Effects of alkali on one-part alkali-activated cement synthesized by calcining bentonite with dolomite and Na2CO3

A novel approach was employed to synthesize one-part alkali-activated cements (AACs) for potential property/cost ratio advantage by calcining low-quality bentonite with dolomite and Na2CO3. The clinkers and the corresponding 80 °C-cured hydrates were characterized with multiple analytical methods. The primitively optimized 80 °C-cured paste made from the clinker calcined at 1100 °C with (CaO + MgO)/SiO2 at a molar ratio of 2.1 and R2O/SiO2 at a molar ratio of 0.4 resulted in the highest 28 day compressive strength of 38.3 MPa, which was twice of that without alkali additive. Accompanied with glassy phases, the poorly crystallized cementing active minerals in the optimum clinker contained C3A, belite, and MgO, as identified by X-ray diffraction analysis. MgO remained inert during hydration of clinkers calcined at 1200 °C or without Na2CO3 additive. Release of Ca(OH)2 during hydration of belite only appeared in the hydrates of the clinkers calcined without alkali additive, and it was used up in the hydrates of belite-containing clinkers with Na2CO3 additive. The 80 °C-cured optimum hydrate was subject to the most seriously carbonization along with the most compact microstructures among all hydrates. The alkali additive improved the cementing activities of one-part R2O-MO-Al2O3-SiO2 cement system in two ways as it not only optimized the phase composition of the clinkers but also facilitated the hydration.