The HOCT, developed for Balfour Beatty Rail, is based on two Nurock NUVM7 mobile concrete batching plants, the company’s seven-cubic-metre truck-mounted unit.
The Nurock unit carries all the ingredients unmixed in separate compartments. It then proportions these according to the mix design and mixes the quantity required in a continuous mixer. The mixer can be stopped and started as needed via a handheld remote control. With no waste or loss of quality in transit, the whole process is computer monitored for quality and accountability.
The mixers come into their own in remote locations or where intermittent demand is needed, typified by rail applications, Nurock said. Only the required amount of concrete is mixed, minimising waste and the need for top up deliveries.
The HOCT was commissioned by Balfour Beatty Rail following award of Phase 1 of the North West electrification project from Liverpool to Manchester. The concept was presented to Network Rail during the tender stage of the bid.
The North West electrification project will see 25kv overhead power delivered to the routes between Liverpool and Manchester, Huyton to Wigan, Preston to Blackpool and Manchester to Preston via Bolton. The work complements the lines that are already electrified in the region – notably the key freight route of the West Coast Main Line, the busiest mixed use railway in Europe.
The HOCT is stabled in Liverpool and places concrete five or six nights a week, supporting a team of 20 involved in the excavating and concreting of formwork located along the side of the rail track. These foundations will support the steel structures for the overhead lines.
The HOCT can deliver up to 16.5 cubic metres of the desired mix design in minutes with no waste; the units have two independent diesel engines to reduce downtime. All mixes are monitored by two computers, which can prescribe up to 50 mix designs and monitor all ingredients of the mix. The mixer units contain use a unique patented system which allows them to batch concrete at cement contents from 50kg to 500kg per cubic while maintaining a constant output rate.
The mixers have been mounted on an ISO container base system, two outer bases holding the independent proportioning units and the central base housing the continuous mixers. These deliver the concrete into a central rotating turret onto which removable delivery chutes can be attached. This allows ingredients from either unit to be mixed as required. The rotating turret’s delivery chutes can place concrete on either side of the track as needed
Considerable redesign of Nurock’s standard NUVM7 unit was required to allow the unit to comply with the rail gauge (tunnel height) requirements but still meet the delivery capacity to make the project a success.
Balfour Beatty Rail engineering and development manager Geoff Brown said: ‘The adoption of a pair of volumetric mixers onto a railway wagon is a first in the UK and has not been without its difficulties. UK rail has one of the tightest structure clearances in Europe, resulting in redesign of hopper size and capacity. Approval processes to use new products on the network are laboriously long and in addition operations can only happen once trains have stopped running which means at night and at weekends.
“However, we are pleased to say that together we overcame all of these difficulties and now have a product that not only improves productivity, quality and cost efficiencies but also provides a sustainable solution to traditional methods.”
The traditional method of delivering concrete for rail infrastructure has been to deliver ready-mix to an access point and cart the concrete up or down track where it is removed and placed by mechanical means. This can cause issues if the quantities are wrong or if there are delays on track, as well as segregation and settlement during transporting. The cost and environmental impact of returning unused ready-mix is also considerable.
Key to making the project a success was the training that Nurock provided to Balfour Beatty Rail to support the transition from concrete procurement to producer. The training package began with training on concrete for all operational staff, followed by on-site instruction with more than 20 staff being trained.
Nurock Mixers managing director Graham Jones said: “Delivering this project with Balfour Beatty Rail has been both challenging and exciting, the Nurock HOCT brings many benefits to the rail industry and is an environmentally friendly alternative to ready mixed concrete and traditional methods.”