L-band ATS 5/Orion/S. S. Manhattan marine navigation and communication experiment Final report

L-band signals relayed by synchronous satellite for navigation and data communicatio

Evidence of formation of an amorphous magnesium silicate (AMS) phase during alkali activation of (Na-Mg) aluminosilicate glasses

There is some ambiguity regarding the fate of Mg during the alkali activation of Mg-rich precursors within the broader field of alkali activated materials (AAMs). The present work addresses this issue by studying the reaction products in AAMs synthesized from (Na-Mg) aluminosilicate glasses. Here, instead of magnesium silicate hydrate (M-S-H) phase, Mg exclusively forms an amorphous magnesium silicate (AMS) phase. Compared to M-S-H, AMS is a more depolymerized phase, which has not previously been well documented. The formation of AMS seems to be driven by the high charge density of the Mg cation which effectively stabilizes the depolymerized silicate species. We also show that the lack of hydrotalcite-group phases is due to aluminum depletion by zeolite formation. This work highlights the need to consider the existence of the AMS phase in Mg-containing AAMs, especially in complex systems, where its identification may be difficult

Durability of alkali-activated Fe-rich fayalite slag-based mortars subjected to different environmental conditions

Fe-rich alkali activated materials (AAMs) require detailed understanding of their durability prior to their real-life application in the construction industry. Three mixes were formulated with fayalite slag (FS) as the main precursor. The effect of incorporation of ladle slag (LS) or blast furnace slag (BFS) on the shrinkage and exposure to physical and chemical attacks representing environmental conditions in cold and tropical regions (acidic solution at room temperature and in freeze-thaw, combined sodium sulfate and sodium chloride solution at room temperature and in freeze-thaw, freeze-thaw in water and dry-wet cycles) was investigated via visual observation, mass loss, compressive strength, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS). Experimental results show the considerable role of incorporated LS and BFS in modifying the gels formed and controlling material degradation of blended AAMs after exposure. In contrast, sole FS-based samples were completely degraded particularly those exposed to freeze-thaw in water, acid, and combined sodium sulfate and sodium chloride solution, indicating their vulnerability to frost and chemical attacks

Field strength of network-modifying cation dictates the structure of (Na-Mg) aluminosilicate glasses

Aluminosilicate glasses are materials with a wide range of technological applications. The field strength of network-modifying cations strongly influences the structure of aluminosilicate glasses and their suitability for various applications. In this work, we study the influence of the field strength of network-modifying cations on the structure of [(Na2O)1–x(MgO)x(Al2O3)0.25(SiO2)1.25] glasses. Due to the higher cation field strength of magnesium than sodium, magnesium prefers the role of network modifier, while sodium preferentially acts as a charge compensator. When magnesium replaces sodium as network modifier, Q3 silicon species are converted into Q2 species. The replacement of sodium with magnesium as charge compensator leads to the following changes: (1) the proportion of aluminum-rich Q4 species [Q4(4Al) and Q4(3Al)] decreases, while the proportion of aluminum-deficient Q4 species [Q4(2Al) and Q4(1Al)] increases; and (2) there is an increased tendency for phase separation between silica-rich and alumina-rich glasses

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

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

Mechanical transformation of phyllite mineralogy toward its use as alkali-activated binder precursor

Abstract The mechanical activation of phyllite for use as an alkali-activated material was studied. Prolonged milling of phyllite resulted in reduced particle size and a structural reorganization of the material, leading to incremental increases in amorphous content, which further resulted in the improved reactivity of phyllite in an alkaline environment. Quantitative X-ray diffraction results showed that the phyllite consisted of quartz, muscovite, chamosite, albite, and X-ray amorphous phases. Among the crystalline phases, muscovite and chamosite underwent the most structural reorganization, leading to a more disordered structure due to prolonged and intensive milling. The structural reorganization was also established through Fourier-transform infrared spectroscopy. Dissolution tests in 6 M NaOH showed incremental increases in leached Al and Si elements with increased milling time. After geopolymerization of mechanically activated phyllite, calorimetric studies showed exothermic reactions, and a 28-day compressive strength of 25 MPa was achieved for paste samples cured at room temperature. This study ascertained the potential utilization of phyllite mineral waste in sustainable cement applications

High-temperature performance of slag-based Fe-rich alkali-activated materials

Abstract Fe-rich alkali-activated materials have been studied for their suitability for high-temperature application up to 1000 °C. The evolution of compressive strength, mineral composition and microstructure was monitored using FT-IR, XRD, TGA and SEM-WDS for the pastes and mortars obtained by alkali activation of fayalite and wüstite non-ferrous slags. For both binders, the changes in compressive strength revealed moderate fluctuations below 400 °C due to water evaporation, a sharp drop in strength to 25 MPa at 600 °C due to collapse of the original gel structure, and reinforcement of the strength above 600 °C due to sintering densification and formation of gehlenite-åkermanite or diopside-albite ceramic. An extensive reaction of the quartz aggregate with a sodium-rich binder resulted in the formation of an iron silicate phase that contributed to a further increase in the strength up to 70 MPa by increasing both temperature and time of heating

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