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Sodium sulfate (SS) is a neutral activator. SS-activated alkali-activated slag cement (AASC) has lower shrinkage. However, it sets slowly, and the mechanical property develops slowly. Slaked lime (SL) is an alkaline substance widely used in industry that can be used as an activator in AASC. In this paper, SL was used alone, and SL and SS were mixed together to prepare AASC. The effects of SL content on the setting time, shrinkage properties and mechanical strength of AASC were investigated. Furthermore, the mechanism was explored with the analysis of microscopic tests. The results showed that SS could not be used as an activator alone, while SL could be used as an activator alone, and SS could be combined with SL to prepare AASC. The setting time of the SL system or the SS-SL mix system decreased with the increase in SL. The mechanical properties of the SL system were poor. The SS-SL system showed the highest mechanical properties when SL was 3%. With the increase in SL, the autogenous and drying shrinkage of the SL system increased, while the former of the SS-SL system increased and the latter decreased. At the same time, due to the different changes in pore structure and mesoporous volume in the two systems, the drying shrinkage showed different changes. Compared with the SL system, ettringite (AFt) with a slight expansion property and more crystal phases were formed in the SS-SL system, which reduced the drying shrinkage. [ABSTRACT FROM AUTHOR]

Water glass (WG) is generally considered to be the most effective activator to prepare alkali-activated slag (AAS) cement in terms of strength and durability. However, the rapid setting and hardening of WG activated slag results in rapid loss of fluidity of AAS concrete mixture, which limits its engineering application. In the paper, the effect of blended inorganic salts containing negative hydration ions on the fluidity, setting time and mechanical strength of AAS cement was studied. The hydration process and hydration products were used to explore the action mechanism. Ba(NO 3) 2 greatly delayed the hydration of AAS cement. The four inorganic salts (KCl, KNO 3 , KBr and NaCl) blended with a small amount of Ba(NO 3) 2 can improve both the initial fluidity and fluidity retention, and a wide setting time range can be obtained to meet engineering requirements. The compressive strength decreased with the increase of inorganic salts. The incorporation of inorganic salt did not change the composition of the main hydration products. Considering the fluidity required by construction, mechanical properties and the durability of structure, it is recommended to add 4%–5% KBr or KNO 3 blended with no more than 0.2% Ba(NO 3) 2 into AAS cement. [ABSTRACT FROM AUTHOR]

Near-neutral salt activated slag cement has better performance in environmental protection and shrinkage behavior than common sodium silicate -activated slag (AAS) cement. However, the growth of mechanical performance is too slow, which limits its application. Reactive MgO can improve early mechanical properties, while it may have different effects on the shrinkage due to changes in alkali-activators. Two near-neutral salts, sodium carbonate (SC) and sodium sulfate (SS), were selected to prepare AAS cement. The influence of reactive MgO on autogenous and drying shrinkages was studied. The hydration process and pore structure were assessed with hydration heat and nitrogen adsorption, respectively. The phase composition was evaluated by thermogravimetry (TG/DTG) and X-ray diffraction (XRD). The results indicate that the addition of reactive MgO increases the autogenous shrinkage of SC and SS activated slag. This is mainly due to accelerated reaction by reactive MgO. The drying shrinkage of AAS mortars activated with SC increases first and then decreases with the increase in reactive MgO. For SS activated slag, the more the reactive MgO used, the lower the drying shrinkage is observed. This is related to the effect of reactive MgO on pore structure and hydration products. When reactive MgO increases from 2% to 10%, the mesopore in SC activated slag increases at first and then decreases, while the SS activated slag group shows a constant decrease. Reactive MgO promotes the formation of hydrotalcite in SC activated slag, while AFt is found in SS activated slag. Hydrotalcite and AFt are crystalline products, which are beneficial to inhibit drying shrinkage. [ABSTRACT FROM AUTHOR]