The article deals with research into the possibilities of creating a material that would be a combination of SEP with alkali-activated systems, which today are referred to as geopolymers. SEPs are ...secondary energy wastes, which are referred to as fly ash, slag and products of flue gas desulfurization technology. Geopolymers are complex composites whose binder component consists of aluminosilicates in combination with alkaline activators.
A simple process to produce sodium silicate powder from glass cullet has been developed. A mixture of glass powder, sodium hydroxide powder, and water was heated at temperatures of 150 to 330 °C. The ...effects of glass to NaOH ratio, temperature and duration, inclusion of water and fineness of NaOH were investigated. Fly ash and fly ash/GGBS blends were the precursors for alkali activated binder (AAB) mortars produced with this sodium silicate. Compressive strengths were similar to or better than those obtained with commercially available sodium silicate and sodium hydroxide solutions. FT-IR tests suggested that the reactivity of the glass derived sodium silicate powder was related to the number of non-bridging oxygen atoms in the silicate structure. Cost comparison between AAB and Portland cement concretes gave similar results for normal strength concretes (35 MPa). AAB concretes with higher strengths (50 and 70 MPa) can be cheaper than equivalent traditional concrete.
The effects of some admixtures, including silica nanoparticles, silica fume and Class F fly ash, on different properties of high performance self compacting concrete (HPSCC) were studied. A fraction ...of Portland cement was replaced by different fractions of pozzolanic admixtures in order to reduce cement content. The rheological properties of fresh concrete were observed through slump flow time and diameter and V-funnel flow time. The thermal properties were studied by TGA and transport properties by water absorption, capillary absorption and chloride ion penetration tests. The results indicated that increasing fly ash content improves the rheological properties of HPSCC and that mechanical and transport properties improved in the mixtures containing admixtures, especially the blend of silica nanoparticles and silica fume. It was also concluded that a higher amount of mineral admixtures combined with small fractions of nanopowders could be promising for the production of high performance concrete as a key material along with energy savings in construction and building technology.
The API method was developed as a test method to rapidly evaluate the pozzolanic activity of fly ash. It was indicated that the quality range defined by the mortar activity index at 28 days and 91 ...days can be evaluated in two days for low CaO type fly ash with CaO content of 10% or less. The physicochemical properties of fly ash were evaluated and the solid and liquid phases obtained by the API method were analyzed to clarify the mechanism of the reaction occurring in the API method and to show the similarity with the mechanism of strength development of mortar.
•Pozzolanic activity of fly ash can be determined in two days by the proposed API method.•Reaction mechanism in suspension of API method is similar to that in mortar and concrete.•Round-robin tests against API methods proved the high reliability of the assessment procedure.
Fly ash (FA) from lignite coal combusted in different Thermal Power Plants (TPPs) was used for the synthesis of zeolites (FAZs) of the Na-X type by alkaline activation via three laboratory ...procedures. FAZs were characterized with respect to their morphology, phase composition and surface properties, which predetermine their suitability for applications as catalysts and adsorbents. FAZs were subsequently modified with metal oxides (CuO) to improve their catalytic properties. The catalytic activity of non-modified and CuO-modified FAZs in the total oxidation of volatile organic compounds was investigated. FAZs were studied for their potential to retain CO
, as their favorable surface characteristics and the presence of iron oxides make them suitable for carbon capture technologies. Thin films of FAZs were deposited by in situ crystallization, and investigated for their morphology and optical sensitivity when exposed to pollutants in the gas phase, e.g., acetone. This study contributes to the development of novel technological solutions for the smart and valuable utilization of FA in the context of the circular economy and green energy production.
In this article, the effects of raw materials’ composition on fresh behavior, reaction kinetics, mechanical properties and microstructure of alkali activated slag–fly ash–limestone blends are ...investigated. The results indicate that, with the increasing content of fly ash and limestone, the slump flow increases. The setting times are shortened when increasing the slag content, while both fly ash and limestone show a negligible influence. The reaction process is slightly accelerated by the presence of limestone due to the extra provided nucleation sites, but the reaction process is mainly governed by the slag. The slag content exhibits a dominant role on strength in this ternary system, while for a constant slag content, the compressive strength increases with the increasing limestone content up to 30%. The microstructure analysis shows that the gel characteristics are independent of the limestone powder content. The presence of limestone in initially high Ca and Al conditions does not lead to the formation of additional crystalline phases, which is different from Portland cement systems. Both physically and chemically bound water contents are slightly increased when limestone powder is incorporated.
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•Two industrial dyes are simultaneously removed using a fly-ash–TiO2 composite.•The adsorption kinetics depends on the dyes molecular structure and flexibility.•The azo dye removal ...involves parallel adsorption and photocatalysis mechanisms.•The anthraquinone dye removal involves concurrent adsorption and photocatalysis.
A novel composite was obtained in mild hydrothermal conditions using fly ash, TiO2 and a cationic surfactant (HTAB). The components were involved in extensive re-structuring processes, evidenced by XRD, FT-IR, SEM, AFM, BET and surface energy measurements. The composite was used as adsorption substrate and as photocatalyst for the simultaneous removal of two commercial dyes (Bemacid Red, BR; Bemacid Blue, BB). The experimental tests were run at the natural pH of the suspension, which was alkaline (pH 10.6). In the experimental conditions electrostatic interactions due are less extensive, and the data can be directly linked to the substrate’s morphology and dyes molecular structure and size. It was found that adsorption efficiency is strongly influenced by the micro-pores on the substrate and the kinetics mainly depends on the dyes flexibility. For the azo dye (BR), photocatalysis was found to run independent from adsorption while for the anthraquinone dye (BB) the process proves to be more complex. Under UV irradiation, the removal efficiencies reached after 240min were of 93% for BR and of 77% for BB.
A machine learning technique provides rapid access to various information models, approaches, complex systems, and algorithms. In the present scenario the artificial neural network, multiple linear ...regression, support vector machine, water cycle algorithm, and linear regression have much accessible. Continuously advancements of these techniques become a high impact on civil engineering, especially for the construction and infrastructure sector. In the present study, the historical perspective of research and development and application of machine learning techniques on fly ash-based concrete is presented. The models, algorithms, and approaches developed for predicting engineering properties of fly ash-based concrete were also discussed. These predictions using machine learning techniques have been much impacted on fly ash utilization in concrete. The utilization of fly ash in concrete also has revolutionary impacts on the environment and human health in the future. Machine learning is a useful and powerful technique that can predict concrete engineering properties and represent the scientific challenge in the construction and infrastructure sectors.
Na2SO4 (NS)-activated slag as a kind of alkali-activated slag (AAS) had great development potential in low carbon cementitious materials field, because NS could be obtained from natural resources ...with much lower CO2 emissions than NaOH and water glass. However, the main issue was its slower strength development at both early and later ages. With intention to mitigate this problem, ultra-fine slag was used, and the increased CO2 emissions caused by ultra-fine slag expected to be balanced by the use of fly ash (FA). In the present study, NS-activated ultra-fine slag/FA was designed. Effects of NS dosage and FA content on the compressive strength were researched, and the activated process was assessed by chemical shrinkage, XRD, TGA, pH value, ion concentration, NMR, and SEM. Finally, CO2 emissions were evaluated. Results showed that compressive strength of slag with D50 = 3.1 μm activated by 4% Na2O-E of NS reached 36.2 MPa and 77.3 MPa at 28 d and 90 d age. The main hydrates of NS-activated slag were ettringite and C-(N)–S–H. Moreover, in the NS-activated ultra-fine slag/FA mortars, 20% FA significantly reduced the 3 d compressive strength, but slightly increased the 28 d compressive strength. CO2 emissions of this blend seemed much lower than that of NaOH or water glass-activated slag. These results suggested one alkali-activated binder with low carbon emissions.
•Slag with D50 = 3.1 μm was efficiently activated NS at ambient temperature.•The increase in NS accelerated the production of C–N–S-A-H and ettringite.•Strength of slag with 20% FA could reach 41.5 MPa and 60.8 MPa at 28 d and 90 d age.•CO2 emissions of NS-activated slag/FA was lower than that of the common AAS system.
In this study, the autogenous and drying shrinkage of alkali activated fly ash (AAFA) pastes prepared with different contents of sodium silicate solution are reported. A higher amount of both Na2O ...and SiO2 resulted in a larger autogenous and drying shrinkage. Although a large autogenous shrinkage was obtained during the first 1–3days, cracking was not observed in the ellipse ring tests. In AAFA pastes, water was not a reactant, but mainly acted as a medium. The experiment results indicate that the autogenous shrinkage of AAFA is not caused by the well-known self-desiccation process that happened in cement paste, but related to the continuous reorganization and polymerization of the aluminosilicate gel structure. AAFA pastes with a larger drying shrinkage exhibited a higher weight loss. The different microstructures lead to the different drying shrinkage of these AAFA mixtures.
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