Fly Ash Ratio Research Articles

Evaluation of Bonding Behavior between Engineered Geopolymer Composites with Hybrid PE/PVA Fibers and Concrete Substrate.

Engineered geopolymer composites (EGCs) exhibit excellent tensile ductility and crack control ability, making them promising for concrete structure repair. However, their widespread use is limited by high costs of reinforcement fiber and a lack of an EGC-concrete interface bonding mechanism. This study investigated a hybrid PE/PVA fiber-reinforced EGC using domestically produced unoiled PVA fibers to replace commonly used PE fibers. The bond performance of the EGC-concrete interface was evaluated through direct tensile and slant shear tests, focusing on the effects of PE fiber content (1%, 2%, and 3%), fiber hybrid ratios (2.0:0.0, 1.5:0.5, 1.0:1.0, 0.5:1.5, and 0.0:2.0), concrete substrate strength (C30, C50, and C70), and the ratio of fly ash (FA) to ground granulated blast furnace slag (GGBS) (6:4, 7:3, and 8:2) on interface bond strength. Results showed that the EGCs' compressive strength ranged from 77.1 to 108.9 MPa, with increased GGBS content significantly enhancing the compressive strength and elastic modulus. Most of the specimens exhibited strain-hardening behavior after initial cracking. Interface bonding tests revealed that a PE/PVA ratio of 1.0 increased tensile bond strength by 8.5% compared with using 2.0% PE fiber alone. Increasing the PE fiber content, PVA/PE ratio, GGBS content, and concrete substrate strength all improved the shear bond strength. This improvement was attributed to the flexible fibers' ability to restrict thermo-hydro damage and deflect and blunt microcracks, enhancing the interface's failure resistance. Cost analysis showed that replacing 50% of the PE fiber in EGC with unoiled PVA fiber reduced costs by 44.2% compared with PE fiber alone, offering the best cost-performance ratio. In summary, hybrid PE/PVA fiber EGC has promising prospects for improving economic efficiency while maintaining tensile ductility and crack-control ability. Future optimization of fiber ratios and interface design could further enhance its potential for concrete repair applications.

Study on the properties of anorthite-based porous sound-absorbing materials prepared by steel slag and fly ash

The efficient utilization of solid wastes, such as fly ash and steel slag, has attracted significant attention across the globe. In this paper, these two kinds of waste materials are used to prepare porous sound-absorbing materials, so as to achieve efficient resource utilization and environmental protection, and promote green manufacturing and circular economy. In this study, steel slag and high-alumina fly ash were used as the primary raw materials to prepare green bodies via organic foam impregnation. Subsequently, a high-temperature sintering process was implemented to get the porous sound absorption material product from the green bodies. The effects of several factors, including the ratio of steel slag and fly ash, sintering temperature, and pore structure, on the sound absorption and mechanical properties of the product were investigated. Based on the anorthite region in the CaO–Al2O3–SiO2 ternary phase diagram region, the composition ratio of the material was designed. The composition and microstructure of the material were characterized by X-ray diffraction and scanning electron microscopy. From the results, with the increase of the ratio of fly ash and steel slag, the composition of low melting point substances in the system decreases, and the amount of liquid phase decreases, which weakens the pore blocking phenomenon inside the material, resulting in the increase of pore size and noise reduction coefficient of the material. Besides, higher sintering temperature tends to correlate to greater density and higher compressive and flexural strengths but lower porosity, and the sound absorption coefficient demonstrated a peak with respect to sintering temperature. Furthermore, when the reduction of polyurethane sponge body pore size was taken into account, the product's sound absorption coefficient also showed a peak. The optimal parameters for our porous materials are as follows: fly ash:steel slag = 48 : 25, polyurethane sponge pore size = 40 ppi, sintering temperature = 1160 °C at 1-h duration (bulk density = 573.98 kg/m3), compressive strength = 1 MPa, porosity = 79.35 %, and noise reduction coefficient = 0.47.

Understanding the synergistic geopolymerization mechanism of multiple solid wastes in ternary geopolymers

The use of ground granulated blast furnace slag (GBFS), fly ash (FA) and steel slag (SS) to form ternary geopolymers consumes several industrial solid wastes and produces high-performance construction materials. However, the unexplored synergistic geopolymerization mechanism of multiple solid wastes limits the design of high-performance ternary geopolymers. This study investigated the synergistic mechanism through testing the macroscopic performances such as unconfined compressive strength (UCS), final setting time (FST) and fluidity, and characterizing the microscopic structure of ternary geopolymers with different mixture proportions. In addition, the influence of variables on strength development of ternary geopolymers is analyzed by developing machine learning models. Results reveal that the highest strength of ternary geopolymers was achieved at a ratio of FA to GBFS to SS of 3:5:2, and alkali activator to precursor materials of 0.08. Addition of 20 % SS refines the pore network, reducing cumulative and detrimental pore volumes, thus enhancing compressive strength. In addition, the SS addition extends the heat generation peak during geopolymerization due to its slower reaction kinetics. Material components (Na/Al, Si/Al, Ca/Si) have a significant influence on UCS, with Na/Al ratio being the most sensitive variable. The study provides a new approach for utilization of bulk industrial wastes.

Study on the high-temperature resistance of metakaolin-fly ash-based geopolymers

The effect of high temperature will trigger the evolution of a series of phase compositions and microstructures within metakaolin-fly ash-based geopolymers, resulting in changes in the deterioration of mechanical properties. To study the high-temperature resistance of metakaolin-fly ash-based geopolymers, the ratio of metakaolin and fly ash was adjusted. This article studied compressive strengths, visual appearance, mass loss ratio, permeability, products, and microstructure. The results showed that as the temperature increases, the compressive strength first increases and then decreases. The geopolymers have the highest compressive strength after exposure to temperatures of 200 °C. The change in compressive strength is determined by both the increase caused by the polymerization reaction and the decrease caused by microcracks. Moreover, metakaolin-fly ash-based geopolymers containing 75% metakaolin (GFMK-75) have the best high-temperature resistance. The residual compressive strengths of GFMK-75 after exposure to 200, 600, 800, and 1000 °C for 2 h are 183.1%, 95.2%, 75.8%, and 65.2%, respectively. Other analyses all confirmed the above conclusions. In summary, the residual compressive strength of metakaolin-fly ash-based geopolymers is highest after exposure to 200 °C, and GFMK-75 shows the best high-temperature resistance compared to others. The findings offer a theoretical foundation for the high-temperature resistance of metakaolin-fly ash-based geopolymers.

Experimental study on CO2 sequestration capacity and mechanical characteristics evolution of solid wastes based carbon-negative backfill materials

The employment of solid waste, notably coal gangue, in carbon-negative backfill mining technology for mineralization and filling in coal mine gobs, is recognized as a productive method for carbon sequestration and waste management, with research primarily dedicated to engineering advanced mineralized backfill materials. Under this background, four variables, including the ratio of gangue to solids (RG-S), water-cement ratio (RW-C), ratio of fly ash to solid wastes providing calcium (Ca) (RA-Ca), and ratio of flue gas desulfurization (FGD) gypsum to carbide slag (RF-CS) were defined to formulate gangue-based mineralized backfill materials, with orthogonal experiments assessing their effects on CO2 sequestration and mechanical characteristics. The results indicate that RW-C consistently emerges as the primary factor influencing both the amount of sequestered CO2 and the mechanical properties of gangue-based solid waste mineralized backfill materials. The amount of sequestered CO2 demonstrates a direct proportionality to RW-C and mechanical strength demonstrates an inverse relationship with RW-C. After 45 minutes of stirring and carbon sequestration, samples in various groups exhibited an maximum sequestered CO2 amount of 18.96 g·kg−1, with a maximum sequestration rate of 0.20 g·kg−1·min−1. The process of CO2 sequestration enhances the compressive properties of mineralized backfill materials derived from gangue based solid wastes.

Low-temperature subcritical water dechlorination composites of waste PVC/coal fly ash with powerful sensing activity for chemiluminescent detection of acetamiprid and imidacloprid

Pesticide residues in agricultural products are serious threat to people's health. Real-time monitoring of pesticides residues in the environment and agricultural products posed challenges to sustainable methods with high analytical performance for pesticide detection. Herein, waste PVC/coal fly ash (the mass ratio of PVC and coal fly ash was 4:1) was dechlorinated in subcritical water at low temperature to achieve nearly 100 % dechlorination of PVC and obtain carbon-based composite materials (CM-Fe/Al/Si-dPVC) with strong sening activity. For CM-Fe/Al/Si-dPVC, CFe bonding resulted in strong electron migration, and nano/μm SiO2 and Al2O3 doping in the layered polyene C matrix provided large specific surface area, and silicon hydroxyl created good heterogeneous catalytic interfaces. CM-Fe/Al/Si-dPVC could strongly trigger luminol chemiluminescence (CL) reaction and produce intense CL signals. Neonicotinoid pesticides (acetamiprid and imidacloprid) bonded with CM-Fe/Al/Si-dPVC through coordination chelation and hydrogen bonding, which shielded the catalytic active site and increased the Fermi level of system, thus quenching CL reaction. Inspired by these, a cheap CL assay was constructed for detecting neonicotinoids combinations of acetamiprid and imidacloprid (NICs). The detection limits of NICs were 0.7 ng/L. Satisfactory recoveries were obtained for real agricultural products and environmental samples. The results of life cycle evaluation (LCA) revealed that the strategy had significantly small global warming potential (GWP). This work presented a sustainable method with environmental benefits for the detection of neonicotinoids, and also opened up new way for the recycling of organic solid wastes.

Multi-objective optimization of ternary geopolymers with multiple solid wastes

The design of the mixtures of ternary geopolymers is challenging due to the need to balance multiple objectives, including cost, strength, and carbon emissions. In order to address this multi-objective optimization (MOO) problem, machine learning models and the NSGA-II algorithm are employed in this study. To train the machine learning models, namely Artificial Neural Network (ANN), Support Vector Regressor, Extremely Randomized Tree, and Gradient Boosting Regression, 120 mixtures with uniaxial compressive strength (UCS) values of ternary geopolymers with fly ash (FA), granulated blast furnace slag (GBFS) and steel slag (SS) as precursor materials were obtained from laboratory tests. Results show that the ternary geopolymer with the ratio of FA:GBFS:SS of 2:5:3 has the highest 28-d UCS of 46.8 MPa. The predictive accuracy of the ANN model is the highest with R = 0.949 and RMSE=3.988 MPa on the test set. Furthermore, the Shapley Additive Explanations analysis indicates that precursor materials exhibit the most significant influence on the UCS, with the content of GBFS being particularly influential. Based on the ANN model and NSGA-II algorithm, a multi-objective optimization (MOO) model is developed to optimize simultaneously the strength, cost and carbon emission of the ternary geopolymer. The derived MOO model can be used to design mixtures of other cementitious materials with multiple objectives.

Investigation and Utilization of Alkali-Activated Grouting Materials Incorporating Engineering Waste Soil and Fly Ash/Slag

The alkali-activated composites technique is a promising method for the in situ preparation of cavity filling/grouting materials from engineering waste soil. To investigate the feasibility of engineering waste soil utilization by the alkali activation process, the macroscopic and microscopic properties of the fly ash/slag-based alkali-activated composites, after solidification/stabilization (S/S) with sandy clay excavated at Baishitang Station of Shenzhen Metro, were studied. The unconfined compressive strength (UCS) test was conducted to evaluate the S/S effect of alkali-activated composites. The results show that the optimum quality ratio of slag and fly ash correspond to 7:3, the modulus of alkaline activator to 1.3, and the alkalinity of alkaline activator to 10%. The alkali-activated composite’s strength under these parameters can reach 45.25 MPa at 3 days, 49.85 MPa at 7 days, and 62.33 MPa at 28 days. A maximum 3-day UCS of 21.71 MPa, 75% of the 28-day UCS, was achieved by an engineering waste soil and alkali-activated composites mass ratio of 5:5, slaked lime content of 4.5%, and a water-to-solid ratio of 0.26, and it can also meet the required fluidity and setting time for construction well. Fluidity is primarily affected by the soil-to-binder ratio, which decreases as the ratio decreases, while the water-to-solid ratio increases fluidity. Slaked lime has minimal impact on fluidity. The setting time is mainly influenced by the soil-to-binder ratio, followed by slaked lime content and water-to-solid ratio, with setting time shortening as the soil-to-binder ratio and slaked lime content increase, and lengthening as the water-to-solid ratio increases. Through Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectroscopy (EDS) tests, microscopic analysis showed that loose granular units are firmly cemented by alkali-activated composites. Based on the results of on-site grouting tests in karst caves, the alkali-activated grout materials reached a strength of 5.2 MPa 28 days after filling, which is 162.5% of the strength of cement grouting material, satisfying most of the requirements for cavity filling in Shenzhen.

Age-dependent deflection analysis of high-volume fly ash RC beams: experimental and artificial neural network modelling

This research examines the influence of high-volume fly ash (HVFA) on reinforced concrete (RC) beam deflections over 180 days of continuous loading. The study comprises eight fly ash-based concrete mixes with varying fly ash ratios (0–60%). Experimental assessments were conducted on two load levels, corresponding to 25% and 50% of the initial cracking load. Thirty-two full-scale RC beams, each measuring 100 × 150 × 1800 mm, were fabricated for both load levels. Long-term deflections were monitored for all concrete mixes through sustained four-point bending tests at ages ranging from 1 to 180 days. A comparative analysis of the overall mid-span deflection between conventional and fly ash concrete RC beams was carried out against established design codes. It was determined that high-volume fly ash RC beams exhibited less creep and shrinkage deflection compared with conventional RC beams. Moreover, artificial neural network (ANN) modelling was also carried out to propose a significant model helpful in predicting the total deflection of RC beams containing any fly ash content and at any age of concrete. The present study offers valuable insights for engineers and designers, facilitating the evaluation of age-dependent deflection patterns in RC beams constructed with reinforced high-volume fly ash concrete.

Effect of magnesium hydroxide fly ash compounded flame retardant on the properties of polyvinyl chloride

Abstract This study investigated the effects of compound flame retardants on polyvinyl chloride (PVC) film. Four F-M/PVC composite film materials (F0.1M0.1/PVC, F0.1M0.2/PVC, F0.1M0.3/PVC, and F0.1M0.4/PVC) were obtained by blending different ratios of fly ash (FA) and magnesium hydroxide (MH(OH)2, MH) compounded flame retardants (F-M) with PVC. The mechanical properties, thermal stability, and smoke density of the composite film materials were examined. The results showed that the loss of mechanical properties of F0.1M0.2/PVC composites was small. TGA analysis showed that the thermal stability of the four F-M/PVC composites was improved. The degradation temperature of pure PVC at T50 was 286.5°C, and that of F0.1M0.2/PVC composites was 335.38°C. Smoke density analysis showed that the maximum smoke density of pure PVC was 6.310, and the maximum smoke density of the composite material (F0.1M0.4/PVC) was reduced to 5.960, which had a better smoke suppression effect. For the comprehensive utilization of Salt Lake magnesium resources, the development of PVC composite film materials to provide the experimental basis has a strong practical value.

Compressive Strength and Water Absorption Capacity on Brick Interlock with Fly Ash Addition

Interlock brick is an environmentally friendly substitute for house wall materials because the manufacturing process is not burned like red brick. This method of installing interlocking walls, like Lego, can function as a structure for sluice gates, columns and ring beams without the need for plastering or painting, so it is more effective and efficient and can reduce cement consumption. Several actions must be taken to minimize the use of cement by using environmentally friendly materials. One of the environmentally friendly materials that will be researched is Interlock bricks made from a mixture of Fly Ash . This research aims to determine the compressive strength and water absorption capacity of Interlock bricks mixed with Fly Ash. The research method begins by looking for interlock brick parameter data in the form of compressive strength and water absorption capacity. Compressive strength is a parameter of the mechanical suitability of interlock bricks , while water absorption is the ability of a material to absorb water. There are 3 variations of the mixture, namely with the ratio Fly Ash : Sand: Cement, mixture I (3: 3: 1) Fly Ash 43% , mixture II (4 : 3 : 1) Fly Ash 50% , and mixture III (5 : 3 : 1) Fly Ash 56% calculation divided based on the percentage of the amount of Fly Ash , obtained the compressive strength value of Interlock brick from the Fly Ash mixture in mixture I 16.0 kg/m2 and water absorption capacity 20%, mixture II 24.7 kg/m 2 and strength water absorption 17.5%, mixture III 10.3 kg/m 2 and water absorption 21.8%. According to SK-SNI-S-04-1989-F Interlock brick mix II with a Fly Ash composition of 50% is close to class K25 (25 kg/m 2 ) and has an absorption capacity value of <20.0% according to the absorption capacity limit based on SNI 15- 2094-2000.Keywords: Interlock Bricks, Fly Ash, Compressive Strength, Water Absorption.

Effects of sisal fiber and fly ash on the mechanical and tribological performances of brake friction composites

AbstractIndustrial development has led to an increase in demand for friction materials, resulting in increasingly prominent environmental issues throughout their entire life cycle, and developing green and eco‐friendly brake friction materials has become a focus in the braking field. This paper explores the mechanical and tribological properties of fly ash (industrial waste) and sisal fiber (natural fiber) as eco‐friendly components to enhance brake friction materials. Four samples containing different ratios of fly ash and sisal fiber were prepared and tested with a variable‐speed friction testing machine. The results show that the eco‐friendly alternative combination can effectively improve the friction coefficient, and reduce friction fluctuations and thermal degradation, but the wear rate will also increase accordingly. In addition, the worn morphology reveals the formation of the contact platform and wear mechanism. A hybrid integration of analytic hierarchy process (AHP) and multi‐objective optimization by ratio analysis (MOORA) was used to weigh various evaluation indicators objectively and rank the samples. The sample with 8% fly ash and 6% sisal fiber exhibited the best comprehensive tribological performance.Highlights Development of eco‐friendly brake friction composites with natural and waste additives. Investigation of the effect of the natural wastes' ratio on prepared composites' physical, mechanical, and tribological properties. Evaluation of brake friction composites with AHP‐MOORA. Sample S6F8 exhibits the best comprehensive tribological performance.

Preparation and characterization of cementitious materials from dedioxinized and dechlorinated municipal solid waste incineration fly ash and blast furnace slag

To address the resource utilization issue of MSWI fly ash, a method has been proposed to prepare cementitious materials using harmlessly processed MSWI fly ash (HPFA). After washing and thermal treatment, The physicochemical properties of HPFA were characterized using QXRD, ICP, XRF, and GC-MS. Cementitious materials were prepared using HPFA, gypsum and blast furnace slag (BFS) as raw materials, Through XRD, TG, FTIR, TEM, and SEM-EDS methods, the hydration and hardening characteristics were investigated, and the leaching of heavy metals from solidified materials in simulated surface water and landfill environments was evaluated using ICP-MS. The results indicate that the harmless treatment can effectively reduce the chloride content and dioxins in MSWI FA but still contains heavy metals. The addition of HPFA (10%-50%) can enhance the compressive strength of cementitious materials, accelerate the exothermic process of cement hydration, and increase the total heat release of hydration, implying an improvement in the degree of hydration of the system.HPFA could effectively promote the hydration of gypsum and BFS, resulting in the higher formation of ettringite and C-(A)-S-H（C/S=1，Al/Si=0.3）.The formation of C(Mg/Fe)-(A)-S-H suggests that the Fe-Mg solid solution phase in HPFA may have participated in the hydration reaction. The increased stability of highly cross-linked (Q4) silicate tetrahedral structure with time implies that the material may have good durability. The leaching amount of heavy metals met the standards of Class I surface water in GB3838–2002 and GB5085.3–2007 which implies that the material has environmental safety. This study innovatively provides a preparation path for harmless MSWI fly ash and cementitious material ratios, reveals the hydration mechanism of HPFA in cementitious materials, evaluates the solidification ability of heavy metals, and provides important ideas for the resource utilization of MSWI fly ash.

Preparation and Properties of Expansive Backfill Material Based on Municipal Solid Waste Incineration Fly Ash and Coal Gangue

To realize the large-scale utilization of municipal solid waste incineration (MSWI) fly ash in the field of building materials and to reduce the cost of coal mine backfill mining, the effects of the mixing ratio of cementitious materials, the particle size distribution of aggregates, and the amount and mass concentration of cementitious materials on the properties of backfill materials were experimentally investigated, and the microstructure of the hydration products was analyzed. The results showed that as the mass ratio of MSWI fly ash to bottom ash increased, the rate of expansion of the cementitious system continued to increase, and the compressive strength of the cementitious system continued to decrease. The Al (aluminum) and AlN (aluminum nitride) in the fly ash reacted with water to generate gas, causing the expansion of the cementitious materials; NaOH increased the alkalinity of the solution, which promoted the formation of more bubbles, thereby improving the expansion performance of the cementitious material. When the content of NaOH was 0.9%, the sample rate of expansion could reach 15.9%. The addition of CaCl2 promoted the early hydration reaction of the cementitious material, forming a dense microstructure, thus improving the early strength and rate of expansion of the cementitious material. The compressive strength of the backfill body increased as the fractal dimension of the aggregate particles increased, and the particle grading scheme of group S1 was optimal. The 1-day, 3-day, and 28-day strengths of the backfill body of group S1 reached 0.72 MPa, 1.43 MPa, and 3.26 MPa, respectively. It is recommended to choose a backfill paste concentration ranging between 78.5% and 80% and a reasonable amount of cementitious material between 20% and 25%. After the MSWI fly ash was prepared as a backfill material, the leaching of potentially harmful elements in the fly ash was greatly reduced, and the concentration of dioxin was reduced to 13 ng TEQ/kg. This was attributed to the dilution of the cement, the physical encapsulation of gel products, and the isomorphous replacement of Ca2+ in calcium aluminate chloride hydrate.

EXAMINING THE APPLICABILITY OF ALKALI ACTIVATED BINDERS (AABS) AS A LANDFILL LINER AND COVER

Landfill liner is a containment system used between landfill waste and the ground soil to prevent the migration of leachate into the soil and groundwater. Clay is typically used as a liner in the landfill barrier system due to efficiency and low permeability. Over the last decade, different types of binders such as cement, fly ash, and slag have been used with clay to improve the mechanical characteristics and reduce hydraulic conductivity of natural clay liners. This study introduced a new sustainable technique where treated dune sand mixed with alkali activated binder (AAB) made with fly ash (FA), ground-granulated blast-furnace slag (GGBFS), and alkali activated solutions are used as a landfill liner system, due to the unavailability of natural clay in most countries. Therefore, lab-scale compacted specimens with different mixing ratios of AABs treated desert sand were prepared and cured for 7 days to conduct a series of compressive strength. The results showed that the 20% binder mixed with 30% FA, 70% slag, and alkali solution of 0.5 have a high compressive strength with 12 MPa compared with other mixing ratios. However, a 10% binder with same precursors ratio of FA and slag has shown a less strength regardless of alkali solution with around 3 MPa. Finally, all mixing ratios have shown that the strength met the requirements of landfill liner system which were greater than 200 kPa.

EXAMINING THE APPLICABILITY OF ALKALI ACTIVATED BINDERS (AABS) AS A LANDFILL LINER AND COVER

Landfill liner is a containment system used between landfill waste and the ground soil to prevent the migration of leachate into the soil and groundwater. Clay is typically used as a liner in the landfill barrier system due to efficiency and low permeability. Over the last decade, different types of binders such as cement, fly ash, and slag have been used with clay to improve the mechanical characteristics and reduce hydraulic conductivity of natural clay liners. This study introduced a new sustainable technique where treated dune sand mixed with alkali activated binder (AAB) made with fly ash (FA), ground-granulated blast-furnace slag (GGBFS), and alkali activated solutions are used as a landfill liner system, due to the unavailability of natural clay in most countries. Therefore, lab-scale compacted specimens with different mixing ratios of AABs treated desert sand were prepared and cured for 7 days to conduct a series of compressive strength. The results showed that the 20% binder mixed with 30% FA, 70% slag, and alkali solution of 0.5 have a high compressive strength with 12 MPa compared with other mixing ratios. However, a 10% binder with same precursors ratio of FA and slag has shown a less strength regardless of alkali solution with around 3 MPa. Finally, all mixing ratios have shown that the strength met the requirements of landfill liner system which were greater than 200 kPa.

Experimental studies on pavement quality geopolymer-based concrete (PQGPC) for high-volume roads: a sustainable infrastructure

ABSTRACT Studies on Geopolymer concrete (GPC) have received a lot of focus over the last several years as a result of its potential as a carbon-neutral construction material. Because of their significant positive impact on the environment and economy, geopolymers are being investigated as a replacement for OPC in pavements. The use of GPC for structural elements has been studied in numerous research, but a few attempts have been made to use it as Pavement Quality Concrete (PQC). This experimental investigation aims to develop a mixed proportion of Fly Ash (FA) and Ground Granulated Blast Furnace Slag (GGBFS)-based Pavement Quality Geopolymer Concrete (PQGPC) which can be utilised for high-volume roads. Investigations include varying the ratio of FA and GGBFS (40% and 50%) in combination with various molarities of sodium hydroxide (NaOH) and alkaline solution to binder ratios (As/Bi). The binder content is fixed at 400 and 450 kg/m3. The mix with a 50:50 ratio of FA and GGBFS with 450 kg/m3 binder content having a 14M NaOH solution with SS/SH of 2.5 at an As/Bi ratio of 0.45 achieved the required workability and strength properties at ambient curing of 28 and 90 days based on the criteria of IRC:58-2015.

Red mud modified phosphogypsum based self-leveling mortar: Hydration mechanism, heavy metal migration law and spatial distribution characteristics

In the production processes of phosphoric acid and alumina, chemical enterprises generate solid waste such as red mud (RM), phosphogypsum (PG), and fly ash (FA). The environmentally friendly utilization of these waste materials is of crucial significance. Therefore, this study focuses on investigating the impact of collaborative modification using diverse solid wastes on the macroscopic properties and internal microstructure of self-leveling mortar. Through a careful selection process, the optimal ratio for red mud and phosphogypsum self-leveling mortar(RPSM) has been identified during the research. This study not only provides substantial support for the effective utilization of solid waste but also contributes to the improvement of overall performance and structural characteristics of the mortar. Based on this, the hydration characteristics, leaching patterns, and spatial distribution characteristics of heavy metals in RPSM were evaluated. The research revealed that the optimal ratios of RM, PG, FA, PC, river sand, and heavy calcium carbonate powder in RPSM were 20.7%, 13.8%, 17.1%, 13.8%, 17.3%, and 17.3%, respectively. Under a water-binder ratio of 0.18, the flexural and compressive strength of the mortar specimens after 14 d of curing can reach 4.3 and 31.6 MPa. Through comprehensive analysis and discussion of the performance, microstructure, and dynamics of the hydration process of RPSM, the main processes of mortar hydration were elucidated. Environmental risk assessments indicated no environmental risks from heavy metals in RPSM. Human health risk assessment suggested carcinogenic risks from Cr and Cd in RPSM through oral exposure, leading to restrictions on the content of characteristic heavy metals in different application scenarios. Furthermore, fitting results of the release kinetics of heavy metals indicated that the leaching of heavy metals in RPSM can be well fitted with kinetic models, allowing the determination of the optimal safe age of RPSM containing harmful heavy metals. Finally, using interpolation and vertical distribution simulation by software such as ArcGIS, the spatial distribution characteristics of heavy metals in RPSM during use were analyzed. The research can supply fundamental academic support for the recycling of solid wastes like RM and the control of environmental risks associated with heavy metal leaching in building materials.

Effect of fly ash and metakaolin on the mechanical properties and microstructure of magnesium ammonium phosphate cement paste

To solve the current application problems of magnesium phosphate cement (MPC), this study investigates the working properties, hydration process, strength performance, bonding strength, and other characteristics of MPC with 10% to 40% substitution of fly ash (FA) and metakaolin (MK) using different mixing methods. Among them, FA has beneficial effects such as spherical effect, microaggregate effect, and volcanic ash effect in the MPC system, and in addition, the aluminum phase material contained in MK has been shown to react with phosphates. This experimental design was aimed at determining the intrinsic link between bond strength and the aforementioned properties of MPC. The findings suggest that the optimal strength performance was achieved with an FA content of 20%, while the best bonding performance was observed at an FA content of 10%. There was minimal difference in peak hydration temperature among different MK admixtures, and no significant deviation was observed in the strength properties. The poor fluidity of the slurry hindered its penetration into the matrix, resulting in weak early bonding strength within the MK group. In the MK=5% mixing ratio of FA and MK (FK), FK-31 exhibited excellent strength performance with distinct advantages in terms of hydration product quantity and morphology, as well as remarkable macroscopic properties. On the other hand, in the MK=10%, FK-22 demonstrated outstanding performance utilizing the FK groups with strength comparable to FA-1 and FA-2. However, its toughness index-C/F decreased to a minimum level, which implied that the toughness of MPC was improved. Simultaneously, it displayed superior bonding properties surpassing MPC by reaching 5 MPa at 7d. The experimental group showed that excellent bonding properties mainly relied on chemical penetration as the bounding mechanism while interfacial damage primarily manifested as matrix damage. The microscopic tests showed that aluminum-containing phase substances were detected in the MK group, which made the equal substitution amount of MK show superior strength to FA. In this study, MK and FA were mixed in two ways: individual and composite mixing to investigate the modification effect of compounding of dopes with different chemical and physical properties and their bonding properties were analyzed. The test results indicated that under appropriate mixing proportions, incorporating both MK and FA for modified MPC could compensate for shortcomings associated with single mixing methods and become a novel option for modified MPC.

Synergy of micron graphite and fly ash for alkali-activated cementitious material: Electromagnetic absorption characteristics and mechanism

To attain a balance between compressive strength and electromagnetic wave absorption performance, this paper combined two electromagnetic wave loss mechanisms (magnetic loss and electrical loss), and prepared an environmentally friendly alkali-activated slag/fly cementitious material (ASFC) using micron graphite (MG) as the absorber and ground granulated blast furnace slag (GGBS) and fly ash (FA) as the precursors. The conductivity, electromagnetic wave absorption characteristics and compressive strength of ASFC with different ratios of GGBS and FA, MG size (800 mesh, 320 mesh, and 100 mesh), and content were investigated. The results indicated that when the ratio of GGBS and FA was 7:3, natural resonance and eddy current loss contributed to electromagnetic waves absorption at 8.2–11.0 GHz and 11.0–15.5 GHz range respectively. Additionally, the conductivity of MG/ASFC showed typical percolation characteristics, with the percolation threshold reached at a dosage of 3 wt%. In the 8.2–18.0 GHz, the incorporation of MG significantly augmented the conductive loss and polarization loss of ASFC. Furthermore, smaller-size MG was more beneficial for facilitating conductive loss of MG/ASFC among three different sizes. By adding 2 wt% of MG with 800 mesh, MG/ASFC can achieve a minimum reflection loss of −27.8 dB with a bandwidth of 3.0 GHz (Reflection loss ˂-7 dB). However, when compared to other cement-based absorbing materials reported, the MG/ASFC prepared in this experiment demonstrated better compressive strength and wave absorption properties. This finding contributing to a better understanding of green building materials with electromagnetic radiation protection capabilities.