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The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio. [ABSTRACT FROM AUTHOR]

This paper investigated rheological behavior and leakage plugging effect of alkali-activated slag (AAS) with the aim of promoting plugging application of slag resources. A series of laboratory tests were carried out to study effects of different activator concentrations (i.e. 1, 2, and 3 mol/L) and temperatures (i.e. 20, 30, and 40 °C) on time-dependent rheological properties (i.e. yield stress, apparent viscosity, and thixotropy) of AAS paste, which was made from ground granulated blast furnace slag (GGBS) and sodium hydroxide activator. The temporal variations in hydration process of AAS paste were examined and analyzed using X-ray diffraction (XRD) and scanning electron microscope (SEM). Moreover, the plugging effect of AAS paste was investigated by tunnel leakage plugging test. The test results indicate that the shearing behavior of AAS paste could reasonably be described by Bingham plastic model. There was a great increase in yield stress, apparent viscosity, and thixotropy of AAS paste with an increase in activator concentration and temperature. The increase in those rheological properties were mainly attributed to the rapid formation of C-S-H gels and aluminum hydroxide magnesium at a higher concentration level and temperature. In addition, a power function was proposed to fit the time-dependent apparent viscosity, which enabled the explicit quantification of activation energy, i.e. the minimum energy required to initiate the hydration of AAS paste. In leakage plugging test, the characteristic of decreasing with the increase of exciter concentration and temperature was seen in both the point of water pressure and the time required to reach 0.5 MPa sealing water pressure. [ABSTRACT FROM AUTHOR]

The effects of steel slag (SS) and fly ash (FA) on hydration heat, fluidity, setting time and rheological properties of alkali-activated slag (AAS) pastes with different silicate modulus (Ms) values were comparatively investigated. The results show that the incorporation of SS shortens the induction period, increases the cumulative hydration heat, improves the initial fluidity and decreases the setting time at low Ms, but the opposite trend is found at high Ms. FA significantly retards the reaction, reduces the hydration heat, increases the fluidity and prolongs the setting time. The addition of SS or FA reduces the yield stress and plastic viscosity of AAS paste. SS improves the rheological properties of AAS paste more significantly than that of FA at high Ms. The yield stress and plastic viscosity of AAS paste with SS or FA rise with the increasing Ms and decline with the increasing water/binder (w/b) ratio.

This study investigated the properties of alkali-activated slag (AAS) pastes with NaOH and a blend of NaOH and Na 2 CO 3 as the alkaline activator. The effects of five different Na 2 CO 3 to NaOH molar ratios (0:10, 0.9:10, 2.5:10, 5.7:10 and 15:10) and three different Na 2 O contents (4%, 6% and 8%) in the alkaline activator on the setting time, mechanical performance and drying shrinkage were tested. The water to slag ratio was 0.35 by weight. The results showed that both the Na 2 CO 3 to NaOH molar ratios and Na 2 O contents are major factors influencing the fresh and hardened pastes. Higher Na 2 CO 3 to NaOH molar ratios yielded a longer setting time and higher compressive strength. The Na 2 O content of 6% was more sensitive to the properties compared with 4% and 8% Na 2 O. When the Na 2 O content was 4%, the drying shrinkage increased as the Na 2 CO 3 to NaOH molar ratio increased; however, when the Na 2 O content increased to 6% and 8%, the drying shrinkage decreased as the Na 2 CO 3 to NaOH molar ratio increased. The main hydration products were C-S-H(I), hydrotalcite, calcite and gaylussite. There was a strong relationship between the drying shrinkage and pore structures of AAS. Consequently, the Na 2 CO 3 to NaOH molar ratio of 15:10 and Na 2 O content of 6% can be regarded as the optimum mix proportion. [ABSTRACT FROM AUTHOR]

Alkali-activated slag (AAS) binders-based composites are considered potential alternatives to conventional cement-based composites. However, the quasi-brittle mechanical behavior of AAS binders-based composites limits their widespread application. In this study, a graphene oxide-SiO 2 (GO-SiO 2) composite was produced to address this issue. The experimental results showed that the flexural strength of an AAS paste increased by 133.2% with 1.5 wt% GO-SiO 2 composite, and its corresponding flexural-to-compressive strength ratio increased 95% i.e. from 0.063 to 0.123. To explore the strengthening mechanism, the stability of the GO-SiO 2 composite in alkaline solutions and the dispersion effect of GO-SiO 2 composite on the mechanical properties of AAS paste were investigated. The experimental results showed that the prepared GO-SiO 2 composite had stable C–O–Si chemical bonds connected GO with hydration products, thereby improving the strength of the AAS paste. The molecular dynamics study revealed the mechanism that the high-dispersed GO-SiO 2 composite could improve the mechanical properties of the AAS paste dramatically. • The prepared GO-SiO 2 composite exhibited excellent dispersibility in an alkaline solution. • The stability of the C–O–Si chemical bond in the GO-SiO 2 composite was investigated. • Flexural strength of alkali-activated slag paste increased by 133.2% for the GO-SiO 2 modification. • Mechanisms of AAS paste reinforced by the GO-SiO 2 composite were clarified. [ABSTRACT FROM AUTHOR]

In this paper, we investigate which factor for a sodium silicate-based activator influences the setting time of alkali-activated slag (AAS) paste. Several factors, such as the pH value of the activator, the alkali modulus (AM) and the alkali activator dosage, were evaluated when the liquid/slag ratio was kept constant. It was found that the pH value and the AM have a strong relationship, however, they have no distinct relationship with the setting time. The activator dosage, which is defined as the sum of the SiO2 and Na2O concentrations, shows a significant trend with the setting time. It was also found that the influence of SiO2 on the setting time is more apparent than that of Na2O. Increasing amounts of SiO2 decrease the pH value of the activator and increasing amounts of Na2O increase the pH value of the activator. Phosphoric acid, used as a retarder, was found to have a strong retarding effect. [Copyright &y& Elsevier]