Abstract
Alkali-activated limestone/metakaolin (AAC-LSMK) pastes of Na2O/Al2O3 = 0.60 and 1.08 and LS/MK = 20/80 and 60/40 were exposed to 300, 600 and 900 °C, and the structural changes were studied. The exposure to 300 °C reduced 21–25% the weight of samples without affecting the structure and strength (~50 MPa) of formulations with high LS/MK, and/or low Na2O/Al2O3. The exposure to 600 °C extended the reactions/dissolution of MK while 1–17% of the N-A-S-H/N-(C)-A-S-H was depolymerized due to a water attack on the stretched Si–O-T bonds, with bridging oxygens transformed into non-bridging oxygen, while limestone favored the formation of C-(A)-S-H; the residual strength was of 30 MPa. The exposure to 900 °C led to the formation of nepheline and decarbonization of the CaCO3, which significantly reduced the strength to residual values of up to 20 MPa. These findings bring new insights on the performance of the AAC-LSMK and the thermally induced structural changes, while highlighting their potential high-temperature applications.
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