Concrete

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Concrete in various forms can be dated back to 5600 BCE, where in Serbia the remains of a hut were found with a floor made of a mixture of red lime, sand, and gravel. In the Roman Empire, a concrete made from quicklime, pozzolanic ash/pozzolana, and an pumice aggregate was used. It was very similar to the modern portland cement concrete which was developed in the 1840’s and is currently in use today.


















  • CONCRETE

    1

    Build your sub-grade. Excavate the site slightly bigger than the size of the pad you are going to pour, and deep enough to have 3 to 4 inches of gravel below the concrete you are going to pour. Fill and spread the gravel, to your desired level. Screed it with one of your form boards, checking for level as you go. Tamp the gravel firmly.

  • 2

    Assemble your forms on the gravel by nailing the ends together. Check them for square by measuring the diagonals, or corner to corner, and moving the form so that they are the same. This will ensure that the form is square. Stake one corner and nail the form at the right height. Stake and nail the rest of first side so that it is level. Stake the opposite side, check your forms for square, and nail them off. Stake and nail the other sides. Double check all the corners with the transit to make sure they are level. Check the height of the gravel and add more if you are below the forms or subtract it if you are high.

    • 3

      Set your rebar so that the pieces are 2 feet on center, making 2-foot squares. Keep the perimeter piece about 6 inches away from the form boards. Tie the rebar together with wire. Set the rebar onto rebar chairs, spaced every two feet. Determine the volume of concrete you need and call in the order to the ready mix plant. The representative will ask you for volume, the psi, and the slump. If you don't know, let him consult you.

    • 4

      Work fast when you begin the pour. Start moving the concrete up to the edges of the forms. Level it out the best you can by sight. Walk around and trowel along the edges. Screed the concrete by "sawing" the board back and forth on the top of the forms. If there are low spots, fill them in and screed over it again. Do this as you go. After the screeding is done, run the bull float over the surface. Set anchor bolts, if needed, into the concrete. When the concrete is starting to stiffen up, complete it with a broomed finish. Use a steel trowel for a smooth finish. Spray the curing compound on after finishing is complete.

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