Mass Ratio Of Ash Research Articles

New geopolymer preparation methods and its application by recycle of double-waste: ground granulated blast furnace slag and fly ash

ABSTRACT This article mainly studies new geopolymer preparation methods by recycle of double waste:ground granulated blast furnace slag (GGBFS) and fly ash as geopolymer precursor, through different mass ratio of GGBFS and fly ash, to prepare geopolymers by alkali activation, the samples is cured at ambient temperature and the mechanical test is carried out together with the analysis of XRD, SEM and EDS to research the mechanism of strengthening and geopolymerisation. After analysis we find that the sample prepared by 30% mass ratio of GGBFS have good initial strength and short setting time, as well as best mechanical performance, which is attributed to moderate Ca2+ introduction accelerates the speed of geopolymerisation and the reactants of N-A-S-H gel, C-A-S-H gel and hydrated C-S-H help to bridge the gaps between the different hydrated phases, unreacted particles and matrix, result in a homogeneous and compacted geopolymeric sample. When GGBFS mass ratio above 50%, the mechanical of samples is deteriorated due to too much hydrated calcium containing compounds are formed and covered on the unreacted GGBFS particles surface to block further geopolymerisation. The acid attack test and water resistance test are carried out to analysis the durability between 30% GGBFS introduced geopolymer and ordinary Portland cement (OPC). In additional, a field application in case of 30% GGBFS introduced geopolymer grouting repair material indicated desirable construction based on visual observation and ground-penetration radar scanning.

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.

The research on the mechanical properties, microstructure, environmental impacts of environmentally friendly Alkali-activated ultra high performance concrete (AAUHPC) matrix with varied design parameters

Alkali-activated material prepared by the silicon aluminum solid wastes are commonly considered as the low-carbon cementitious material, which has important significance for promoting the sustainable development of construction materials. The mechanical properties, reaction mechanisms, and microstructure evolutions of Alkali-activated Ultra High Performance Concrete (AAUHPC) matrix with 7 design parameters were comprehensively studied through testing the fluidity, 28 days compressive strength, 28 days flexural strength, hydration heat, and microstructures. The environmental impacts including carbon emissions and energy consumption are evaluated. Appropriately increasing Na2O dosage, silicate modulus (Ms), and granulated blast furnace slag (GBFS) to fly ash (FA) mass ratio (GBFS/FA) and decreasing silica fume (SF) content and water to binder ratio (W/B) are conducive to accelerating the early reaction of AAUHPC. High Na2O dosage, Ms, SF content, and W/B are not conducive to increasing the 3 days reaction degree of AAUHPC, while the moderate GBFS/FA is corresponding to the higher 3 days reaction degree of AAUHPC. The optimal Na2O dosage, Ms, GBFS/FA, SF content, sand to binder ratio (S/B), fine sands content in quartz sands, W/B are 8 %, 1.4, 4.5:1, 10 %, 1.0, 50 %, and 0.34 for the 28 days mechanical properties. The acquired AAUHPC matrix with fluidity of 218 mm and the lowest porosity has 28 days compressive strength of 114.8 MPa and 28 days flexural strength of 10.6 MPa, whose microstructure has more high polymerization degree C(N)-A-S-H gels with higher Al/Si, lower Na/Al, and lower Ca/Si molar ratios. Compared to the traditional Ultra High Performance Concrete (UHPC), the environmentally friendly AAUHPC can reduce the carbon emission by 42%–52 % and the energy consumption by 5%–18 %. The total CO2 emission of per unit compressive strength (1.0 MPa) of concrete per cubic meter (CI) is in range of 2.5–3.7 kg, which is significantly lower than the traditional UHPC (6.98 kg/MPa•m3).

Deep learning–based prediction of compressive strength of eco-friendly geopolymer concrete

The greenhouse gases cause global warming on Earth. The cement production industry is one of the largest sectors producing greenhouse gases. The geopolymer is produced with synthesized by the reaction of an alkaline solution and the waste materials such as slag and fly ash. The use of eco-friendly geopolymer concrete decreases energy consumption and greenhouse gases. In this study, the fc (compressive strength) of eco-friendly geopolymer concrete was predicted by the deep long short-term memory (LSTM) network model. Moreover, the support vector regression (SVR), least squares boosting ensemble (LSBoost), and multiple linear regression (MLR) models were devised to compare the forecast results of the deep LSTM algorithm. The input variables of the models were used as the mole ratio, the alkaline solution concentration, the curing temperature, the curing days, and the liquid-to-fly ash mass ratio. The output variable of the proposed models was chosen as the compressive strength (fc). Furthermore, the effects of the input variable on the fc of eco-friendly geopolymer concrete were determined by the sensitivity analysis. The fc of eco-friendly geopolymer concrete was predicted by the deep LSTM, LSBoost, SVR, and MLR models with 99.23%, 98.08%, 78.57%, and 88.03% accuracy, respectively. The deep LSTM model forecasted the fc of eco-friendly geopolymer concrete with higher accuracy than the SVR, LSBoost, and MLR models. The sensitivity analysis obtained that the curing temperature was the most important experimental variable that affected the fc of geopolymer concrete.

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.

Investigation on ash fusion characteristics and mineral transformation mechanism of sorghum straw by paper-making sludge addition

The co-combustion of sorghum straw and paper-making sludge (PMS) is beneficial to alleviate the ash-related problem in sorghum straw combustion process. In this paper, the mineral migration and transformation behavior in sorghum straw ashes with the addition of PMS ashes under an oxidizing atmosphere were investigated using an X-ray diffractometer, thermogravimetric-derivative thermogravimetric, scanning electron microscopy-energy dispersive X-ray detector, and FactSage software. The results demonstrated that the increase in the PMS ash mass ratio led to an increase in ash fusion temperature (AFT) of sorghum straw mixtures. The generations of high melting-point (MP) calcium feldspar (e.g., Ca2MgSi2O7, Ca2Al2SiO7, Ca3MgSi2O8, and Ca7Mg (SiO4)4) and phosphates (e.g., Ca3P2O8, Ca5P2SiO12, and Ca7P2Si2O16) caused the increases in the AFT. The maximum weight loss of sorghum straw ashes decreased with the increasing PMS ash mass ratio, and the surface of the ashes underwent the transition from smooth to a whole loose and rough, which alleviated the ash-related problems of sorghum straw. The addition of PMS ashes decreasing the liquid-phase content calculated by FactSage at the same temperature also explained the sorghum straw AFT increase. The changes of AFT and its corresponding mechanisms in the sorghum straw with PMS ash addition under an oxidizing atmosphere provided the support for large-scale combustion of biomass.

Low-carbon shape-stable phase change composite utilizing semi-coke ash for building thermal energy storage

To enhance the efficiency and cost-effectiveness of heating, air-conditioning, and solid waste recycling in buildings, this work proposed the solid waste semi-coke ash as skeleton material and the sodium carbonate as phase-change material to produce shape-stable phase-change composites using the cold compression-hot sintering method for building thermal energy storage. Eight shape-stable phase-change composites were prepared and the detailed chemical compatibility, thermal property, structural and mechanical performance, and micromorphology were investigated by X-ray diffraction, differential scanning calorimetry, laser flash analysis, N2 adsorption and desorption method, constant speed pressurization method, and scanning electron microscopy. Results demonstrated that semi-coke ash is suitable with sodium carbonate for fabricating shape-stable phase-change composites. The optimal mass ratio of semi-coke ash to Na2CO3 powder for sample CC3 was determined to be 52.5:47.5. This particular sample demonstrated a thermal energy storage density of 961.58 J/g and a maximum thermal conductivity of 1.306 W/(m ∙ K). It also exhibited excellent chemical compatibility between its components. Furthermore, sample CC3 displayed a mechanical strength of 23.57 MPa, with elements evenly distributed throughout. Importantly, CO2 emission from the production of sample CC3 was significantly low, indicating great potential for commercialization.

Adopting green absorbent for CO2 capture and agricultural utilization: Biogas slurry and biomass ash case

Previously, the once-through CO2 chemical absorption process by biogas slurry was experimentally verified to offer the unique advantages like low energy consumption, cost-effectiveness, and feasibility of CO2 fixation in plants. However, this technology also faces some challenges and limitations, including a low CO2 absorption rate and performance. To improve the effectiveness and reliability of this innovative carbon capture, utilization, and storage (CCUS) technology, this study proposes a novel method to enhance the CO2 absorption performance without affecting agricultural applications of CO2 by mixing biogas slurry with biomass ash as the green CO2 absorbent. The results indicate that when the solid-liquid mass ratio of biomass ash to biogas slurry is 5:10, the CO2 loading of the biomass ash and biogas slurry mixture (BA-BS) reaches 936.7 ± 59.1 mmol/kg. Furthermore, the pH of the BA-BS remains stable at 6.9, meeting the rhizosphere pH requirements for plant cultivation. The CO2 absorption of the BA-BS liquid phase, referred to as improved biogas slurry (IBS), reaches its maximum at 230.4 ± 3.5 mmol/L, which is 126.8% higher than that of the unimproved biogas slurry. The nitrogen content in the BA-BS solid phase, calling improved biomass ash (IBA), also reaches its maximum at 4.24 ± 0.74 mg/g, thereby expanding the agricultural utilization of biomass ash. The most reasonable and effective way of utilizing CO2-rich mixed biogas slurry and biomass ash involves use IBA as the base fertilizer for tomato cultivation, supplemented later with IBS to promote growth. This optimal application allows for substantial utilization of CO2, introduced into the tomato cultivation environment by IBA and IBS. The carbon fixation of a single tomato has improved by 108.2%. This study thus provides a feasible solution for high-value negative carbonization of biogas slurry and biomass ash.

Characterisation of arsenic levels in acid-treated arsenic-containing sludge after steel slag-fly ash gel curing

ABSTRACT Arsenic-containing sludge (ABG) is a common hazardous waste in the metallurgical industry and poses a serious threat to environmental safety. However, its instability and mobility have a significant impact on the environment. Traditional curing methods are time-consuming and costly, often resulting in incomplete curing. In this study, we introduce a curing/stabilisation method with a steel slag-fly ash gel material after ABG acid treatment. The toxic leaching of arsenic from ABG was reduced to 220 mg/kg by treating the sludge with acids (H2SO4-H3PO4) at different solid-to-liquid ratios. Afterward, H2O2 was added to oxidise As(III) to As(V). The ABG was cured/stabilised using an alkali-activated steel slag-fly ash gel material. The cured product exhibited optimal arsenic fixation under an ABG/steel slag/fly ash mass ratio of 1:4:2, a curing temperature of 60°C, a curing time of 20 h, and an ambient pH of 12.5. Under these conditions, steel slag-fly ash facilitated Ca-As precipitation, resulting in a hydration reaction that produced C-S-H gel. Additionally, the reaction generated calcium hydroxide, calcium and iron pyroxene, silica, and iron ferrite, which adsorbed part of the free arsenic, completing the curing of the acid-treated ABG and stabilising arsenic leaching toxicity. The leaching of arsenic in the ABG was much lower than the Chinese ‘Hazardous Wastes Leaching Toxicity Identification Standard’ (GB5085.3-2007) (5 mg/L), with an arsenic curing rate exceeding 99%. The mechanism of arsenic solidification involves the combined effects of chemical precipitation, physical encapsulation, and adsorption. Collectively, our findings demonstrated that the use of steel slag-fly ash gel as a functional material for ABG curing holds considerable environmental and economic benefits. Therefore, this study provides theoretical guidance and provides insights into the experimental feasibility of ABG treatment.

Study of the Design and Mechanical Properties of the Mix Proportion for Desulfurization Gypsum–Fly Ash Flowable Lightweight Soil

In order to solve the global problem of bridge head jumping caused by the insufficient compaction of the roadbed in the transition section of highways and bridges, a desulfurization gypsum–fly ash flowable lightweight soil without vibration, capable of self-compaction, low bulk density, and economic and environmental protection, has been developed. This study selected low-grade cement, industrial waste (fly ash and desulfurization gypsum), and Yellow River silt as the raw materials for the design of the mix ratio of a desulfurization gypsum–fly ash flow-state lightweight soil mix. Through multiple indoor experiments, the influence of cement content, silt content, and the fly ash/desulfurization gypsum quality ratio on its fluidity and mechanical properties was systematically studied. The stress–strain relationship under uniaxial compression was analyzed and the strength formation mechanism was revealed through scanning electron microscopy (SEM). The results show that the mechanical properties of the prepared desulfurization gypsum–fly ash flowable lightweight soil meet the engineering requirements. Increasing both the cement and fly ash content results in the decreased fluidity of the desulfurization gypsum and fluidized fly ash. However, as the mass ratio of fly ash to desulfurization gypsum increases, the fluidity reaches its maximum when the mass ratio of fly ash to desulfurization gypsum is 2:1. Based on the stress–strain relationship test results, a uniaxial compressive constitutive model of the desulfurization gypsum–fly ash flowable lightweight soil was proposed. The model was fitted and analyzed with the test results, and the correlation was greater than 0.96. The high degree of agreement showed that desulfurization gypsum can promote the disintegration of fly ash, thereby increasing the specific surface area. This provides more contact points, promotes the hardening process, and enhances the interlocking force between particles and the formation of cementitious substances, further enhancing strength.

Mechanical and Thermal Conductivity Study of Inorganic Modified Raw Soil Materials Based on Gradient Concept

Based on the inorganic modification of raw soil materials by using cement, fly ash, lime and other admixtures, the influence of modified jute fiber content on the strength of raw-soil-based wall materials was studied. The effects of the gradient distribution of inorganic admixtures on the mechanical properties and thermal conductivity of raw-soil-based wall materials were studied and compared by designing the gradient distribution and homogenous distribution of admixtures in raw soil materials. The results show that when the mass ratio of raw soil, sand, cement, fly ash and lime is 30:10:5:3:2, the compressive strength and flexural strength of the modified raw soil specimen at 28 d are 6.4 MPa and 2.9 MPa, respectively; on the basis of the further addition of 0.8 v% jute fibers, the strength can still be enhanced by 20% and its thermal insulation properties will also be improved. Gradient design can further improve the mechanical properties of modified raw-soil-based wall materials and can weaken the loss of its inherent thermal insulation function.

The Effect of Secondary Aluminum Ash on the Properties of Reactive Powder Concrete.

Secondary aluminum ash is a kind of common solid waste which will pollute the environment without any treatment. In this study, the influence of secondary aluminum ash on the rheological properties and the initial setting time of fresh reactive powder concrete (RPC) are researched. Meanwhile, the mechanical properties and the drying shrinkage rates of RPC with the secondary aluminum ash are determined. The electrical parameters of RPC with the secondary aluminum ash are measured. Scanning electron microscopy is obtained to reflect the internal structure of RPC. Results show that the addition of secondary aluminum ash can lead to decreasing the fluidity and increase the yield shear stress of fresh RPC paste by varying rates of 16.1% and 58.3%, respectively. The addition of secondary aluminum ash can decrease the flexural and compressive strengths of RPC cured for 1 day by the decreasing rates of 0~18.7% and 0~19.3%. When the curing age is 28 days, the flexural and compressive strengths of RPC are increased by 0~9.1% and 0~19.1% with adding the secondary aluminum ash. The secondary aluminum ash can promote the condensation of RPC. The addition of the secondary aluminum ash can decrease the electrical resistance of RPC by an order of magnitude. The relationship between the electrical resistance and the electrical reactance fits the quadratic function equation. The electrical resistance of the pore solution increases in the form of a quadratic function with the mass ratio of the secondary aluminum ash. The dry shrinkage rates of RPC cured for 1 day and 28 days are decreased by 0~36.4% and 0~41.3% with the increasing dosages of secondary aluminum ash. As obtained from the microscopic testing results, the secondary aluminum ash can improve the compactness of hydration products.

A TiO2 modified whisker mullite hollow fiber ceramic membrane for high-efficiency oil/water emulsions separation

Design and preparation of membranes with ultrahigh separation performance and antifouling property for oil-in-water (O/W) emulsions remains challenging. In this study, a high flux mullite/TiO2 ceramic composite membrane was prepared via multi-precipitation of TiO2 on a whisker mullite hollow fiber support synthesized by combining phase inversion and high-temperature sintering techniques. The results showed that the generated whisker mullite structure improved the permeation flux, and the micro-nano structured TiO2 functional layer endowed the membrane surface with superhydrophility and stability. The retention of the optimal composite membrane (M20T13) that was soaked in the titanium solution 20 times for 13 min each time for the O/W emulsions like n-hexane, toluene and engine oil maintained over 98 %, and the flux after 6 h filtration was 668.34 L·m−2·h−1, 487.25 L·m−2·h−1 and 258.66 L·m−2·h−1, respectively, much higher than that of the optimal substrate (F3A1, mass ratio of fly ash: Al2O3 = 3:1). Moreover, the flux recovery rate of M20T13 was much higher than that of F3A1 after chemical backwashing. This work manifests great potential in O/W treatment fields.

Waste semicoke ash utilized to fabricate shape-stable phase change composites for building heating and cooling

The use of industrial semicoke ash as skeleton material is proposed in this study to fabricate low-cost thermal energy storage materials and shape-stable phase change composites as well as recycle industrial solid waste for building heating. Eight samples with different mass ratios of semicoke ash to NaNO3 are manufactured. Key performance of NaNO3/semi-coke ash shape-stable phase change composite is then investigated using differential scanning calorimetry, laser flash analysis, scanning electron microscopy, X-ray diffraction, and constant-speed pressurization method. Results showed that the sample CC2 with a mass ratio of semicoke ash to NaNO3 of 5:5 demonstrates the absence of visual leakage and deformation and reaches a maximum thermal energy storage capacity of 325.91 J/g in the range of 100 °C to 380 °C, mechanical strength of 96.98 MPa, and maximum thermal conductivity of 1.004 W/(m∙K). In addition, semicoke ash is chemically compatible with NaNO3. Both thermal energy storage capacity and thermal conductivity of sample CC2 increase slightly after 4027 heating/cooling cycles.

Impact of micro characteristics on the formation of high-strength Class F fly ash-based geopolymers cured at ambient conditions

• The Class F fly ash-based geopolymer pastes with 28 d’s strength over 75 MPa is produced under ambient conditions. • The mechanical properties are strongly related to the synergistic action of amorphous phase content, reactive phase’s Si/Al molar ratio, and porosity. • Water content plays a critical role among the options of adjusting mix proportions in improving the micro characteristics. The high-strength Class F fly ash-based geopolymer pastes cured at ambient conditions with 28 d compressive strength over 75 MPa is rarely reported. Herein based on such reference, the geopolymer pastes synthesized by cognate fly ash with lower activity are produced to investigate the combined effects of geopolymer’s micro characteristics, such as amorphous phase content, Si/Al molar ratio of reactive phase, and porosity, on the enhancement of mechanical properties. The fly ash-based geopolymers are prepared with different Si/Al molar ratios, Na/Al molar ratios, and water/fly ash mass ratios. The results at the micro-level indicate that the development of mechanical properties of fly ash-based geopolymers is mainly affected by the reactive phase’s Si/Al molar ratio, followed by the porosity and then amorphous phase content. In addition, experiments show that decreasing the water/fly ash mass ratio leads to the positive promotion in all the micro characteristics with small reactive phase’s Si/Al molar ratio, low porosity, and high amorphous phase content. Therefore, the dramatic increase in the compressive strength and Young’s modulus of geopolymer specimens can be obtained. In summary, it can be concluded that, given the workability of precursor preparation, the application of a water/fly ash ratio lower than 22.5 % can increase the strength close to 75 MPa, which is beneficial to the potential application of fly ash-based geopolymers in practical engineering. The other related characteristics of high-strength fly ash-based geopolymers will be investigated in future studies to further reveal its latent practicability.

Electrochemical response of solidification Cu2+ contaminated soil influenced by red mud/fly ash ratio

The main purpose of this work was to study a new method for evaluating the solidification of contaminated soil based on electrochemical impedance spectroscopy (EIS). To explore how the EIS parameters were affected by the pore structure and mesostructure of the cured system, the physical and mechanical properties, leaching toxicity, microstructure, and EIS of the stabilized contaminated soil were tested after 7, 28, 60, and 90 days of curing. Based on the EIS results, a physical and equivalent circuit model of the stabilized contaminated soil's impedance response was established to reveal the mechanism of binder-heavy metal ion-soil interaction. The results showed that as the red mud (RM)-fly ash (FA) mass ratio and curing age increased, the strength and structural compactness of the solidified body also increased. The best curing effect was achieved with an RM-FA mass ratio of 7:3 after curing for 90 days. The equivalent circuit model of the solidified body obtained by EIS was Rs (Q1 (Rct1W) Q2Rct2). The pore solution resistance Rs, solid-liquid interface ion transfer resistance Rct 1, and unconfined compressive strength (UCS) qu all showed an increasing trend with increasing RM-FA mass ratio and increasing curing time. Fitting the model demonstrated that both Rs and Rct1 were closely correlated with the strength of the solidified bodies. These conclusions were further verified by scanning electron microscope (SEM) experiments. Overall, this work demonstrates that the strength characteristics of solidified bodies can be evaluated by EIS and reveals the microscopic mechanism of the solidification of Cu2+-contaminated soil.

Utilization of water-based drilling cuttings from offshore oil development to manufacture lightweight aggregates: a case study in the Bohai oil field, China.

Offshore water-based drilling cuttings (OWDC) are by-products of offshore oil-well drilling, whose effective management has become an urgent environmental and engineering issue. This study investigated the feasibility of recycling OWDC from the Bohai oilfield in China as a raw material for manufacturing lightweight aggregates (LWA). The effects of OWDC content (0-50%), preheating temperature (300-500 °C), and sintering temperature (1050-1200 °C) on the physical-mechanical performance of the resulting LWA were investigated through single-factor experiments. The microstructural and expansion mechanism analyses were determined based on X-ray diffraction analysis, scanning electron microscopy, and energy-dispersive X-ray spectrometric microanalysis. The results showed that under the optimum preparation conditions (mass ratio of OWDC and fly ash at 50:50, preheating at 400 °C for 30 min, and sintering at 1150 °C for 30 min), the OWDC-based LWA could meet the requirements of Chinese standard GB/T 17431.1-2010. The incorporation of OWDC lowered the aggregate melting points and promoted dense structure formation inside the aggregates due to the presence of flux agents (e.g., Na2O and K2O). Besides, OWDC additions promoted the formation of the liquid phase and gases inside the pellets, which was beneficial to the expansion behavior and lightweight performance of the aggregates. However, OWDC also had a negative effect on the compressive strength of the aggregates owing to the formation of enlarged pores. Furthermore, the results of the environmental performance tests indicated that the LWA were safe for the environment. This study provides a reference for recycling water-based drilling cuttings from offshore oilfields and contributes to the circular economy.

The investigating on mechanical properties of engineered cementitious composites with high ductility and low cost

The engineering application of engineered cementitious composites(ECC) has always been limited by its cost, which mainly due to the high price of imported PVA fibers. In order to balance the mechanical properties and cost of ECC, this study presents an engineered cementitious composites with high ductility and low cost. The compressive strength, uniaxial tensile strain and uniaxial tensile strength of this ECC were 21.33 MPa, 5.10%, and 2.93 MPa, respectively. The high ductility and low cost of this ECC are mainly attribute to the reasonable combination of four materials, including PVA fibers, fly ash, CaCO3 whiskers(CW) and nano-CaCO3(NC). The optimal mixing ratio of the four materials is that the content of PVA fiber is 1.3%(vol%), the mass ratio of fly ash to cement is 3.0, 1% CW(vol%), and 1% NC(wt.%). The average crack width and the maximum crack width on the surface of the tensile specimen prepared according to the optimal mixing ratio can be controlled at about 42 μm and 100 μm, respectively. This excellent crack control ability mainly comes from the crack inhibition effect of PVA fibers and CW. Compared to classic ECC-M45, the total value coefficient and total cost of the specimens prepared according to the optimal mixing ratio were 112.59% and 36% of that of ECC-M45, respectively. And the designed ECC with high ductility and low cost has the applicability of engineering application, which has been proved by comparison with the mechanical properties of a sprayable ultra high toughness cementitious composites (UHTCC) that has been applied in practical engineering cases.

The Impact of Variable Curing Conditions on the Properties and Microstructures of Mixtures of Ground Granulated Blast Furnace Slag and Circulating Q1 Fluidized Bed Combustion Ash

The use of Portland cement, an important construction material, is encountering growing challenges because of its adverse environmental impacts. In this study, a new hydration system without Portland cement, which blends ground granulated blast furnace slag (GGBFS) and circulating fluidized bed combustion (CFBC) ash, was developed and tested. The variables included the effect of different types of CFBC ash, the mass ratios between CFBC ash and GGBFS, and different curing temperatures. The mortar properties were determined through the compressive strength test, absorption test, shrinkage test, X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. The main results were as follows: (1) The compressive strength of mortar specimens made with this ecologically friendly hydration system reached at least 40 MPa under a 35°C curing temperature. (2) Mortar with finer CFBC ash as an activator had higher compressive strength and lower absorption. (3) A proper mass ratio of GGBFS to CFBC ash is necessary for engineering applications. The present findings indicate that to maximize compressive strength, the particle size and the mass ratio of CFBC ash to GGBFS must be considered. According to the result, the type A ash with 3:7 mass ratio of CFBC ash to GGBFS is recommended.

Improving the A/S ratio of pretreated coal fly ash by a two-stage roasting for Bayer alumina production

Coal fly ash has been considered as a potential resource for alumina production by Bayer process. However, the implementation is always limited by low alumina-silica mass ratio (A/S) of coal fly ash. Previously, we reported an approach to realize the desilication of coal fly ash and the A/S could reach 5.34. However, this A/S was still not high enough for Bayer process. Following the previous study, herein we systematically optimize the desilication conditions to further improve the A/S, and also evaluate the applicability of desilication residue for Bayer alumina production. First, the digestion properties of amorphous silicon dioxide and γ-alumina in the two-stage roasted calcines are analyzed by thermodynamic calculation. The results indicate that their alkali-digestion properties become remarkably different at relatively high temperature, thus amorphous silicon dioxide could be digested while γ-alumina is preserved in the residue by controlling the pH and digestion temperature. The desilication ratio and the A/S ratio could reach 82.27% and 7.46 at the optimal conditions of 116 g/L Na2O, 95 °C, 15 min digestion time and 1/10 solid-to-liquid ratio. The obtained desilication residue becomes acceptable and economical high grade raw material for Bayer process, which is confirmed by the production of standard alumina (AO-2, China). This research could provide an alternative economic process for recycling alumina from high-alumina coal fly ash.