As global housing programs are gearing up, the world will need a staggering amount of construction material over the next few decades. This will put a strain on resources; moreover, it will produce a lot of CO2, as the vast majority of modern construction is on the basis of Portland cement, responsible for a stunning 5% of total global CO2 emissions. Moreover, rates of recycling of demolition waste are very low, in many countries below 10%, and even in the EU at a meagre 46%. Precision in the construction industry, with the benefits this would entail, would require a minimum of resources (including energy) and a maximum of recycling. Lack of precision could jeopardise the industry’s sustainability, and in the long run, the industry itself.
Construction industry: problems ahead
The major CO2 emissions of Portland cement production are due partly to the decomposition of limestone (calcium carbonate) into calcium oxide and CO2 as the cornerstone of the production process; partly to the very high temperatures (typically 1450 oC) required to process calcium oxide to clinker, by mixing it with additives like clay as a source of aluminium and silicon. In principle, concrete based on Portland cement is a high-quality and versatile material that carries many benefits to the construction industry. Its main disadvantage (its low tensile strength) can be overcome by adding steel reinforcements. But many concrete structures will be damaged during their lifetime, often because the steel reinforcements are not perfectly shielded from contact with air and water, and start to corrode; they then expand and cause fissures in the surrounding concrete, which causes more corrosion. Concrete degradation is so widespread that the UK spends £ 40 billion per year on the repair and maintenance of its ageing infrastructure, while the US is reported to need about $ 3 trillion over a five year period to raise the overall quality of its infrastructure from poor to acceptable.
Remarkably, there are viable alternatives for Portland cement, some of them suggested by ancient Roman and Egyptian structures that have withstood thousands of years; whereas modern concrete structures are designed for a lifetime of ca. 100 years. Fortunately, World Economic Forum and Ellen MacArthur Foundation addressed the issue. Many of the ‘innovative’ alternatives emit much less CO2 in their production, up to 93% emission reduction over the production chain. Instead of clinker, the ancient Egyptians and Romans used materials like diatomaceous earth and volcanic ash as a binding material; this was established by prof. Michel Barsoum and his team at Drexel University in Philadelphia, and dr. Marie Jackson and her team at the University of Utah. These ancient concretes not only required much less energy in their production, they also reinforced themselves long after construction was finished through a so-called pozzolanic reaction, producing a calcium aluminium silicate that filled the voids. In other words, these ancient forms of concrete proved to be self-healing, a sorcerer’s stone still chased by modern researchers. Precision in the construction industry would require precisely the key to this problem.
New materials for better precision in the construction industry
As a matter of fact, a promising self-healing technology was developed by Hendrik Jonkers of Delft Technical University in the Netherlands; it uses bacteria and is commercialized by Basilisk Concrete. In their self-healing concrete, these bacteria produce limestone if triggered by contact with water and air, and in doing so they repair the crack. Basilisk uses this autonomous repair system in several products that are applicable both for new constructions and in existing structures. At Ghent University in Belgium, they research more options of self-healing concrete. Bacterial repair is one of them. Like Basilisk, the Ghent researchers embed the bacteria in microcapsules or microgels, where they may survive for hundreds of years, whereas they would not be long-lived when introduced into the concrete mixture right away. But they also investigate the use of these hydrogels as such. And of encapsulated polymers such as polyurethane, methyl methacrylate, water repellent agents and elastic polymers. And of simply a slight overdose of fly-ash or blast-furnace slag, with some unreacted particles encapsulated that will form new concrete as they get wet. Some researchers get excited at the prospect of adding graphene to concrete, which might eliminate the problem of steel corrosion altogether, the most expensive result of a lack of precision in the construction industry.
A wider range of construction materials might contribute to better construction industry precision. The most radical solutions in this field make use of the activity of bacteria to produce bio concrete. With bacteria, the resources might be little more than sand as the source of silicate, and limestone as the source of calcium, both available in large quantities throughout the world. The North Carolina start-up company Biomason grows bricks from these materials on an industrial scale. The company has won major prizes and funding for its bricks. The bacterial action can produce unexpected effects, unachievable by industrial methods. ‘We can make bricks that glow in the dark, bricks that absorb pollution, bricks that change colour when wet,’ Ginger Dosier, the company’s founder, told Wired Magazine. Tuned to specific tasks, that is.
And then, there is the question of demolition waste that also testifies to a lack of precision in the construction industry. Up to 95% of demolition waste can be economically recycled. In the Netherlands, even 98.5% of demolition waste is recycled. Recycling rubble produced by earthquakes would seem to present a clear-cut case. Why not reuse it and produce new construction materials from it? This solution was developed by the Mobile Factory. But they seem to have a difficult time establishing themselves, even in a country that has much suffered from earthquakes like Haiti. As might have been expected, the construction industry opposes this innovative scheme. As it seems to oppose most innovations – or should we call this undue conservatism? Precision in the construction industry is still far away.