One critical process in the production of quality concrete at the construction site is curing [1]. To achieve optimum performance, it is important to minimize the evaporation of water from the concrete surface during the first few days of hydration. Furthermore, as cement paste hydrates under sealed conditions, it undergoes self-desiccation due to chemical shrinkage (the reaction products occupying less volume than the reactants) [2,3]. Thus, in high-performance, low water-to-cement ratio (w/c) concretes, there may be insufficient internal water for complete curing, so that additional water supplied from the exterior surface could greatly enhance final properties. To better understand water movement during curing of concrete, fundamental studies are needed to examine the spatial and temporal water distribution within the concrete element.
Recently, at the Technical University of Denmark, an X-ray environmental
chamber has been constructed to examine building materials exposed to
various drying environments [4]. Both relative humidity and
air temperature can be conveniently varied within the chamber, which
also serves as a shield from the X-ray source. In this preliminary study, the
X-ray environmental chamber is used to monitor water movement during the
drying of small cement paste specimens, as a first step in understanding
water movement during the curing of concrete. Because the X-ray absorption
is proportional to the density of the materials through which the X-rays are
passing, a high w/c ratio (less dense) paste will absorb less X-rays than
a lower w/c ratio paste. Similarly, a paste which has dried out will absorb
less X-rays than the same paste under its initial saturated conditions.