Phase Development of NaOH Activated Blast Furnace Slag Geopolymers Cured at 90 deg. C

Geopolymers were synthesized from blast furnace slag activated with different levels of NaOH and cured at 90 deg. C. The crystalline and amorphous phases of the resulting geopolymers were characterized by XRD quantitative analysis, and 29Si and 27Al MAS NMR. Amorphous species are predominant in materials at all NaOH levels. In the amorphous phase, aluminium substituted silicate species (Q2(1Al)) dominated among the species of Q0, Q1, Q2(1Al) and Q2(where Qn(mAl) denotes a silicate tetrahedron [SiO4] with n bridging oxygen atoms and m adjacent tetrahedra substituted with an aluminate tetrahedron [AlO4]). In addition, it was also found that 4-fold coordination aluminium [AlO4] species (27Al chemical shift 66.1 ppm) in low NaOH containing materials differs from the species (27Al chemical shift 74.3 ppm) in high NaOH containing materials.