Effect Of Fly Ash Content Research Articles

Modeling of effect of fly ash amount on microstructure and chloride diffusivity of blended fly ash-cement systems

Reasonable utilization of industrial fly-ash wastage in concrete engineering has been regarded as an effective way to reduce carbon emissions. By adding the reasonable dosage of fly ash to cement paste, the compactness and microstructure characteristics of the blended cement systems can be significantly improved, thereby effectively enhancing the durability of concrete structures. The vector hydration model of blended fly ash-cement systems with the interference effects of different hydration layers of fly ash and cement particles, the solubility equilibrium of solid phases and the electrical neutrality of the pore solution involved is established. By fully comparing with the experimental data of hydration degree, capillary porosity and CH content, the accuracy of the developed hydration model is verified. Based on the hydration model, the effect of fly ash content on the concentration of different ions and pH in the pore solution with curing time is discussed. Additionally, the evolution characteristic of hydration degree, capillary porosity and CH content with curing time at different fly ash content is also analyzed. Based on the reconstructed microstructure of blended systems, the rolling sweep (RS) technique is used to determine the pore size distribution of capillary pores. The effect of fly ash content on cumulative pore size distribution and differential pore size distribution at different curing time is quantitatively evaluated and discussed. By utilizing the first-passage cube, the dual-probability-Brownian motion method is constructed to predict the chloride diffusivity of blended cement systems. After diffusion model is verified by multi-group experimental data, the optimal dosage of fly ash at different water-binder ratio is calculated, which can provide theoretical guidance for practical applications in concrete engineering.

Influence in the mechanical properties and salt erosion resistance of recycled sand UHPC made from fly ash content

This study aims to explore the impact of fly ash (FA) as a partial replacement for cement on the durability of recycled sand (RS) ultra high performance concrete (UHPC). The effects of FA content on the mechanical properties, resistance to chloride salt freezing-thawing coupling, and resistance to sulfate dry-wet cycling coupling of F-RUHPC were investigated. The results showed that FA improved the mechanical properties of F-RUHPC, with a compressive strength of up to 120.8 MPa. It also resulted in higher tensile strength compared to the control group and demonstrated excellent resistance to chloride salt freezing-thawing and sulfate dry-wet cycling. Microscopic analysis revealed a low content of free chloride ions within F-RUHPC, all below 0.08 %. Additionally, the permeability coefficient of F-RUHPC with 10 % FA was found to be the lowest under chloride salt freezing-thawing conditions. Microstructural characterization demonstrated the dense structure of UHPC. The addition of 10 % FA was found to be beneficial in improving the mechanical properties and durability of F-RUHPC, providing a theoretical reference for the development of environmentally friendly UHPC.

Properties and microstructure of a low-carbon clinker-free cementitious binder and its extrusion-based printing performance

The extensive use of cement binders in the construction industry limits the progress of carbon emission reduction. A low-carbon clinker-free cementitious binder (CFCB) was developed by using wet grinding to activate granulated blast furnace slag (GGBS), combining fly ash (FA) spheres as rheology-modified material and calcium carbide slag (CS) together with sodium metasilicate (NS) powder as the compound activator. The effects of FA content and CS/NS ratio on the hydration, performances, and microstructure were systematically investigated. The printability and mechanical anisotropy of extrusion-based printed CFCB were also analyzed. The results show that lower fly ash content and CS/NS ratio positively influenced the yield stress and improved rheology and thixotropy within a certain range. The compressive strength of the CFCB mortar reaches a maximum of 46.6 MPa at 28 days. At the same time, the decrease in the CS/NS ratio is conducive to the development of the hydration process, generating a higher amount of hydration and forming a denser microstructure. The FA20-CS18 group shows suitable extrudability, buildability, and shape retention ability with a height loss of only 0.8 %. The existence of interlayer property differences causes the extrusion-based printed mortar to exhibit anisotropic mechanical properties, with the highest flexural and compressive strength in the Z-direction. The anisotropy coefficient was below 0.25 before 7 days.

Safety and Effect of Fly Ash Content on Mechanical Properties and Microstructure of Green Low-Carbon Concrete

Based on the promotion and application of green and low-carbon technology, this study aims to develop a high-safety performance cement concrete incorporating a large dosage of fly ash (FA). The safety and effect of FA content on the mechanical properties of FA composited cement were studied through compressive strength, flexural strength, and microscopic tests. The results show that when the FA replaced 20% cement, the properties of concrete were the best in this study. The flexural strengths and compressive strengths of the standard cured concrete for 28 days with 20% FA content are 0.82 MPa and 4.32 MPa larger than that of the pure cement concrete. The XRD and SEM analysis suggested that the mechanical properties of the composite cement FA system are improved significantly since the replacement of cement by FA promotes secondary hydration of calcium hydroxide in the concrete, leading to a more compact and safe interface between cement and FA.

Strength and microscopic pore structure characterization of cement-fly ash stabilized organic soil under freeze-thaw cycles

In seasonal frost areas, an organic soil stratum is often encountered during engineering construction due to the widespread existence of organic soils. The soil stratum will experience frost heave in winter and thaw settlement in summer, resulting in a significant variation in its engineering behaviour, especially for organic soil stratum. In this study, with the help of cement, fly ash, and fulvic acid, cement-fly ash stabilized organic soil (CFOS) specimens were prepared and the unconfined compressive (UC) and mercury intrusion porosimetry (MIP) tests were carried out on CFOS specimens. The effects of fly ash content, number of freeze-thaw cycles (FT-N), and curing period on the strength, resilient modulus, and porosity were investigated. Test results revealed that the fly ash content increased from 0% to the optimum content of 5%, the unconfined compressive strength (UCS) and resilient modulus of CFOS with FT-12 increased by 50.30% and 118.92%, respectively. The pore size distribution (PSD) curve and fractal dimension (Dn) of specimens were obtained from the MIP test. The proportion of macropores was the main factor affecting the UCS of CFOS. With the increasing FT-N, the macropore proportion of CFOS with 5% fly ash content increased by 333.33%, and the UCS decreased by 28.25%. Based on a freeze-thaw damage model, the damage parameters of the CFOS specimens were extracted with the Dn as an independent variable. The microscopic pore characteristics and the relationship between the strength, Dn and damage parameter were analyzed. The microscopic pore structure of specimens with different fly ash contents experienced a change subjected to freeze-thaw cycles. The lower the strength, the lower the Dn of CFOS. The damage parameters quantitatively reflected the damage degree of specimens after freeze-thaw cycles on the micro scale. The damage parameter of CFOS with 5% fly ash content increased by 341.57% with the increase of FT-N. The introduction of fly ash was able to reduce freeze-thaw damage to the specimens. The damage parameter and CFOS strength exhibited a significant correlation. The relationships of the strength and microscopic pore structure of CFOS subjected to freeze-thaw cycles were conducive to a better understanding of the freeze-thaw damage mechanism of CFOS on the micro scale. These findings are beneficial for engineering construction design in seasonal frost areas.

Mechanical Properties and Hardening Mechanism of Magnesium Ammonium Phosphate Cements Modified by Fly Ash

High hydration heat and poor water resistance are the main factors restricting the application of magnesium ammonium phosphate cement (MAPC). To alleviate the problem, fly ash was used to partially replace dead-burned MgO and NH4H2PO4 in this paper. The effect of fly ash content on MAPC properties, such as setting time, fluidity, mechanical properties, and water resistance, was investigated. The micromorphology of hydration products and the influence mechanism of fly ash on the macrocharacteristics and hydration process of MAPC were also discussed. The results showed the mechanical properties of fly ash-modified MAPC decreased with the increase of the fly ash content, but their increments at later hydration were greater than the control MAPC. Meanwhile, fly ash could improve the water-resistance significantly and reduce the total hydration heat. The fly ash refined the struvite crystal and increased the compactness of MAPC, although no obvious hydration products of fly ash were observed. So, when the content of fly ash is 30 wt%, the MAPC has appropriate mechanical properties, while its water resistance is significantly improved, and its hydration heat is reduced compared with the control group.

Rheological and mechanical performance analysis and proportion optimization of cemented gangue backfill materials based on response surface methodology.

Cemented backfill mining is a green mining method that enhances the coal mining rate and the safety of mined-out regions. To transport the cemented gangue backfill material (CGBM) into the mined-out regions, it is essential to ensure high flowability and adequate compressive strength after hardening. Based on the response surface methodology (RSM), 29 experiments were conducted in this paper to test the yield stress and plastic viscosity of CGBM slurry. Cubic specimens with dimensions of 100mm were prepared and underwent uniaxial compression tests to obtain the compressive strength at a curing age of 28days. Quadratic polynomial regression models were established for yield stress, plastic viscosity, and compressive strength to explore the effects of fly ash content, water-cement ratio, mass concentration, and superplasticizer dosage on the properties of CGBM. Multi-objective optimization was conducted to determine the optimal material proportion of CGBM. The research results indicate that (1) the mass concentration most profoundly affected the yield stress and plastic viscosity of CGBM, and it increased with an increase in mass concentration. Fly ash content had an inverse relationship with compressive strength. Superplasticizer was found to improve the flowability and strength of CGBM. (2) The established response surface model could reflect the relationship between CGBM's material proportion and rheological and mechanical properties, and predict relevant parameters. (3) Multi-objective optimization determined the optimal proportion of CGBM to be 80% fly ash content, 54% water-cement ratio, 79% mass concentration, and 3% superplasticizer dosage. The research findings offer valuable guidance to mining backfill engineering.

Time-dependent similarity and micro-mechanism of chloride diffusivity of fly ash concrete in different environments

Based on the exposure test of fly ash (FA) concrete in different environments, chloride diffusion coefficients and main microstructural parameters measured by mercury intrusion porosimetry and their time-dependent properties were analysed. Then, the effect of FA content on time-dependent chloride diffusivity and microstructural parameters was investigated. Finally, according to similarity theory and Jaccard coefficient, the similarities of instantaneous chloride diffusion coefficient and main microstructural parameters between two environments were discussed. Results show the proportion of pores with size ≥100 nm has the best correlation with chloride diffusivity of concrete. Besides, chloride diffusion coefficients and main microstructural parameters decrease with exposure time. The decreasing rate increases with the increase of FA content. Moreover, in the laboratory environment with high temperature and high salinity, an acceleration effect on chloride diffusion can be observed. Results of similarity analysis indicate that chloride diffusivity and the main microstructural parameters at an exposure time of 320 days in the laboratory environment are the most similar to those on site at an exposure time of 840 days. For concrete with FA content not more than 40%, the Jaccard coefficients of similar criterion parameters related to chloride diffusivity and microstructural parameters are all greater than 0.87.

Preparation and properties of anorthite‐based ceramics by using metallurgical solid waste and fly ash

AbstractA large amount of metallurgical solid waste accumulation poses a serious threat to the environment. Study on synergistic reinforcement of synthetic process of metallurgical solid waste‐based ceramics with fly ash is of great significance in reducing environmental pollution and resource utilization. A metallurgical solid waste‐based ceramic used as building ceramic was developed with the erosion part of used MgO–C bricks and fly ash as main raw materials, and the amount of solid waste added to the prepared ceramics was at least 60 wt% and up to 90 wt%. The effects of fly ash content and sintering temperature on the crystalline phase transitions, morphologies, and the main physical and mechanical properties of ceramics were investigated by X‐ray diffraction, scanning electron microscopy, and mechanical testing. The results show that the obtained ceramics presented maximum bending strength and minimum water absorption, 80.14 MPa and 5.04%, respectively, when the raw material proportions were the erosion part of used refractories accounted for 60 wt%, fly ash 20 wt%, pyrophyllite 10 wt%, and quartz sands 10 wt%, and the process parameters were the sintering temperature 1150°C, sintering time 120 min, and molding pressure 15 MPa.

Effect of Fly Ash Content on the Microstructure and Strength of Concrete under Freeze–Thaw Condition

To understand the influence of fly ash (FA) content on the microstructure and strength of concrete under freeze–thaw cycles (FTCs), four groups of concrete with different FA contents (0–30%) were tested under FTC condition. Mass loss rate, relative dynamic modulus of elasticity (RDME), splitting tensile strength and other damage indicators were selected to describe the impact of macro properties. The micro physical changes, porosity and pore size distribution parameters were obtained through scanning electron microscope (SEM) and nuclear magnetic resonance (NMR) experiments. The influence mechanism of FA content on the frost resistance durability of concrete under FTC was discussed from the macro and micro perspectives. The results show that under the action of FTC, the addition of FA fills the pores, reduces the pore spacing, improves the strength of concrete, and makes the RDEM and splitting tensile strength of concrete increase first and then decrease. Among them, 20% FA concrete has the best frost resistance. The pore structure parameters show that the content of pores smaller than 100 nm has a great impact on the frost resistance durability of FA concrete, and increasing the content of these pores can improve the frost resistance durability of concrete.

Investigation of the effect of fly ash content on the bonding performance of CFRP-concrete interface in sulfate environment

The present study focuses on the investigation of the interfacial bond behavior of carbon fiber-reinforced polymer (CFRP)-concrete under dry–wet sulfate cycles by double-sided shear testing. Besides, the effects of fly ash content on the interfacial failure characteristics, interfacial debonding bearing capacity, CFRP strain distribution, and interfacial shear stress peak were analyzed. The interfacial debonding capacity, maximum CFRP strain, and peak value of interfacial shear stress of the CFRP-concrete interface decreased with increasing erosion time under the sulfate dry–wet cycle's action, according to the sulfate dry–wet cycle test results. The sulfate resistance of the CFRP-concrete interface increased after the addition of fly ash. However, the final decrease amplitude of interfacial debonding capacity, CFRP maximum strain, and maximum interfacial shear stress all reduced as the fly ash content increased. The effective bond length of the interface gradually increased with increasing erosion time; however, the change in fly ash content had little effect on the effective bond length, and the final effective bond length of the samples with different fly ash content was the same. Moreover, the CFRP-concrete interfacial bearing capacity model under the sulfate dry–wet cycle was established by introducing sulfate's comprehensive influence coefficient and considering fly ash content's influence. In conclusion, the comparative analysis of the prediction model and test results revealed that the prediction model could well reflect the degradation law of interfacial debonding bearing capacity with sulfate attack time.

Study on fine-toned fly ash content for lightweight strain-hardening cementitious composites (LSHCC) with low fiber content

• The lightweight strain-hardening cementitious composites (LSHCC) were developed by using a low fiber content of 1.2% by volume. • By fine-toning the fly ash content, the tensile strain capacity of LSHCC increased from 2% to 3%. • The properties of LSHCC were explained by pore structure and hydration product content determined by MIP and TGA, respectively. Fly ash content has been suspected of influencing the mechanical properties of strain-hardening cementitious composites (SHCC) by affecting the fiber–matrix interface. However, it has rarely been considered in the material design procedure. This study investigated the effect of fine-toned fly ash content on the tensile performance of lightweight strain-hardening cementitious composites (LSHCC) with fly ash cenospheres and 1.2 vol% of polyvinyl alcohol (PVA) fiber, aiming to find a proper fly ash content with which strain capacity can be improved while tensile strength can be maintained. The effect of fly ash content on the mechanical behavior and impermeability were examined by conducting compressive tests, uniaxial tests and rapid chloride permeability tests (RCPT), which were subsequently explained by the pore structure and hydration product content obtained by mercury intrusion porosimetry (MIP) and thermo-gravimetric analyses (TGA), respectively. The results showed that the tensile strain capacity of LSHCC could be efficiently improved by fine-toning the fly ash content. When the fly ash content exceed 25%, the tensile strain capacity of LSHCC increased from 2% to 3%, while the compressive and tensile strengths were maintained. Base on the desire to achieve a strength-ductility balance and the raw materials used in this study, fly ash content between 25% and 37.5% is deemed appropriate for creating sustainable LSHCC.

Experimental study on effect of fly ash content on self-compacting concrete

Self-compacting concrete (SCC), concrete flows by its own weight, is a recent innovation in concrete industry. In recent times, the usage of self-compacting concrete was increasing. Self-compacting concrete will be form, if it had sufficient binder content and required water content. The strength of concrete majorly depending on water to powder ratio. However, there were workability problems associated while fixing the water powder ratio as per target mean strength when SCC was made, especially for design mix for low strength and high strength of concrete. Apart from this, binder content and mineral admixture will also responsible for strength of concrete. As mineral admixture content increases the strength will reduce. If a relationship between compressive strength and mineral admixture content was found, mix proportions of SCC can be made easily. In this area more research has to be focused. This research is an attempt to assessing the grade of concrete with respect to fly ash content and relationship was developed between fly ash content and compressive strength of concrete. IS 10262-2019 and EFNARC guidelines are used in mix design. A water content of 200 kg/m3 and water powder ratio = 0.4 is kept as constant. Cement was partially replaced with fly ash at proportions of 10%, 20%, 30%, 40%, and 50%. In this research the fresh properties, mechanical properties, and Sulphate attack test of each proportion were tested. The workability properties are measured under different chemical admixture levels, such as 0.5%, 0.6%, and 0.8%. Strength properties are determined with a chemical admixture dosage of 0.6%. The fresh properties of concrete were measured by slump flow test, L–box test, and V–cone test. Mechanical properties such as compressive strength, flexure strength and split tensile strength were determined. Sulphate attack test also conducted by immersing cube specimens in 5% of H2SO4. Further, correlation study was done between compressive strength & fly ash content and also correlation between compressive strength & flexure strength.

Effect of fly-ash as fine aggregate on the workability and mechanical properties of cemented paste backfill

An experimental study was conducted to investigate the effect of fly-ash(FA) as a fine aggregate on filling performance. The effect of FA content on the gradation distribution and compactness of the dry mixture is tested. Slump, bleeding rate, and unconfined compressive strength (UCS) of cemented waste rock-FA backfill (CWFB) samples were also tested at different FA content, solids content, and cement-sand ratio conditions. Results show that FA as a fine aggregate can effectively improve the mixture gradation performance. Short-term (3d/7d) strength increases with FA content, while long-term (28d) strength and slump first increase and then decrease, reaching a maximum value of 8.58 MPa and 27.4 cm respectively at 30% FA content. The bleeding rate first decreased and then stabilized (about 5.2%) with FA content. The UCS showed higher sensitivity to high solid content. The slump reduction rate of samples with high FA content decreases with solid content. Larger cement content will weaken the fluidity. When the cement-sand ratio increased from 1:6–1:4, the slump decreased from 27.5 cm to 23.5 cm, and the bleeding rate decreased to 4.05%. However, the mechanical properties are significantly improved with cement content. This study has positive implications for recycling the FA.

Cyclic Polarization of Corrugated Austenitic Stainless Steel Rebars in Acid Rain: Effect of Fly Ash, pH and Steel Type

The present work studies the effect of fly ash content (0–25 wt.%), pH (8, 12.5), and steel type (316L, 304L) on the cyclic polarization of stainless steel rebars in electrolytes, simulating fresh concrete exposed to acid rain and corroded concrete cover that has exposed the reinforcement to direct acid rain attack. At the same time, it tries to elucidate the corrosion inhibition activities of a Greek lignite fly ash that is a high-Ca fly ash with a questionable effect on the corrosion resistance of concrete. A higher pH results in lower corrosion rates for both steels and all fly ash content. However, different passivity trends are noted for the two steels as a function of pH. The partial replacement of Ca(OH)2 with fly ash up to 20 wt.% has a beneficial effect on the electrochemical behavior of the stainless steel rebars, in terms of both uniform and localized corrosion resistance. However, this trend is reversed at 25 wt.% FA. The reasons for such trends are explored via microstructural examinations of the steels after polarization and XRD analysis of fly ash, as well as reinforced concrete containing fly ash.

Effect of Fly Ash Content in Shotcrete on Mechanical Properties

As one of the key technologies of NATM (New Austrian Tunnel Method) construction, shotcrete has advantages such as simple, fast and adaptable technology, and becomes an indispensable modern construction method in tunnel construction. Adding some fly ash into shotcrete can reduce cracks, compensate shrinkage and improve workability. In this paper, raw materials are selected for mix design, and the mechanical properties of shotcrete with different fly ash content are experimentally studied. The test results show that the 28d compressive, flexural and tensile properties of sprayed concrete shotcrete gradually decrease with the increase of fly ash content. In order to avoid too much strength reduction and ensure structural safety, the fly ash ought to be controlled within a certain amount in the actual construction process.

A study on engineering properties and environmental impact of sustainable concrete with fly ash or GGBS

In this study, we investigated the compressive strength, drying shrinkage, creep, and CO2 emissions per unit volume of concrete containing fly ash or ground granulated blast-furnace slag (GGBS) as part of cement or fine aggregate. We introduced a parameter KL to capture the effect of fly ash content in the creep prediction model. The results showed that mixing fly ash as part of the fine aggregate in concrete can effectively increase the strength of concrete and reduce shrinkage and creep. Therefore, introducing a parameter to capture the effect of fly ash content in the prediction model can accurately predict the creep strain of concrete.

Time-Dependent Gas Permeability of Class C Fly Ash Concrete and Correlation with Its Microstructural Parameters

Based on the field tests of fly ash concrete with a maximum exposure time of 840 days, the effects of fly ash content and exposure time on gas permeability of concrete were studied. A time-dependent gas permeability coefficient model considering the influence of fly ash content was established. The pore structure parameters of fly ash concrete with different exposure times were measured by the nuclear magnetic resonance (NMR) method. In addition, the time-dependent relationship between microstructural parameters and gas permeability coefficient was discussed. Results show that adding 20%–40% fly ash into concrete can effectively reduce the gas permeability and improve its microstructural features after exposure of 360 days; concrete with 30% fly ash has the minimum critical pore size and average pore size, which have the most significant effect on reducing the gas permeability. With prolonged exposure times, fly ash concrete can increase (decrease effectively) the proportion of pore diameter of 10–50 nm (100–500 nm). Total porosity and critical pore diameter can better characterize the time-dependent gas permeability.

Research Summary on the Processing, Mechanical and Tribological Properties of Aluminium Matrix Composites as Effected by Fly Ash Reinforcement

Fly ash is the main waste as a result of combustion in coal fired power plants. It represents about 40% of the wastes of coal combustion products (fly ash, boiler ash, flue gas desulphurization gypsum and bottom ash). Currently, coal waste is not fully utilized and waste disposal remains a serious concern despite tremendous global efforts in reducing fossil fuel dependency and shifting to sustainable energy sources. Owing to that, employment of fly ash as reinforcement particles in metallic matrix composites are gaining momentum as part of recycling effort and also as a means to improve the specifications of the materials that are added to it to form composite materials. Many studies have been done on fly ash to study composite materials wear characteristics including the effects of fly ash content, applied load, and sliding velocity. Here, particular attention is given to studies carried out on the influence FA content on physical, mechanical, and the thermal behavior of Aluminium-FA composites. Considerable changes in these properties are seen by fly ash refinement with limited size and weight fraction. The advantage of fly ash addition results in low density of composites materials, improvement of strength, and hardness. It further reduces the thermal expansion coefficient and improve wear resistance.

Effects of Fly Ash Content on the Strength Development of Soft Clay Stabilized by One-Part Geopolymer under Curing Stress

AbstractThe objective of this study was to evaluate the effects of fly ash content on the strength development of soft clay stabilized by one-part geopolymer (OPG) under K0 stress conditions. In th...