Concrete Technology and It's Importance in Construction Industry

Concrete is the mother constituent of the construction industry and the largest manufactured material in the world after water. According to...

CEMENT - Material that Changed the World

Cement may be a worldwide developed and improved binding material, but the use of cementing material is quite old actually. It is a material that has truly changed the world. It is used for its strength and durability and it is the key ingredient to making a hunk of good quality concrete. It is strong, durable, and easy to work with due to its versatility for various infrastructures, making it an ideal choice for a wide range of construction projects.

Cement: A Material that Changed the World

Generally, cement is described as binding material where cement paste acts as a glue to bind aggregate and make a cohesive mass. This bonding is important for the strength and durability of concrete.

CEMENT - Material that Changed the World

If we talk about the history of cement, it was patented by Joseph Aspdin on 21st October 1824 A.D. but Issac Charles Johnson developed it in the form of present-day cement in 1845 A.D.

Joseph Aspdin ground hard limestones and mixed them with fine clay to form a slurry and heated the mix in a furnace till carbon dioxide was released completely but the temperature up to which the mixture was heated, was not enough to form clinker. Then the end product was ground into a fine powder, which when hardened resembled a natural stone found in Portland, England. Hence, the portland cement was named after this incident.

Similar procedures had been adopted by other inventors too but Issac Charles Johnson calcined the mix to the temperature to form clinker and established factories to make better cement. He produced this modern cement by burning a mixture of chalk, clay, and silica to a temperature of  1400-1450 degrees Celcius which fused together to form small spherical balls called 'Clinker'.

As I've mentioned in the first sentence of this blog post, the use of cementing material is quite old. In the early period, Egyptians used a mixture of lime and gypsum as mortar in the making of the Great Pyramids. Similarly, the Greeks and Romans used calcined limestone. The raw constituents used for the binding materials were the same but there was a difference in temperature up to which the mix was calcined.

Later, the cement was produced by combining lime with volcanic ash with active silica and the end product was known as "Pozzolanic Cement' because the volcanic ash used in the cement was collected from a village called 'Pozzuoli'. The modern-day cement is called 'Hydraulic Cement' due to its properties of setting and hardening in various conditions.

Production of Portland Cement

Modern cement is also known as 'Ordinary Portland Cement.' The raw constituents required for the manufacturing of OPC cement primarily consist of
  • Calcareous materials such as limestone or chalk, (Calcium Carbonate)
  • Argillaceous materials such as clay or shale, (Aluminium Silicate)
  • Silicious material such as silica.
The process of manufacturing cement involves the following activities
  • Proportioning
  • Grinding and intimate mixing
  • Calcinating

The process of manufacturing cement starts with proportioning of raw constituents and mixing them intimately depending upon their purity and composition. The primary goal is to prepare a kiln feed that permits the production of clinker of the desired quality with the lowest possible energy consumption and overall cost.

The raw mixes are prepared, computing the modulus values and Bogue's equations. This process is known as the 'Raw Mix Design'. The two main constituents, Calcium Carbonate and Aluminium Silicate raw mix can be easily calculated by prefixing certain target parameters for the resulting clinker, which include the following aspects

  • Composition,
  • Burnability,
  • Energy Consumption and
  • Cost

Once the raw mix has been designed, the process starts with crushing, pre-blending, grinding, and homogenizing the lumpy raw materials. Then the raw mix when entered into the kiln is called 'Raw Meal' or 'kiln Feed'. 

The next step of the process is called raw milling, grinding basically. Usually, each raw constituent is stored separately in silos equipped with a weighing and batching system for mix control in the grinding mill. There are three main types of the raw milling system

  • Ball Mills
  • Vertical Roller Mill (VRM), primarily raw grinding installation,
  • Hydraulic roll press, used particularly in upgrading existing ball mill circuits for increased production or decreased specific power consumption.

All the raw grinding systems are closed-circuited with separators known as classifiers and their performance depends upon a few important parameters such as feed size, grinding behaviour, drying capacity, required fitness of cement, grinding power available, etc. After grinding intimate blending of fine powdery material is involved, also known as the post-milling homogenization process.

Then the most important step of the process is the calcination or burning process. Due to intense heat in the kiln, at 1300 to 1500 degrees Celsius, the material sinters and fuses together to form nodular-shaped clinker. It is then cooled and ground with the addition of gypsum of about 3 to 5%. The end product received by using this procedure is Portland cement.

There are two methods of production of cement. One is 'Wet Process' and another is 'Dry Process.' The first and most traditional method is slurry mixing in wet process plants. The dry process plants involve mechanical, pneumatic and gravity systems.

The wet process method was popular earlier because of the possibility of more accurate quality control in the mixing of raw materials. The process of intimate blending or post-milling homogenization was not available then. After the development of the intimate blending process, the dry process became popular and the primary choice in the cement industry as it requires much less fuel as the material is already in the dry state. In the wet process, the slurry contains about 35 to 50% water, thus requiring more fuel for the slurry to come to a dry state.

We'll learn about the dry and wet methods of cement production later in a separate post. I have tried to keep it as simple as possible to make this blog understandable for everyone either an engineer or a contractor.

Although a small effort has been made to present this blog simple and down-to-earth, yet if there are any suggestions kindly write in the comment section.