Figure 1 - Concrete delivery truck
As it is with many industries the concrete industry has its own terminology when it comes to selling their products.
First and foremost is to understand the difference between cement and concrete.
Cement is a product made of limestone, clay and gypsum, the most common blend for all construction, including mortar, is Portland cement. It is a powder that without the addition of moisture does little.
Concrete is a product made of cement, one or more aggregates and water. What you require for a slab or column is concrete NOT cement.
You can create your own concrete by purchasing suitable quantities of cement, aggregate and adding the appropriate amount of water. Or, you can purchase bags of pre-mixed concrete, just mix in water or you can order ready-mix concrete from a local supplier.
Bags of concrete are sold by the pound the most common being 60lb and 80lb. These bags have the correct proportions of cement, sand and gravel.
Ready-mix concrete is sold by the yard
. A yard of concrete is actually a cubic yard of material (27 cubic feet). It is delivered to the location already mixed with water and only needs to be hauled from the concrete delivery truck, Figure 1, to the location on your property where it is required.
A concrete calculator is provided that will advise how many bags or yards of concrete you require for the most commons shapes - square, rectangle, circle, column (sono tube).
Their are advantages and disadvantages to both. With bagged concrete you can work at your own pace, whereas concrete delivered by a truck requires you off-load it immediately and work to finish it before it cures. Bagged concrete (if your project requires more than a few bags), generally means buying or renting a concrete mixer and at the end or the day is much harder on your back!