Ever wonder about the basic materials that are mixed to make your concrete? In this article I’ll be going through each of the main materials and what part they play in your concrete.
Cement in your concrete is essentially a binding material that forms as a glue for the other materials in your concrete.
It is made by combining silicon, aluminium, iron, calcium, chalk, clay, slate and limestone with other chemicals in a controlled mixture. When combined and water is added, it reacts with the other materials to heat and harden, binding the fine and large aggregate together that make up your solid concrete structure.
The fine aggregate (sand), is a very fine material which can assist concrete to solidify, giving the necessary strength required. Sand can fill up the pores or voids inside the concrete which is also a contributing factor for the strength of the concrete. Its considerable hardness and resistant to weathering makes it the perfect material for the mixture.
Course aggregates are the larger stones in your concrete mix. They are also considered somewhat of a filler material making your concrete mix stretch further, but they are also one of the main strengthening properties of your concrete. 20mm aggregate is considered the base size and has the best strength properties. Once you lower the size of the large aggregates to 10mm you are weakening the strength of your concrete, so typically to make up for this you MPA rating will be raised (amount of cement) to counter the loss in aggregate. There is also an option for “reduced line” aggregate, which is basically a reduced mixture of large aggregates that are used. Personally, I would never place reduced line concrete as it’s strength properties are far below anything I would be confident in placing and standing behind as a contractor.
Water in the mix makes the concrete workable during placement. During the setting process, the cement materials start to super heat, which in turn makes the water start to evaporate and be forced out of the concrete mix, making all the properties start to harden and bind together. As a general rule of thumb, it will take only a few hours for the water to evaporate enough for the concrete to begin to harden to the point it can be finished and by the next day, enough water has removed from the concrete to harden enough to walk on without damaging it. It can take up to a month for 100mm concrete to cure properly with all the water evaporating from within the concrete.