Surface-modified Fly Ash Research Articles

Utilization of surface-modified fly ash cenosphere waste as an internal curing material to intensify concrete performance

Fly ash cenosphere, as one of the coal-burning related industrial wastes, causes significant negative consequences to the environment. Therefore, it is necessary to explore an ecological way to take full advantage of the cenosphere. In this study, the utilization of the cenosphere as an internal curing material to partially replace cement in concrete was evaluated. An improved surface modification process was proposed to remove the glassy-phase on top of the cenosphere. It was proved to be effective given that excellent water desorption characteristics were obtained in a practical relative humidity variation in the concrete simulated with saturated salt solutions. The surface-treated cenosphere was identified as a performance enhancer to concrete mechanical properties given that an increase of 7.07% and 6.85% in compressive and flexural strength, respectively, was observed. Due to the coupling effect of the internal curing and pozzolanic reactivity of cenospheres, a significant amount of C–S–H gel with a low Ca/Si ratio and tight bond between cenospheres and surrounding pastes were characterized through SEM-EDS and XRD investigations, leading to a strengthened microstructure. This study demonstrated that the surface-modified cenosphere could be utilized as an internal curing material to benefit the concrete performance.

Interactions of Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation

Heat-aided ballasted flotation using industrial waste heat is a cost-effective and eco-friendly technology to harvest microalgae from aquatic environment. However, the underlying mechanism of this process is not yet fully understood. This study investigates the interactions between Chlorella vulgaris and fly ash cenospheres in heat-aided ballasted flotation based on the Extended Derjaguin-Landau-Verwey-Overbeek approach. The results indicated that Lifshitz-van der Waals interaction played an important role in the attachment of algal cell on fly ash cenospheres. Furthermore, the Lewis acid-base interaction changed from repulsion to attraction in the system due to heating, which promoted the algal cells to attach on fly ash cenospheres, resulting in a higher harvesting efficiency. However, when the temperature was increased to 90 °C, the Lifshitz-van der Waals interaction was reversed, which resulted in an energy barrier. The total attractive interaction increased with the decrease in pH from 10 to 4, due to changes in electrostatic interaction. After surface modification of fly ash cenospheres, the electrostatic interaction was always attractive in this system at pH of 7 regardless of temperature variations. Finally, according to the experimental results and the Extended Derjaguin-Landau-Verwey-Overbeek analysis, the usage of surface modified fly ash cenospheres for heat-aided ballasted flotation can be advantageous for environmental safety and high efficiency.

Design of a Comprehensive Experiment for Materials: Surface Modified Fly Ash and Its Application in Rubber

Design of a Comprehensive Experiment for Materials: Surface Modified Fly Ash and Its Application in Rubber

Polyethyleneimine modification of activated fly ash and biochar for enhanced removal of natural organic matter from water via adsorption.

In this study, fly ash (FA) and biochar (BC), two common industrial byproducts, were activated and surface-modified with polyethyleneimine (PEI) to enhance their capacities to remove natural organic matter (NOM) from water via adsorption. Different fluorescent components were identified using fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) to explore the individual adsorption behaviors of different organic constituents in a bulk NOM. The NOM adsorption was quantitatively examined via adsorption isotherm and kinetics models. Compared to the pristine adsorbents, the functionalized adsorbent with increased surface area and positive surface charge achieved higher NOM adsorption. By evaluating the adsorptive behaviors of UV-absorbing and fluorescent moieties, it was concluded that the operative mechanism of adsorption included electrostatic attraction, hydrogen bonding, and π-π interaction. At the optimal pH of 3, the surface-modified FA and BC (i.e., FA-PEI and BC-PEI) had adsorption capacities for NOM that were ∼3 times higher than the capacities of the pristine materials. Due to its aromatic features, π-π interaction may have enhanced BC and BC-PEI selective adsorption of aromatic NOM components compared to FA and FA-PEI. Kinetic modelling showed that the mesopores of FA-PEI were available for NOM adsorption and diffusion of NOM molecules into the mesoporous structures was rate-limiting. On the other hand, PEI-modification may have further reduced NOM diffusion through the narrow micropores in BC such that external adsorption primarily occurred on BC-PEI. The modified adsorbents showed a faster adsorption kinetics than the pristine counterparts and a high durability in repeated adsorption-desorption cycles.

Effect of surface-modified fly ash on compressive strength of cement mortar

This paper presents the experimental results on the impact of modified coal fly ash on mechanical performance of cement materials. Fly ash used in the experiments was received from Burshtyn thermal power plant (Ukraine). The surface modification was carried out by the acidic treatment in order to increase its pozzolanic activity. The impact of raw fly ash and surface-modified fly ash on the cement mortar strength have been compared. It was found in the experiments that the replacement of cement by 5% (wt) of modified fly ash increase the compressive strength value from 61.3 MPa to 63.2 MPa compared to unmodified fly ash at age 28 days. The mineral phase formation, structure and chemical compositions of the modified fly ash/cement composites were analyzed by XRD, SEM and EDS. This research is of great importance and opens a new way for the future investigation and utilization of coal fly ash.

Surface-modification of fly ash and its effect on strength and freezing resistance of slag based geopolymer

The surface of Grade III fly ash particles was modified by addition of gypsum and mineralizing agent (anhydrous calcium chloride) at 960 °C for 2 h. The mineral phase formation, structure and chemical compositions of the modified fly ash were analyzed by XRD, FESEM and EDS. Moreover, the influences of surface-modified fly ash on the compressive strength and freezing resistance of slag based geopolymer were also investigated in this work. The results showed that the β-2CaO·SiO2 (β-C2S) and 3CaO·SiO2 (C3S) phases were formed on the surface of fly ash particles after surface-modification. When adding modified fly ash into slag based geopolymer, due to the filling effect and functions of active agents (β-C2S and C3S), the strength and freezing resistance were improved markedly compared with that of the geopolymer added with original fly ash.

Surface Modified Nano Fly Ash as an Activator in the Reduction of Ketones

Surface modified nano fly ash has been used as an activator, in the reduction of a few cyclic and acyclic ketones with NaBH4 as reducing agent. Exclusive formation of trans-4--butyl cyclohexanol was observed in such case. Reduction of 3-methylcyclohexanone yielded only cis-3-methylcyclohexanol (equatorial -OH). In case of reduction of other substituted cyclohexanones, propensity to form more of equatorial alcohol was observed. The chemical yields of various alcohols were high (∼95-99%). The rates of reductions of the ketones were also appreciably high. It appears that the silanol groups present in the surface modified fly ash cause nucleophilic activation of the carbonyl groups leading to faster reaction rate. Exclusive formation of the epimer with equatorially disposed -OH group is most likely due to the same reason. Finally, the advantage of the activator lies in its low cost.

Surface Modification of Fly Ash Concrete Through Nanophase Incorporation for Enhanced Chemical Deterioration Resistance

The global warming gas, CO2, is liberated when clay and limestone are crumbled for the production of cement. About 8–10% of the universal CO2 emissions are emitting from the cement factories. With concerns arising over environmental issues associated with cement usage, it is the need of the hour to reduce its consumption. Fly ash, the waste material from thermal power plants, is a widely used supplementary cementitious material that extends the life of the concrete structures. The intervening of nanotechnology into construction industry has provided wider opportunities to better the performance of concrete in rigorous conditions, especially acids and alkali environment. This work endeavours to study the effect of surface-modified fly ash concrete through the addition of nanoparticles against sulphate attack and calcium leaching. Nanophase modification was performed by integrating nano-TiO2 and CaCO3 for enhanced durability and corrosion resistance. Four types of concrete mix, namely fly ash concrete (FA), FA with 2% TiO2 nanoparticles (FAT), FA with 2% CaCO3 nanoparticles and FA with 2% TiO2:CaCO3 (FATC) nanoparticles, were designed and casted as cylindrical concrete blocks. The specimens were immersed in 1% sulphuric acid solution and sea water to study the resistance of concrete against sulphate attack and calcium leaching, respectively. Results showed that nanophase modification of fly ash concrete improved the resistance to sulphuric acid attack and calcium leaching. Among the nanophase-modified specimens, FAT and FATC specimens showed superior performance.

Influence of axial compressive loads on buckling and free vibration response of surface-modified fly ash cenosphere/epoxy syntactic foams

This work deals with experimental buckling and free vibration behavior of silane-treated cenosphere/epoxy syntactic foams subjected to axial compression. Critical buckling loads are computed from compressive load–deflection plots deduced using universal testing machine. Further, compressive loads are applied in the fixed intervals until critical loading point on different set of samples having similar filler loadings to estimate natural frequency associated with the first three transverse bending modes. Increasing filler content increases critical buckling load and natural frequency of syntactic foam composites. Increasing axial compressive load reduce structural stiffness of all the samples under investigation. Syntactic foams registered higher stiffness compared to neat epoxy for all the test loads. Similar observations are noted in case of untreated cenosphere/epoxy foam composites. Silane-modified cenosphere embedded in epoxy matrix registered superior performance (rise in critical buckling load and natural frequencies to the tune of 23.75% and 11.46%, respectively) as compared to untreated ones. Experimental results are compared with the analytical solutions that are derived based on Euler–Bernoulli hypothesis and results are found to be in good agreement. Finally, property map of buckling load as a function of density is presented by extracting values from the available literature.

Investigations on the Fixed-Bed Column Performance of Acid Brown 75 Adsorption by Surface Modified Fly Ash Granules

Adsorption potential of surface modified granule (SM-G) to remove acid brown 75 (AB 75) from aqueous solution was investigated using fixed-bed column mode. To produce SMG, lignite fly ash was agglomerated into porous granules by an extruder at 800°C and surfacemodified with a cationic surfactant, Hexadecyltrimetylammonium Bromide (HDTMABr). The performance of the fixed-bed column was evaluated to assess the effect of various process variables, viz., of bed height, flow rate and initial feed concentration on breakthrough time and adsorption capacity. The bed depth service time (BDST) model was applied to the data for predicting breakthrough curves and to determine the characteristic parameters. The highest experimental and theoretical bed capacities were obtained to be 55.3 mg of AB 75 adsorbed per gram of SM-G. The results indicated that the SM-G is a suitable adsorbent for the removal of AB 75 from aqueous solution.

Effect of surface modification of fly ash on the mechanical, thermal, electrical and morphological properties of polyetheretherketone composites

Poly (ether ether ketone) (PEEK)/fly ash (FA) composites were prepared using melt blending technique. To improve the interfacial interaction of fly ash with the PEEK matrix, fly ash was chemically modified with calcium hydroxide, at different concentration. Various characterization studies like dynamic mechanical thermal analysis (DMTA), modulated differential scanning calorimetry (MDSC) and scanning electron microscopy (SEM) have been carried out to evaluate the storage modulus, tan δ, crystallinity, and morphology in the composites. SEM micrographs showed more uniform dispersion and interaction in the modified composites than unmodified counterpart. Surface modified fly ash improved the interfacial adhesion between fly ash and PEEK which is confirmed also through improved mechanical strength. The dynamic modulus of PEEK composites exhibited over 133% increment at 100–250 °C, indicating improvement of elevated temperature mechanical properties. The modified fly ash reinforcements also showed improvement in glass-transition and crystallization temperature.

Adsorption of phenol and o-chlorophenol on surface altered fly ash based molecular sieves

The contamination of water by organic pollutant viz. phenolic compounds is a worldwide environmental problem due to their highly toxic nature. Surface modified zeolite materials have been developed from a waste material like fly ash which are being used for adsorption of phenol and o-chlorophenol from wastewater. The comparison of adsorption of phenol and o-chlorophenol on commercial zeolite-Y, fly ash based zeolite (FAZ-Y) and surface modified fly ash based zeolite (SMZ-Y) were studied. It was observed that the adsorption of phenol on SMZ-Y was 4.05 and 3.24 times higher than the FAZ-Y and commercial zeolite-Y, respectively. For o-chlorophenol the efficiency is higher by a factor of 2.29 and 1.8 for FAZ-Y and commercial zeolite-Y, respectively. This may be attributed to the hydrophobicity imparted by surfactant molecules on the surface of fly ash zeolite, consequently leading to organic partitioning. The effect of various parameters like adsorbent dose, pH and initial concentration were studied for their optimization. The rate of adsorption of phenol and o-chlorophenol was found to be maximum at neutral pH. The effect of the presence of anions on adsorption of solute was also studied. It was found that the salts have a substantially detrimental effect on adsorption of phenol and o-chlorophenol. Equilibrium adsorption data for phenol and o-chlorophenol were analyzed by using Freundlich adsorption isotherms model.