Concrete Work
In this module, we will dive into the properties of concrete as well as its common uses for it. These things are important to carpentry as you may not only be creating the forms for the pour, but it is also likely you may pour yourself.
Precautions when
using Concrete
It is important to understand the characteristics of concrete for the appropriate handling of the material. A hardhat, gloves, safety glasses and when mixing use a respirator. When working with concrete be sure to:
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Wear protective clothing when working with freshly mixed material
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Wash any skin that has been exposed to wet concrete
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If any material gets in the eye, wash it out immediately.
Ready & Site Mixed Concrete
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The advantage of using ready mix concrete is that variables such as compressive strength, workability, proportioning of ingredients, water-cement ratio and slump can be controlled and moulded as per the requirement of the project. Whereas Onsite concrete is concrete manufactured to a set recipe and batched right on the job site. This process allows special mixtures to be created based on the specific needs of the job and also guarantees you will never get a "hot load," as the material is mixed right there on site.
Concrete Reinforcement
Concrete is a commonly used material in construction due to its high compression strength. Although this material is solid on its own concrete does not have much tensile strength. The low tensile strength makes concrete prone to cracks and failure. To offset this Rebar and Wire Mesh are often placed inside the concrete to prevent cracks and provide more strength for the concrete.
Rebar
Rebar is one material used to reinforce concrete. Rebar can be made from Carbon Steel, Fiberglass, carbon fiber, Coated steel, or basalt fiber. Rebar is often tied together with steel wire, to help it maintain the desired grid and stay where installed until the concrete is placed. Rebar can be used in walls, floors and anywhere extra tensile strength is needed to prevent the concrete from cracking.
Wire Mesh
Wire mesh is often used on concrete slabs and between masonry courses. Wire mesh is not as strong as its rebar counterpart, however, it can be used in applications where rebar will not work due to its thin profile.
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Preparing Concrete Forms
All sawdust, nails, and other debris must be removed prior to placing the concrete. The interior form surfaces are sprayed with form oil for easier removal however no oil should get on the steel reinforcement.
Slump Test
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The concrete slump test measures the consistency of fresh concrete before it sets.
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It is performed to check the workability of freshly made concrete, and therefore the ease with which concrete flows.
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It can also be used as an indicator of an improperly mixed batch
Placing of Concrete
in Forms
How you place concrete in forms can vary depending on the type of concrete work that is being done. When placing concrete in a form for a slab, you can fill it right to the top and run a board across the top of the form to achieve a level surface. However, if the form is for something such as a foundation wall, then placement becomes a little different. When concrete is fresh off the truck and hasn't begun to settle or harden there is immense pressure against the forms. If you pour directly into larger forms and go right to the desired height this can lead to a blowout (when the forms fail and concrete comes out.) that is why when pouring large amounts of concrete, (let's say a foundation wall), you move around the foundation only placing a foot or two of concrete at a time until you finally reach the desired height. This puts less strain on the forms.
Consolidation of Concrete
Consolidation is the process of inducing a closer arrangement of the solid particles in freshly mixed concrete or mortar during placement by the reduction of voids, usually by vibration, centrifugation, rodding, tamping, or some combinations of these actions.
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What it means to consolidate concrete is to make the fresh concrete that is being placed have fewer voids and be an overall stronger product. To make this happen usually a concrete vibrator will be used as well as tapping the sides of the forms with a hammer (vibration). This reduces common issues such as honeycombing in concrete work.
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Finishing Concrete
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Screeding - striking off the excess concrete to bring the top surface to proper grade
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2. Floating - consists in removing the irregularities on the surface of the concrete that is left after screening
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3. Troweling - final operation of finishing. It provides a smoother finish which is hard and abrasion-resistant
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Curing Concrete
Concrete typically takes between 24 to 48 hours to dry
Moisture - the cement interacts with water. Less water in the mix helps the concrete cure quicker, however, If there's more water in the mix it will make the cure and working time longer.
Temperature - When the environment is hot or the direct sun is on the concrete, moisture evaporates faster meaning the concrete will cure at a faster rate and won't have as much work time. In colder environments, freezing is a major issue for concrete (if this happens the concrete needs to be torn out and replaced). To prevent this from happening there are specially designed insulated concrete blankets that prevent the concrete from freezing. Additives also exist for warmer and colder environments to help the concrete cure properly.
Overall
Now that you have read over the module and seen all the steps leading to a proper finished product, we at Snyder Construction will help you perfect these skills.
