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Mix proportion optimization and performance of one-part multi-solid-waste geopolymer matrix under multi-factor coupling
Wang Chaozhong;Liu Yang;Xu Binbin;Liu Jiao;Li Sen;Ren Weikai;Wang Heming;Wang Ziqun;[Objective]To address the complex interactions among multiple solid-waste components, the difficulty in balancing workability and mechanical performance, and the relatively high cost and carbon emissions associated with solid alkaline activators. [Methods] An orthogonal experiment with three factors and four levels was conducted to investigate the effects of fly ash, calcium carbide slag, and anhydrous sodium metasilicate on the performance of a onepart geopolymer matrix, with ground granulated blast-furnace slag used as the remaining binder component. Fluidity, setting time, and 7 d and 56 d flexural and compressive strengths were measured. Material cost and carbon emissions were also evaluated, and a strength development efficiency factor was introduced. A multi-objective assessment was then carried out using the technique for order preference by similarity to ideal solution(TOPSIS) combined with the analytic hierarchy process(AHP). [Results]The results show that fly ash had the greatest influence on fluidity and strength, while anhydrous sodium metasilicate had the strongest effect on setting time. Reducing the fly ash content and increasing the slag content promoted strength development, but also affected workability and overall benefits. Anhydrous sodium metasilicate was the dominant factor affecting material cost and carbon emissions. Although a higher dosage promoted precursor activation, it also increased the economic and environmental burden. Under the evaluation system adopted in this study, the recommended mix proportion was 60% fly ash, 6% calcium carbide slag, 6% anhydrous sodium metasilicate, and 28% slag. This mixture achieved a 56 d compressive strength of 33.10 MPa and a fluidity of 131 mm, providing a reasonable balance among mechanical performance, workability, economic efficiency, and low-carbon performance. [Conclusion]The results provide a reference for the engineering mix design and lowcarbon optimization of one-part multi-solid-waste geopolymer matrices.
Research on the hydration and hardening characteristics of cement-based materials with ultrafine fly ash
Yin Shaoning;Pan Dong;Yuan Peng;[Objective]Ultra-fine grinding is one of the key methods to enhance the added value of fly ash, studying its hydration and hardening characteristics in cement-based materials is of great significance for guiding its scientific application in the cement and concrete fields. [Methods]This paper takes the selected grade Ⅱ fine fly ash as a reference and investigates the influence of ultra-fine fly ash with different specific surface areas(TKT1:533 m2/kg, TKT2: 714 m2/kg, TKT3: 876 m2/kg, and TKT4: 1 019 m2/kg) on the hydration heat, non-evaporable water content, hydration products, thermogravimetric analysis, and pore structure of cement, the aim is to reveal the hydration mechanism of ultra-fine fly ash in cement. [Results]The results show that compared with grade Ⅱ fine fly ash, the addition of TKT4 ultra-fine fly ash significantly increases the heat release rate and total heat release of the cement paste. The nonevaporable water content of the ultra-fine fly ash-cement paste gradually increases with the increase in the fineness of the ultra-fine fly ash. At a water-cement ratio of 0.3, the non-evaporable water content of the TKT4 group at 28 d is 8.7% higher than that of grade Ⅱ fine fly ash and exceeds that of the reference cement. At 90 days, the non-evaporable water content of the TKT3 group is 15.0% higher than that of grade Ⅱ fine fly ash and is on par with the reference cement. The content of calcium hydroxide in the ultra-fine fly ash-cement paste decreases with the increase in the fineness of the ultra-fine fly ash. At 28 d, the calcium hydroxide content of the TKT4 group decreases by 3.47%. Moreover, ultra-fine grinding is conducive to the dissolution of active Al_2O3 in fly ash and promotes the formation of ettringite. The addition of ultra-fine fly ash is beneficial to improving the pore structure distribution of the hardened cement paste, increasing the proportion of harmless and slightly harmful pores, and reducing the proportion of harmful and highly harmful pores. At 28 d, the total pore volume, average pore diameter, and porosity of the TKT4 group decrease by 15.0%, 18.7%, and 11.6%, respectively. [Conclusion]Overall, the finer the fineness of ultra-fine fly ash, the higher its hydration activity, and the lower the water-binder ratio, the higher the degree of hydration of ultra-fine fly ash.
Review on resource management of waste photovoltaic modules
Wang Yaoting;Jiang Wenqian;Ma Guowei;Wang Yujie;Wang Jinshi;[Objective] In response to the environmental risks and governance pressure of waste photovoltaic modules caused by the rapid expansion of the installed scale of photovoltaic modules, this paper systematically combs the governance challenges of photovoltaic waste materials, aiming to explore the construction of a sustainable photovoltaic waste management system through the summary of technological progress and the analysis of policy mechanism. [Methods] Conduct a comprehensive analysis based on recent literature(over the past five years) on photovoltaic module recycling and typical engineering demonstration data, from the perspectives of technology, circular economy, and policy. At the technical level, advances in PV module recycling processes from structural disassembly to material purification are reviewed, and a comparative analysis of material recovery efficiencies across different recycling technologies is conducted. At the circular economy level, the potential of recycling path in reducing environmental impact and improving the sustainability of waste management from the perspective of circular economy are demonstrated. At the policy level, comparative reviews of domestic and international policies and regulatory frameworks were conducted, and the mechanisms by which different governance structures influence the large-scale development of recycling systems are analyzed. [Results] The research shows that the recycling technology of photovoltaic modules continues to develop, and the material recycling efficiency and process innovation provide the possibility of high-value recycling.Recycling path has significant potential in reducing environmental load and improving resource recycling. A sound policies and regulatory framework are the key support to promote the large-scale development of the recycling industry. The comparison of domestic and foreign systems highlights the importance of improving the standard system and incentive mechanism. [Conclusion] To meet the challenge of photovoltaic waste, we need to rely on the two ways of technology research and development and institutional innovation. In the future, we should focus on the breakthrough of high-value recycling technology of key materials, and build a green governance system covering the whole life cycle of components by improving the standard system and market incentive mechanism.
Mechanism of solidifying sulfate saline soil using fly ash-based cementitious materials
Li Hongliang;Zhang Jie;Yu Hao;Cheng Yin;Li Tianbin;Ma Yi'ao;Hu Rui;Li Qindong;Luo Lizhen;Shi Hongyu;Liu Zunqing;[Objective] To address the issue of efficiently treating sulfate-stained soil roadbeds in Xinjiang region using fly ash-based solid waste materials, it is necessary to reveal the mechanism of solidifying sulfate-stained soil with fly ashbased solid waste. [Method] In this paper, fly ash, blast furnace slag, calcium carbide slag and other solid waste materials are used to prepare fly ash-based cementitious material curing agent, which is used to solidify sulfate saline soil. The strength of solidified soil and the change law of hydrate type and production amount are studied, and the mechanism of curing agent solidifying sulfate saline soil is revealed. [Results] The results showed that:(1) when the dosage of the solidifying agent was fixed at 10%, with the increase of the salt content in the saline soil, the strength of the solidified soil gradually decreased, the generation amount of ettringite(AFt) in the solidified soil gradually increased,while the generation amount of AFm-SO42- salt gradually decreased.(2) When the salt content in the soil increased from 5% to 20%, the 28-day strength of the solidified soil decreased by 2.43 MPa, the proportion of AFt generation in the solidified soil increased from 0.5% to 22%, while the proportion of AFm-SO42- salt generation decreased from 6% to 2%.(3) For the soil samples YT15 and YT20 with salt contents of 15% and 20%, respectively, as the dosage of the solidifying agent increased, the strength of the solidified soil gradually increased, the generation amount of AFt in the solidified soil first increased and then decreased, while the generation amount of AFm-SO42- salt gradually increased.(4) When the dosages of the solidifying agent reached 10% and 15% respectively, the growth rate of the strength of the solidified soil and the generation amount of AFm-SO42- salt accelerated, and this was also the turning point when the generation amount of AFt changed from increasing to decreasing. Based on above results, the mechanism of fly ash, blast furnace slag and calcium carbide slag solidifying sulfate saline soil is proposed as follows: the CAH generated by the hydration of fly ash and blast furnace slag can convert the SO42- ions in the sulfate saline soil into AFm-SO42- salt, significantly reducing the generation amount of AFt, thereby strengthening the role of AFm-SO42- salt in filling the pores of the solidified soil and significantly weakening the role of AFt expansion in destroying the cementation structure of the solidified soil, achieving the growth of the strength of the solidified soil. [Conclusion] The results of this paper can provide a scientific basis for promoting the large-scale resource utilization of solid waste in coal-fired power industry.
Research progress on chemical degradation recycling technology for decomissioned wind turbine blades
Liu Xianghui;Yan Xinying;He Faquan;Zhan Chenyu;Wang Hongliang;Li Zihan;Zhao Jing;Liu Minghui;[Objective] With the rapid growth of global wind power installed capacity, early-stage wind turbines are gradually entering their decommissioning period. The disposal of large quantities of retired wind turbine blades has become a serious environmental and resource challenge. To overcome the environmental pollution and resource waste caused by traditional landfilling and incineration, and to address the bottlenecks of existing mechanical and pyrolysis methods that struggle to achieve high-value recycling, it is necessary to systematically explore the key role and technical pathways of chemical degradation in achieving green, efficient, and high-value recycling of retired wind turbine blades. [Methods] By comprehensively reviewing and comparatively analyzing mainstream chemical pathways including acid degradation, catalytic degradation, supercritical fluid degradation, ionic liquid degradation, and hybrid degradation, this study elucidates the technical characteristics of various methods regarding the directed depolymerization mechanisms of epoxy resins, reaction condition optimization, fiber structure protection, and product recovery and utilization. Furthermore, integrating quantitative data from Life Cycle Assessment(LCA), a comprehensive comparison and sustainability analysis of different recycling paths were conducted from the dimensions of energy consumption and environmental-economic benefits. [Results] The results indicate that:(1) Chemical degradation effectively disrupts the three-dimensional cross-linked structure of resins, achieving efficient resin depolymerization and high-quality fiber recovery(with carbon fiber strength retention frequently exceeding 95%), significantly outperforming mechanical and pyrolysis methods.(2) While strong acid systems(e.g., nitric acid) and supercritical fluid technologies demonstrate outstanding fiber protection capabilities, they face considerable challenges regarding environmental load(e. g., the environmental benefit of the nitric acid method is merely 0.10 yuan/kg, accompanied by negative eutrophication potential).(3) Catalytic degradation and organic acid systems exhibit promising industrial potential due to their mild reaction conditions and recyclable solvents.(4) Although pyrolysis demonstrates significant carbon reduction benefits based on LCA analysis, chemical degradation plays an irreplaceable role in resource perpetuation and "upcycling." It is concluded that chemical degradation, leveraging its excellent fiber protection capabilities and highvalue conversion potential, constitutes the key technology for realizing the closed-loop recycling of decomissioned wind turbine blades. [Conclusion] Future efforts should focus on developing green and low-toxicity reagents, establishing closed-loop reagent circulation, deepening research on reaction mechanisms, and following a tiered development roadmap of "short-term engineering scale-up, mid-to-long-term source design" to promote the transition of retired wind turbine blade recycling from "downcycling" to "upcycling, " thereby supporting the sustainable development of the wind power industry.
Research on solid waste disposal and application of decommissioned wind turbine blades and photovoltaic modules
Huang Luwen;[Objective] Aiming at the large-scale disposal problems of decommissioned wind turbine blades and photovoltaic modules under the global energy transition, this paper focuses on the efficient, clean and high-value utilization of composite materials and complex components, avoids resource waste and environmental risks, and explores the bulk consumption and industrialization paths. [Methods] This paper systematically combs the generation scale, material composition and pretreatment technologies of decommissioned wind turbine blades and photovoltaic modules at home and abroad, and analyzes the physical and chemical characteristics of recycled materials as aggregates, fillers and reinforcing materials. Through literature induction, comprehensive analysis and case studies, the applicability of these scenarios such as building materials, transportation roads and mine backfilling is demonstrated. A life cycle assessment framework is used to evaluate the technical feasibility, economic cost and environmental benefits of different resource utilization paths. [Results] After mechanical crushing and sorting pretreatment, Recycled Fiberreinforced Polymer(RFP) and photovoltaic glass powder can partially replace natural aggregates/mineral admixtures for the preparation of concrete, asphalt mixture and filling materials. Recycled fibers can improve the crack resistance and toughness of cement-based composites, photovoltaic glass micropowder has potential pozzolanic activity, and synergistic utilization of multi-source solid waste can optimize material properties and economic benefits. Life cycle analysis confirms that reasonable resource utilization paths can achieve bulk consumption of solid waste, with both carbon emission reduction and resource saving benefits. [Conclusions] The resource utilization of decommissioned new energy solid waste has systematic technical feasibility and comprehensive benefits, which is a core way to solve the disposal problem and support circular economy. In the future, it is necessary to deepen material performance research, improve technical standards, improve the industrial chain and policy incentives, promote large-scale and industrial application, and help the green and low-carbon transformation of infrastructure.
Effect of rubber particle size on the low-velocity impact response and damage evolution of fly ash-based geopolymer concrete
Xu Yun;Zhang Qian;Meng Xiaohuan;Wang Ziqun;Jiang Yilin;Wu Haoliang;Cai Jingming;[Objective] To examine the effect of rubber particle size on the mechanical response and damage evolution of fly ash-based geopolymer concrete subjected to low-velocity repeated impact, aiming to support the high-value utilization of fly ash.[Methods] A one-part fly ash-based geopolymer concrete was prepared using fly ash, slag, and carbide slag. With a fixed rubber volume fraction of 15%, different rubber particle sizes were used. Compressive and low-velocity impact tests were conducted. [Results] As the rubber particle size decreased, the compressive strength increased, while the impact toughness first increased and then decreased. Concrete beams with 10-mesh rubber showed the best impact performance while maintaining strength. The absorbed energies in the first two impacts reached 10.61 J and 10.81 J, which were the highest among all rubber-modified groups. Digital Image Correlation(DIC) characterization of the strain evolution during the impact process revealed that the 10-mesh specimen exhibited smaller residual strain after the first impact and more stable strain development during the second impact. The strain was more uniformly distributed, delaying crack formation.[Conclusion] At a rubber content of 15% and an impact energy of 10.81 J, 10-mesh rubber provides the best balance between impact resistance, energy absorption, and damage stability without significantly reducing load capacity.
Analysis and suggestions on the development of offshore wind power in China
Zhang Jiuming;Wang Rong;Sun Liping;[Objective] Under the background of the carbon peaking and carbon neutrality goal and the construction of new power system and new energy system, China's renewable energy is developing rapidly. Offshore wind power has become an important support for promoting clean and low-carbon energy transformation in coastal areas due to its advantages such as superior resource endowment, less land occupation, large scale potential and relatively good gridconnected conditions, but it also faces some development difficulties. [Methods]This paper systematically reviews the development status of offshore wind power in the world and China through literature and market research. Combined with the development trend of large-scale, far-reaching and large-scale offshore wind power, this paper analyzes the comparative advantages of China's development of offshore wind power, and systematically evaluates the main challenges facing China from the aspects of technology, economy and institutional mechanism. [Results] The research shows that China's offshore wind power has made remarkable progress in the continuous expansion of installed capacity, the rapid increase of single-machine capacity and the expansion to the deep sea. The engineering cost and technical level are constantly optimized, but it still faces problems such as unbalanced industry development, pressure on project economy, key core technologies to be broken through, obvious differences in development stages between offshore and deep sea, and imperfect relevant policies and market systems. Taking a project with a capacity of 500,000 kW as an example, the sensitivity analysis of its economic influencing factors shows that the investment cost(or nontechnical cost) of the project is reduced by 10%, the internal rate of return(pre-tax) of the total investment of the project is increased by about 1.4 percentage points, and the internal rate of return of capital is increased by 3.2 percentage points. The project electricity(electricity price) increases by 10%, the internal rate of return(pre-tax) of the total investment of the project increases by about 1.5 percentage points, and the internal rate of return of capital increases by 3.5 percentage points. The project loan interest rate is reduced by 10%, and the internal rate of return on capital is increased by 0.6 percentage points. [Conclusion] In order to promote the high-quality development of offshore wind power in China, it is necessary to strengthen the strategic guidance and overall planning at the national level, focus on key core technologies and materials, and promote the integration of intelligence, informatization and industry to continuously reduce costs and increase efficiency. At the same time, we will improve the electricity price formation mechanism and market-oriented trading rules, improve the supporting policy system, and promote the integrated development of offshore wind power and marine economy through the coordinated promotion of offshore quality and efficiency improvement and far-reaching sea demonstration.
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Introduction
Electric Power Technology and Environmental Protection
Bimonthly issued
CN 32-1808/X
ISSN 1674-8069
Governed by:
China Energy Investment Group Co., Ltd.
Sponsored by:
China Energy Group Science and Technology Research Institute Co., Ltd.
Academic support：
State Key Laboratory of Low-carbon Smart Coal-fired PowerGeneration and Ultra-clean Emission
Columns:
Thermal Energy Engineering, Clean Power Generation, New Energy Generation, Integrated Power Generation.
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