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Precast cladding in demand
Precast concrete firms in the Architectural Cladding Association are winning more work on the back of the revival in the multistorey residential market. Estimates suggest that there are 89 high-rise residential buildings being planned or under construction in the UK, and precast cladding has already been selected for a number of prestigious London projects such as St George Wharf in Vauxhall and Discovery Dock in Canary Wharf.
Stephen Maddalena, chairman of the ACA, believes that more clients are appreciating the benefits that precast cladding can bring to their projects. He says: “The reasons for this are obvious: precast concrete is a robust material that offers design flexibility with incomparable choices of finishes and 3D capability. Economy is achieved with reasonable repetition, and prefabrication is the clear way forward for construction.”
Maddalena says clients and architects are attracted to the range of finishes available. These include lightly textured reconstructed stone, polished concrete, coarse exposed-aggregate surfaces, natural stone and brick or terracotta tile facings. Buildings can be faced in almost any colour imaginable by selecting different hues of brick, stone, and aggregates, or by adding pigments to the concrete.
He adds: “Precast concrete cladding produced in accordance with BS 8297:2000 and BS 8110 has a life expectancy of 60-plus years and is generally regarded as being maintenance-free.”
Lafarge unveils latest products
Lafarge, Britain’s largest cement maker, is offering free advice to contractors and specifiers. It comes in a 58-page Builders’ Guide, available on www.lafargecement.co.uk. The guide covers general concreting works, mortars, renders, floor screeds and ready-to-use products such as pre-mixed concrete.
There are sections on selecting types of cement for particular applications, details of mixes and a ready reckoner to help calculate the quantity of materials required.
Advice is also given on the correct methods of construction to use when concreting, bricklaying, rendering or laying floor screeds.
Another development from Lafarge is the introduction of three types of ready-to-use concrete. Two are structural grade mixes with a guaranteed strength of 40 N/mm2 with a maximum aggregates size of either 20 mm or 10 mm. The third is a multipurpose mix with a strength of 20 N/mm2 and suitable for paths, drives and fixing posts. All three come in 25 kg bags and only require mixing with water.
Researchers at BRE are about to publish guidance on enhancing the durability of concrete that is subjected to aggressive ground conditions.
Special Digest 1 is the culmination of years of research into minimising the deterioration of concrete where sulfates and acids are present in the soil or groundwater.
It gives advice on the types of cement to use, the minimum cement content of the mix and the best water to cement ratio. The digest also advises on cements blended with ground granulated blast furnace slag and pulverised fly ash. A significant change is the acceptance that concrete made with calcium carbonate aggregates, such as limestone, are not as vulnerable as previously thought.
The key findings of SD1 will also be included in a new version of the code of practice covering concrete, BS 8500, which is due for publication later in the year.