Overview - A typical Roadstone Wood operation.
The Roadstone Wood Quarry at Belgard in West Dublin is one of the largest in Europe, producing in excess of 2million tonnes of crushed stone each year. It is a vertically integrated facility producing both primary products and finished materials. The quarry was acquired by the Company in 1968 by the visionary Tom Roche, a founder member of Roadstone Wood, and production began two years later in 1970.
The complex has expanded over time to include production of concrete, blocks, paving and blacktop products. The quarry floor has reached a dept of 45 meters and estimates indicate at least another 50 years of production remain. The entire process is highly automated. Environmental and quality control procedures are operated to the highest standards. Quality management systems are audited to ISO 9002.
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Extracting and Crushing
The first stage in the process is the extraction of limestone rock from the quarry face. This is done by first removing the top-soil and blasting the rock face. A number of holes are drilled down into the rock and are packed with explosive charges. These charges are detonated in a sequence along the quarry face, separated by a gap of several milli-seconds. Up to 60,000 tonnes of rock is released during this process.
The loose rock is then collected by a loading shovel which is one of the largest in the country. The shovel picks up 20 tonnes of rock at a time and loads it into dump trucks for transportation to the primary crusher. Each dump trucks carry between uo to 60 tonnes, enough stone to build a typical house.
The dump trucks empty each load into the primary crusher, which uses a gyratory action to break the rock into pieces smaller than 200mm. The surfaces of the crusher are coated with manganese in order to improve the wear resistance for the throughput of up to 800 tonnes of stone per hour. The crushed stone is then carried by conveyor to the secondary building where it is screened and separated into three products; minus 200mm material, 50mm stone and finer "screenings". The 200mm stone is then passed through a further stage of crushing to produce 125mm stone. These products are then stored in stockpiles before being used in the second stage of aggregate production.
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Aggregate Production
All of the storage areas and conveyor systems in the quarry are centrally controlled, allowing free movement of stone to various parts of the quarry. In this way, production can be fine-tuned in order to vary the quantities of aggregates produced to match market demands. The stone required for the second stage of crushing and screening is automatically taken by feeders located underneath each of the stockpiles. It is transported by covered conveyor to the second stage crushers where it is crushed into smaller sized pieces.
After crushing, the aggregates are transferred by conveyor to the storage silos where the stone is screened into eight different sizes. Dust suppression systems including enclosed transport and water sprays using re-cycled water, ensure that dust levels are kept to a minimum. A complex sequence of multiple screens and feedback systems for filling the storage silos, allow the production to be constantly monitored and controlled. The aggregates are also sampled and tested to ensure that they comply with the appropriate specifications. Each of the eight silos has a capacity of 1,500 tonnes. The aggregates in the silos are stored until required by one of the production plants also located in the quarry.
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Clause 804 Sub-Base Material
The main structural element in the sub-base of a road is a granular material. Clause 804 of the Department of the Environment Specification Roadworks - "The Green Book", defines the requirements of this material.
The special properties of 804 is that the stone has an appropriate strength. The grading must also fit into a specified grading envelope. The fine aggregate is especially important in that it is clean, that is non plastic and is present in sufficient quantity to ensure that when laid that material will be tightly bound and be capable of being fully compacted.
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Asphalt Plant
Coated materials, Asphalt and Macadam are produced at Belgard for a wide range of uses, from macadam driveways and carparks to highly specialised road asphalt surfacing used in major road and motorway construction. Each mix composition uses carefully selected and graded aggregates to ensure the appropriate strength and wear characteristics of the surfacing are achieved.
Coated materials contain aggregates and limestone filler bound together by bitumen. The materials are mixed and stored at the appropriate temperature for coating and laying. Mix recipes are stored in the computerised batching system in the control room. This dispenses the exact quantities of each component for production as required. A conveyor running along the base of the silos transports the aggregates in the correct proportion to a heating drum.
The blended aggregates are heated to temperatures of up to 180 degrees Celsius as they pass through the drum. After heating, the aggregates are rescreened and separated into hot bins, so that the target grading can be achieved using the computer stored recipe. Dust generated by the process is collected by a bag-filtering system and is re-cycled as filler.
At this stage quantities of both the limestone filler and the hot aggregates are dispensed into the pug-mill, where the hot bitumen is added and the components are mixed by paddles, ensuring that each stone is evenly coated and that the filler is evenly dispersed. The finished material is kept in hot-storage silos at the appropriate temperature where it can be loaded into insulated trucks for transportation to the road construction site.On some projects Roadstone Wood lay the finished material to produce the roads and motorways of Ireland.
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Concrete Plant
The concrete plant at Belgard operates a demand driven process, where production is scheduled daily to ensure that customer orders are fulfilled as quickly as possible. The plant uses wet-batch process utilising twin Wingate tilting-drum mixers. The four types of aggregate required for production are transferred from the main storage silos by conveyor and are stored in fifty tonne compartments in a silo along with two grades of sand. In the control room, specific recipes are entered from customer orders received. As each batch of concrete is started, specific weights of aggregates and sand are dispensed from the storage silo and are transferred to one of the twin mixing drums.
Cement, stored in two 50 tonne, and two 300 tonne silos, is also dispensed into the mixer. A full range of concrete admixtures are available to cater for all specification requirements. At this stage, water is added and the mix is constantly monitored to ensure that it exactly matches the customer specification. When the mixing process is complete, trucks parked below the mixers are filled by tilting the mixer drums and opening the chutes underneath. Each batch contains 3.5 cubic metres of concrete and by alternating mixes between the twin drums, two trucks can be fully loaded from start to finish in just seven minutes.
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Mortar Plant
The mortar plant produces trowel ready mortar which is delivered on site for building construction. The delivery is very flexible, allowing individual sites to take different quantities and colours daily as required. The control system for the plant operates in a similar way to the concrete plant, transferring the two sand aggregates to the mixer by conveyor.
The cement is held in fifty and twenty tonne silos located above the mixer, and the control system dispenses the correct amount of cement into the mixing drum for each batch. A retarder is also added to the mix in order to keep the mortar in a workable consistency for up to 72 hours. Water is added in a controlled way to the dry mixture until the correct batch parameters have been reached. The mixed mortar is then filled into a truck waiting below the mixer chute.
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Concrete Block Plant
The new Rekers concrete block plant at Belgard has an annual capacity of 30million 100mm solid concrete blocks making it one of the biggest such production facilities in the world. The plant uses state of the art process controls to ensure high standards are maintained throughout the production process. The aggregates used for production are carefully selected to ensure consistency of composition of the finished blocks. Cement used in the block making process is brought from the Irish Cements production plant in Platin. The production process is automated using a production control system which despenses the exact quantities of aggregates, cement and water into the mixer. Mixing is carefully controlled to ensure that the correct moisture content is achieved.
The mixed concrete is fed into a feed drawer in the block press where it is filled into mould boxes which define the shape of the finished block. Excess material is removed from the top of the mould and controlled vibration is applied to compact the block to the correct height. After compaction the mould box is lifted and the palettes containing the formed blocks pass along a conveyor where the blocks are cleaned to remove any excess material. The blocks are then stacked in elevators, ready for curing. A finger car picks up 10 palettes of blocks at a time, transferring them to curing chambers where they are kept for up to 24 hours.
After the curing process is complete, the finger car removes the palettes and transfers them to the final stage of production. Samples of the blocks are removed for testing and the blocks are measured to confirm that they are the correct height. The finished blocks are then moved to the stacking area, where the palettes are removed, washed and recycled back into the production process. The blocks are automatically stacked into cubes and are tagged, wrapped and strapped, ready for transfer to the storage yard outside.
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Paving Block Plant
The Rekers Concrete paving block plant is a high volume production process currently producing a variety of different paving blocks including both the Cobbleset and Castlestone ranges. The particular manufacturing process used by Roadstone Wood produces a two layered block, consisting of a high strength concrete base and a fine textured topping layer. A single layer block is also manufactured.
The cement used is delivered in bulk tankers from Irish Cement, another major CRH company based at Platin, near Drogheda. The entire mixing process is totally automated and controlled by PLC's to ensure consistency of manufacture and orderly storage and curing of the blocks.
The aggregates for production are delivered by truck into a ground feed hopper from which each material is fed into covered storage bins. A batching system dispenses the exact quantity of each material by measuring the weight of the aggregate with load cells above the conveyor. The blended aggregates are transferred into a holding hopper above the concrete mixer. Cement is fed to the mixer and water is added in a carefully controlled way so that the resulting concrete has the correct moisture content and consistency. Pigment is added to the mix during the mixing process.
At the start of the process, a palette is moved into position in the block press, the mould-box is lowered onto the palette and the feed drawer fills the mould box with mixed concrete. Flat compaction heads are lowered onto the mould and heavy vibration is applied to compact the block to size. The mould is then lifted and the palette containing the wet paving block moves down the production line.
Palettes containing the formed paving blocks are moved to a storage elevator which stores up to 22 palettes at a time. When the storage elevator is full, a finger car automatically lifts the palettes and transfers them to one of the curing chambers. During the following 24 hour period, the heat developed by the hydration of the cement cures the paving blocks. The curing chambers are highly insulated to contain the heat and humidity produced during the curing cycle.
After 24 hours curing, the paving blocks are transferred by the finger car to lowerators where the product is continually inspected and sampled for laboratory testing. Hydraulic grabs lift the blocks from the palette and stack them into cubes which are strapped and wrapped for protection during storage. Each cube is individually tagged with both a tracking code and a product description prior to being moved from the conveyor for storage in the yard. The blocks are kept in storage until the appropriate strengths have developed. Safe handling strength for secondary processing is achieved at 7 days and full strength for release to sale at 28 days.
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Flag Plant
The concrete flag press produces a variety of paving flags. Rubber mats in the moulds are used to create different textured finishes. The materials required are transferred by feed hoppers and conveyors to enclosed storage bins. The aggregate, sand and cement are batched into two separate concrete mixers - one for the backing layer and one for a colored topping layer. The batches are mixed using precise control over the moisture content of the concrete, and pigment is added to the topping mix as required.
Paving flags are manufactured upside down. In the two position process the mould is first brought to the working station where the facing concrete is deposited into the mould. Vibration takes place to give a uniform thickness of facing mix in the bottom of the mould. The backing concrete is then dispensed into the mould. At this point the mould is moved to the pressing station where heavy vibration and pressure are applied by a 500 tonne press. This gives the flag its density and strength. The flags are lifted by individual vacuum pads and are moved into a vertical stacking position for curing. A washing stage is used for flags with an exposed aggregate finish. The flags are stored in the factory for 24 hours to allow the concrete to cure to handling strength. When the flags have reached handling strength they are removed to the storage yard for a further 28 days curing prior to release for sale.
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Tile Plant, Clondalkin , County Dublin
Roof Tile Plant, Currabeg, Ovens, County Cork
The concrete roof tile plant uses a highly automated process in order to produce high volumes of various profiles, colours and sizes of roof tiles. The plant uses a computer controlled batching system which allows complete control over the production process. Washed and graded sand is fed into hoppers and is screened before being dispensed in controlled amounts by the weigh hopper, located above the mixer.
At this stage, water, cement and pigment are added to the mixer in pre-determined amounts and in the correct sequence. After mixing, the mortar is transported to the tile press by conveyors. The tile press shapes and compresses the mortar to form the tiles onto palettes. The formed tiles are then transferred to temperature controlled chambers where they are cured overnight.
After curing, the tiles are washed, and are taken from the palette for surface finishing. They are then transported by conveyor to an inspection and quality control area. After inspection, the tiles are strapped, counted and are stored in a slotted conveyor system before being loaded by forklift to trucks for delivery.
Recently the Plant has added two new products to its range, Roadstone Wood Minislate and Gemini TwinTile. The NEW products required an additional dedicated production line with an investment of approximately €1 million .
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