Ian Purton reports on the impact of the new Eurocodes, the increase in post-tensioned flooring and recent cost changes in the sector
The concrete sector is worth about £5bn a year, with up to 120 million tonnes of concrete being used in UK construction projects every year.
The concrete market has remained steady over the past 18 months, with the exception of reinforcement prices, which are still volatile. Last year, the net material price dropped from a high of £375/tonne to level off at £320/tonne. However, this is expected to rise again and could end up back at £370/tonne by the end of this year.
Research has shown that there has been a significant increase in the use of post-tensioned floor construction, especially in the residential sector. The advantage of this solution is it creates thinner slabs, which means a reduction in the overall floor-to-slab height. This has the knock-on benefit of saving on cladding and other trades. With greater planning restrictions on building heights, this has allowed some residential developers to build additional storeys within the same heights as traditional construction.
The introduction and implementation of BS EN 1992 Eurocode 2 Design of Concrete Structures (EC2) is a significant event for the UK construction industry. This will ultimately supersede all the UK standards dealing with the design of concrete structures. The general rules are now available from the BSI. The National Annexe, which will contain UK-specific information such as safety factors and durability issues, is expected to be published later this year.
The timescales for the implementation of EC2 is that all conflicting British Standards are expected to be withdrawn in 2010. However, BS 8110 for Design of Reinforced Concrete Structures may be withdrawn as early as 2008. In common with all EU countries, public authorities will have to accept EC2 as a valid method of design on major work. Ultimately, EC2 will become the single design code for all concrete structures in the UK and Europe.
It has been reported that there may be a material cost saving in the use of EC2 of up to 5% compared to using BS 8110.
The average lead time for insitu concrete frames has remained reasonably static at five weeks from the time of order. The primary factor in determining the lead time remains the procurement of steel reinforcement.
Trade contractors have reported that they can mobilise and be on site in three to four weeks, but the detailing of reinforcement and issuing of bar bending schedules by engineers tends to lag behind this timescale. These are required 10 to 15 days before the steel is needed on site to avoid the additional cost of express ordering.
The supply price of concrete increased about 10% on 3 January 2006.
This rise incorporates an increase that was originally expected in September 2005 but never materialised.
Trade package preliminaries covering supervision, setting out and so on, overheads and profit are currently in the order of 20-25% of the trade package cost.
Typical all-in estimating rates inclusive of trade preliminaries, overheads and profit for C40 concrete for a typical concrete-frame building are outlined in the table below. The rates have been expressed as a range to reflect ease of placement, quantities involved and complexity of design.
The typical range of costs for supply and fix of reinforcement average from £800/tonne to £860/tonne.
Many concrete contractors are still unwilling to provide a fixed lump-sum price for reinforcement at tender and are treating it as a prime cost sum, providing the supply price of reinforcement at the time of tender to be adjusted on placement of order.
Formwork costs have remained relatively unchanged and current prices have only increased in line with inflation. Typical cost see table attatchments.