Ultrafine Fly Ash Research Articles

Preparation of environment-friendly ultrafine fly ash based superhydrophobic demoulding coating

The superhydrophobic surface can be used to separate castable concrete materials and moulds instead of waste oil which has the risk of contamination. In this study, a low cost superhydrophobic demoulding coating was prepared using waste materials. Solid waste ultrafine fly ash (UFA) as micron particles. Nano-sized CaCO3 nucleated on the surface of UFA with Ca(OH)2/calcium carbide slag(CCS) slurry under constant CO2 bubbling condition. Fluorosilanes were used to provide low surface energy. Powder coating was used as the base coating to provide intermediate bonding. Through SEM and AFM analysis, it was found that after carbonization, nano-sized CaCO3 particles were distributed on the surface of UFA particles and form large protrusion, and the surface roughness was significantly increased. The contact angle of the coating water was greater than 150° under the optimal condition. Compared with the original UFA, the amount of fluorosilane was reduced from 2% to 0.1%, which reduced the cost. The composite interface between the liquid droplets and the coating surface was formed to intercept air bubbles. The hydrophobic model of the coating met the Cassie theory. The coating can replace the release agent to achieve easy release effect.

Research on sustainable development of fine-grained material cement slurry

Sustainability has become a major focus of the cement industry, largely due to the carbon dioxide emissions associated with Portland cement production. In grouting engineering, ordinary cement slurry has high viscosity, poor fluidity and groutability and is prone to blockage. In this study, a cement slurry was designed using superfine cement (SC). Fine-grained ultrafine fly ash (UFA) waste was used, part of which is used to replace cement, and a certain amount of nontoxic mSiO2·nH2O (SH) is extracted from limestone waste and mixed with the commonly used admixture polycarboxylic acid water reducer (PAWR) to ensure its physical properties in practical engineering applications while reducing its viscosity, increasing its fluidity, and reducing the occurrence of clogging. To determine the optimal mix ratio of the cement slurries mixed with various materials, the characteristics of each material were analyzed through the single-factor test of the multiperformance test, and the orthogonal test mix ratio was designed based on the single-factor test results. Through the Taguchi grey correlation analysis method, the orthogonal test data were analyzed to find the optimal mix ratio. A performance test of the cement slurry with the optimal mix ratio was carried out, and its sustainability was analyzed. Combined with the Discrete Element Method (DEM) and the Voronoi Calculation Method (VCM) methods, UDEC numerical simulation software is used to simulate and analyze the general laws of cement slurry fluidity. The results show that the cement slurry with the optimal mix ratio of SH, SC, PAWR and UFA materials has good fluidity and groutability, has the characteristics of sustainable development, and can be applied to practical projects.

Effect of NaOH concentration on properties and microstructure of a novel reactive ultra-fine fly ash geopolymer

This study used reactive ultra-fine fly ash (RUFA) as the primary raw materials in the preparation of a novel RUFA geopolymer. Note that the solution to binder weight ratio was maintained at the same level by varying the concentration of the NaOH solution. Extensive analysis was conducted to characterize the flowability and mechanical properties. X-ray diffraction (XRD), Scanning Electron Microscope-Energy Dispersive Spectrometer (SEM-EDS), Fourier transform infrared spectroscopy (FT-IR), mercury intrusion porosimetry (MIP), thermogravimetric (TG), and zeta potential analyses were used to examine the microstructure of RUFA geopolymers. Increasing the concentration of NaOH also led to an increase in compressive strength. A high NaOH concentration of 12 mol/L resulted in compressive strength of 97.6 MPa at 28 days. Finally, increasing the concentration of NaOH increased the formation of the primary reaction geopolymerization product, N-A-S-H gel, resulting in a denser microstructure with lower porosity.

Study on the effect of fineness and dosage of fly ash on mechanical properties of concrete

Ultrafine fly ash concrete is one of the main directions for the development of concrete materials in the future. In order to study the mechanical properties of ultra-fine fly ash concrete, the compressive strength, splitting tensile strength and flexural strength of concrete under different ages and different ultra-fine fly ash particle sizes and dosages were tested. (1) The slump of concrete mix under different fly ash particle size increases with the increase of ultrafine fly ash content, but the rate of increase decreases gradually. Under the same fly ash content, the smaller the particle size of ultrafine fly ash particles, the greater the slump of the corresponding fly ash concrete, and it has the exponential relationship between the particle size and the particle size of fly ash. (2) The smaller the particle size of ultra-fine fly ash, the larger the optimum dosage in concrete. When the particle size of ultrafine fly ash is less than 5μm, the optimal dosage of ultrafine fly ash in concrete is 30% to ensure 60d compressive strength. (3) When the concrete curing age is 60d, the splitting tensile strength and flexural strength of ultra-fine fly ash concrete under different particle sizes increase first and then decrease with the increase of ultrafine fly ash content. The law of variation is that the split tensile strength and flexural strength of fly ash concrete are the highest when the content of ultrafine fly ash is 20%-30%.

Comparative Analysis Between Fly Ash Geopolymer and Reactive Ultra-Fine Fly Ash Geopolymer

This study investigates novel geopolymers by combining Reactive Ultra-fine Fly Ash (RUFA) with 4M sodium hydroxide as an alkali activator. Comparing with general fly ash geopolymers, RUFA geopolymer pastes are characterized in terms of compressive strength, microstructure, and crystalline phases. The RUFA geopolymer is successfully obtained as alumina-silicate bonding materials with the same properties as the general fly ash-based geopolymer. The high compressive strength of the RUFA-based geopolymer samples (13.33 MPa) can be attributed primarily to Ca-based alumino-silicate hydration products and Na-based alumino-silicate complexes. This research presents an innovative application for geopolymers using RUFA. In the follow-up study, the influence of synthesis and concentration of alkali activator can be considered in RUFA-based geopolymers.

Geopolymer Concrete Compressive Strength via Artificial Neural Network, Adaptive Neuro Fuzzy Interface System, and Gene Expression Programming With K-Fold Cross Validation

The ultrafine fly ash (FA) is a hazardous material collected from coal productions, which has been proficiently employed for the manufacturing of geopolymer concrete (GPC). In this study, the three artificial intelligence (AI) techniques, namely, artificial neural network (ANN), adaptive neuro-fuzzy interface (ANFIS), and gene expression programming (GEP) are used to establish a reliable and accurate model to estimate the compressive strength (f′c) of fly ash–based geopolymer concrete (FGPC). A database of 298 instances is developed from the peer-reviewed published work. The database consists of the ten most prominent explanatory variables and f′c of FGPC as a response parameter. The statistical error checks and criteria suggested in the literature are considered for the verification of the predictive strength of the models. The statistical measures considered in this study are MAE, RSE, RMSE, RRMSE, R, and performance index (ρ). These checks verify that the ANFIS predictive model gives an outstanding performance followed by GEP and ANN predictive models. In the validation stage, the coefficient of correlation (R) for ANFIS, GEP, and ANN model is 0.9783, 0.9643, and 0.9314, respectively. All three models also fulfill the external verification criterion suggested in the literature. Generally, the GEP predictive model is ideal as it delivers a simplistic and easy mathematical equation for future use. The k-fold cross-validation (CV) of the GEP model is also conducted, which verifies the robustness of the GEP predictive model. Furthermore, the parametric study is carried via proposed GEP expression. This confirms that the GEP model accurately covers the influence of all the explanatory variables used for the prediction of f′c of FGPC. Thus, the proposed GEP equation can be used in the preliminary design of FGPC.

Profile Control Using Fly Ash Three-Phase Foam Assisted by Microspheres with an Adhesive Coating

Foam-assisted steam flooding is a promising technique to alleviate gas channeling and enhance sweep efficiency in heterogeneous heavy-oil reservoirs. However, long-term foam stabilization remains problematic at high temperatures. Three-phase foam (TPF), containing dispersed solid particles, has been proposed to improve foam stability under harsh reservoir conditions. We fabricated a novel TPF system by adding ultrafine fly ash particles, as well as high-temperature resistant microspheres with an adhesive coating layer. This work aims at assessing the ability of the generated TPF in controlling steam channeling and enhancing oil recovery. Static and core flood tests were performed to evaluate foam strength and stability. Our results suggested a stronger foamability at a lower consolidation agent concentration, while a longer half-life period of foam and settling time of solid particles at a larger consolidation agent concentration were observed. Bubbles suspended independently in the liquid phase, with sizes varying from 10 to 100 μm, smaller than that of the conventional foam, suggesting a significant enhancement of foam dispersity and stability. The plugging rate was close to 90% when the temperature was as high as 300 °C, demonstrating a well-accepted plugging effect under high temperatures. A larger pore volume injection of TPF yielded a higher EOR in parallel cores, which substantiated the effectiveness of the three-phase foam system in sealing high-permeability channels.

Improving durability of heat-cured high volume fly ash cement mortar by wet-grinding activation

This work investigated the durability performances of heat-cured high volume (30 wt%–70 wt%) fly ash (FA) cement mortars by using different particle sizes (19.7 μm, 4.29 μm and 2.51 μm) and amounts of wet-grinded fly ash slurries. Wet-grinding technology was used to prepare ultrafine fly ash slurry and improve the durability of heat-cured high volume fly ash cement mortar. Results indicated that the smaller the particle size of wet-grinded fly ash, the better the durability improvement effect of heat-cured high volume fly ash blended mortar. Autogenous shrinkage was increased with the reduced particle size of wet-grinded fly ash. Sulfate attack resistance coefficient, capillary water absorption and electric flux of heat-cured high volume FA mortar were efficiently decreased by wet-grinded FA, within 50 wt% content. As for carbonation resistance, lower carbonation depth than the reference mortar was observed with wet-grinded F3 content of 30 wt%. Results highlight that wet-grinding treatment of fly ash could provide an efficient way to improve the durability performance of heat-cured high volume fly ash composites.

A Research on Durability Degradation of Mineral Admixture Concrete.

In order to study the degradation laws and mechanisms of admixture concretes with single-added SO42− and composite of Mg2+ and SO42−, respectively, the durability tests were conducted on three types of mineral admixture concretes (concretes with single-added metakaolin (MK), single-added ultra-fine fly ash (UFA), and composite of metakaolin and ultra-fine fly ash (MF), and one reference concrete. In these tests, the 10% Na2SO4 solution and the 10% MgSO4 solution were used as the erosion medium, and the drying-wetting circle method was applied. It can be seen from the compressive tests and grey relational analysis that the MK admixture can improve the anti-Na2SO4-erosion capability of the concrete significantly, but weaken its anti-MgSO4-erosion capability; the UFA admixture can improve both the anti-Na2SO4-erosion and the anti-MgSO4-erosion capability of the concrete; and the composite admixture has superimposed effects and can enhance erosion resistance against these two erosion mediums. The phase composition and the changes of the macro morphology and the micro structure during the erosion process caused by mono sulfate ions and complex ions has been observed through X-ray diffraction (XRD), FTIR spectrum (FTIR), and scanning electron microscope (SEM), based on which it was determined that the erosion of single-added SO42− ions can produce erosive outputs of ettringite, gypsum, and mirabilite in the concrete, and cause corner scaling or deformation. Mg2+ and SO42− reacted in the concrete and produced brucite, M-S-H, ettringite, and gypsum, etc. The erosion of complex ions can cause scaling of the cement mortar and aggregate from the surface or the desquamation of corners.

Controlling the early-age hydration heat release of cement paste for deep-water oil well cementing: A new composite designing approach

During the deep-water oil well cementing process, the concentrated heat release of cement paste reduces the zonal isolation quality of the cement sheath. A new approach is proposed in this work to lower the hydration heat release of cement paste and meanwhile give the assurance to the early-age strength development at low curing temperature. This is achieved by the synergistic effects of the admixtures addition, which includes 20% ultrafine fly ash (UFA), 1% C-S-H seeds, 1% nano-SiO2 and 0.3% polycarboxylate super plasticizer. Combined methods of ICC, XRD, SEM and MIP are used to characterize the phase and microstructure evolutions in cement paste. The results show that when compared with the original low-density cement paste without UFA addition, the cumulative heat release after 24 h of hydration decreases by 28% from 75.7 J/g to 54.6 J/g. The concentrated hydration heat release peak is separated into two moderate peaks, because the silicate reaction is accelerated, and the sulfate depletion is delayed. The compressive strength of the paste cured at 10 °C for 24 h is 3.8 MPa, which increases by 41%.

Study on the pozzolanic activity of ultrafine circulating fluidized-bed fly ash prepared by jet mill

The pozzolanic activity of ultrafine circulating fluidized-bed (CFB) fly ash prepared by jet mill has been investigated in this research. The ultrafine powder properties and the hydration heat release process of the cement blended with ultrafine CFB fly ash have been obtained. Furthermore, the dissolution characteristics of SiO2 and Al2O3, the Ca2+ absorption capacity in saturated Ca(OH)2 solution, and the polymerization degree of Si-O and Al-O polyhedrons have been studied to further clarify the mechanism of ultrafine grinding on pozzolanic activity. Compared to raw CFB fly ash (RCFA), the particle morphology, the pore structure of ultrafine CFB fly ash (UCFA, D50 ≤ 5 μm), and the pozzolanic activity of UCFA are significantly improved. The hydration rate of cement blended with UCFA is accelerated, and the total heat release is close to that of pure cement within 72 h. Ultrafine grinding increases the SiO2 and Al2O3 dissolution rate of CFB fly ash and Ca2+ absorption capacity in saturated Ca(OH)2 solution, mainly due to the decrease of polymerization degree of Si-O and Al-O polyhedrons and particle size of CFB fly ash.

High-volume ultrafine fly ash-cement slurry mechanical properties and strength development model establishment

This paper, orthogonal experiments were designed to study the changes of water separation rate, concretion rate and uniaxial compressive strength (UCS) without side pressure of ultrafine fly ash (UFA)-cement slurry with high volume. Low field-nuclear magnetic resonance (NMR) was used to characterize the pore structure characteristics. The relationship between UCS without lateral compression and pore characteristics, FA content and water-cement ratio of specimens was studied. The results show that the water-cement ratio has the greatest influence on the water separation rate and the concretion rate of the specimen, and the FA content has the greatest influence on the UCS of the specimen, and the changing trend was polynomial function. With the increase of FA content, the UCS without side compression of specimens decreases, and the elastic modulus decreases, but the ductility deformation is improved. Based on Feret classical equation and maturity formula, a model is proposed to predict the strength of FA-cement, where just three variables (i.e., the FA content, the water-cement ratio and the curing time) can characterize this complex model. The optimal ratio of FA-cement slurry is optimized according to the actual demand of mine. At present, this method has been widely applied in the mine and achieved good results.

Comparative study on chemical and morphology properties of nano fly ash in concrete

Nano concrete is the new technology used in the material to produce highly dense and high performance concrete to withstand maximum load using nano sized materials in the concrete. Making of ultra fine fly ash and nano fly ash has been done with the help of ball milling process. The size of the nano particles are confirmed through scanning electron microscope (SEM) analysis and the characterization with the help of XRD test. By eight hours of continuous ball milling process, gives the nano fly ash of size 10 to 200 nm. The X–ray diffraction (XRD) test result also showed the chemical constituents present in the nano fly ash and ultra fine fly ash. Similarly the SEM analysis provides the morphology of the core specimen and the size of molecules.

Multi-Response Optimization of Ultrafine Cement-Based Slurry Using the Taguchi-Grey Relational Analysis Method.

The grouting technique is an important method in underground engineering that prevents water seepage and reinforces fractured rock mass. In this research, ultrafine cement-based grouting material, including ultrafine cement (UC), ultrafine fly ash (UFA), polycarboxylate superplasticizer (SP), colloidal nanosilica (CNS), sodium sulfate solution (SS) and water, was developed. The flow time, viscosity, bleeding, setting time and uniaxial compressive strength of the UC-based slurry were measured by orthogonal experiments, and the optimal mix proportion of the UC-based slurry was obtained based on the Taguchi-Grey relational analysis method. Microstructure analysis of the UC-based slurry was conducted using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) tests. The results showed that the Bingham model could provide a satisfactory description of the rheological properties of the UC-based slurry. The addition of CNS and SS could promote the hydration of the UC-based slurry and improve the microstructure of the hardened slurry, thereby increasing the strength of the hardened slurry. The optimum ratio for the UC-based slurry was water/solid (W/S) ratio of 1.0, and the contents of UFA, SP, CNS and SS by mass of UC were 40%, 0.2%, 4% and 4%, respectively.

A comparison of water curing and standard curing on one-part alkali-activated fly ash sinking beads and slag: Properties, microstructure and mechanisms

The commonly used curing regime in one-part AAFSS is air curing or sealed standard curing. In this research, one-part alkali-activated fly ash sinking beads and slag (AAFSS) was prepared by using composite activators. The difference between standard curing and water curing was investigated, and the influencing mechanism of water curing was also studied. Experimental results indicate that the strength after 28 days of water curing stops increasing, and even decreases to some extent. The use of ultra-fine fly ash sinking beads (FASB) and Na2CO3 can ameliorate the water resistance index defined as the ratio of compressive strength of specimens after the same days of standard curing and water curing. And the acid resistance of water-curing AAFSS is poorer than that of standard-curing AAFSS. The mechanical properties and durability of one-part AAFSS after water curing are affected by ions leaching and destruction of microstructure. XRD and TG-DTG analysis reveal that 28 days of water curing does not change the types of hydration products, but decreases the number of gelatinous products and calcite. An interesting finding is that the intensity of diffraction peaks of gelatinous products of specimens under water curing is higher than that under standard curing. Water curing makes the microstructure much coarser, and large microfracture could be found in SEM images. The use of FASB and Na2CO3 can improve the microstructure of one-part AAFSS after water curing.

Prediction of compressive strength development for blended cement mortar considering fly ash fineness and replacement ratio

Utilization of upgraded fine fly ash in cement-based materials has been proved to be an effective method to improve compressive strength at early ages. The addition of fine fly ash has introduced dilution effect, enhanced pozzolanic reaction effect, nucleation effect and physical filling effect into cement-fly ash system. In this study, an integrated reaction model is adopted to quantify the contributions from cement hydration and pozzolanic reaction to compressive strength. A modified model related to the physical filling effect is utilized to calculate the compressive strength increment considering the gradual dissolution of fly ash particles. Via combination of these two parts, a numerical procedure has been proposed to predict the compressive strength development of fine fly ash mortar considering fly ash fineness and replacement ratio. The reliability of the model is validated through good agreement with the experimental results from previous articles. In addition, parametric analyses are performed to further analyze the effects of fly ash fineness and replacement ratio on compressive strength. The results indicate that compressive strength increases linearly with the increase of fly ash fineness. While its slope is less affected by fly ash replacement ratio, it increases along with the extension of curing time. Moreover, the fineness of fly ash can improve the relationship between compressive strength and replacement ratio. For ultrafine fly ash mortar, the 28-day compressive strength of mortar shows an evident trend of first increase and then decrease with the increase of replacement ratio. Under the condition of ensuring the same compressive strength, upgraded finer fly ash can replace more cement, thus realizing energy saving and CO2 emission reduction.

Effect of ultra-fine fly ash on concrete performance and durability

In the present study ultra-fine fly ash as a novel by-product obtained by a dry and closed separation process was investigated as cement replacement in concrete. The impact of ultra-fine fly ash on material properties was investigated following an upscaling as an approach considering paste, mortar and concrete properties. Two types of cement, Portland cement (CEMI) and slag cement (CEMIII), two types of ultra-fly ashes, one with particle size d90 < 9.3 μm (FA1) and second with d90 < 4.6 μm (FA2) were used. At paste- and mortar- level, cement was replaced at 0%, 15%, 25%, 35% and 50% with FA1 and FA2. At concrete- level, cement was replaced at 0%, 15% and 25% with different ratios of FA1 and FA2. The results at paste- and mortar- level showed that an increased fineness of the fly ash (FA2) contributes to better workability of the mix. For CEMI, the compressive strength of concrete with FA2 at 25% cement replacement was already equal to the reference 0% replacement concrete at the age of 28 days. For CEMIII, the compressive strength of concrete mix with FA1 with 15% and FA2 with 25% cement replacements reached the reference concrete value at the age of 91 days. Regarding the durability, replacing cement with ultra-fine fly ash (FA2) had a positive influence on the resistivity, chloride migration coefficient and alkali-silica reaction (ASR), and a negative influence on the carbonation resistance.

Experimental study on durability characteristics of composite fiber reinforced high-performance concrete incorporating nanosilica and ultra fine fly ash

This study is aimed at investigating the durability properties of Composite Fiber Reinforced High-Performance Concrete. A 15% partial replacement of cement by weight was done with ultra-fine fly ash. The addition of nanosilica was in fractions of 0%, 1.5%, 3.0% and 4.5% by weight of cement. For each of the above combinations, 1.0% steel and 0.25% polypropylene fibers, respectively, by volume of the binders were added. A constant aggregate binder ratio of 2.0 and varying water binder ratios of 0.275, 0.300, 0.325 were used in this investigation.The sorptivity test was performed to assess the rate of absorption, and the rapid chloride permeability test (RCPT) was performed to assess the permeability of concrete. Test results revealed that all the mixes attained low to very low chloride permeability. The decrease in chloride ion permeability for mixes with nanosilica and ultra-fine fly ash ranged from 53.83% to 71.45% for 28 days curing period and 55.88% to 74.27% for 56 days curing period, as against the reference mix.‘Residual Compressive Strength’ and ‘Percentage Weight Loss’ for 28 and 56 days of immersion in 5% concentrated solutions of HCl, H2SO4, and MgSO4 were evaluated to study the effects of aggressive ions such as chlorides and sulfates on concrete. The weight loss observed ranged from 7.09% to 2.07% in the case of HCl, from 7.96% to 2.86% in the case of MgSO4, from 17.93% to 11.02% in case of H2SO4 for water binder ratio of 0.275 and 56 days of immersion. The percentage reduction in strength after 56 days of immersion for mixes with water binder ratio of 0.275 ranged from 14.39% to 8.92% in HCl, from 14.53% to 9.66% in MgSO4 and 14.81% to 10.92% in H2SO4.The outcomes of the study showed that a combination of 15% ultra-fine fly ash and 3% nanosilica is the optimum replacement level to achieve increased durability, reduced porosity and permeability due to improved macro and micrometer densities of concrete. In addition, steel and polypropylene fibers have also made a small contribution towards improving the durability of Composite Fiber Reinforced High-Performance Concrete.

Effect of steam curing on compressive strength and microstructure of high volume ultrafine fly ash cement mortar

Utilization of high volume fly ash is generally limited in steam-cured concrete products due to the delayed strength development. In present work, ultrafine fly ash (UFA) with a median particle size of 2.3 μm was prepared with wet-grinding technology. The influence of different FA fineness, UFA content (30–70%) and curing regimes on the compressive strength and microstructure of steam-cured high volume fly ash cement composites were studied. Both the early and late compressive strength of steam-cured FA blended composites were enhanced by wet-milled UFA with replacement level as high as 50%, and the strength was even higher than that of pure cement group. Pore structure of steam-cured high volume FA blended composites was effectively refined by UFA. The amount of CH after steam curing was generally lower than that with standard curing. Furthermore, the main chain length and Al/Si of C-S-H gels under steam curing were improved by UFA. Compared with prolonging the curing duration, increasing the curing temperature seems more efficient for the incorporation of aluminum from fly ash into the calcium silicate hydrates.

Preparation of Ultrafine Fly Ash-Based Superhydrophobic Composite Coating and Its Application to Foam Concrete

The waterproof and thermal insulation property of foamed concrete is very important. In this study, the ultrafine fly ash (UFA)-based superhydrophobic composite coating was applied onto foam concrete. The UFA-based base coating that closely adhered to the concrete initially improved the waterproofness of the test block, and the silane coupling agent-modified UFA-based surface coating further achieved superhydrophobicity. The UFA on the coating surface and the asperities on the surface jointly formed a lotus leaf-like rough micro–nanostructure. The 154.34° water drop contact angle and 2.41° sliding angle on No. 5 coating were reached, indicating that it was a superhydrophobic surface. The water absorption ratios of the composite coating block were 1.87% and 16.6% at 4 h and 7 days, which were reduced by 97% and 75% in comparison with the original foam concrete. The compressive strength and heat conductivity coefficient after soaking for 4 h of the composite coating block were higher than 4.0 MPa and 0.225 W·m−1·K−1, respectively. The UFA-based superhydrophobic composite coating proposed in this study and applied onto foam concrete is simple and cheap, requires no precise instrument, and can be applied in a large area.