geopolymer is a three-dimensional network structure with amorphous and semi-crystalline characteristics formed by alkali-stimulated silicon-aluminum precursors, with silicon-oxygen tetrahedrons and aluminum-oxygen tetrahedrons connected at the vertex angles. Material. In recent years, with the development of alkali-activated solid waste-based materials, in addition to silicon-aluminum solid waste, calcium-containing solid waste has also been used as raw materials for geopolymers.
So, which solid wastes are suitable for use as raw materials for geopolymers? In order to ensure the stable performance of geopolymers, what should we pay attention to in solid waste utilization? Our reporter recently interviewed Professor Guo Xiaolu, School of Materials Science and Engineering, Tongji University.
Guo Xiaolu pointed out that the "dual carbon" strategy has brought new opportunities to the development of geopolymers and opened up new ways to reduce carbon emissions. Geopolymer has the ecological and environmental benefits of "two no and two lows": no limestone raw materials are used in production, no carbonate is decomposed, no CO₂ is directly emitted, and the solid waste utilization rate is high; no silicates are needed Calcined at high temperatures like cement , raw materials can be used directly or after low-temperature pretreatment (350~750℃); the energy consumption is low, 1/20 of ceramics, 1/70 of steel, and 1/150 of plastics; the required fuel Less, the NOx and SOx emissions are very low, accounting for only 1/10~1/5 of Portland cement, and basically no toxic gases are produced. Therefore, in the context of "double carbon", there are broad application prospects.
Geopolymers are divided into types of raw materials, and the more common ones are metakaolin-based polymers and fly ash-based polymers. Metakaolin-based polymer raw materials require calcined clay and other natural resources. In contrast, silicon-aluminum-based raw materials from a large amount of industrial and mining solid waste are more suitable for application in geopolymers and come from a wide range of sources. For example, fly ash-based polymers use fly ash as the main body. At the same time, fly ash-based polymers can be used to co-process water plant sludge, desulfurization gypsum, metallurgical sludge, waste incineration fly ash, steel slag powder, and red. Mud , coal gangue , construction waste powder, etc.
Geopolymer itself is a three-dimensional network inorganic polymer structural system, which has excellent properties such as high temperature resistance, flame retardancy, and corrosion resistance. At present, no matter from different solid waste raw materials, to the appropriate ratio, to the reaction process, and various From component effects to performance control, it can be said that the research is relatively systematic and a large number of theoretical research results have been formed. However, there are still many issues that need to be paid attention to and solved in terms of how to transform these research results into products and apply them to actual projects to meet application performance requirements under different working conditions.
"Currently, how to ensure the stability of geopolymer performance is difficult and key." Guo Xiaolu pointed out that the wide range and volatility of raw materials cause instability in performance. First of all, the stability of the performance of raw materials needs to be guaranteed. However, since the "raw materials" for solid waste resource utilization are themselves solid waste or even hazardous waste, its properties are difficult to guarantee. To use industrial and mining solid waste to make geopolymers, it is recommended to subdivide the solid waste or hazardous waste from the source and control the quality to make it a commodity in the sense of supply. Of course, this requires multi-industry collaboration and even the entire social chain. s hard work.
In terms of raw material composition and ratio control of solid waste-based polymers, Guo Xiaolu believes that solid waste and hazardous waste have strong intrinsic characteristics, and the disposal and utilization of each type of waste has its own characteristics and difficulties. For certain solid waste or the disposal of certain hazardous waste, corresponding adjustments and adaptations must be made based on its source, physical and chemical properties, etc., and it even needs to be pre-treated in order to make better use of it. The technical difficulties in the promotion and application of solid waste-based polymers are also reflected here. The raw materials fluctuate and change greatly, and performance control is difficult.
The research and development of admixtures that match the geopolymer system is also crucial. The compatibility and adaptability of admixtures are important aspects for the application promotion and performance guarantee of solid waste-based polymers. Guided by application performance requirements, the action mechanism and synergistic effect of different admixtures such as alkali activators, water reducing agents, and coagulants in geopolymer systems, the compatibility and compatibility between geopolymers and admixtures and different admixtures The adaptability is worthy of study to meet the different requirements for geopolymer performance under different working conditions and ensure its application performance and service performance.
In addition, it is necessary to speed up the construction of geopolymer-related standards.At present, the standards that can be retrieved are basically enterprise standards or local standards, such as the 2007 Shanghai Municipal Engineering Bureau professional standard "Technical Regulations for Polymer Grouting Reinforcement of Highway Subgrade and Base Level", and the 2016 Henan Provincial Local Standard "Road Non-Group Reinforcement". "Technical Specifications for Excavation Type Geopolymer Grouting Reinforcement and Disposal" and the 2018 Jiangsu Province Engineering Construction Standard "Technical Specifications for Modified Geopolymer Grouting Reinforcement of Urban Roads". Geopolymer-related industry standards and national standards need to be jointly promoted by everyone.
This article was originally published in the 9th edition of China Building Materials News on June 20
China Building Materials News reporter: Wu Yue
Editor: Ding Tao
Proofreading: He Xinlong
Supervisor: Han Fengfeng
