Concrete Works

Phase 1: Concrete Works

Mixing Concrete On-Site

If mixing concrete must be done on-site you need to use aggregate and water that is clean and absent of any organic material or other substances that can damage the concrete. When adding air-entraining admixture it must be done according to the manufacturer’s recommendations. When in doubt speak with the manufacturer about mixing portions and be sure to specify the use. Too much admixture will decrease the strength of the concrete and using admixtures should only be done when you are using a motorized mixer. Concrete works for building your own house should be well planned and prepared properly since this will be your foundation.

Ready-Mix Concrete

Depending on which part of the home you are using the concrete for, you would need different psi strengths. We used ready-mixed concrete for our concrete work and this can be purchased at most locations. When ordering concrete for foundation walls, interior slabs and footings you need to specify that a minimum strength of 2200 psi (MPa) is needed.

For driveways, exterior steps, carport floors and garage floors a minimum of 3600 psi (25 MPa) air-entrained concrete is needed (air entrained refers to the introduction of air bubbles into the concrete mixture to increase durability). For these purposes, the air-entrained concrete must be between 5 to 8 percent. The system of minute air bubbles will make the concrete more workable and more easily placed than plain concrete and will also be more protected from frost. For all exterior concrete work it is necessary to use air-entrained concrete, and it is also recommended for other applications to improve workability and durability.

Placing Concrete

Concrete works and placement begins with using forms to properly place the concrete. If you cannot access all point s of the forms you can use a wheelbarrow, buggies or chute to move concrete to all points in the form. When placing concrete into forms ensure that the concrete does not fall into the forms from a height of more than 5 ft, as this will case the concrete to segregate. Concrete should be put into the forms continuously in horizontal lifts no more than 12 to 18 inches (300 to 450 mm). When placing the concrete from a higher drop, use a vertical pipe to properly pour the mixed concrete.

When depositing the concrete it is important to remember that the concrete should be spread out and levelled by raking or shovelling, rather than pouring the concrete in a pile. We used pumping to place our concrete, but sometimes this equipment is not available on site. In any event, we found it was easier to use pumping so we recommend having this equipment onsite. A vibrator can be used to consolidate the concrete once the placement has been done. Next, you need to uniformly compact the concrete by using tamping hand tools (such as puddling sticks), or by a vibrator (which was the best choice based on our experience).

Note: concrete operations should not take place when it is at or below 41 °F (5°C), or when you expect the weather to take a turn in that direction within 24 hours. The ideal temperature range is between 50 °F (10°C) and 77 °F 25°C) for mixing and placement. Additionally, the concrete must be maintained at a temperature of no less than 50 °F (10°C) for at least 72 hours while curing. This can be accomplished by mixing the concrete with heated water. Any snow or ice should be removed from the framework and the concrete should not be placed against frozen soil.