Basic Informations on Cement and Concrete

You might ask what the two pictures you can see here have in common and how they are related to our problem with cement and concrete. The picture on the left shows you a mountain which consists mainly of limestone. The picture on the right shows a heating coil after a long use in hard water.

How does the limestone come into your tap water? The rainwater solves the carbondioxide that’s in the air and the carbonic acid that results from this reaction solves limestone and other minerals in the soil. These minerals are resposible for the hard water.

But there are not only negative effects coming from this solution process. By solving limestone caves are created over thousands of years.

The temperatures in the created caves are lower than above the surface and less minerals are solved in cold water than in warmer water. This leads to small deposits of limestone at the ceiling and the ground of the caves. The formations that are created in this process are called stalaktites and stalagmites.

Man has used the circle of limestone for building houses since ages. Limestone (CaCO3) is heated in a lime kiln and burnt lime (CaO) is created in this process. It’s mixed with water then and you get slaked lime (Ca(OH)2). If you mix that with sand and other additives you get lime mortar which reacts with the carbondioxide in the air and forms hard limestone again.

To create buildings like this bridge you need a better material than limestone. This brigde is made of cement and concrete. Both are mainly based on limestone.

Many of our main building materials are based on the same basic ingredients like kalziumoxide (CaO) or siliconoxide (SiO2) as well as aluminiumoxide (Al2O3). The amount of each part is different as you can see here for cement, glass and bricks.

Portland Cement is the most common type of cement. It’s so called because it was made first by a local bricklayer on the Isle of Portland in England in There are three fundamental stages in the production of cement. Firstly the preparation of the raw mixture consisting of limestone – which is mostly located where the production site can be found – and clay and iron ore as well asbauxite and recycled materials containing these minerals (here called corrective material). These materials are crushed to fine powders in the raw mixture mill. It’s important that the raw mixture doesn’t contain large particles in order to complete the chemical reactions in the rotating kiln. The reactions that take place in the rotating kiln are the second stage in the cement production process.

Here you can see the rotating kiln where the raw mix is heated up to 1400 – 1450°C and where the complicated chemical reactions take place. Shortly said the material is sintered, which means it’s partly melted but doesn’t form lumps. If the temperature in the kiln is too high you don’t get “clinker” you then get a molten substance which is similar to glass. The produced clinker can be stored for a long tim before the third stage in the cement production process takes place.

The third stage in the process is cement grinding. In order to achieve the desired setting qualities in the finished product a quantitiy of about 5% of calcium sulfate is added to the clinker and the mixture is finely ground to the cement powder. The size of the particles depends on the specific use of the cement. The most common use for cement is the production of concrete. Concrete is a composite material consisting of gravel/sand, cement and water. Concrete can be cast in almost any shape desired, and once hardened, it can be used as a structural element.

Here you can see the microstructure of the concrete during the hardening process. The water will fill the gaps between the cristalls and will change their structure. Cement particles are linked and the mobility of the concrete decreases steadily. The setting starts after approximately 3 hours and is mostly finished after 24 hours. There are many different types of concrete which are related to the specific use and the climate conditions under which the endproduct will be used.

Safety and Environmental Aspects For your own safety use gloves, goggles and a filter mask, when you are mixing cement with water. Wash your hands after contact with cement very carefully. There is a chemical reaction that produces a highly alkaline solution (pH 13) which causes serious burns on the skin. For your own safety use gloves, goggles and a filter mask, when you are mixing cement with water. Wash your hands after contact with cement very carefully. There is a chemical reaction that produces a highly alkaline solution (pH 13) which causes serious burns on the skin. When the cement mass is hardened it can be touched without gloves. When the cement mass is hardened it can be touched without gloves. Cement manufacturing causes environmental effects at all stages of the production. Cement manufacturing causes environmental effects at all stages of the production. There are emissions of airborne pollution in the form of dust and gases and there is a lot of noise and vibrations when the machinery is operating and during the blasting in the quarries. There are emissions of airborne pollution in the form of dust and gases and there is a lot of noise and vibrations when the machinery is operating and during the blasting in the quarries.

A big amount of carbondioxide (CO2) is produced during the manufacturing process. An independent research concluded that the biggest environmental problems in the cement industry are caused by the production of greenhouse gases. There is carbondioxide emission during all stages of the manufacturing process as you can see on the next picture. A big amount of carbondioxide (CO2) is produced during the manufacturing process. An independent research concluded that the biggest environmental problems in the cement industry are caused by the production of greenhouse gases. There is carbondioxide emission during all stages of the manufacturing process as you can see on the next picture.

Carbondioxide sources CO 2 from decarbonation of limestone 0,47- 0,54kg/kg cement CO 2 from decarbonation of limestone 0,47- 0,54kg/kg cement CO 2 from kiln fuel combustion 0,24- 0,65kg/kg cement CO 2 from kiln fuel combustion 0,24- 0,65kg/kg cement CO 2 produced by vehicles in cement plants and distribution CO 2 produced by vehicles in cement plants and distribution 0,002- 0,005kg/kg cement 0,002- 0,005kg/kg cement CO 2 produced for the electrical energy consumption CO 2 produced for the electrical energy consumption 0,09- 0,15kg/kg cement 0,09- 0,15kg/kg cement Sources 1 and 2 must be reduced by innovations

But cement plants can also be used to burn combustible waste material. But cement plants can also be used to burn combustible waste material. Due to the high temperatures in cement kilns the following waste materials can be used as a fuel supplement and can substitute a part of the fossil fuel normally used – so the carbondioxide emissions will be lower. Due to the high temperatures in cement kilns the following waste materials can be used as a fuel supplement and can substitute a part of the fossil fuel normally used – so the carbondioxide emissions will be lower. There is also the possibility to add environmentally damaging waste from power plants to the cement so that you don’t have to deposit it somewhere else. There is also the possibility to add environmentally damaging waste from power plants to the cement so that you don’t have to deposit it somewhere else. All this is very helpful for our environment but we think there is still a lot to be done. All this is very helpful for our environment but we think there is still a lot to be done.

Waste materials as fuel supplements 1. car and truck tyres 2.Waste solvents 3. Hazardous organic waste 4. Bone meal (slaughterhouse waste) 5. Waste plastics 6. Rice shells 7. Sugar cane waste you can also add Slag and fly ash from power plants as well as synthetic gypsum Waste materials as fuel supplements 1. car and truck tyres 2.Waste solvents 3. Hazardous organic waste 4. Bone meal (slaughterhouse waste) 5. Waste plastics 6. Rice shells 7. Sugar cane waste you can also add Slag and fly ash from power plants as well as synthetic gypsum Special thanks to C.C.Buchner Verlag, Klett Verlag and Wikipedia Special thanks to C.C.Buchner Verlag, Klett Verlag and Wikipedia