Abstract
This thesis presents two separate applications of ionising radiation in Civil Engineering. The first is an investigation to determine the cement content of concrete using gamma-rays from the naturally occurring isotopes 238U, 232Th and their decay chains as well as 40K. Two sets of equations are derived and discussed. Spectra from cement, aggregate and concrete samples were made and the useful full energy peaks from the above sources identified. Two concrete samples were prepared using the same cement, but, containing two different aggregates: a granite based aggregate and a flint based aggregate. A third concrete sample was then prepared where the cement content was not initially known. Data from the first two tests was then used to determine the mass of cement used in the blind test. A great deal of valuable information has also been accrued concerning the interaction of statistical errors in the equations for the prediction of cement content. Spectra from four different cements were collected at regular intervals over a 24 month period and the variation in the activity of each cement over this period is discussed. The second section of this work presents an imaging technique that uses pair production annihilation photons to examine the state of steel reinforcement in concrete structures. Computer simulations along with experimental work have been used. The experimental work used a 226Ra needle as a photon source as it provided a range of gamma-rays with energies over the pair production threshold of 1022keV. A 31mm rebar with 30mm of concrete cover was successfully located during the experimental work. The data collected from the computer simulations has shown that the geometry and the material between the photon source, rebar and detector is of great importance.