Cement: an essential element in construction

If there is one ubiquitous material in construction, it is cement. Already used in Antiquity, cement has essential properties: speed, resistance, durability. Essential in the industrial environment, this versatile material comes in different forms. In construction, each cement has its particular properties and is used in a specific way. Where does cement come from, how is it made, what are its properties, what is it used for…? We tell you everything.

Once upon a time there was the “caementum”…

Imagine that the word “cement” comes from the Latin “cæmentum”, which translates as mortar. Why this Latin origin? Well because the Romans already used this binder in construction. Cement as we know it took shape in the 19e century. In 1824, a Scot named Joseph Aspdin invented “Portland cement”. This classic cement, without addition, is still the most widely used in construction today. But since that time, new cement formulas have been invented, each meeting a particular need: resistance to humidity, heat, wear… And when you know that cement is used in the composition of mortar and concrete, we understand better how essential it is. Incidentally, it should be noted that the place of world leader in the cement industry has been occupied by France since the twentieth century.

What is cement?

Cement is an industrial product made from natural minerals.

  • Like lime, cement is a hydraulic binder. Once powdered cement is mixed with water, it hardens and becomes strong and stable.
  • Cement is thus classified into two main families: clayey and pozzolanic. Most cements are that is to say they are composed of clay and limestone, the combination of which at very high temperatures forms clinker. Portland cement is one of them. As for the cements pozzolanic, they are formed from volcanic ash (called pozzolan).
  • For friends of chemistry, here is the composition Portland cement. Its main component is lime, which accounts for nearly 65% ​​of cement. Silica comes second (20 to 25%). Then, in order of importance, we find alumina (about 5%), iron oxide, plaster, magnesia and alkali. Just to tell you that, in its apparent simplicity, cement is a more complex product than it seems.

Why does construction like cement? 5 reasons.

If cement is used so much in construction, it is because it has great qualities.

  1. Cement is first of all a hydraulic binder of very high quality. With water, it quickly hardens in air. It takes place through a chemical reaction called hydration.
  2. Cement easily adapts to any mixture. Mortar or concrete, it makes the perfect link between all the components to form a homogeneous and coherent mixture.
  3. The cement is super resistant. Some cements being more so than others… This material withstands fire, but also compression and mechanical traction.
  4. It lasts long time and lends itself easily to repair. Its vulnerability to humidity can be compensated by a waterproofing treatment.
  5. He is facile to use and relatively inexpensive.

The manufacture of cement in 6 steps

Many manipulations are necessary for the manufacture of powdered cement.

  1. L’mining of minerals is done with a bulldozer and mechanical shovel. Limestone, chalk, shale and clay are thus taken from quarries and transported to the crushing hall.
  2. The raw preparation is done after the raw materials have been crushed, dried and mechanically crushed. New elements are added, such as slag or pozzolan. The mixture is ground. The raw cement then comes in the form of a very fine powder.
  3. The raw cooking is done in stages. First subjected to a temperature of 800° C to be decarbonized, the raw material is then preheated and dried in a gas oven. The dry material is inserted into a rotating cylindrical oven which will cook it at a very high temperature (1400 to 1600° C). After 20 minutes to an hour of cooking, the raw material turns into an incandescent granule.
  4. After the cooling fast from the vintage, we obtain clinker. This raw material looks like blocks of solid lava.
  5. L’adding new components, adjuvants, makes it possible to formulate different cements. To obtain Portland cement, for example, gypsum and plaster are added to the clinker. The calcium sulphate thus added does not form more than 3 to 5% of the final product.
  6. The grinding is the final step in the process. The clinker is crushed by a mill, which can be ball, roller or vertical, until a very fine and homogeneous powder is obtained: cement.

Cement: 3 ways to use it in construction

In the field of construction, cement is omnipresent. Usable as such, it also allows the manufacture of mortar and concrete.

  1. The cement mixed with water is used in slurry and grouting. For joining layers of concrete, bonding tiles or coverings, etc.
  2. With water and sand, it forms the mortaruseful for seals, finishes, coatings, screeds, etc.
  3. With water, sand and gravel, cement turns into concrete. This super-resistant material is essential for certain major works: foundations, slabs, lintels, etc.

Composition of cement: 8 different formulas

As we have seen, Portland cement is by far the most widely used in construction. But it is not the only one: other types of cement have been developed in response to different needs.

  1. The ciment Portland is therefore mainly composed of clinker (at least 95%) with a maximum of 5% of added materials.
  2. The Portland cement compound is made up of clinker and another material which may represent 35% of the mixture, no more. It can be silica fume, slag, pozzolan, calcined shales or fly ash (from thermal power stations).
  3. The blast furnace cement contains some clinker (5 to 19%). The main element (81% minimum) is blast-furnace slag, from iron and steel factories.
  4. The compound cement consists of clinker (in a proportion ranging from 20 to 64%), fly ash (18 to 50%) and blast-furnace slag. The proportions vary according to the type of cement produced.
  5. The white cement is free of iron oxide. It is its richness in pure raw materials, limestone and kaolin, which gives it its very light hue.
  6. The natural quick cement is the result of an argillaceous limestone cooked at a temperature not exceeding 1200° C.
  7. The ciment d’aluminates de calciumor molten aluminous cement, is obtained by fusing limestone and bauxite.
  8. The pozzolanic cementclose to Portland, is not made in France.

Use: 7 cements for targeted uses

Why are there so many cement recipes? We will see that each cement has a particular use, linked to its specific properties. Composition, resistance, speed of setting and hardening, all these qualities can vary. Each cement corresponds to a use, sometimes limited by climatic constraints or the presence of aggressive agents. For the most demanding sites, cements suitable for the production of High Performance Concretes will be used.

1 – Portland cement (CEM I)

  • Used for the manufacture of reinforced concrete and prestressed concrete.
  • Appreciated in prefabrication for its rapid stripping.
  • In aggressive environments, sea or sulphated water, Portland PM cements are used.

2 – Composite Portland cement (CEM II)

  • Perfect for masonry work.
  • Massive work in moderate temperature.
  • Versatile in reinforced concrete and prestressed concrete.
  • PM cements are suitable for work at sea and ES for sulphate waters.
  • Attention : these cements are avoided when the aesthetic requirements are important, because of the variations in color linked in particular to fly ash.

3 – Blast furnace cement

  • Used in hydraulic works, foundations, underground works, injections, construction of dams…
  • Suitable for working in aggressive waters, not only at sea but also in industrial, selenitic and pure waters.
  • Suitable for agricultural equipment: storage, silage, slurry, etc.
  • Attention : this type of cement is not used in cold weather.

4 – Natural quick cement (CNP)

  • Prompt cement has an ultra-rapid setting and its high resistance in the very short term makes it particularly useful in certain emergency works (waterways for example).
  • Sealing, sealing and work at sea, underground work, shotcrete, etc.
  • Coatings and special coatings against aggressive water or chemical attacks. It is ideal for agricultural equipment subject to lactic acid and manure (livestock, silos, etc.).

5 – Calcium aluminate cement (CA)

  • Very suitable for high and fast resistance needs: industrial floors (resistant to shocks, corrosion, traffic), beams and lintels, etc.
  • Sealings, in combination with Portland cement.
  • Manufacture of refractory concrete, for ovens, fireplaces, etc.
  • Agricultural equipment, pipes, sanitation works, repairs.

6 – Masonry cement (CM)

  • Its limited resistance reserves it for the manufacture of masonry mortars, coatings, plasters… (It is not suitable for the manufacture of reinforced or high-stress concrete.)
  • Used in the manufacture of artificial cast stone.

7 – White cement

  • Used in the composition of exposed concrete due to its whiteness.
  • With the addition of pigments, beautiful colored concretes or decorative coatings are obtained.

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