Concrete can be used as a load-bearing construction material because of its high compressive strength. When made correctly, it can provide a strong durable surface that can survive any number of climates and uses. Simply, concrete consists of sand, aggregate, cement and water. Once combined, the wet mixture can be forced into forms and left to cure over a set period of time during which the concrete dries out and hardens. Picking the right concrete mixture for your footing support is crucial to insure a strong and stable foundation for your construction project.
Types of Concrete
There are a variety of concrete types to fit any sized footing or scope of project. Differences exist among the types of mixtures, from general purpose premixed to fast-setting concrete. Variables to look for when deciding what mixture to use include setting time, compressive strength, shrinkage, density and air content.
General Purpose Premixed Concrete
This premix of Portland cement, gravel and sand is generally rated at 4000 psi (pound-force per square inch) for compressive strength and is sometimes called fast-setting concrete. It has a setting time of 90 minutes, depending on the project environment. This type of concrete is best for projects that don't require a form, such as setting posts for decks, fence posts, mailboxes and swing sets.
Reinforced Concrete Mix
The addition of reinforcing fibres to the sand and gravel aggregates can be quickly implemented in projects where impact is expected, such as steps, walkways and garage or shed floors, which normally require a compressive strength of 6000 psi. A more advanced method of reinforcing poured footings is the implemention of rebar, which can increase the compressive strength of the footing, making it less likely to crack or splinter.
High Performance Concrete
The strength of a concrete mix can be manipulated through the careful selection of ingredients and mix design. The addition of plasticisers will improve the density and toughness of a concrete mixture. For extended durability, the addition of fly ash is recommended, also adding to the workability of the concrete. These additions can raise the compressive strength of the cement to above 10,000 psi.