|Costain trialled Tarmac's innovation submission to the portal at London Bridge Station project. The benefits and lessons are stored on the portal for future best practice implementation.|
|Pouring & Compacting ready mix concrete||TopFlow Self-Compacting concrete|
TopFlow self-compacting concrete, manufactured by Tarmac, is an innovative construction material that aims to improve quality in the construction process. It can be defined as a fresh concrete which possesses superior flow ability under maintained stability, therefore allowing for self-compaction. TopFlow contains a mix of additives, including superplasticizers, that keep the concrete highly fluid and other chemicals that cut down on the water needed. These enable the concrete to consolidate under its own weight without mechanical vibration.
It can be poured quickly, flowing and spreading effortlessly to provide a highly aesthetic finish. It can save both time and money, as well as reducing noise and eliminating vibration, which help to considerable improve conditions on site.
TopFlow uses innovative mix technology to combine the benefits of two seemingly opposite physical properties; fluidity and stability. Fluidity is essential to provide easyconcrete placement and a high-quality finish with minimum effort. Stability is necessary to prevent segregation. Together, this dynamic fusion delivers the ultimate free-flowing, self-compacting concrete.
- Fast flowing
Free flowing TopFlow concrete can be placed fast, and consolidates easily under its own weight.
- Easier placement
Placement is also easy. The pour requires fewer pour points, less formwork, reduced manpower and no vibration.
- No vibration
By eliminating vibration and greatly reducing noise pollution, working conditions on-site are greatly improved, and pours can be safely carried out even in built-up environments.
- Smoother surfaces
TopFlow provides an excellent, smooth surface finish that can be laid perfectly flat for slabs and floors, eliminating the need for floating, and therefore labour.
- Perfect for intricate moulds
As the TopFlow mix has a very low viscosity, it can fill intricate moulds and wrap around complex structures and still produce a smooth finish.
- Ideal for high seismic activity areas
The increased fluidity also makes it ideal for use in areas of high seismic activities, where structures are heavily reinforced with rebar. Trying to use a vibrating poker to compact standard concrete with dense rebar can be very hard, if not impossible. TopFlow self-compacting concrete eliminates this problem.
London Bridge Redevelopment Project
According to Tarmac, laying a 60-cubic-meter slab of regular concrete requires eight people and takes about 8 hours. Using self-compacting TopFlow concrete can reduce this time to just a couple of hours, requiring as few as two people.
At London Bridge, 1500m3 of this bespoke self-compacting concrete, with a perfect F3 finish is required for the 21 concrete columns and crossheads. These will hold the bridge decks above, and allow for a spacious, open concourse below. A perfect F3 finish is required on the columns, a demanding requirement made more difficult to achieve due to the bespoke steel formwork being used. The solution was to use TopFlow self-compacting mix, which contained both ground granulated blast furnace slag (GGBS). This enhanced the finish while maintaining a high CEEQUAL (sustainability) rating.
- Does not require any compaction using a vibrating poker, saving time and making the process safer.
- Less labour required to complete a concrete pour, which saves money.
- Pours are complete quicker compared to the traditional methods.
- Use of GGBS and limestone filler – not always the case in regular ready-mix concrete.
- Fewer blow holes as no vibrating poker used, therefore improved surface finish.
Quality – The quality of the surface finish of the concrete is maintained at a high level (in this case to a F3 finish). In some cases the finish can be improved as self-compaction eliminates blow holes caused by a vibrating poker.
Cost - Although the cost of the material itself is higher than conventional ready-mix concrete, it requires less labourers to place the concrete, therefore saving on wages. Also the enhanced quality of the finish means less maintenance and remedial works, which cost money, will be required.
Time – Time is saved as there is no compacting using a poker. This means labour will be available to work on other parts of the project sooner than if conventional ready mix concrete was used.
Safety & Welfare – Reduction in manual labour as no compaction with vibrating poker needed.
Environment – A recycled material, GGBS, is used in the mix design for TopFlow concrete. This reduces its environmental impact and enhances its sustainability.
Construction Method – Much improved construction method. Allows intricate and dense rebar cages to be used, maintains a good surface finish and can save vast amounts of time when pouring concrete, especially on large pours such as the column and crosshead pours here at London Bridge.