NEW X-RAY ABSORPTION TECHNIQUE TO STUDY CONCRETE.

The amount and movement of water in the microstructure of concrete controls the material properties. The ability to measure the presence and movement of water in concrete and other porous materials has recently been greatly enhanced using an x-ray absorption technique. This technique was invented at the Technical University of Denmark and used in the first prototype unit. The second such x-ray absorption unit in the world has recently been delivered to NIST. The transmission of x rays through a specimen is indicative of the materials local density, which can in turn be related to water movement within the material. This unit, which is totally automated and computer-controlled, has already been successfully applied to examining water movement during drying/curing of hydrating cement pastes and the influence of shrinkage-reducing admixtures on drying kinetics and the resultant moisture spatial distribution. It can move in three dimensions, and scan in two dimensions, with a resolution of 0.1 mm. The use of this unit is expected to become a standard technique in the building materials community, and it should be equally applicable to other porous materials.