Aggregate and Concrete
At the heart of the Group is Gallagher Aggregates, engaged in the mineral extraction industry and now the only company actively quarrying Kent Ragstone.
From the main quarry at Hermitage Farm close to Junction 5 of the M20 near Maidstone, the extracted mineral is fully processed into a full range of construction materials and supplied to customers throughout the South East.
The premium quality Ragstone aggregate is used in our own BSI accredited ready mixed concrete operation also based at Hermitage Farm. The quarry operation is highly mechanised and benefiting from considerable investment in the latest innovative and technically advanced well maintained machinery and equipment. Hermitage Quarry has a nominal production capacity in excess of a million tonnes per annum with an attitude and ability to substantially increase output should demand require. The product range includes everything from basic fill-type materials, through sub-base and capping layers, rock armour, walling and gabion stone to premium grade single sized washed aggregates and sands.
This is a far-cry from hundreds of years ago when the Ragstone was crafted by hand and used as the main building medium on many old heritage buildings throughout Kent London and Essex. Today, some of those buildings require repair and renovation works and whilst there may be alternative stones that appear to match, the fact is that those alternatives weather differently and within a few years are noticeable in their appearance and detract from the original beauty.
In the scheme of things, the volumes required for these renovation works is not significant, but Gallagher takes its obligations to the country’s heritage seriously and is embracing the challenge to provide authentic replacement stone.
As well as quarrying, the aggregates division is also engaged with the processing of minerals including the recovery and recycling of both construction and demolition waste streams into secondary materials. We operate two landfill sites at Hermitage Farm and at Ryarsh, both operating with the benefit of Pollution Prevention and Control (PPC) Permit and importing inert material, ultimately leading to restored land for agricultural or amenity use.
Processing
Kentish Ragstone is recovered from the Hythe Formation where it is found in relatively thin layers (up to 900mm) inter-bedded between layers of soft “greensand” known locally as hassock. Generally, the hassock contains too much silt and clay to be considered an aggregate in the true sense although it meets the technical criteria set for many of the construction materials’ product range.
The proportion of Ragstone to hassock varies from 20% to 55% of the formation and it is the only hard rock source in southeast Britain. The objective when processing is to separate the two minerals to avoid contamination of the Ragstone by the hassock and Gallagher has, through its own experience, found that the most efficient means of separation is by using a trommel screen. Cleaned Ragstone is then crushed and screened in much the same way as any other conventional mineral. Hassock can be further processed by means of washing to remove the silt and clay and produces a range of products that include sub-base and pipe-bedding type materials.
Only the best quality Ragstone after washing, is suitable as an aggregate for ready mixed concrete production.
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