In our last blog, we learnt about the interesting history of concrete and the birth of portland cement. Today we’re going to look at the modern process used to create the enormous amounts of portland cement necessary for residential and commercial concrete services all around the world – let’s get right into it.
Portland cement – the world standard
For those of you who don’t know, portland cement is the most commonly used type of cement in the world. And what is cement? Cement is one of the key ingredients used to create concrete and mortar which our society relies so heavily on for infrastructure and buildings. Several different types of portland cement suit different applications.
- Type I is a general-purpose cement.
- Type II is suited for structures that are to be built in soil or water that contain a moderate amount of sulphate.
- Type II(MH) is a specialised cement that is moderately resistant to sulphate and also generates a reasonable amount of heat whilst it cures.
- Type III delivers high strength early in the curing process – usually within a week or less.
- Type IV is great for structures such as dams as it moderates heat caused by hydration.
- Type V is resistant to chemical attacks from the soil and sulphate-high water.
- Type IA, IIA, II(MH)A and IIIA all have the same properties as the non-A variants except they’re used for air-entrained concrete (which means they feature billions of microscopic holes for water to expand into when it freezes – this takes internal pressure off the concrete).
In addition to the standard grey portland cement, white portland cement is also produced. The prime differences between the two (other than their colour) are that white portland cement contains little to no iron or manganese. These are the two substances that give standard portland cement its grey colour.
Common materials used
Cement is made up of numerous different materials including:
- Chalk; and
- Marl – which is usually combined with:
- Blast furnace slag;
- Silica sand; and
- Iron ore.
The original portland cement, which was invented by Joseph Aspdin in the 1820s, was made by crushing limestone into a fine powder and then burning it with clay. This was done in Aspdin’s kitchen stove. Today, cement is made in a bit of a more economical and large-scale fashion.
The manufacturing process
The “dry” method is the most common manufacturing process used for portland cement.
- The first step in the dry method is to extract the limestone, clay and other raw materials and then crush them. The crushing itself is broken down into two phases:
- The first phase crushes the rocks so they’re larger than six inches.
- The second phase brings them down to three inches or less.
- The crushed rock is combined and ground with iron ore – and other similar ingredients – and put into a cement kiln – which is a large, steel, cylindrical rotary object that is lined with special firebrick.
- The kiln heats the ingredients to just under 1500° The heat is generated by a flame that’s the result of a precisely controlled burning of powdered coal, oil and alternative fuels.
- Whilst in the kiln, particular elements are converted into gases. The remainder ends up in the physical form of grey balls the size of marbles. This new substance is called clinker.
- Due to the extreme heat of the freshly produced clinker, cooling machines are used to bring their temperature down. To save fuel and increase burning efficiency – the heated air from the coolers are rerouted into the kiln for use next time.
- The final stage is where the balls of clinker are ground and mixed with small amounts of limestone and gypsum. The cement is now ready to be packed and sent to businesses that provide residential and commercial concrete services.
In terms of the “wet” method – the only difference is that the raw materials are ground with water before going into the kiln. The “wet” method consumes more fuel and energy during the process and is more expensive.
Looking for commercial concrete services?
If you’re looking for an experienced and premium concrete company for your next commercial construction project – then look no further than Prestige Concrete Services. We provide quality concrete solutions in a timely and professional manner. Take a look at our portfolio to see a selection of the projects we’ve worked on.
If you’d like to know more about our commercial concrete services, then please contact us through our website or by calling 0411 440 157.