Non-destructive testing of concrete uses various methods to assess the strength and durability of concrete structures without damaging them. Common non-destructive testing methods described in the document include rebound hammer testing, pull-out testing, ultrasonic pulse velocity testing, and radioactive testing. Each method has benefits and limitations for providing information on properties like compressive strength, uniformity, presence of cracks, and condition of reinforcement. The results of non-destructive testing can be used to evaluate existing structures and monitor concrete quality during construction.