By Dominic Laurie
European business reporter, BBC News, Brussels
China's economic boom has driven demand for building materials
Wherever you walk in Brussels, it seems they are knocking buildings down and putting them up again.
The problem is that building construction eats up concrete, and to make one tonne of cement - a key ingredient of concrete - 900kg of carbon dioxide (CO2) are released into the atmosphere.
Production of cement causes twice as many carbon emissions as the world's airline industry currently does. However, it also generates a fraction of the bad headlines.
And the people who run the world's cement companies would prefer to keep it that way.
They have been meeting at a conference organised by the Cement Sustainability Initiative (CSI) in the smartest hotel in Brussels.
Eighteen major producers - who produce a combined one billion tonnes of cement a year - just under half the global output - are members of CSI.
With the industry expecting to experience rapid growth in coming years - particularly from China's booming economy - and plants in Europe already facing pollution caps under the emissions trading scheme, CSI's members are understandably nervous about future regulation.
As a result, its members are hoping to take steps that would pre-empt any legislation being forced on the sector.
Its goal is to make its members more aware of, and therefore reduce, the environmental impact of their business.
For example, one thing it does is ask members to publish their carbon emissions.
Dimitri Papalexopoulos, the boss of Titan Cement - a medium-sized Greek firm and CSI member - says he recognises the scale of the problem.
"The cement industry is responsible for 5% of the world's man-made carbon emissions," says Mr Papalexopoulos.
FROM CEMENT TO CONCRETE
Limestone is crushed, then blended with other materials containing the right proportions of calcium, silicon, aluminium and iron oxides
Blended substance is heated to about 1,500C in kiln - components react and partially fuse, producing clinker
Clinker is cooled and ground with a small proportion of gypsum and other additives to produce cement
Cement is mixed with sand, gravel, and water to produce concrete
SOURCE: Cement Sustainability Initiative
"And if you look at that figure in proportion to the sales or the turnover of this industry, it's a huge percentage."
Cement firms are already taking steps to clean up their manufacturing processes.
One is using different types of minerals in the cement oven to neutralise some of the carbon produced, while other techniques are more unexpected.
Fifty kilometres outside Brussels, there is a waste treatment plant run by a firm called Geocycle. An unlikely place for a solution to cement's environmental dilemma, perhaps.
But here, Geocycle turns waste products into fuel that can fire the kilns, or ovens, at a cement plant just a few km away.
"The materials which come here are normally paint waste, ink waste, dyes, glues, adhesives, organic residues from distillation processes, from production processes," explains Michel Langeveg, a senior executive at the firm.
"The material is then mixed with sawdust, so that the physical state of the material will change into a compost-like product. You can inject that directly into a cement kiln."
But, fuel derived from waste cannot provide a total solution.
For example, its use does not completely stop CO2 going into the atmosphere, and still only a small proportion of fuel for cement ovens is made from waste products, rather than fossil sources.
Geocycle processes waste for reuse in cement production
But whether the take-up and efficiency of greener techniques improves or not, the cement industry is certainly not going to disappear.
As Dimitri Papalexopoulos says, concrete is the second most-used material in the world by man after water.
"Over three tonnes are used on average for each person on this Earth. It is a very basic material, with no obvious substitutes in terms of satisfying basic needs of housing and infrastructure all over the world," he adds.
And with no substitutes available, the industry will continue to try to come clean about emissions and greener technology.