Do Something Concrete
By: Jill Widenmaier
McNamee Concrete Ltd.
Now that spring is upon us you may be seriously thinking of pouring that concrete slab in your garage or perhaps a nice sized patio in your backyard. Contrary to some points of view there really are many factors involved in a concrete project from start to finish. The preparation prior to the placing of the concrete is very important. Such preparation would include compacting and moistening the sub-grade, erecting the forms and the placing of reinforced steel or other items securely if applicable. In hot weather moistening of the sub-grade is most important. This process keeps the sub-grade from drawing out water from the concrete.
As well, in cold weather the sub-grade must not be frozen. The forms should be set accurately and well braced. If using wood forms they should be moistened, otherwise the wood will absorb water from the concrete and swell. And finally, equipment that will be used to place the concrete should be clean and in good working condition.
The concrete mix design or strength of concrete you will require will be determined by what you are pouring. A concrete project that will be exposed to the elements will require a higher strength of concrete than that of a project that would be protected from the elements, for example; a basement slab would require a mixture of cement, aggregate and water that is different compared to an outdoor slab. The mixture creates a paste that binds materials such as sand and gravel into a rock like mass. The higher the cement content the higher the strength of the concrete.
Units of measurement in the concrete world are done through 'Mega Pascal' (MPa). McNamee Concrete Ltd. can recommend to you what type of mix you should use. We may also recommend that an admixture (chemical agent) be included in your mix. Some important concrete characteristics upon which admixtures have an effect include; fresh concrete: air content, workability, bleeding, setting time, curing and finish-ability; hardened concrete: strength and durability. The admixture is usually placed into the mix before the truck leaves the plant. One of the most commonly used agents is the air entrainment admixture. This is one of the greatest advances in concrete technology. Principally, this agent improves the concrete's resistance to freezing and thawing by allowing small air pockets to develop in the concrete which allows for expansion and contraction in cool or warm weather. It also improves the workability of the concrete.
The importance of the placing the concrete will depend on the project. Less concern can be taken when pouring a hydro trench compared to pouring basement or garage slab. When pouring a slab the concrete should be stared along the perimeter at one end with each batch poured against the previously placed concrete. Concrete should not be poured in separate piles then worked together. This practice will result in segregation of the mix.
Concrete should be placed as near as possible to its final position. The next step in the process is the compacting of the fresh concrete to mould within the forms. This can be accomplished by hand or with mechanical tools. A mix that can be compacted easily by hand tools should not be compacted by mechanical methods, because the concrete may segregate. With regards to the concrete slab there are many ways it can be finished. This will depend on the intended use of the slab. Some slabs may only need screeding to achieve proper contour and elevation. Other slabs may require a broomed, floated or trowelled finish. A finishing crew should be large enough to handle the placing, finishing and curing of the slab, with regards to the setting time of the concrete and the size of the project. The curing process protects the slab from rapid drying and from extreme changes in temperature. With proper curing, concrete will become stronger, more resistant to stress, abrasion, freezing and thawing. We can recommend a proper curing method for your project.