Chemical and Physical Properties of the Nanoscale Building Blocks of Concrete

1. Calcium silicate A nanometer (nm) is one-billionth of a meter. Bound water Surface water Free water 5 nm Chemical and Physical Properties of the Nanoscale Building Blocks of Concrete Dan Neumann, National Institute of Standards and Technology, DMR 0454672 Using NSF-funded instruments at the NIST Center for High Resolution Neutron Scattering (CHRNS), scientists have made important new discoveries regarding a key component of one of the most prolific manufactured materials, Portland cement concrete. The key component, known as calcium-silicate-hydrate (C-S-H) gel, is produced when cement is hydrated (mixed with water). It binds the agglomerate, giving concrete its strength. The composition and density of solid C-S-H is notoriously difficult to obtain due to its uncertain water content under different humidity conditions. Combining neutron and x-ray measurements, small angle scattering was used to determine, for the first time without recourse to drying, the composition and density of C-S-H in its native state. The figure schematically shows the nanoscale structure of C-S-H particles in the gel. The results of this work have implications for a better understanding of the properties of concrete such as its response to mechanical loads and changes in temperature and humidity. A.J. Allen, J.J. Thomas and H.M. Jennings; Nature Materials, 6, 311 (2007).