The best way to clean concrete is with a pressure washer. If the concrete is in fairly good condition and shows no signs of stains, a regular pressure washer is great. If the concrete has years of stains, gum, or mold, then a heated pressure washer is a better alternative. Pressure washing can help to remove:
There are a few different attachments that can be used. As shown in this video, the first attachment is called a Turbo or Rotary nozzle. These types of nozzles add power to the spray capacity by creating a circular spray pattern. The extra agitation magnifies the cleaning power. This tool isn't required, but it add that much more power to the cleaning process. The second attachment is just a spray nozzle (most common). Spray nozzles allow for a directed flow of water.
Oil, gas, and rust stains can sometimes be removed with a pressure washer, but in severe cases, a cleaner will need to be required. Degreasers are very common, and in some cases, acid based cleaners as well. If an acid based cleaner is used, it is important to also neutralize the concrete before sealing. If a cleaner was used, it is important to make sure that any residue left behind by the cleaner is also removed. There are several concrete cleaners on the market, most concentrated cleaners offer similiar benefits.
Once the concrete has been cleaned, you want to seal the concrete in order to prevent damage, deterioration, and future staining. The most common concrete sealers are: