Cement & Concrete
Definitions and uses of cement & concrete
We all know the words, but what are they and how are they made and why are they used in structures as diverse as single family homes, bridges, dams and even the Sagrada Familia.
What's in a word?
The words cement and concrete are not interchangeable, but they are intrinsically connected. Cement is a key ingredient of concrete. It is the binding agent that holds everything together.
Early forms of cement were first used thousands of years ago. No one knows for sure who first came up with the idea to use a cement substance to bind materials together to make concrete, bricks, and other building materials. The process can be traced back to Ancient Macedonia, but was more widely popularized during the Roman Empire. Early forms of cement used things like lime and pozzolana, a type of volcanic ash. The Romans were able to produce massive structures like the Pantheon and the Roman aqueducts using this formula.
The most common cement used in the making of modern concrete is Portland cement. Joseph Aspdin, a British stonemason patented the process in 1824. He heated a mixture of finely ground limestone and clay and then ground the mixture into a powder that hardened with the addition of water.
Concrete is a mixture of cement, water and aggregates. Aggregates make up approximately 70-80% of the mixture and cement and water make up the rest. Aggregates are usually inert coarse materials like gravel, crushed stone, sand or recycled concrete. The type of aggregate selected depends on the local availability and the application of the concrete.
The benefits of concrete, from strength and durability to fire-resistance and sustainability
Concrete is widely used for architectural structures, foundations, walls, pavements, bridges, motorways, roads, runways, parking structures, dams, reservoirs, pipes and staircases. It is used to make furniture and is even used in ships.
There are many good reasons why concrete is so widely used all over the world:
STRONG AND DURABLE
Concrete is used for its strength that actually increases over time, and is not weakened by moisture, mould or pests, which reduces maintenance.
LOCAL AND AFFORDABLE
In relation to other alternative building materials, concrete is less costly to produce and remains extremely affordable as all of its raw materials are sourced locally.
As it is naturally fire-resistant, concrete forms a highly effective barrier to fire spread.
EXCELLENT THERMAL MASS
Concrete walls and floors slow the passage of heat, reducing temperature swings, making buildings more energy efficient.
Concrete is a low carbon construction material compared to steel etc. Concrete is made from materials that are abundantly available and can contribute to the circular economy by integrating industrial by- products or waste as raw material. When the structure reaches the end of its useful life, concrete can be recycled.
Research and carbon reduction options relating to cement production emissions
The world population is estimated to reach 9 billion by 2050 with 70% of all people living in cities. As countries develop, there will be an ever increasing demand for building materials, especially concrete. Cement production is thus set to increase to 5 billion tonnes per year.
Concrete is the ideal material to meet many of the challenges the world will face in the coming decades: It is low-carbon made from abundant resources, capable of integrating large quantities of waste and by-products and is extremely durable.
Using alternative construction materials would, in many cases, not be a sustainable solution. Forest growth would not be able to compensate a dramatic increase in the use of wood and increasing steel production for construction would lead to higher emissions. Furthermore, concrete is the only viable material for many applications such as foundations, high rise structures, or dams.
Nevertheless we should explore all possible options to reduce the emissions linked to cement and concrete production and save resources.
Emissions in cement production are threefold:
- From the production of the electrical energy used to grind the raw materials and clinker;
- From the fuel burned to heat the raw materials in a kiln to 1450°C to form clinker, which is later crushed and blended with gypsum to make cement;
- Process emissions: as the limestone is heated, it changes into lime and CO2. These emissions represent 60 to 65% of total emissions linked to cement production.
Since process emissions, caused by the use of limestone, are responsible for most of the emissions, it would make sense to think that we simply have to use another raw material. However, there is a catch. Limestone is widely available close to almost all places where cement is used, and no viable substitute has yet been found despite many decades of intense research. It is possible to envisage niche products using alternative materials, but the bulk cement will still be Portland cement using limestone as a main raw material.
This is why our research does not focus on finding a revolutionary type of new cement, but rather on making concrete even better.
We study cement and concrete at a microscopic level to help understand the scope of physical and chemical reactions that occur when using different cement types or materials in the concrete mix. Furthermore, we look at how the concrete is likely to perform in the future.
Fundamental research is needed to study these complex materials and their interaction with the environment that surrounds them.
Using advanced techniques like atomic force microscopy, X-ray diffraction and transmission electron microscopy we get a better understanding on what goes on inside concrete. Gaining this knowledge will help develop solutions that will lower the carbon impact of concrete.
Our research supports several parallel pathways of reducing concrete's carbon impact:
- Improved prediction of performance of new types of cement and concrete. Because safety comes first, there has been a tendency to use a concrete that is stronger than actually needed. Increasing our understanding of how each concrete will perform for the next 50 to 100 years will increase the use of cement and concrete types with lower emissions per tonne.
- Research into the performance of different mixtures could lead to concrete types that use less cement whilst ensuring equal structural integrity over time.
- Increase understanding how concrete deteriorates and ensure new materials will be durable.
- In Europe, more than 20% of clinker is replaced by waste materials or industrial by-products like blast furnace slag or fly ash. Decreasing the amount of clinker reduces both process emissions (originating from the decomposition of limestone) and thermal emissions. Our research looks into the performance that different cement types with alternative materials have today and might have over time.
- Our research actively explores possibilities for new replacement materials such as calcinated clays or pozzolans or optimising the use of the replacement materials used today.
- We investigate the impact of chemical admixtures on concrete performance. Admixtures can help improve the properties of concrete, making it more durable and sustainable.
Find out more on the European cement industry's (CEMBUREAU) Low Carbon Roadmap
Sustainability & Emissions
The growth of cement production, sustainability and emissions paradox
The industry favourite
Concrete is the most commonly used man-made material in the world, its production equivalent being almost three tonnes of concrete per person, twice as much as all other construction materials put together.
Concrete is inherently a low carbon constructional material that can be produced just about anywhere in the world using local resources, which lower transport emissions. However, volumes are very large. In 2011, global cement production totalled 3.4 billion tonnes, cement representing only 10 to 15% of the concrete mix.
It is predicted that its unique qualities will make concrete ever more popular, and as developing countries and emerging economies expand their infrastructure and building stock, more and more concrete and, thus, cement will be needed. Cement production is estimated to reach over 5 billion tonnes by 2050.
The emissions paradox
Compared to other building materials concrete has a low carbon footprint, i.e. it emits less CO2 per tonne. And yet, the enormous volumes used mean that concrete production accounts for about 3 - 8 percent of the man-made CO2 emissions worldwide.
Comparative relative energy and CO2 per construction material
However, given the very large volumes, total emissions are considerable. Because a small reduction in emission can make a real difference, our team of researchers can punch well above their weight and lay the basis for a global reduction of millions of tonnes of CO2 annually.
Emissions & Research
Emissions related to cement production, from energy use to decomposition of limestone and ways to accelerate the reduction of CO2 emissions
There are many different ways to reduce CO2 emissions: switch off the lights when you can, take public transport to work and recycle packaging. Doing all these things can help, but to really tackle global emissions, we need to look at practical ways to reduce large emission volumes.
Transport, heating & cooling of buildings and power generation are all obvious choices, but let us not forget cement and concrete. Cement and concrete are low carbon construction materials, but they are produced in very large volumes. Cement production, therefore, accounts for 3 to 8% of global CO2 emissions and as emerging economies develop, cement use is set to double by 2050. Any reduction will make a substantial difference.
Energy use represents about 35 to 40% of the emissions related to cement production. Energy is used to produce heat and operate equipment that grinds the raw materials at several stages during the production process.
Over the past decades, the cement industry has steadily reduced its energy use. A modern cement plant will only need about half the energy needed 30 years ago. Continuous improvements are still being made to plants to make them even more energy efficient. Furthermore, cement plants use an increasing proportion of waste, industrial by-products or biomass as fuel sources.
Cement manufacturers and equipment suppliers drive innovation and a continuous improvement in energy efficiency.
DECOMPOSITION OF LIMESTONE
Clinker is an intermediate step in the production of cement. These marble sized lumps are made by heating the raw materials used in cement production (mainly limestone and clay) at high temperatures. During this process, limestone decomposes with emission of CO2.
CaCO3 + heat = CaO + CO2
A simple formula that is responsible for the majority of the emissions in cement production. The emissions per tonne of cement vary from plant to plant but are on average around 760 kg of CO2.
So what can we do?
The objective is fairly simple. The researchis not. Our research focuses on cement at a nano-scale level: fundamental chemistry and physics. We research ways in which we can:
- Reduce or substitute the proportion of limestone in the clinker, i.e. change the formulation of the clinker.
- Mix clinker with other materials (which is already being done at a very large scale in today's cement industry). Less clinker means less decarbonated limestone, and thus reduced emissions.
- Increase the use of waste materials or industrial by-products as a raw material, thus promoting resource efficiency.
- Change the composition of concrete by using less cement without affecting its performance.
- Extend the life of structures by developing concretes that are more resistant to deterioration.
Why is it that hard?
Bags of cement are not used as decorative items. Cement is predominantly mixed with water, sand and gravel to form concrete. Concrete is used to build houses, bridges, roads, hospitals, dams and other things that are supposed to last. Changing the chemical composition of cement affects its properties and its performance. Changing the properties of the cement will have an impact on the concrete it is used in.
One might think, simple: test its strength and you will know. Unfortunately, it’s not that easy. As is the case with most materials, time and the environment play a critical role. Concrete is not used in a vacuum, it ‘interacts’ with air, water and other materials, and this over a period of at least 50 to 100 years.
If we change the chemical composition of cement, we have to make sure that it will perform as well, or better, than what is currently used.
That is what we do. Fundamental research into cement and concrete that will emit less emissions when produced, but will continue to offer the required level of performance, today and fifty years from now.