Hello and welcome.
Today we'll have a look at aggregates when it comes to aggregates.
We are generally talking about one of two things sand or stone by definition anything that passes through
a four point seventy five millimeters serve is classed as sand.
Anything bigger is classed as Stone and I'll leave it up to you to decide when it officially becomes
a bolt of
aggregates make up between 60 to 80 percent of the volume of concrete.
In most cases and is introduced to reduce the cost of concrete concrete made up of only cement would
be incredibly expensive for this course we'll just run through each of the main areas of concern fairly
quickly.
The most important of which is strength whenever checking in aggregate.
You need to be certain that it is at least as strong as the concrete you specified.
It's a bit pointless specifying it makes designed to be 40 NPA when your stone will crush long before
that.
We then have the grading that refers to the average size and mix of the aggregate.
If you were to have an aggregate that consists of sand only then it would only really be suitable for
certain situations most situations have it need a balanced mix of aggregate to not only provide the
strength but also differing sizes to make sure every potential void is actually filled this may be released
the smaller aggregate.
It's not uncommon these days to have a graded mix of sand with 20 mil diameter stones only.
In fact it's actually the most common these days.
Probably grain the sand we use a series of things that get progressively smaller from top to bottom.
We would then use the percentage of each material retained in each individual sieve to work out the
fine.
This modulus which is effectively just the average size the fineness modulus is not actually measured
in millimeters but it's a position on a standardized graph of the difference of sizes
we would also consider the relative density its density relative to water its bulk density.
How much can fit into a meter cubed.
The shape and texture and the type of rock for example is a granite called sandstone that sort of thing
okay.
So that's all well and good but let's run through how these properties actually affect the concrete
properties.
When looking at a sand grading if it is lacking in a couple of the required sizes it will reduce the
workability of the concrete what you really need is for there to be sufficient variance so that every
void can be filled.
If we have a shortage of particles zero point three millimeters or smaller the concrete will be prone
to segregation and bleeding which we really don't want unless it's very carefully controlled another
one that affects bleeding and segregation is the relative density.
This makes sense because if the aggregate is all much heavier than the cement paste then the aggregate
is more likely to sink to the bottom.
The bulk density is less influential on the properties of concrete but say it more influences the mixed
design and how much water is acquired
similarly.
The particle shape will influence the water requirements but it will also influence the workability
nice smooth round because it will create a much more workable concrete and long flat jagged aggregates
in today's Edge.
Sustainability is an important consideration.
We are seeing more and more recycled materials being used in concrete.
It can come from many sources to a few of the main ones are building rubble crushed concrete sawdust
and more byproducts from the steel industry.
This is great and should be encouraged.
However you do need to be careful these recycled materials can often negatively affect your concrete.
Personally I have yet to use recycled aggregates in any major structural applications such as in a more
slab It's mainly suited for mass concrete where the overall strength is not as important that'll do
for today.
We'll see you in the next 1.