conflict is the most important material in construction every year 25 million tons are
used in uk only that's why you need to know what it is what types of concrete are used and
why the right mix is so important so let's go my name is Greg and welcome to SITENG so what the
concrete is really the concrete is a composite material where the cement is the matrix and the
aggregate is the filler to make it simple guys we need the cement we need water we need the
fine aggregate which is typically sun and we need a coarse aggregate gravel or some type of stone to
give you rough idea about the proportion of this i used a very old formula which says one two three
where one was a cement two was the sand and three was the aggregate and then we need water of course
in general concrete is a great construction material which is easy moulded easy form
and still relatively cheap every year here in uk only we're using 25 million tons of
red mix concrete so it's crazy guys let's talk now about the concrete strength which is the
most important property of concrete really and i'm going to be talking about fck which is the
characteristic strength of concrete like C16/20 C30/37 C40/50 you C50/60. so what does it mean
really so c4050 that means that after 28 days of curing your concrete should achieve a compressive
strength of 40 and 50. so the reason why we have two numbers here it's because we got different
samples of concrete and in first case with this 40 it's for the cylindrical sample where we're
going to be compressing actually the cylinder made of concrete and the second number 50 is
actually for our lovely cube here and we're going to be actually as the side engineers as working on
side gonna be mostly interested in this number so the second number and what it really means
is a 50 newtons per millimeter square so that's the pressure actually so that's the compressive
strength of it called sometimes 50 megapascals as well or 50 kilonewtons per meter square so guys
generally speaking what you're going to be looking for is actually you're going to be looking for the
minimum 50 newtons per millimeter square so that's the minimum concrete strength you're going to be
looking actually after crushing the cube after 28 days and if you look at the graph guys actually 95
of all the concrete ports should be more than your 50 newtons per millimeter square
so it's only five percent of concrete that you can be little bit below your characteristic concrete
strength so please make sure inside that your cubes are correctly made and correctly stored
before you send them to the laboratory for the crushing another way of measuring the concrete
strength on site really are the thermocouples and uh these are the sensors which you put into the
concrete while you pour in then guys based on temperature of concrete you got the live graph
of growing strength of concrete and this actually is perfect for early strike and stuff like this
and these guys are typically calibrated at the beginning of the job to make sure they got the
closest result based on that temperature really and if you want to know a little bit more about
it i'm going to leave the link below in the description so you can have a look yourself
so let's go guys to the concrete mix now and what it really is so the concrete mix is actually the
design formula matching the particular job the particular environment and actually the particular
element to be constructed so first thing i'm going to start from water to cement ratio you
can see here a fragile relationship i found this nice page here i'm going to leave the link below
you can see here water with cement always come together but as you can see here there's a nice
graph here i want you to remember this actually you can see here the weight and the proportions
here are shown to 0.45 to 0.473 and maximum to 0.52 as you can see the more water we're going
to be adding the less compressive strength we're going to get and this is actually pure weakening
of concrete guys and as i mentioned in the last of my videos guys we as a site engineers we need to
keep an eye on this as guys really try to add in water sometimes when they shouldn't do it please
remember don't add water to concrete as the one you're getting on site that's the ready mix just
to be poured straight into the element so when you're gonna be building by the sea you need
actually some resistance to the salt really and if you're going to be putting your concrete into
the ground you need some resistance for the different attack and for all these situation
guys you're going to see actually the concrete exposure classes which going to be resisting
corrosion or some other chemical attack and i'm going to leave the table in the description guys
as well so we're going to have a look but these are like XA XS XD meaning the different type of
codes of corrosion when we talk about the mix guys one of the important things as well
is the aggregate size and this is dependent of the element you're going to be pouring actually
sometimes the congestion of the steel is so big that you actually need the smaller chip
the smaller stone so that might be actually the 10 mil aggregate typically what you're going to
find on side is a 32 mil stone 20 mil stone and 10 mil gonna be as i said in the cases of steel
congestion when you want to make sure the concrete is going to be filling all the element and the
concrete going to be getting just in between the steel and everything going to be working as
designed let's go now to the concrete slump and this is a big thing for us especially where we
work in own construction site as we want to make sure our concrete is workable to the point we want
it and for these guys we should actually slam each lorry of concrete coming onto the side and
as you can see on this video that's the concrete sample here that's how it's made really
and that the way you're going to be measuring this and then later you're going to have a look if you
are actually in the range of your concrete strap so let's have a look at the table here now what
concrete consistencies we have here what we're going to be looking for and what's going to be
actually our target slump when we're going to be measuring so on sites really we're actually going
to be mostly working with the s2 s3 classes but i'm going to show you this so you can see s1 is
actually target slam is just 20. so that's a very dry mix so as we go from number one to number five
really they're going to be more wet and more wet concrete so the class s2 is going to be the target
slam going to be 70 but if you're between 50 and 90 you still actually all right for it that should
be still your concrete you are looking for in case of uh s3 guys we actually aiming for 130 but
we are still good to go between 100 and 150 and this is obviously guys a recommended range here
but let's say if you're going to be 95 and you're going to be looking s3 you're probably still good
to go for it but you need to be very careful and have a look at this but once you measure from 100
and 150 in terms of s3 you're just good to go and you don't need to really think about it too much
so from site engineering site from construction site perspective guys what you're going to be
looking for you're going to be looking for some pumpable mix and you want to make sure when you're
using a concrete pump or you have especially when you have a long line of concrete you want
to make sure you got a pumpable mix for it and the details for the mix you probably are going to work
out actually with your concrete supplier and then you're going to get it approved by designer but
that's very important guys as you don't want any blockage on site and they really happen sometimes
so guys i could be talking hours and hours about the concrete about the cement so let me know if
you wanted more videos like this and if you want any particular information about the concrete now
leave the comments below with the questions and as always guys just don't forget to leave
the thumbs up and subscribe to the channel to join the best community of engineers here in uk