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This study presents an investigation of the effects of the precursor, alkalinity and temperature on the rheology and structural buildup of alkali activated materials. Here, 100% fly ash, 100% slag and blended mixes of fly ash and slag were activated by 4 M, 6 M, 8 M or 10 M (only for sodium hydroxide) solutions at 25 °C, 35 °C, 45 °C and 55 °C. The rheological properties were investigated to obtain the flow curves, viscosity, storage modulus, and loss factor of these materials. The results showed that for the presence of slag, a higher molarity of the alkali activating solution and a high temperature all caused greater interparticle force, leading to an increase in the shear stress and viscosity of the alkali activated materials. It was also observed that slag had the greatest effect on the increase in the storage modulus of the blended mixes. Furthermore, the higher alkalinity and temperature levels were instrumental in initiating the dissolution of fly ash and improving its rate of structural buildup. Moreover, the interdependence of various factors showed that the type of precursor, as well as the concentration of alkali activating solution, were the primary influencing factors on the polymerization process, as well as the rheological measurements of alkali-activated materials. [ABSTRACT FROM AUTHOR]

This study assesses the characteristics of preplaced aggregate concrete prepared with alkali-activated cement grout as an adhesive binder. Various binary blends of slag and fly ash without fine aggregate as a filler material were considered along with different solution-to-solid ratios. The properties of fresh and hardened grout along with the properties of hardened preplaced concrete were investigated, as were the compressive strength, ultrasonic pulse velocity, density, water absorption and total voids of the preplaced concrete. The results indicated that alkali-activated cement grout has better flowability characteristics and compressive strength than conventional cement grout. As a result, the mechanical performance of the preplaced aggregate concrete was significantly improved. The results pertaining to the water absorption and porosity revealed that the alkali-activated preplaced aggregate concrete is more resistant to water permeation. The filling capacity based on the ultrasonic pulse velocity value is discussed to comment on the wrapping ability of alkali-activated cement grout. [ABSTRACT FROM AUTHOR]

• Oyster shell waste was calcined to produce an environmentally friendly and economical solid activator. • Production of one-part alkali-activated slag with calcined oyster shell was extensively studied. • Improved mechanical properties and microstructural characteristics were observed. • Calcined oyster shell powder at excessive dosages induced a negative effect. This study focuses on an environmental friendly, non-corrosive and non-viscous activator during the production of one-part alkali-activated slag using calcined oyster shell (COS) powder. Test results demonstrate improved mechanical and microstructural characteristics for specimens prepared with COS powder as an activator. The highest increment in the strengths was revealed with a 5% COS addition due to the resulting enhanced pore refinement, whereas an excessive dose resulted in a delayed rate of C-S-H formation and a significant amount of large capillary pores, thus decreasing the strength. The mineralogical and microstructural properties of the paste were also analyzed, and these findings revealed that COS powder is suitable for use as an activator to produce one-part alkali-activated materials. [ABSTRACT FROM AUTHOR]

The solidification and stabilization of calcium carbide residue (CCR) using granulated blast furnace slag was investigated in this study. CCR binding in hydrated slag was explored by X-ray diffraction, 29Si and 27Al magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy, and thermodynamic calculations. Mercury intrusion porosimetry and and compressive strength tests assessed the microstructure and mechanical properties of the mixtures of slag and CCR. C-A-S-H gel, ettringite, hemicarbonate, and hydrotalcite were identified as the main phases in the mixture of slag and CCR. The maximum CCR uptake by slag and the highest volume of precipitated solid phases were reached when CCR loading in slag is 7.5% by mass of slag, according to the thermodynamic prediction. This feature is also experimentally observed in the microstructure, which showed an increase in the pore volume at higher CCR loading. [ABSTRACT FROM AUTHOR]

The effect of carbonation on the abrasion resistance of alkali-activated slag (AAS) was investigated. Various activator sets were selected for synthesizing AAS specimens, and the compressive strength was measured before and after carbonation. The abrasion resistance of the specimens was measured in accordance with the ASTM C944 test method. The relationship between the mass loss caused by abrasion and compressive strength was analyzed to understand the effect of matrix strength on abrasion resistance. Test results showed that the decrease in compressive strength of AAS specimens by carbonation reduced their abrasion resistance. In addition, the abrasion resistance of AAS before and after carbonation was sensitively influenced by activator type. It can be concluded that additional caution is required when using AAS where abrasion may have occurred. [ABSTRACT FROM AUTHOR]

• The effect of sillimanite sand on the properties of AAS mortar at elevated temperatures was investigated. • The strength properties of AAS mortar improved by substituting the silicious normal sand with sillimanite sand. • The compressive strength of AAS mortar prepared using sillimanite sand improved up to the 250 °C exposure. • Sillimanite sand significantly reduced the cracks on the surface of AAS mortar after being exposed to elevated temperatures. The change in the properties of fine aggregate has significant potential in altering the efficacy of alkali-activated slag. Therefore, this study investigated the influence of sillimanite sand on the mechanical and microstructural properties of alkali-activated slag (AAS) mortar at ambient temperature, and after exposure to elevated temperatures (250, 500, 750, and 1050 °C). In addition, the effect of the concentration of sodium hydroxide solution (6, 8, 10, and 12 M) was evaluated. The silicious normal sand was replaced with sillimanite sand at 25, 50, 75, and 100 % by volume. The results show that the superior physical properties of sillimanite sand improved the strength of the AAS mortar, compared with silicious normal sand. After heating at 250 °C, all AAS mortar mixes showed a significantly higher increase in compressive strength compared to unheated samples. Utilization of the largest concentration of sodium hydroxide solution (12 M) as well as sillimanite sand resulted in a residual compressive strength equivalent to the control sample after 500 °C temperature exposure. A significant drop in residual compressive strength was observed for all mixes at 750 °C. Visual observation of the heated samples revealed that casting the mortar samples with sillimanite sand limited the number, width and extent of thermal cracks. XRD analysis revealed the decomposition of C-S-H and the formation of silica oxide at 750 °C. The results of this study suggest that replacing silicious normal sand with sillimanite sand can help the modification of the engineering properties of AAS mortar at ambient temperature, and after exposure to elevated temperatures. [ABSTRACT FROM AUTHOR]