SubscribeLightweight foam concrete has been used in the United Kingdom since 1970, although it took ten years or so to become accepted as a main-stream building material by a traditionally cautious construction industry.
Location: Greenhithe, Kent, UK
Main Contractor: Seer Restoration Ltd
Client: Kent County Council
Since then, the superior flowing, self-levelling and self-compacting properties of foam concrete have proved their worth time and time again with the versatile material becoming increasingly popular with many engineers and contractors, looking for an effective, fast-track, environmentally friendly and competitively priced void-fill solution.
Foam Concrete: Compressive Strength
Volumetric masses of between 250 and 1600 kgs/m3 and compressive strengths of between 0.2 and 12.0 N/mm2, combined with superior rigidity, thermal insulation and water absorption properties in particular, have encouraged more and more engineers and architects to specify foam concrete in a wide range of applications.
As part of the 'Kent Thameside' regeneration programme in the north west of the county, reclamation works are in progress to facilitate the redevelopment (for housing) of a number of chalk-pits which were formerly part of the Blue Circle Northfleet cement works.
A network of tunnels, ranging in age from the Victorian era through to the 1960's, criss-cross the area connecting a number of outlying chalk-pits to the main works. Some of the smaller tunnels were built for pedestrian or hand-cart traffic, whilst several were used by the narrow gauge railway which served the massive site.
Kent County Council (KCC) insisted that as part of the proposed redevelopment, one tunnel in particular, situated in the north east corner of one pit in Greenhithe, should be in-filled to negate the risk of subsidence to a main road and residential properties built high above the tunnel. The tunnel ran for a distance of some 90 metres, at a depth of around 50 metres beneath the A296, into another redundant quarry, now better known as the 'Bluewater' shopping and leisure destination.
The KCC specification initially called for total fill to be achieved using shaped polystyrene blocks with grout injected into any remaining voids. For mainly logistical reasons however, it was agreed to carry out the works using a 400 kg/m3 density, 0.5 N/mm2 compressive strength foam concrete.
Lightweight Foam Concrete Batching Plant
Due to the rapid programme, the topography of the site and the low density of the foam concrete specified, Kent-based Foam Concrete Limited was appointed to supply the contract using a high output, mobile on-site batching plant.
Capable of manufacturing up to 600m3 of high quality, lightweight foam concrete during a normal working day and able to pump over distances of 0.5 kilometre, the plant requires far fewer deliveries of raw materials to produce a given quantity of finished material than would be the case if using a ready-mixed concrete company to supply sand/cement slurry for foaming on site.
The northern end of the tunnel had already been sealed during the construction of 'Bluewater', which meant that shuttering was only required at the southern end where the batching plant was sited. It was decided to construct an earth bung-wall, the height of which could be easily raised as required by the progress of the work. By the end of the pour, the top of the bung-wall would be around one metre higher than the crown of the tunnel, ensuring that total fill had been achieved.
Foam Concrete Tunnel Infill
Infill of the tunnel was successfully completed in 9 working days and required 1300m3 of foam concrete made with around 350 tonnes of powder delivered in 12 bulk materials tankers, water and protein admixture manufactured in Scotland by sister company Provoton Ltd.
Advantages of using foam concrete for tunnel infill:
Ease and speed of placement:
When judged against other more labour/time intensive infill methods like polystyrene/grout, the ability to produce up to 600m3 of foam concrete a day means that construction times can be significantly reduced, showing significant cost savings.
Total void-fill:
The superior flowing and self-compacting properties of foam concrete ensure that all voids are completely eliminated.
Good energy absorbing qualities:
As foam concrete is compressed during collapse or subsidence of material above, due to its cellular structure, the resistance of the foam concrete increases, absorbing the kinetic energy.
Susceptibility to breakdown:
Unlike some synthetic, lightweight foams (polystyrene for example), hardened foam concrete is not susceptible to breakdown due to the presence of hydrocarbons, bacteria or fungi. Foam concrete is insect, rodent and fireproof.
Environmentally sound:
Foam Concrete Limited's commitment to sustainability in the construction industry was recognized when the company received a commendation at an awards ceremony for the Environment Awards for Kent Business 2006.
The exclusive design and technology employed in Foam Concrete Limited's on site batching plants allow recycled materials such as fuel ash and limestone dust to be used in many of the mixes. These industrial by-products are often disposed of in landfill sites but, by blending them with cement, they are encapsulated within the foam concrete, thereby mitigating any adverse effects on the environment.
One of the most startling comparisons of energy usage between foam concrete from Foam Concrete Limited's on-site batching plant and that made by foaming-up a base-mix from a ready-mixed concrete supplier, only becomes apparent when you add up the approximate number of vehicle movements required to produce - in this example - 1000m3 of 1000kg/m3 density foam concrete by each method:
| Foam Concrete Ltd - On-Site Plant | Movements | Base-mix Via Concrete Company | Movements |
| Batching plant & 2 silos to/from site | 12 | Foaming pump & van to/from site | 2 |
| Support van to/from site | 2 | Admixture truck to/from site | 2 |
| Admixture truck to/from site | 2 | Sand trucks to/from concrete plant | 60 |
| Bulk materials tankers to/from site | 48 | Bulk materials tankers to/from concrete plant | 16 |
| Concrete truck-mixers to/from concrete plant | 284 | ||
| Total Movements: | 64 | Total Movements: | 364 |
Using Foam Concrete Limited''s on-site batching plant means less traffic disruption both on-site as well as on roads in the surrounding area.
With fewer truck movements and vastly reduced emissions, this process of manufacturing foam concrete makes it safer, quieter and cleaner for both site-workers and local residents and dramatically reducing the environmental impact of your site.