Poured Concrete Foundation Quality Control Procedures

Basics

• The Portland Concrete Association, as well as state governments, create and utilize various tests for foundation-grade, or structural, concrete. This sort of concrete must have a very low water content. This is essential because too much water in foundational concrete will freeze in winter and shrink as the foundation dries. Low water content in foundation-grade concrete increases its durability, resists weathering and increases the bonding strength with reinforcing metal and wood components. Therefore, specifically for foundations, the water testing is essential.

Slump

• One significant test of water is the “slump test.” This is a simple procedure, but is done globally to test the strength of fresh concrete mixtures. The “slump” is the amount of movement and change a fresh upright slab of wet cement will go through after a certain amount of time. A very wet concrete batch will just splash into a heap, while too dry cement will not change at all. For foundation concrete, some limited slump is needed, since the concrete needs to give a bit to resist immediate cracking. Too much foundation slump will create a foundation that will give too much and settle. For a good, workable slump, about 50 millimeters of total change overall is acceptable. This 50 millimeters is not in one place, but over the entire standardized sample.

Air Testing

• Air testing is also essential. This measures the amount of air bubbles remaining in concrete both when wet and after it dries. Different state and private procedures exist for this, but the goal is to see if there is too much air. Too much air leads to weak cement. If too much air is found in the tested samples — both wet and dry — then chemical admixtures that remove air are added to the new wet batches of cement. For foundations, the acceptable percentage is about 5 percent. For both water and air tests, many states mandate the placing of a concrete sample in a large cylinder. The cylinder is then closed, and a large hammer presses down on the concrete. If the concrete buckles before it is supposed to, the manufacturer can face fines. It will then have to alter its production techniques.

Compression Tests

• Compressive tests are also significant. These assume that a concrete sample that contains the proper and acceptable amount of water and air will always stand up under pressure. Dried concrete is placed in a pressurized cylinder, sometimes for a long period of time, depending on local regulations. A sample with too much air will quickly crack. A sample with too much water will begin to “smush,” while a sample with too little water will become brittle. It is easy to tell, by the reaction of the sample, what the cause of the breakage is. The concrete is then adjusted at the factory to respond to the tests. On some occasions, the concrete can be treated chemically to remove or add ingredients.