EARLY MICROSTRUCTURE DEVELOPMENT OF ACTIVATED LIME-FLY ASH PASTES

The effect of activators Na2SO4 and CaCl2 on early microstructure deve lopment of lime-fly ash pastes was examined. The control lime-fly ash pastes did not show a significant strength up to 28 days. The addition of 4% Na2SO4 increased both the early and later strengths of lime-fly ash pastes significantly. CaCl2.2H(2)O (4%) was less effective at 3 a nd 7 days, but more effective at 28 days than Na2SO4. Scanning electro n microscope observation and X-ray diffraction analysis indicated that very limited amount of C-S-H, ettringite (AFt) and monosulphoaluminat e (AFm) formed in the control pastes even at 28 days. C-S-H and AFt fi lled most spaces between fly ash particles in the Na2SO4 activated pas tes at 3 days, and the structure became denser with time. CaCl2 activa ted pastes also exhibited a dense structure at 3 days, in which most v oids between fly ash particles were filled with C-S-H and the solid so lution of Ca4Al2[(SO42-)(X)(Cl-)(Y)(OH-)(2-2X-Y)].nH(2)O (X<1 and Y<2) . The amount of the solid solution increased drastically from 7 to 28 days, which resulted in a denser structure and a higher strength than Na2SO4 activated pastes.