That takes care of all the dry ingredients.
Let's start looking at the wetlands.
The first of which is a chemical admixture.
There is a bit of controversy around these and some older engineers are not really big fans of using
chemical and mixtures.
I believe this is due to the days when these were unregulated and some people would sell at mixtures
promising the absolute world but it wouldn't actually do anything at all it would just cost money and
have no positive effect.
But since then a lot has changed.
And the biggest supplies have tried and tested their ad mixtures for many years with loads of research
to back up the results.
They have also been around long enough that we have evidence of their long term repercussions in the
structure.
Unlike mineral and mixtures which are used to extend the cement and give additional properties chemical
and mixtures are only used to modify the properties it should never be used to fix a bad mix.
But to add to a good one they also need to be designed and controlled correctly.
It's very rarely safe to use them in a site based mix.
It is much safer to use them as a battering plant where the mixing and volumes can be controlled very
carefully.
When and how to add add mixtures is very specialist and product specific.
The manufacturer's guidance is always your best bet for this information to change the rate of hydration
are accelerating and retarding agents which do exactly as you would expect.
The accelerator increases the speed of hydration which creates a stronger concrete quicker the dosage
of these IV mixtures must be calculated very carefully because they can have significant negative impacts
when done incorrectly.
You could have issues placing the concrete compaction and even the thermal cracking accelerators are
often made by adding additional calcium chloride into the mix please note that you do need to be careful
here when there is reinforcement in the concrete as the additional chloride can corrode the reinforcement
in this case a chloride free accelerated admixture would be required the retiring agent slows the speed
of hydration and is often used in large slow pores with the initial set of the concrete would cause
a break in the final concrete product it can also be used when the vacuum plant is far away from the
site or for aesthetic reasons is applied to the concrete shuttle or directly onto the concrete surface.
The top layer of cement paste can be wiped away leaving the exposed aggregate look as we can see here.
They extend the setting time between 60 to 400 minutes any longer than that is a bit dodgy.
You don't really want to mess with the hydration process unless you have to.
There are also more practical concerns when using a retiring agent.
The concrete may bleed more than usual and it will remain in its green state for longer making it more
vulnerable to bad curing practices or wind cracks.
You also need to be aware that the retiring agent doesn't just slow the initial set it slows the entire
hydration process down which means you may not get the required strength at 7 or 28 days.
We didn't have plastic sizes and super plus sizes.
He's improved the workability of the concrete with a low water cement content and as you remember the
lower water content the stronger the concrete.
A super plaster size that is really just a plaster size or on steroids that can reduce the water content
by up to 20 percent poly Carbo oscillate ethers can actually get a reduction as high as 35 percent.
Care must be taken with these as they can lead to issues with the final set of the concrete and overdosed.
These are the most common.
As the added workability is almost always welcome on site especially when looking at the likes of self
compacting concrete where this control is vital to the quality of the final product.
Error in training ad mixtures and tiny bubbles to the concrete which is most useful in cold areas due
to the freeze thaw effect.
As expected the more air bubbles included in the mix the weaker it gets.
So the tradeoffs need to be carefully considered.
It does also have a few almost secondary benefits such as better cohesion and workability reduction
and bleeding and is lighter than the equivalent known air and train.
Concrete on the aesthetic side of things.
You could also add a colored pigment to change the colour of the concrete if you ever need to use coloured
concrete.
Please bear in mind that the colour between the different mixes will be slightly different.
Often a client will expect the exact same colour consistently throughout the structure.
However this is rarely if ever achieved the last item I'd like to touch on in this section is curing
the process of concrete hardening is called hydration for a reason.
Most of the concrete strength is achieved in the first 28 days which you'll see come up in a bit in
later sections this relies heavily on the first three days post cast as this is when the hydration process
is at its fastest procuring leads to an increased strength durability and reduces the likelihood of
cracking due to premature drying out of the surface.