Concrete strength is usually determined by the extraction of concrete core samples with the cores being subjected to compression testing in accordance with British Standards. Ideally a 100mm diameter core should be extracted using an electric rotary core drill.

In overhead or confined space situations the cores should be extracted using either a hydraulic or compressed air drill. 

 

Due to reinforcement congestion smaller diameter cores can be utilised and these typically produce conservative results depending on the ratio of diameter to aggregate size.