One of France's biggest road contractors is taking a pragmatic approach to recycling.
Roads contractors in Paris have a problem. The nearest sources of virgin aggregates for blacktop and concrete are more than 200km away.
The city of Paris has an even bigger problem. All its landfill sites are full.
Incineration is its preferred route for the disposal of domestic waste, but this still leaves ash from the incinerators and demolition waste to be disposed of.
Eurovia, Europe's largest road contractor, produces more than half the virgin aggregates consumed in France every year - some 48Mt. It also recycles more than 9Mt of demolition waste and reclaimed asphalt. Around Paris, four recycling centres process demolition waste into aggregates for fill and for concrete and bituminous mixes. And at its laboratories outside Paris research continues into the use of processed bottom ash from the domestic waste incinerators.
Incinerator ash is a controversial material, with opponents claiming it can contain dangerously high levels of leachable heavy metals and dioxins. In France, however, the government is actively encouraging its recycling.
Eurovia's results are encouraging, says technology transfer manager Samir Soliman.
'We use only bottom ash from second generation incinerators which has much lower levels of metals and dioxins than the mixtures of bottom ashes and fly ashes from the chimney precipitators that have been used in the past.
'This bottom ash is then left outside for several months on a specially-drained hardstanding before being processed to remove any organic remains and metal fragments.' Ferrous and non-ferrous metals recovered are sold for recycling, maximising economy.
Once processed, the ash can be bound together with a range of bituminous emulsions and foams, or cement, sometimes in conjunction with pulverised fuel ash from coal-fired power stations. End uses include road bases and light to medium duty surfacing.
With the ash particles encased in relatively watertight matrices, leaching of any potentially toxic constituents should be minimal. And any potential pollution has to be weighed against pollution produced by the fleets of HGVs that would otherwise be hauling virgin aggregates into Paris from hundreds of kilometres away - and hauling 800,000t of incinerator ash to landfill sites on their way back.