Title: Microstructure of Highly Expansive Cement Pastes
Author(s): Yan Fu, Shamim A. Sheikh, and R. Douglas Hooton
Publication: Materials Journal
Appears on pages(s): 46-53
Keywords: cement pastes; expansive cements; ettringite; microstructure; high-alumina cements; x-ray diffraction; Materials Research
An investigation at the microstructural level was carried out to interpret the mechanisms of hydration processes and the properties of highly expansive cement pastes before and after set. Results from this investigation, which included analyses from X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and scanning electron microscope (SEM), are presented. Some crucial behavior occurring in the hydration of expansive cement paste, such as quick setting and adverse effects of admixtures on expansion properties, are discussed. The mineral composition of such a material is also studied with respect to its durability. Formation of calcium sulfoaluminate immediately after the solid materials are mixed with water was observed to be mainly responsible for the quick setting behavior of expansive cements containing high-alumina cement (HAC). Use of hydrated HAC instead of HAC as the Al-bearing material delayed the formation of sulfoaluminate (SA), resulting in a more workable cement paste.