Hello and welcome.
Today we'll take a look at what concrete is as well as a condensed look ahead at what we'll be covering
in a lot more detail as the course goes on
concrete is an incredible material that has been around for ages.
The earliest of which looks to me around 7000 B.C. where a version of it was made using lime water and
stone around 200 B.C. The Romans were using concrete us which is where we actually get the word concrete
from this concrete.
This is a lot closer to what we use today due to the silica and alumina in the volcanic ash.
They were using they mix this with lime and seawater back in the day.
They didn't know exactly why it was so strong but they knew it was and they knew how to make it over
and over even back then.
Amazing structures such as the Pantheon were possible.
And the fact that it's still around today shows you the durability of well-made concrete back then they
didn't know what we know now.
And their only way to design was by trial and error.
You can guarantee that the amazing buildings that we can see today like the Pantheon we're not the first
second or third attempt that they may have done they could keep going on and on just correcting as they
go.
Now the history behind the invention of concrete can be very interesting.
But for now let's jump back to the modern day and take a look at what we actually do know about concrete
so there weren't concrete generally relates to a mix of the three main ingredients cement water and
aggregate.
There is a fourth admixture yes that's not necessary to make concrete but it is so common these days
that it's found in most concrete mixers.
We'll take a deep dive into each of these ingredients.
But for now here is a brief overview of what we'll be looking at.
Starting off with the most important of these ingredients the cement the binder the glue.
The most common of which is called Portland cement.
Now Portland Cement is made by heating limestone with clay and grinding the result into what we call
clinker.
A very fine powder.
The limestone provides the calcium and the clay provides the silicon aluminium and iron before being
used.
The concrete needs a source of solve it.
This is usually done by mixing gypsum in which has its place in the hydration process which will cover
later on when combining cement with our second ingredient water it forms a cement paste the amount of
water is very important here.
The more water use the easier the concrete is to handle but the weaker it becomes and the source of
water will also play a very big part as well.
Impure water can cause problems with the ultimate strength and rate of strength gain and using seawater
water as they did back in their day in ancient Rome is really not recommended.
The seawater introduce an additional chloride which can then corrode the reinforcement.
We can't deal with this but we'll discuss electron so this Amine pace can either be mixed with sand
to produce mortar or sand in stone to produce concrete and the correct ratio and grading of the sand
and stone ensures that all of the little gaps are filled while maintaining the added strength provided
by the larger stones these three ingredients alone are enough to form concrete strong enough for most
applications.
But sometimes you'd like to get additional features out of this concrete and this is where add mixtures
come in and mixtures are in the form of either powder or fluid that is added to the mix to effectively
power up the concrete.
There are two main types about mixtures that will look at their eyes the chemical and mixtures and mineral
at mixtures.
Okay so that's it in a nutshell.
Thanks for taking the course and I'll see you the next one.
But not so fast.
Although that all seems perfectly logical and simple there is actually a lot more going on behind the
scenes that we are going to spend the rest of the course investigating but before we do that.
Your assignment for this lecture is a pretty simple one.
I'd like you to take a picture of the most impressive concrete structure in your neighborhood and either
posted to the group's Facebook page or just keep it safe somewhere where you can occasionally look at
it.
And as this course goes on you'll be amazed at how quickly you'll start to see and understand more about
that same very structure in the next lecture.
We'll get moving on the properties of concrete starting off with the cement binder where the magic happens.