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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]

• Effective foam ratio is put forward to express stability of foam in paste slurry. • Pore size and distribution greatly affect physical and mechanical properties. • Foam stability is the main factor affecting pore structure of AAS foamed concrete. • AOS can be preferred to prepare AAS foamed concrete. Alkali-activated slag cement has the characteristics of high viscosity, quick hydration, setting and hardening, and high strength, which are suitable for the preparation of foamed concrete. Three foaming agents of sodium α-olefin sulfonate (AOS), sodium dodecyl sulfate (K12) and sodium alcohol ether sulphate (AES) with the same foam stabilizer of silicone resin polyether emulsion FM-500 (MPS) were used to prepare foam. The three foam properties are similar and foam stability of AOS and K12 is better than that of AES. Effective foam ratio is put forward to express stability of foam in paste slurry. Effective foam ratio and porosity has a great effect on dry apparent density of water glass-activated slag foamed concrete. With the increase of foam content, effective foam ratio of AES decreases obviously, while that of K12 and AOS show a slight decrease. At low foam content, AES can better reduce the dry apparent density. Increase foam content of AOS and K12 appropriately may reduce dry apparent density. R sd and compressive strength of foamed concrete with AOS foam is the highest. When porosity is similar, average pore size and pore size distribution has a great effect on thermal conductivity and mechanical properties of AAS foamed concrete. Average pore size of O3 is smaller than that of K3 and E3. O3 also shows the narrowest air-void size distribution with the majority of the voids smaller than 400 μm. Average roundness of three type foam is much the same. Foam stability is the main factor affecting pore structure of AAS foamed concrete. AOS can be preferred to prepare AAS foamed concrete. [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]

• The negative hydration of inorganic salt ions is used to regulate the properties. • The inorganic salt improves the fluidity and setting time of AAS paste. • The inorganic salt makes the ζ-potential of AAS suspension more negative. • The inorganic salt deceases the yield stress and plastic viscosity of AAS paste. Alkali-activated slag (AAS) cement is a low-carbon environmentally friendly cementitious material. Water glass (WG) activated slag cement has excellent physical and mechanical properties, but it is not conducive to the construction due to its rapid setting and hardening, easy loss of fluidity. Negative hydration ions can reduce the viscosity of aqueous solution. So, in the present paper, inorganic salt composed of negative hydration ions were used to adjust the fluidity and setting time of AAS paste. The results show that with the increase of NaCl, KCl, KBr and KNO 3 , the initial fluidity of AAS paste increases slightly, and the 30 min fluidity increases a lot, while the fluidity at 60 min is greatly affected by the amount of inorganic salt. KNO 3 shows the greatest initial fluidity increase. When 0.2% Ba(NO 3) 2 is added with other four inorganic salts, the fluidity retention is significantly improved, especially the fluidity of 60 min. When 5% NaCl, KCl, KBr and KNO 3 respectively mixed with 0.2% Ba(NO 3) 2 are added, the fluidity retention of AAS paste at 60 min are 97.4%, 92.7%, 100%, 82.5% respectively. Compared with the AAS paste without inorganic salt, when 5% NaCl, KCl, KBr and KNO 3 respectively blended with 0.2% Ba(NO 3) 2 are added, the initial setting time increase by 228.6%, 285.7% 307.1% and 239.3%, while the final setting time increase by 175.6%, 222.0%, 231.7% and 178.0% respectively. With the inorganic salt, the ζ-potential of the originally negative AAS cement suspension become more negative, both yield stress and plastic viscosity coefficient decease, especially the plastic viscosity coefficient greatly reduces. This may be the reason for the change of fluidity and setting time of AAS paste. [ABSTRACT FROM AUTHOR]