Development of C—S—H microstructure in ultra high performance concrete with QENS, 29Si NMR and XRD

Ultra High Performance Concrete (UHPC) is an innovative building material whose high strength is advantageous for future applications in highly filigree structural members and even as a replacement for steel building components. The mechanical and chemical properties of UHPC are determined by the formation of the strength-giving amorphous calcium silicate hydrates C—S—H from the clinker phases, silica fume and water. For the optimization of UHPC performance, a scientific working knowledge of microstructure formation depending on temperature and composition is necessary. At present, the development of C—S—H microstructure and the bonding of water are not well understood. Therefore the quasi-elastic neutron scattering technique (QENS) has been used to study the kinetics of water-bonding in the C3S—SiO2—H2O system with different compositions. Parallel investigations are being performed with 29Si NMR to observe the structure (polymerisation) of the silicates and with XRD to examine the formation of Ca(OH)2 and the consumption of C3S in the hydration process. After preparing the paste samples, QENS, XRD and NMR are used to follow the hydration process for up to two weeks. The results of first investigations are promising.

Author: T. Gutberlet, H. Hilbig, R.E. Beddoe

Section: Concrete

Keywords: hydration, tricalcium silicate, quasielastic neutron scattering