Hard X-ray characterization of fly ash geopolymers
Calcium map of an activated fly ash geopolymer displays regions of high calcium concentration (circled). Their distribution suggests localization as a discrete calcium-rich phase within the lower-calcium aluminosilicate geopolymer gel.
Use of the Hard X-Ray Nanoprobe (HXN) has provided the first access to the nature of heterogeneity in real fly ash-derived geopolymers at the nanoscale. Direct evidence of the formation of discrete high-calcium nanometer-sized particles within a hydroxide-activated geopolymer synthesized from a low-calcium fly ash has been obtained using HXN fluorescence characterization. Additionally, the team of CNM users from the University of Melbourne, the Universidad del Valle of Colombia, and the Advanced Photon Source has shown that the level of readily available and toxic chromium is significantly lower than the total chromium content of the precursor fly ash. Geopolymers may be environmentally beneficial replacements for cement in concrete production, offering comparable performance and cost while reducing greenhouse gas emissions. Geopolymer structure is not well understood, however, in particular the role of calcium within the geopolymer structure and the possibility of the release of toxins into the environment.
J.L. Provis, V. Rose, S.A. Bernal, and J.S.J van Deventer, Langmuir, 25(19) (2009)