Published: September 2019 (10 Min Read)

We allocate substantial proportions of our clients’ money to infrastructure investments. On the one hand they have provided consistent and inflation protected income, and on the other hand these investments can improve the lives of many millions of people.

These are investments in schools and hospitals, in green energy sources such as wind or hydro-electric power, in water quality such as sewers, and in transport such as bridges and railways. But there is a cost which is less obvious than the simple monetary expense.

It is a cost which causes environmentalists concern. Carbon emissions.

Cement, which is used to create concrete, is the glue which binds all these social constructs together, but it is made by being separated out from limestone.

Most limestones form in shallow, calm, warm marine waters. That type of environment is where organisms capable of forming calcium carbonate shells and skeletons can easily extract the needed ingredients from ocean water. When these animals die, their shell and skeletal debris accumulate as a sediment which forms limestone. Limestones formed from this type of sediment are biological sedimentary rocks. Their biological origin is often revealed in the rock by the presence of fossils.

Concrete has a problem. The material is used so widely that world cement production now contributes 5 or more per cent of annual global CO2 production. And the problem looks set to get worse:  by 2050 concrete use is predicted to reach four times the 1990 level.

The reason concrete has a big carbon footprint is that huge quantities are used because it is a remarkably good building material.

But scientists argue that it is also a carbon-efficient material. “The reason there’s so much concrete is because it is in fact a very low impact material,” says Karen Scrivener, head of the construction laboratory at the Swiss Federal Institute of Technology, Lausanne. “If you replace concrete with any other material, it would have a bigger carbon footprint. Many people have the idea that if you built in steel, you’d make things better – but in fact you’d make things worse.”

The cement industry is actively seeking solutions, and the largest global cement producing companies are attempting to mitigate the carbon footprint of cement, but they cannot eliminate it.

They are attempting to separate limestone at lower temperatures. Cement is separated out by intense heating in kilns, and the design of these kilns is being reviewed so that lower temperatures (1200C, rather than 1500C) can be used.

Lower temperatures require less energy; if the CO2 emissions could be kept separate from other flue gases then the CO2 could be captured without requiring a separation process which requires further energy; recent advances in steel technology allow more heat to be conveyed by radiation, and more tubes to be used, which allows the CO2 to be kept isolated from the other gases.

Others are looking at the possibilities of re-using the concrete found in the rubble of old buildings, which could also re-capture some of the original CO2.

If the CO2 is captured the storage of it in empty oil and gas fields under the sea is already well established and accepted as a solution.

Another solution is to change the recipe for concrete so that, rather than needing water to solidify, it uses CO2 to create a type of stone rather than concrete. This would only work in the pre-cast market because it requires moulds and is less than 25% of the concrete market. But it all helps.

Human ingenuity is actively seeking solutions, but the process requires time, and is unlikely to enable zero emissions. But would society be better without concrete?