Why Does Concrete Pit?

Concrete is one of the strongest and most widely used materials in home-foundation building and industrial-building construction. However, it does have a weakness. Concrete can pit along the surface, creating tiny holes, or divots, that pockmark the once-smooth surface. This is typically frustrating on concrete driveways. Driveways can pit from several factors, including weather, elements and other variables that occur when the concrete is poured.

Accelerators

Concrete pitting can sometimes be traced back to the pouring of the material. When contractors pour concrete, they do so on a schedule. They will try to pour the driveway or foundation when it is convenient for them and when the weather allows. During a pour, if too much accelerator is used, used so the concrete sets before bad weather comes, it can cause a pitting to occur. The accelerator will force water to dry faster inside the concrete, and this creates the dimpled, pitted surface in driveway. Also, the accelerator may not have been properly mixed throughout the concrete. When this is the case, some sections dry slower and cause the pitting.

Frost

If a frost occurs after the concrete driveway has been poured, it will cause pitting. Water droplets will freeze inside the top layer of the concrete and expand, causing the top layer to break apart. In wet concrete that is still drying, this results in pockmarks, and, in more severe cases, the entire surface can look like a pane of broken glass. The extent of the pitting is also related to the range of temperature changes before and after the frost. Very large temperature changes can cause extensive pitting to occur because warmer water molecules are larger, so they will shrink more when freezing occurs.

Weather

There are many other causes of pitting related to weather and the elements. The first is rain. Rain damages the flat surface of the concrete and saturates the material in an uneven fashion. This will affect the drying time of the concrete and eventually cause pitting. Rain can also saturate the ground underneath the concrete, which can make it soft and uneven. This also results in pitting because the concrete will slide into the gaps formed by the softer ground.

Damage

Excessive weight or contact with steel also causes pitting. Weight can shift the ground under the concrete and, after an extended period of time, press certain parts of the concrete into the ground. This causes one form of pitting that is less common. Other pits can be actual chips that are formed from hard objects striking the concrete, although these are also less common. Age also factors into pitting. The surface of the concrete can crack and be penetrated by water droplets that will freeze and cause pits in the surface layer. Burnished concrete surfaces are a little more robust and therefore prevent this type of pitting to some extent.

Pouring

In some cases pitting is caused by the contractor because the concrete is not poured correctly. Concrete must be poured on a flat surface that has a consistent, uniformity of material. Clean fill, which is dirt that is free of rocks and debris, must be used to create a pit-free concrete surface. If there are rocks or debris in the fill, it will affect the concrete above, forming pits on the surface. This is because the concrete does not set correctly and evenly.