In order to help identify concrete problems, it is important to understand a few basics about concrete. Many of the terms and / or description used are oversimplified to accommodate someone with little or no concrete experience. Only an experienced concrete contractor can confirm what your concrete needs are, but hopefully this section will provide you with the basic information needed to help send you in the right direction.
A good start might be to explain what concrete actually is. Oversimplified, concrete is a mixture of rock, sand and cement. When mixed with water the mixture can be placed into forms and when properly finished and maintained will give years of service. During the time period between when concrete is mixed and when the concrete is cured, the materials go thru a series of changes. The most noticeable change is that the concrete hydrates (dries). During the hydration process, the concrete actually becomes denser as the water from the mix is forced out. In order for the material to become denser, it has to shrink. Too much water in the mix causes the concrete to shrink excessively. It will also cause the concrete to lose its strength and elasticity, causing it to become brittle. Obviously this is just touching the basics, but it should give you enough information to get you started.
The concrete is only one part of a complex procedure. Prior to pouring the concrete there are many steps that must be completed. If there is existing concrete in the location of the new concrete, the first step would be demolition. Concrete is very heavy and typically is removed with a skid-steer loader or other small heavy equipment. The concrete itself can be recycled and dumped free of charge if it does not contain any trash or hazardous materials such as polyurethane foam. Because the concrete is heavy, it can be expensive to have the debris hauled to the recycle center. With weights exceeding 3200 lbs per yard, it will require a heavy truck or trailer to haul it.
Next step would be to grade and compact. Anytime a machine has turned around several times to load debris, the ground will be highly disturbed. Compaction required some dirt knowledge and not just a compactor. Soils need to be identified and at optimum moisture, or the compaction may not reach suitable levels. Soil compaction is often overlooked, but is in fact one of the most critical factors in the longevity of the concrete. Without proper compaction, the new concrete will inevitably fail at some point in the future.
Next would be setting forms. The forms establish the outside edges of the concrete. Forms must be sturdy enough to withstand the lateral pressures of the wet concrete. Shoddy form-work will typically result in crooked edges. Additionally, and more importantly, the forms establish the elevations. Improper elevations may result in water ponding, improper drainage, improper slope, failure to meet ADA slope or side-slope requirements, or a entire array of other issues. Therefore, it is very important that any individual building concrete forms, has the required knowledge to do so.
Next, the area within the forms should be fine graded. Fine grading is essential, to ensuring the concrete is poured at a uniform depth. When concrete is deep in some places and shallow in others, the concrete can not dry evenly. When portions of the concrete are dry and other portions are wet, it is nearly impossible to achieve a uniform finish. Sand is become popular to use as a fine grading material. Sand is easy to grade and cheap to purchase. However, sand can not be compacted. You can run the compactor over it all day and still leave footprints in it. Sand does not bond together. This means if water get access to the sand, it will wash out. Sand draws water and enough sand can hold enough water to cause elevation problems if the temperature drops below freezing. For this reason alone, we never recommend that sand be used to fine grade anywhere susceptible to below freezing temperatures. A better material would be a sandy clay. With optimal moisture, it can be compacted to 100%.
Next we finally get to pour the actual concrete. This sounds simple but also has complexities. First off, the correct concrete mixture, with the correct additives for a particular application must be ordered. Using the wrong mixture or not adding the proper admixtures can end in problems. Once the concrete arrives, it is important to check the slump level. This tell you how much water needs to be added to the concrete for your specific application. Too little water makes it difficult for the concrete to to consolidate and makes the job much harder to do. To much water can destroy the structural integrity of the concrete. Additionally, concrete poured too wet will have excessive shrinkage and is more susceptible to shrinkage cracks.
Once the concrete is placed, or during the placement, there are many steps to perform to insure a correctly completed project. One of the most important would be to use a jointer to cut the control joints into the wet concrete. By using a jointer and correctly placing the control joints, you are able to control the shrinkage and basically prevent any shrinkage cracks. As stated there are many steps involved in correctly finishing the concrete. Because we are not giving a class, but merely attempting to supply some basic knowledge, we will not go into all of the required steps.
After the concrete has dried, the forms can be removed and the new concrete back-filled. Back-filling is important, because it helps prevent water from having access under the concrete. Other important steps would be to caulk all of the joints and seal the concrete.
Having said all of that, I am well aware that most of the people currently pouring concrete, are not following the proper procedures. Why? mostly because people are wanting the work completed as cheep as possible. The only way to do it cheaper, is to skip steps. This may be something to think about if you are needing to get an estimate for concrete replacement. We always recommend a scope of work, so that all bidders are all bidding on the exact same thing.
We hope you found this information helpful. Don’t forget that you can also e mail or call us with any questions, and estimates are always free. Just go to the Contact us Page.