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e tested has to be reduced in accordance with methods outlined in BS 812-102:1989, by using a sample divider or by the process of “quartering”.
Once the reduction has been completed, the sample is again dried in an oven at 105 ± 5 oC (95 – 105 oC) to achieve dry mass. The dry mass has to be in accordance with table 1.2 below before conducting flakiness index testing.
Nominal size of material (mm)
Minimum mass of test portion after rejection of oversize and undersize particles (kg)
50
35
40
15
28
5
20
2
14
1
10
0.5
Table 1.2 – Extract from BS 812-105.1:1989 “Minimum mass of test portion”
The material is then sieve tested using the same method mentioned above for size grading and any aggregate retained on the 63.0 mm and passing the 6.30 mm sieves are discarded.
Weight of remaining fractions are taken and stored in separate trays so masses of fractions can be calculated.
Now sample is combined again and measured using a thickness gauge, each size gauged is again separated and weighed.
Using the results a flakiness index is determined for each section of the sample. The whole samples flakiness index is then determined by summing the individual fraction results. If this is less than 40%, the material can be used for track ballast.
[Hardy Aggregates Ltd/Aggregate Industries; Case Study]
Hardy Aggregates Limited supplies the UK Rail Industry with large amounts of ballast for use on the UK Railway to fulfil requirements for top and substructure ballast.
[Quarrying & Material Process]
Hardy’s procure their supply of track ballast from a Quarrying and Asphalt Company called Aggregate Industries Ltd. (formerly Foster Yeoman Ltd.), who are the owners of the Glensanda quarry in Scotland, and therefore the sole provider of Strontian Granite for the UK. Glensanda is a coastal quarry, located on the banks of Lock Linnhe near Oban in Scotland; the logistics involved in transporting quarried aggregate involves shipping as well as road transport. Material is mined using a mixture of blasting and drilling, as well as a large scale crushing operation located in-situ, using two Atlas Copco DM45 Drillmaster machines (see figure 1.2), capable of drilling and blasting at depth. Once the drilled aggregate is collected it is loaded into a primary crusher that serves a 300m (4 metre in diameter) deep shaft known locally at the mine as the “Glory Hole”, the shaft then feeds a 1.8 km length conveyor at the base, which carries the aggregate to its secondary and tertiary crushing phases. Once secondary and tertiary crushing has taken place, the aggregate can be stored in large bins to await transport.
Glensanda quarry and its surrounding area has recently been declared (2002) as an environmental conservation area, whilst this does not undermine the mining and removal of Granite, Aggregate Industries Ltd has been required to modify its transportation logistics in direct relation to the local area by a large degree. The glory hole tunnel is considered a long term solution to the environmental and economic factors that could hinder the transportation of such vast amounts of material, as it allows Aggregate Industries to transport the material down to sea level ready for ship loading, without the need for vehicles capable of carrying such large loads. This reduced mechanisation for loading lessens