Dual measurement mode rotational viscometer

Abstract A novel dual method concept to widen the viscosity measurement range of magnetic actuation and sensing based viscometer is presented. A phase slipping detection is used for high viscosities, while fluids with low viscosities are studied by applying a step-stress and detecting early stage strain oscillations. Developed dual mode concept was tested and verified by studying water-glycerol solutions with different concentrations. The results show that proposed method significantly improves the measurement capability of the rotational viscosity probe without increasing the overall cost of the system or compromising the advantages (non-contact, non-optical, disposable, hermetic measurements) of it

Alkali activation of ladle slag from steel-making process

Abstract Ladle slag, currently an under-utilized crystalline metallurgical residue, was studied for use as a precursor for alkali activation. An activating solution containing sodium silicate and potassium hydroxide was used in activating the slag with varying compositional ratios in order to optimize the compressive strength. Ladle slag is commonly regarded as having limited reaction with alkalis, and in previous studies, it has been therefore mixed with reactive precursors, such as metakaolin. However, based on our results, ladle slag shows potential as a sole precursor for alkali-activated binders. X-ray diffractometry reveals that the major minerals in the ladle slag were identified to be γ-dicalcium silicate and mayenite. After alkali activation, the major reaction product was a silicate hydrate according to DRIFT analysis–sodium-substituted calcium aluminosilicate hydrate gel, C–(N)–A–S–H. XRD analysis supports the hypothesis by revealing an amorphous “halo” in the alkali-activated slag. The unconfined compressive strength of the optimized alkali-activated ladle slag paste specimen was 65 MPa at 28 day

Properties and durability of alkali-activated ladle slag

Abstract This paper examines the durability of alkali activated ladle slag mortars. Ladle slag, currently an under-utilized crystalline metallurgical by-product, is a promising raw material for alkali activation. However, there is no information about the durability of this material. The aim of this study is to investigate the durability of the alkali activated ladle slag mortar and the effect of aggregate content on the properties. The mechanical strength tests were carried out at 7, 28, 56 and 90 days. In addition, the samples were subjected to drying shrinkage, freeze–thaw, and water absorption tests. Furthermore, the reaction products conversion related to the strength properties were also analysed through thermal analysis. Overall, significant strength and durability properties was attained and significantly influenced by the mix design

Rockwool waste in fly ash geopolymer composites

Abstract Mineral wool waste is often considered unrecyclable, due to its difficult-to-process physical composition, and potential microbial contamination in the post-consumer products. Total mineral wool waste generated in the EU is growing continuously and is currently over 2.3 Mt annually, volumetrically accounting for the largest single waste source in some landfills. Here, we take advantage of the alkali-soluble nature of the rockwool waste, and use a combined mixing and dissolution method to prepare this otherwise unusable waste for geopolymerization, with up to 33 % inclusion in the final product. This mixing and dissolution step enables sufficiently high solids content to form a castable geopolymer paste, which forms a rigid matrix and a compressive strength of 12.8 MPa, sufficient for structural applications. This is the first time mineral wool waste has been used as a geopolymer precursor. FESEM and XRD analysis of the formed products were performed to verify geopolymer formation. Using the preparation reported here, otherwise unrecyclable mineral wool waste can potentially be turned into a valuable raw material for geopolymer materials

Effects of activator properties and curing conditions on alkali-activation of low-alumina mine tailings

Abstract The mining industry generates a notable amount of mine tailings (MTs). Disposal of MTs creates environmental impacts such as air pollution and the release of heavy metals into surface and underground water. The European Union (EU)-funded project “Integrated mineral technologies for more sustainable raw material supply” (ITERAMS) includes an effort to produce eco-friendly backfill materials to enhance operation and mine safety and covers for surface deposits of tailings based on geopolymerization technology. This paper investigates the effects of activator concentration, curing temperature and time on alkali-activated materials based on low-alumina MTs from the Cu/Ni mine in Northern Finland. Alkaline activators containing sodium silicate solution (Na2SiO3) at different concentrations were used and two different curing temperatures, 40 °C and 60 °C, for periods of 7, 14, and 28 days were considered. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) were performed to investigate the structure, morphology and phase compositions of the alkali-activated products. The effect of curing temperature and alkaline solutions on mechanical strength and water absorption were investigated. The results indicate that the alkalinity and curing temperature affect the mechanical and microstructural properties of the compositions of alkali-activated MTs. The 30 wt% Na2SiO3 addition enables the alkali activated MT to improve the compressive strength with a highest value of 6.44 and 15.70 MPa after 28 days of curing at 40 °C and 60 °C, respectively. The results of this study deliver useful information for recycling and utilization of MTs as sustainable material through the alkali activation

Milling of peat-wood fly ash:effect on water demand of mortar and rheology of cement paste

Abstract The milling of fluidized bed combustion fly ashes is a promising method to improve ashes’ properties as a cement replacement material. Two fly ashes from the co-combustion of peat and wood, as well as inert sand were milled at varying times. The physical properties of materials, water demand of mortar and rheology of cement paste were studied. At 25% cement replacement rate, the milling decreased the water demand of mortar by 10% and the yield stress of cement paste by 33%. It was found that milling disintegrated irregularly shaped particles, which were the main reason for high water demand of ashes, and tapped density could be used as a simple parameter to estimate the water demand for all studied materials

Multi-fiber reinforced ettringite-based composites from industrial side streams

Abstract The development of high-performance cementitious composites from industrial side streams, which has both economic and environmental benefits, is of high demand. Ladle slag is a promising by-product from the steelmaking industry, which can form an ettringite-based binder. This experimental investigation focuses on the mechanical properties of different hybrid and mono fibers reinforced by ettringite-based binders from the ladle slag. The experimental results reveal that fibers greatly enhance the mechanical properties of the developed mixtures. The composites exhibit strain-hardening behavior with multiple cracks under flexural and tensile loading. In addition, the compressive strength of the composites can be 130% higher than the plain materials. To attain a balance between mechanical and economic aspects, a multi-criteria ranking method was used to evaluate 12 different mixtures. The ranking method suggests that a polypropylene micro fiber reinforced composite is the best mixture. The study recommends the efficient use of this industrial by-product for valuable applications in the construction industry

Utilization of green liquor dreg in lightweight aggregates:effect of texture on physical properties

Abstract Green liquor dreg (GLD) is a side stream generated by pulp industry. Due to its complex physicochemical nature, it has been reported to be difficult material to utilize. Here, a novel approach towards utilization of moist and dry green liquor dreg as binder and filler in alkali-activated lightweight artificial aggregates was developed. Dried GLD and moist GLD were granulated with blast furnace slag (BFS) and Bioash in different mixtures using alkali activation. The effect of the GLD nature (dried and moist) on strength, microstructure and durability of the lightweight granules were determined and compared. Results show that the method used in homogenizing the moist GLD and other powders was efficient and improved the frost resistance. The reaction product identified in the granule’s includes calcium silicate hydrate, Mg–Al layered double hydroxides, and ettringite. These results demonstrate the potential of GLD as a binder and fillers in cementitious applications

Improvement of mechanical strength of alkali-activated materials using micro low-alumina mine tailings

Abstract Low-alumina mine tailings (MTs) have shown the possibility of being a precursor in the production of alkali-activated materials (AAMs). The effects of the addition of sub-micron MTs (10 wt%) with the average size of 400 nm to improve the performance of AAMTs with alkali activator (10, 15, 20, and 30 wt% sodium silicate) were investigated by using X-ray diffractometry (XRD), Attenuated total reflection-Fourier-transform infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), and nitrogen adsorption technique (BET). The mechanical properties of the materials were also analyzed. The results indicate that the addition of sub-micron MTs to AAMTs plays an important role in mineral compositions and enhances the mechanical strength performance in comparison to plain AAMTs, especially after just 7 days of aging. This result is attributed to the different microstructure between AAMTs and sub-micron MTs. BET results showed that the addition of sub-micron MTs reduces the total porosity of alkali-activated products and changes the pore structure. The pores of AAMTs were refined by the filling effects of sub-micron particles and the enhancement of the hydration process due to the nucleation effect of those sub-micron particles. This could be a significant reason for the increase in early age mechanical strength. This work introduces a novel approach to improve the performance of tailings-based alkali-activated materials using nano-sized precursors

Immobilization of sulfates and heavy metals in gold mine tailings by sodium silicate and hydrated lime

Abstract Gold mining produces hazardous tailings wastes with elevated sulfur content and high levels of heavy metals including oxyanion elements such as V and As. This research investigated activation of these tailings with calcium hydroxide and sodium hydroxide/sodium silicate as a way to stabilize the material and limit leaching of harmful components. The effects of thermal treatment on the reactivity of the tailings and the use of different activating solutions on the physical properties, microstructure and leaching of harmful components are reported. The effect of adding ground granulated blast furnace slag to the tailings is also assessed. The use of 5 wt % Ca(OH)₂ activating solution produces optimum performance increasing the immobilization efficiency of sulfates, arsenic and the other harmful elements. Heat-treating mine tailings at 900 °C slightly improves the reactivity but did not improved the immobilization efficiency. Microstructural analysis by TEM and XRD confirmed that stabilization is based on calcium sulfate and/or ettringite formation during alkali-activation. All materials achieved reasonable compressive strength after 28 days of curing and the potential for using alkali activation as a method to treat tailings from mining is discussed