Concrete is the most frequently used building material worldwide, no other material can be shaped in any way and is at the same time stable, resilient, durable and inexpensive. No tunnel, no bridges and hardly a foundation can do without the building material. Cement, water, sand or gravel – that’s all it takes to make concrete. But concrete has come under fire: the high CO2 emissions in cement production are responsible for around 6 percent of human-made CO2 emissions worldwide. There is a need for action and countermeasures through more efficient manufacturing processes and recycling are absolutely necessary.
Concrete: Versatile all-rounder
By varying the components (cement, water, aggregates, admixtures, additives, and air), concrete has very different processing and usage properties. It depends on the mix how heavy, light, pressure-resistant, or heat-insulating concrete is.
The problem with cement
The biggest problem with concrete is the cement used. Around six percent of global CO2 emissions are due to the substance. More than four billion tons of cement are produced and installed every year, and the trend is growing rapidly. When we talk about cement today, it is mostly Portland cement. 98% of the cement used worldwide falls into this category. Limestone, clay, sand, and blast furnace slag are ground and heated to around 1450 degrees Celsius. During the burning process, the lime turns into calcium oxide and CO2 is released.
The fuel for the systems can be supplied from renewable energies. For the chemical process, however, a minimum energy requirement is necessary so that the limestone contained in it is deacidified. Here, CO2 is released and, and that cannot be prevented.
However, there is still room for improvement in the use of recycled materials and, substitute fuels.
Circulatory materials as a solution
The fact that the recycling potential of building materials is not fully exploited is primarily due to the costs. The recycled building material should be cheaper than the natural material, but it is not. Recycled mineral building materials are tested more intensively, which increases costs.
As a rule, the use of recycled concrete only makes sense if the transport routes for the recycled grain from the processing site to the concrete plant are not too long. The amounts of construction waste that could be reprocessed are more than sufficient, but the number of disposal companies that can provide the recyclate is still relatively small.
To reduce the amount of lime in the cement, other substances such as blast furnace slag, ground slag or fly ash can also be added. However, this cement must also comply with strict guidelines.
First and foremost, work must be done on the infrastructure to be able to use recycled concrete and other more sustainable additives across the board in an environmentally friendly and economically viable manner. It is also important to continue researching concrete to optimize the physical properties and thus save material.