DE-MYSTIFYING TONNAGE
When I order for items from a building material supplier – say sharp sand, laterite, granite or even iron rods – these items are mostly quoted in tonne. You hear things like “25 tonnes of sharp sand”, etc. For me, the first thing that crosses my mind is “why quote in tonnage when volume is much easier to visualize?” It is a bit confusing to be honest, especially for novice like me.
First, tonne is a measure of mass, not of volume. Secondly, there are several variant of tonne – metric tons, US tons and imperial tons. Until I find a fellow Nairalander to give me a better insight into which one is used in Nigeria construction clime, I will go ahead and assume it is Metric Tons.
1 Metric Ton is equal to 1,000kg.
If my secondary school physics still serves me right, to obtain the volume of each item quoted in tonnes, I need to know what the density of the material is. For example, the density of Portland cement is 1,500kg per cubic meter, sharp sand is 1,700 kg per cubic meter and granite is 1,650 kg per cubic meter (I believe).
In essence, a 25 tonnes sharp sand would be about 15.5 cubic meters (25,000kg / 1,600kg/m3) while a 30 tonnes granite would be about 19.7 cubic meters.
Subject to correction, most tipper trailers (double axles) have a haulage capacity of 30 tonnes with an 18 cubic meters volume capacity. It means that when fully loaded, a tipper trailer of this size will deliver 18 cubic meters in volume of the material it carries (I am presuming here).

DE-MYSTIFYING VOLUME
Now that we see how they relate, why is volume important?
When talking in terms of concrete mixture for example, my guess is that the ratios are quoted in volume. Or is there more to it? I am hoping someone can help out here!
Going further, a standard wheelbarrow mostly used in construction work is about 0.09 cu. meter by volume.
Now, let’s do some basic mathematics…
A bag of Portland cement is 50kg by mass. That means that the volume occupied by that bag of cement is 50kg / 1500 kg per cu. meter = 0.033 cu. meters. In essence, about 3 bags of cement is expected to fill a wheelbarrow.
Now it gets a bit more complicated! The volume we get when calculating from mass in kg (or tonnes) and density is called ABSOLUTE VOLUME. The actual volume occupied by materials in their container (e.g. cement in a wheelbarrow) is called APPARENT VOLUME.
I have wondered why so much complications myself! Volume should be volume! Which one is absolute and apparent volume again!
Well, apparent volume is the volume of a material including spaces between its particles. This is what we can see and make sense to in real terms. I like to believe that to make up for the voids, most suppliers (and workers) heap the materials – I hope I am right at this junction because heap is as vague as it can be measured.

APPLICATION #1
So, why all this? Well… at the end of the day, it all boils down to how much of material we need for what we want to do. Let’s take the first example: Concrete slab.
Suppose we want to construct a concrete slab without re-enforcement, just to make it easy for novices like me, we first need to calculate the total surface area of the slab – call it A.
The next item is the thickness of the slab – call it d.
Ok, with A and d, we can calculate the absolute volume V (let’s just say volume, to Keep It Simply Simple K.I.S.S.). That is, V = A x d.
From the volume of the concrete and the mixture ratio, we can now estimate the volume of each constituent.
For example, for a slab of 3.5 meters width by 1 meter length, with a thickness of 4 inches (0.1 meters), we can calculate the volume as:
3.5 x 1 x 0.1 = 0.35 cubic meters
Then, breaking that to its constituent, we have:
Cement = 1 / 7 x 0.35 = 0.05 cubic meters
Sand = 2 / 7 x 0.35 = 0.10 cubic meters
Granite = 4 / 7 x 0.35 = 0.20 cubic meters
Remember that one bag of cement (50kg) will occupy 0.033 cubic meter and a wheelbarrow is approximately cubic meters by volume:
We can conclude that approximately 2 bags of cement, 1.5 wheelbarrow of sand and 2.5 wheelbarrow of granite is what is expected to be used for the mixture.

TO BE CONTINUED…


Disclaimer:
I am not an expert in the field of quantity surveying neither am I a civil engineer or architect. I am a just an ordinary nairalander trying to learn, and all that is contained within this thread are plainly my opinion and should not be used as a basis for making outright decisions. I have tried doing a bit of googling to answer some persistent questions and this is the result I have come up with on my own and by myself.
However, I believe it might come in handy for someone like me to have a basic idea and help in personal budgeting and material management.
I however welcome any contribution or constructive criticism (including grammar and spelling corrections) that may crop up.

Thanks very helpful

Thanks