Investigation of the microstructure of alkali-activated cements by neutron scattering

Abstract

Significant research has been devoted to understanding and modeling the neutron scattering behavior of Portland cement pastes. The present work examines the potential of neutron scattering to noninvasively evaluate the properties of alternative cementitious materials encountered in the field. To interpret the scattering of both alkali-activated and slag-cement systems, alternative models to those typically adopted for Portland cement pastes were considered. Investigation of alkali-activated and slag-cement coupons were conducted for different sample thickness (∼0.5, 1, 2, 4, 6, 8 and 12 mm) over a wide scattering vector ( Q) range (0.0005< Q>0.03 nm −1 and 0.04< Q>4 nm −1) on both ultra (USANS) and conventional small-angle neutron scattering (SANS) spectrometers. This wide Q range allowed determination of the fractal properties of the microstructure as well as the radius of the main scattering particle in the material. An empirical correction for multiple scattering was made based on the Dexter–Beeman equation and demonstrated that for thicker sample widths the theory correlated reasonably well. Alkali-activated fly ash was found to have the largest R value while the OPC and slag mix exhibited the largest Guinier radius. This difference was attributed to variations in the extent of multiple scattering for the samples. Successful application of this model was limited to sample thickness ≥1 mm. A combined power law–Sabine expression was also utilized to successfully model the SANS data over a Q range of 0.04–4 nm −1.