Abstract
Orthogonal tests were conducted in this paper to study the mechanical properties of the heightened temperature curing steel slag (SS)-ground blast furnace slag (GBFS) cementitious materials without clinker based on four factor: A) the mass ratio of SS/GBFS; B) the mixing milling time of the cementitious materials; C) the mass ratio of Ca(OH)2/gypsum (from flue gas desulfurization waste, FGDW); D) curing temperature. The hydration products and microstructure of the heightened temperature curing SS-GBFS system was also studied. When the four factors are 1:2, 480 m2 kg-1, 2:1 and 35 ºC, respectively, the highest compressive strength was observed with the values of 18.36 MPa, 26.89 MPa and 45.32 MPa at the ages of 3 days, 7 days and 28 days, respectively. The influence of the four factors on the mechanical properties is in the order of D > A > B > C. The results from X-ray diffraction (XRD) and scanning electron microscope (SEM) indicate that ettringite and C-S-H form from the reactions between C2S from SS and amorphous phases from GBFS, and FGDW during hydration, which greatly contributes to the early-age strength. As the curing time increases, more ettringite forms due to the reaction of SO42- from FGDW, OH- from Ca(OH)2 and AlO2- from GBFS, and the formed ettringite (AFt) intervened with C-S-H gels, which provides the framework of the microstructure and thus improves the strength of the specimens.
