“Our discipline is evolving all the time”, Brouwers says. In part, that’s because of the ever-stricter environmental demands in construction concerning raw materials and energy.” Innovation in construction is a must, then. Like almost everyone else at TU/e, Brouwers is constantly searching for better, more environmentally-friendly, and cheaper alternatives. “And the latter two go hand in hand remarkably often.”

On top of that, every innovation in construction has a major impact because of the sheer size of the industry. “Construction - and I’m not just talking buildings here, but infrastructure, roads, too – is made up of about 95 percent of all materials used by man.” So in absolute terms, even a relatively modest saving involves lots of money.

Choosing building materials can help the environment in one of two ways, the professor says. “On the one hand, people can choose to recycle by reusing construction and demolition waste, or products can be made in a way that makes them more economical and more sustainable in use. Think of buildings that can do with less ventilation, or materials that store heat.”

The Netherlands are already very active when it comes to recycling. Consumer waste is separated for plastic, paper, glass, and other waste. Separating demolition waste has become quite common here as well, says Brouwers. “We’ve really come a long way in twenty years’ time. The Netherlands are definitely at the forefront in that respect.”

Recycled concrete, for example, is crushed to separate the cement from the aggregate (sand and gravel), so both can be recycled. “The crushing is done by a machine with huge steel jaws. We’re working on improving that method. It turns out that by placing the jaws more parallel, the concrete grains don’t break in half, but the crack rather occurs on the interface of the aggregate. By smart crushing, as we like to call it, the two components can be separated better, and be recycled for more high-grade uses. Our lab tests have shown the method works and the company VAR has produced one of those smart crushers already, and is planning to use more of them on a wide scale.”

 “In many countries ashes are simply disposed of, but to us it’s of economical value”

A very different example of recycling in construction is the processing of combustion gases. The ash that’s left after coal combustion in coal plants is known as fly ash (which needs to be captured in the chimney, as opposed to bottom ash), and in the Netherlands one hundred percent of it is recycled for building materials, concrete mostly. “In other countries the ash is often dumped, or sometimes simply lost through the chimney, but in our country it has a positive economical value. And we don’t need space to dump it anymore.”

Brouwers even wants to take things a step further by seeing whether residual ashes from the incineration of garbage, paper sludge, and biomass may be used to build houses or make roads. “Depending on the source the ashes will have to undergo some final processing”, he says. “It often has to be burned again, washed or sieved. Sometimes it’s done to meet environmental requirements, but it’s also needed to make strong concrete.”

Brouwers’ group also focuses strongly on nanomaterials. Again, freeways and office buildings might not spring to mind right away, but mixing in relatively small amounts of nanosilica – waste material from the production of computer chips and solar panels – with the concrete is very beneficial. “A kilo of nanosilica can replace up to four kilos of cement. It’s a way to reduce the amount of cement, which is the most expensive and environmentally harmful component in concrete, by dozens of percent.” Although their origin is entirely different, what nanosilica and combustion gases have in common is their grainy structure; they’re granular materials.

Whether or not concrete is strong enough for construction purposes mostly depends on the size of the various grains in theconcrete mixture. One of the thing Brouwers’ group specializes in, is the computer simulation of such materials. “We study the grains with models, and the mineralogy too: how do the grains interact? As far as experiments go, we have it all. We can characterize the materials both chemically and physically, make the building material ourselves, and test them in the lab to check if they meet our requirements.” It’s all done on a small scale, though. For large-scale tests the group relies on contacts with the industry. And there are plenty. One of the direct results of Brouwers’ models is ultra-lightweight concrete: through an optimum distribution of grain sizes it’s almost as tough as regular concrete, but much lighter and thermo-insulating at that.

Titanium oxide gives materials air-purifying and self-cleaning properties

The most appealing of Brouwers’ research topics might be titanium oxide. By adding that to concrete pavers, wallpaper, or cement-bonded woodwool boards, you can create materials that have air-purifying and self-ventilating properties. The effect of titanium oxide is based on photocatalysis. Light causes the titanium to convert harmful gases like nitrogen oxide, sulfur oxide, and volatiles into harmless substances. A large-scale test with the air-purifying concrete pavers in Hengelo last year was picked up by the BBC.

“We’ve realized that the effect of nanotitanium can be optimized further by mixing in nanosilica, which could be important for indoor use. Furniture, paint, and computers give off small amounts of toxins like formaldehyde and toluene. Because it’s hard to measure there are no real regulations concerning the matter yet, but we now have the equipment to measure the harmful indoor gases. A way to render the gases non-noxious could be by building walls and ceilings containing titanium.”