Radioactive Method

Here X-rays and gamma rays are used. When X-rays and gamma rays are passed through concrete, the electromagnetic spectrum penetrates concrete but undergoes attenuation in the process. The degree of attenuation is a function of the kind of matter traversed, its thickness and the wavelength of the radiation. Further, the intensity of the incident gamma-rays and the emerging gamma-rays after passing through the specimens is measured. These two values are used to calculate the density of concrete.

The gamma-rays transmission method is particularly used to measure the thickness of concrete slabs of known density. This is achieved by passing gamma rays of known intensity to penetrate through the concrete. The thickness of the concrete is measured based on the intensity of gamma rays measured on the other end.