Anyone who has stared out at the taxiway while waiting for take-off will know there is a lot of concrete used for airport pavings. What they probably do not realise is that the pavement represents vast quantities of carbon dioxide. Manufacturing a single tonne of cement releases 0.932t of CO 2into the atmosphere.
Reducing BAA's greenhouse gas 'footprint' has been a principal target for the BAA Pavement Team at all of its airports - Heathrow, Gatwick, Stansted and Southampton - says the team's performance improvement programme head Andy Delchar. Since the Pavement Team was formed under a framework agreement in 1995, it has poured about 120,000m 2of450mm thick concrete paving per year. There is huge scope to cut back emissions.
So far innovations have achieved an estimated 46% reduction in CO 2, equivalent to 47,000t. They include recycling concrete, cutting back on quantities of new concrete used and reducing cement content. Of the 650,000m 2of paving done to date, some 500,000m 2is new, laid as part of airport redevelopment. However, 150,000m 2isreplacement paving - in other words, nearly a quarter of all paving can be carried out using recycled concrete.
Recycling has become viable only since the pavement framework contract was put in place.
Paving used to be done piecemeal, and most individual contracts did not produce enough waste to justify the expense of crushing and keeping it. Material was generally carted off to landfill. When concrete was re-used or stockpiled, quality was never monitored. It was generally treated as hardcore.
'But we have set up a management system for the concrete, crushing it, maintaining a stockpile and assessing quality, ' says Delchar. Even small quantities, for example, crushed cubes from laboratory compression testing and waste arising when individual panels are replaced, are salvaged and added to the stockpile.
Each airport is able to assign recycled materials to projects as they come through, ensuring that they are fit for use at design stage. The process saves on lorry movements taking concrete off site and bringing back new materials such as aggregates. Keeping transportation to a minimum also keeps CO 2emissions low.
Beyond recycling, the Pavement Team has been cutting back quantities of concrete used by reducing the thickness of the top pavement layer. The strength of concrete mixes exceeds specification - it is generally up to 60N/mm 2- allowing 10% reduction in slab thickness.
Extra strength comes about partly as a result of the 'additional safety factor' that designers, contractors and suppliers always throw in 'just in case', says Delchar. The long-term nature of the framework agreement means it is possible to track pavement strength over a long period. Knowing exactly what performance is being achieved enables designers to refine design parameters on successive jobs.
The team is also reducing cement content in the mix while achieving the same strengths by using pulverised fuel ash. PFA, seldom previously used for paving, now makes up 30% of cement content. Suppliers have helped improve the performance of mixes by developing additives to help with plasticity and curing.
Delchar believes that, to deliver improved environmental performance, it is necessary to innovate. This inevitably means that, from time to time, mixes will not work as intended. There has to be 'scope to fail', he says.
The framework contract offers that freedom.
Amec/BAA (Pavement Team) PJ Brown Grace Construction Products Ash Resources Topmix
Why the team won
Its work has demonstrated significant and quantifiable environmental and financial benefits.
The work/process has a high degree of applicability throughout BAA and elsewhere in the industry.
Demonstration of integrated team working/partnering approach.
Team working/partnering has enabled innovation.
High degree of enthusiasm to identify environmental opportunities in a part of the business where environmental gains are not often obvious.