Hello and welcome back.
Today we'll have a look at the properties of concrete namely cement will dive deeper into cement issues
materials by looking at how it is made and the chemical process that facilitates it.
By the end of this lecture I would like to have an appreciation of the process.
But don't worry about memorizing all of the chemical names I'll be throwing your way I'll highlight
the important ones as we go along and the rest just keep in your mind portland cement is the most common
cement because it is relatively cheap.
It sets well and it's best to given this course we will be looking at masonry cements the product of
which is known as mortar in any great detail.
The only thing you need to be aware of is that it's effectively a workable weaker concrete with no stone
just sand.
This is a massive oversimplification I know but you get the idea portland cement is a mix of four main
oxides lime silica and you Mena and iron and yes that was alumina not aluminium the lime and silica
are both hydrating elements which means they are important in the hydration process from the lime a.k.a.
calcium carbonate which has the chemical compound S.A. C0 3.
We need to extract the calcium oxide CIO.
This is done by heating limestone to release CO2 which leaves us with only the calcium oxide from these
silica.
We need a silicon dioxide S I O 2 which is found naturally in some plays and rocks so there is no need
to do much processing here.
The alumina and iron are both flexing agents which means that they are able to facilitate the process
more than actually being ingredients in the final outcome.
Their main purpose is to help bring down the required temperature in the kilns for the compounds to
unite and form the clinker the aluminium can be found in recycled aluminium or clay and the iron can
also be found in clay or in scrap iron.
Fly ash which is pure iron ore okay.
We now have all of the ingredients ready to go.
So let's get cooking literally.
Step one is to crush the rock until it consists of pieces that are about 7 centimeters or smaller in
size.
After this the aluminium and iron oxides are added in the correct proportions and mixed together ready
for the ovens.
This is either done using a wet or dry method either all same outcome this is then mixed and fed into
the first kill at about 900 degrees Celsius to release the CO2 in the line before moving on to the hotter
kilns at 1 4 5 0 degrees Celsius 1450.
This is where the four oxides unite to form a new substance called the clinker which looks like little
grey marvels the clinker is incredibly hot at this stage and must cool down before it can be used.
Once it has cooled the clinker is then milled into a very fine powder and gypsum is then added.
Now the gypsum is added to retard the hydration process for the more experienced and very consciously
ignoring mineral admixture is at the stage.
I'll come on to these a little bit later once we've really covered the hydration process and a bit more
detail before we move on to the hydration process.
Let's quickly look at what this new pink compound is composed of.
The names are not particularly important so we'll run through them pretty quickly.
We have tried calcium silicate dying calcium silicate Ted for calcium eliminate and Tetra calcium aluminium
Feride magnesium gypsum and free lime thankfully.
These can be abbreviated which we absolutely will do it's worth noting that the tri calcium silicate
is what actually differentiates Portland cement from other different cement the two compounds we are
most interested in as you try calcium silicate and the DI calcium silicate as these are what provides
the majority of the strength going forward will refer to these by their abbreviated names C three S
and C to s okay.
Let's stop there for today.
I know the chemical processes it can be a bit tricky to get your head around at first next time we'll
have a look at the hydration process but before we do that there is a quick quiz coming up to help you
remember the important terms now don't worry I'm not gonna be asking you about the chemical names only
a few of the more important ones that we'll be dealing with a lot more detail.