Galliford Try Lagan Construction Joint venture (GTLC) secured a prestigious £135 million contract earlier this year with the Defence Infrastructure Organisation (DIO) to improve infrastructure and facilities at RAF Marham, near Kings Lynn in Norfolk.
The contract is to reconstruct the two main runways and taxi-ways as well as design and build a new aircraft hangar with associated support buildings for a new fleet of twelve F-35B Lightning II fast jet aircrafts from which they will deploy to Queen Elizabeth Class carriers.
Vertical landing pads will also be added to RAF Marham, accommodating the F-35B’s ability to land vertically, a capability previously covered by the Harrier jets.
To ensure Lagan Construction could deliver world-class Marshall asphalt on time they required a state-of-the-art reliable asphalt plant that was capable of delivering high production tonnages whilst being mobile, compact, low profile and could be installed with minimal site foundations. Having used the highly efficient Parker RoadStar 3000 and 2000 (240tph and 160tph respectively) on dozens of other commercial airports and military projects, Lagan Construction again turned to British manufacturer, Parker Plant.
The concept of the Parker mobile asphalt plant was originally designed in 1966 and first launched in 1969. In total there have been over 1400 installations of the ‘Super-Blackmobile’ worldwide with a large population of them still in operation today. The new RoadStar supersedes this concept and is designed to meet a wide range of market requirements, offering flexible low cost operation, with maximum production rates.
The new RoadStar 3000 mobile batch production asphalt plant, designed with emphasis on mobility, incorporates the latest in asphalt technology and meets all the required mix specifications whilst satisfying environmental standards. The plant has a production output rated at up to 240tph at 3% initial moisture.
Designed to provide significant operational benefits and cost savings the new plant is capable of producing a wide range of high quality mixes required to reconstruct both run-ways. The RS3000 will be operational on-site for a total of 18 months; however, contractors have already been impressed during its first 19 day ‘Bolthole’ during which it produced 14,000 tonnes of various 20mm heavy duty binder courses immediately after the commissioning phase to meet tight deadlines.
The eight bin cold feed system consists of two mobile units; one mobile unit containing three aggregate hoppers and the other mobile unit with two additional static bolt-on hoppers each with heaped capacity of 15m3 with frequency controlled side-walled belt feeders to ensure accurate delivery and blending of materials. Marshall asphalt requires high volumes of sand and fines, so to ease material flow designated hoppers are fitted with side wall vibrators. Both mobile feed units are guarded and sheeted, top, back and sides. The canopy is a separate structure bolted down to comply with wind protection regulations.
Adjacent to each other, the 650mm wide S-bend collecting conveyors transfer material onto a 650mm dryer feed conveyor delivering the materials into the dryer drum. The direct fired aggregate dryer drum is 2.5m in diameter and is 9m in length. Mounted on a mobile chassis the drum is insulated and galvanised clad for heat retention and noise reduction. Operating in a counter-flow fashion the drum is friction driven by four support rollers each through individual 22kW geared motor units. Heat is directly provided by a Turbo-Jet burner suitable for use with light oil such as kerosene and is energy efficient. An infrared dryer outlet pyrometer measures the dryer discharge temperature relaying it back to the operator’s control desk.
The mobile secondary dust collection system is rated at 93,360Nm3/hr and is sized for the dryer and mixing section nuisance ducting, achieving dust emission levels of less than 20mg/m3. 28 cast manganese steel cyclones form the primary dust collection system which is mounted on the mobile dryer chassis to separate out any coarse dust from the air-stream created by the drying process. Coarse dust is collected in the hopper below the cyclones and is transferred back to the hot stone elevator feed boot via two 4kW transfer screws that also form part of the mobile dryer unit.
Dust is also collected from nuisance points at the screen, batch elevator head and hot stone elevator for filtration. A particulate impingement type dust monitor is fitted in the exhaust stack to provide a remote readout to the operator’s cabin for data logging and as a result the plant meets the most stringent dust control regulations. The exhaust fan is inverter controlled to minimise energy consumption and optimise the vacuum inside the dryer drum. Clean air is released to the atmosphere through the plant’s free standing 12m high exhaust stack supported with ballast boxes.
To complement the mobile bag filter, a 45m3 mobile horizontal reclaimed filler silo was supplied to store and transfer reclaimed dust back to the mixing section’s filler weigh hopper. Any surplus dust can be processed via a twin-shaft dust conditioner where water is introduced providing a safe and environmentally friendly method of purging reclaimed dust.
Hot aggregates from the dryer discharge point are elevated to the screen level of the mobile mixing section by a totally enclosed bucket elevator which features a heavy duty twin strand chain and bolt-in wear resistant steel buckets. The elevator is driven by a fully accessible top-mounted 15kW geared motor unit and features safety backstop with externally located bearings for ease of maintenance.
A transfer chute with liner plates guides material onto the screen mesh. The screen measures 2.1m wide by 6m in length and has two decks providing four sizes. The drive is a high torque 18.5kW motor unit that is mounted externally with full guarding, but easily accessible via external platforms for screen mesh changes, maintenance and greasing. The hot storage section beneath the screen has a total capacity of 28 tonnes, discharges into the aggregate weigh hopper and is controlled sequentially by pneumatically operated radial doors that accurately regulate material flow.
Accurate weighing out of the ingredients is achieved by separate load-cell mounted weigh hoppers, comprising a 3000kg aggregate weigh hopper under the hot stone bins and a 630kg filler weigh hopper and 480kg insulated bitumen weigh hopper located directly above the mixer. The weighed material in the aggregate weigh hopper is transferred directly into the mixer by a totally enclosed inclined continuous batch elevator driven by a 15kW geared motor unit. The mobile plant’s 3000kg twin shaft paddle mixer is driven by two 37kW geared motors with timing shaft while soft starts are utilised to reduce the starting current. There is a pyrometer mounted under the mixer to record discharge temperatures with temperature indication on the existing VDU and computer batch print out.
Hot mixed asphalt discharges from the paddle mixer into a 3250kg skip which runs on inclined tracks to distribute the material into various sized silos with a total storage capacity of 350 tonnes. The mixed material storage system has high level indication in each silo and is fully insulated and clad. The top cover doors and radial discharge doors are all pneumatically operated and feature heating in the discharge doors to prevent any blockages.
Bitumen is stored in two 50,000 litre electrically heated mobile bitumen storage tanks that again complement the mobility of the plant whilst providing an on-board 36,400 litre/hr bitumen delivery pump with temperature controlled insulated pipe work to the bitumen weigh hopper. Each tank is fitted with high level and ultimate high level audio and visual alarms and an emergency shower to RBA requirements is provided to meet safety regulations.
Imported hydrated lime is stored adjacent to the plant in a 45m3 mobile horizontal imported filler silo and is necessary for the HDM mixtures required for the runway specification. The imported filler is transferred to the filler weigh hopper by an 11kW inclined feed screw.
SMA pelletised additive is delivered to site in 500kg flexible industrial container bags and is loaded and stored in a 1.5m3 nominal capacity silo. The additive is accurately weighed in a load cell mounted weigh hopper before introduction directly into the mixer via a pneumatic conveyor.
The entire plant is controlled by a Parker RTS2017 control system which contains plant mimic colour diagrams and displays all functions. The system includes the storage of recipes, plant parameters and production data. Operational and energy usage data is also captured.
The RS3000 has motor isolation switches fitted to all drives, remote camera surveillance to the cold feed, dryer entry, mixer discharge and mixed material silo top discharge area as well as external plant lighting for night operation.