Activation of Blast Furnace Slag with CFB Fly Ash as a Supplementary Binder Material: Hydration Products and Effects of Sulfate Attack

Circulating Fluidized Bed (CFB) combustion is a clean technology for burning, with advantages of adapting to a large variety of fuel, high combustion efficiency, lower NOx emissions, and stable operation. The residue collected from the ash-hoppers of the electrostatic precipitator of the CFB boiler is called CFB fly ash. This paper presents the hydration development on the application of CFB fly ash to activating blast furnace slag (BFS) as a supplementary binder material (SBM) for replacement of Portland cement in making concrete. Investigation of the hydration products of cement pastes prepared with combinations of BFS and CFB fly ash were conducted by means of X-ray diffraction, thermal gravimetric analysis, and scanning electronic microscope. Test results show that the main hydration products of the CFB fly ash-BFS blended pastes were found to be hydrated calcium silicate (C-S-H), ettringite, gypsum, and some portlandite. Considering that CFB fly ash produced from the combustion of high-sulfur coke has high SO3 contents, the volume stability of mortar made from CFB fly ash-activated BFS was subjected to tests in accordance with ASTM C1012 and ASTM C1038 for evaluating the internal and external sulfate attack, respectively. The results indicate that, due to the high sulfur (SO3) content of CFB fly ash, the expansion caused by internal sulfate attack (ISA) increased with increasing proportion of CFB fly ash in the mixture. In contrast, no significant expansion was observed in the external sulfate attack (ESA) test, regardless of the proportion of CFB fly ash in the mixture. In order for the CFB fly ash to serve as a supplementary binder material and to maintain adequate volume stability, the amount of CFB fly ash used for the activation of BFS is recommended to be no more than 20% of the SBM.

Study on Mechanical and Microscopic Properties of Nickel–Copper-Contaminated Soil Solidified by Cement, Fly Ash and Desulfurization Gypsum Under Carbonization Condition

The engineering characteristics of remediated soil are easily affected by CO2 erosion in nature. However, there are limited investigations on the mechanical and microscopic properties of heavy metal-contaminated soil. This study introduces effect of accelerated carbonization on the mechanical and microscopic properties of nickel–copper-contaminated soil, and the soil has been treated with a novel curing agent, formed by mixing cement, fly ash and desulfurization gypsum (CFG). The objective of the study is to ascertain CO2 erosion resistance of nickel–copper-contaminated soil solidified by CFG. Using unconfined compressive strength (UCS) tests, carbonization depth, X-ray diffraction, and scanning electron microscopy, the sample’s characteristics are investigated under different carbonization times and heavy metal ion concentrations. The results demonstrate that the UCS of samples of Ni0Cu0, Ni0.02, and Ni0.4 decrease with the increasing carbonization time, while that of Ni1, Cu1, and Ni1Cu1 increase initially and then decrease; in addition, when the concentration of heavy metals is lower, the effect of carbonization on UCS of samples is more significant. Moreover, the carbonization depth of samples increases with the increasing carbonization time, and the prediction model is given. Furthermore, the microscopic analysis demonstrates that calcium carbonate is the main carbonization product. The decomposition of hydrated calcium silicate gel leads to poor integrity of the structure and more pores produced in samples, which is the main reason for the decrease of the UCS in the process of carbonization. The outcomes of this investigation provide a reference for the durability in practical engineering of heavy metal-contaminated soil solidified by CFG.

Modified Composite Fine-Grained Concrete

The paper presents the findings of the experimental investigation conducted to identify the effect of composite admixtures including a plastifying agent and soot production wastes on the proper-ties of fine grained concrete. The joint effect of the cement and sand matrix and soot wastes was investigated, too. The investigation identified the effect the complex admixture of a plastifying agent and soot wastes on structure formation, physical, mechanical properties and strength of the fine grained concrete. It was found that the micro particles of soot wastes concentrate the grains of the quartz sand around them as well as the products of the new formation of cement stone such as hydrated calcium silicate and others. This ensures a higher density of micro structure and increased strength of the fine grained concrete.

SPECIFIC FEATURES OF THE FORMATION OF THE MICROSTRUCTURE OF GRANULAR AGGREGATES ON DIFFERENT BINDING COMPOSITIONS (PART 2)

This article is a continuation of the previous research. It includes analysis of the formation of the structure of granular aggregates during the hydration of the binder composition of BC-2 (PC 500-D0-N + 20 % quartz sand), prepared in a jet vortex mill. The study reveals the features of the dispersion of the quartz mineral filler (fractions ≤0.16; ≤0.315; ≤0.63 mm) and the main patterns of influence on structure formation at hydration of binders, differing in the composition and dispersion of particles. The paper analyzes physical and mechanical tests of the samples with the best strength characteristics and studies the features of their microstructures. The study of the microstructures of the samples reveals regularities, consisting in the formation of crystalline phases of different densities. It is noted that the introduction of 20 % mineral finely dispersed filler into PC 500-D0-N, in the form of quartz sand, ensures the formation of dense sub-microcrystalline hydrate phases when using a filler fraction ≤0.63 mm, which contributes to an increase in the additional strength of the samples by more than 20 %. It has been found that the mineral filler plays the role of crystallization centers, binding individual grains of fillers and sealing general structure of the composite. More compact healing of the pore space has been established for the composite with small crystalline new formations of hydrated calcium silicate

THE STUDY OF THE PROPERTIES AND STRUCTURE OF CEMENT BINDING COMPOSITION ON ELECTROLYTE ACQUEOUS SOLUTIONS ACTIVATED BY MECHANOMAGNETIC METHOD

In the present paper, the issues of studying the influence of complex activation of grouting fluid on the structure and properties of the hardened cement paste and concrete are considered. The problem is relevant for manufacturing of building materials. In the paper, there was used the method of applying in the concrete mix composition of the elementary chemical substances undergone special physical treatment by means of mechanomagnetic activation. For more profound study of the structure formation processes in the hardened cement paste, the method of differential thermo gravimetric analysis has been used. As the research results have shown, the concrete samples on the activated electrolyte solutions are characterized by improved strength. In addition, on the base of differential thermo gravimetric analysis, it was proven that in the studied samples of the hardened cement paste on the electrolyte solutions activated by the method of mechanomagnetic treatment, the less calcium hydroxide and the more hydrated calcium silicate with amorphous and fine crystalline is formed. The obtained results for cement composites could be applied when manufacturing effective binder for concretes and mortars in the production of building materials and structures.

Role of Promaxon-D in Controlling Tribological Performance of Cu-Free Brake Pads

Copper appears to be an indispensable ingredient of non-asbestos organic (NAO) brake friction materials owing to its multifunctionality. However, recent findings proved it as a threat to aquatic life and efforts were initiated worldwide over the last few years to find a substitute for it. Recently, the authors’ group had reported on the potential of particulate Promaxon-D (hydrated calcium silicate), a porous material for enhancement of noise–vibration (NV) performance of Cu-free brake pads. It was felt necessary to investigate how Promaxon-D (PD) contributes to controlling tribo-performance of brake pads since this aspect is most important for the brake friction materials. A series of five types of brake pads was developed by keeping parent composition fixed and varying the theme ingredient PD content from 0–20 wt.%. The tribo-performance was evaluated on a full-scale brake inertia dynamometer as per the JASO C406 test standards. The increase in PD contents led to a reduction in density, hardness, and thermal conductivity while an increase in porosity and compressibility. With the increase in PD contents, almost all tribo properties such as average μ, fade ratio, and recovery ratio got enhanced, sensitivity of µ for pressure, speed, and temperature lowered but at the cost of wear resistance. Finally, the worn surfaces of pads and discs were observed under a scanning electron microscope equipped with energy dispersive X-ray (SEM-EDX) to find out the presence of various elements at the contact zone and to monitor specific topographical events responsible for wear mechanism.

Adsorption of Lead Ion from Wastewater Using Non-Crystal Hydrated Calcium Silicate Gel

In order to obtain low-cost and excellent adsorption materials, this paper used calcium acetate and water glass as raw materials to synthesis hydrated calcium silicate gel by precipitation method. The performance and structure of hydrated calcium silicate gel were systematically studied by X-ray photoelectron spectroscopy, fourier transform infrared spectroscopy, specific surface area analyzer and scanning electron microscope. Studies have shown that, non-crystal hydrated calcium silicate gel (CSH) were successfully prepared, and the removal rate of lead ion using CSH reached more than 90%. The adsorption process is consistent with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, and the limit adsorption capacity reaches 263.17 mg·g−1. The acid treatment experiment proved that the adsorption capacity of lead ion using CSH was satisfactory, and the adsorption rate remained at >60% after 5 cycles. The research may provide a low-cost, high-efficiency and high stability adsorbent.

Silica extraction from bauxite reaction residue and synthesis water glass

Bauxite reaction residue (BRR) produced from the poly-aluminum chloride (PAC) coagulant industry is a solid acidic waste that is harmful to environment. A low temperature synthesis route to convert the waste into water glass was reported. Silica dissolution process was systematically studied, including the thermodynamic analysis and the influence of calcium and aluminum on the leaching of amorphous silica. Simulation studies have shown that calcium and aluminum combine with silicon to form hydrated calcium silicate, silica–alumina gel, and zeolite, respectively, thereby hindering the leaching of silica. Maximizing the removal of calcium, aluminum, and chlorine can effectively improve the leaching of silicon in the subsequent process, and corresponding element removal rates are 42.81%, 44.15%, and 96.94%, respectively. The removed material is not randomly discarded and is reused to prepare PAC. The silica extraction rate reached 81.45% under optimal conditions (NaOH; 3 mol L−1, L S−1; 5/1, 75°C, 2 h), and sodium silicate modulus (nSiO2:nNa2O) is 1.11. The results indicated that a large amount of silica was existed in amorphous form. Precipitated silica was obtained by acidifying sodium silicate solution at optimal pH 7.0. Moreover, sodium silicate (1.11) further synthesizes sodium silicate (modulus 3.27) by adding precipitated silica at 75°C.

A new type of inorganic binder curing agent for soft soil

Aiming at the defects of traditional curing agent in strengthening soft clay, a new type of inorganic binder type soil curing agent has been developed. Compared with P.O 42.5 cement, the new soil stabilizer has smaller fineness and larger specific surface area. The strength of the soil solidified by the new curing agent is lower at the initial stage, but it increases rapidly after 24 hours. When the dosage is 10%, the 28-day strength of the soil solidified by the new curing agent is 2.1 times that of the soil solidified by cement. The soil solidified by the new curing agent can form more calcium hydroxide crystals and hydrated calcium silicate gel with more compact structure. After solidification, there are fewer fine particles in the soil.