Title:
Pozzolanic Reaction and Microstructure of Chemical Activated Lime-Fly Ash Pastes
Author(s):
Caijun Shi
Publication:
Materials Journal
Volume:
95
Issue:
5
Appears on pages(s):
537-545
Keywords:
activation; cement pastes; fly ash; hydration; lime; microstructure;
DOI:
10.14359/396
Date:
9/1/1998
Abstract:
The reactivity of low-calcium fly ash (LFA) and high-calcium fly ash (HFA) was measured in the presence of activators Na2SO4 and CaCl2. Tests were performed on the blends consisting of 80 percent fly ash and 20 percent hydrated lime by mass at 50 C. The addition of 4 percent Na2SO4 significantly increased the early strength and did not affect the later strength of lime-LFA pastes, and significantly increased both the early and later strengths of lime-HFA pastes. The addition of 4 percent CaCl2.2H2O slightly increased the early strength and significantly increased the later strength of lime-LFA pastes and slightly increased the strength of lime-HFA pastes at early and later ages. The measurement of free lime content indicated that the addition of Na2SO4 or CaCl2.2H2O accelerated the depletion of Ca(OH)2 in lime-LFA at early and later ages, and no more Ca(OH)2 could be detected in CaCl2 activated pastes after 7 days. The depletion of Ca(OH)2 in lime-HFA was slightly accelerated at early ages, but not at later ages. Scanning electron microscope (SEM) and X-ray diffraction (XRD) examinations showed that the addition of Na2SO4 or CaCl2 changed hydration products and microstructure of hardened lime-fly ash pastes.