, Granite from many other locations is suitable for use (and is used) for track ballast, and as can be seen