The circular economy is a closed cycle that allows one to reuse the industrial waste, as well as minimize the energy and resources losses during the production process. This paper presents an innovative idea of the application of a geopolymer cable backfill for underground power cable system installation. The closed cycle, in this case, is formulated as follows: the primary resource is the waste from the combustion of fossil fuels, i.e., fly ash that is utilized to form the geopolymer matrix. The geopolymer then is used as thermal backfill in underground power cable systems. Utilization of combustion by-products in the form of a geopolymer is a highly profitable solution since landfill waste disposal, in this case, generates considerable costs for the electrical energy producers. In typical applications, geopolymers are used as insulators. By adding individual components, the thermal conductivity of 2.0 W/(m K), higher than of typical thermal backfills (Fluidized Thermal Backfill), which value is close to 1.5 W/(m K), is reached. What is very important, geopolymers can absorb water better than typical sand–cement mixtures. As a result, a high thermal conductivity with the temperature increase is maintained. The application of geopolymers as thermal backfills has the potential to improve the flexibility of underground power cable systems, as well as to minimize the material costs of installation. The case study is presented to show the economic benefits of using the combustion by-products as a geopolymer thermal backfill. The finite element method model of an underground power cable system is developed, and optimization of backfill dimensions is provided to minimize the material costs using the geopolymer thermal backfill and to maximize the underground power cable system performance. The main result of this paper is that the application of geopolymers leads to a decrease in underground power cable system costs, compared to traditional backfill (sand–cement mixture). The reason is the higher value of thermal conductivity, which allows selecting a cable with a smaller cross-sectional area. Also, the environmental benefits of geopolymer application for cable bedding are discussed.

Graphic abstract

中文翻译：

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地聚合物材料作为地下电缆热回填的应用可能性分析

循环经济是一个封闭的循环，使人们可以重复利用工业废物，并最大程度地减少生产过程中的能源和资源损失。本文提出了一种在地下电力电缆系统安装中应用地质聚合物电缆回填的创新思想。在这种情况下，封闭循环的公式如下：主要资源是化石燃料燃烧产生的废物，即用于形成地聚合物基质的粉煤灰。然后，将地质聚合物用作地下电缆系统中的热回填。利用地质聚合物形式的燃烧副产物是一种非常有利可图的解决方案，因为在这种情况下，垃圾填埋场的处置会给电能生产商带来可观的成本。在典型的应用中，地质聚合物被用作绝缘体。通过添加单独的组件，可以达到2.0 W /（m K）的导热率，该导热率高于典型的热回填（Fluidized Thermal Backfill），其值接近1.5 W /（m K）。非常重要的是，地聚合物比典型的沙-水泥混合物吸收水更好。结果，随着温度升高保持高导热率。地质聚合物作为热回填的应用有可能提高地下电力电缆系统的灵活性，并使安装的材料成本降至最低。案例研究表明了使用燃烧副产物作为地聚合物热回填的经济效益。建立了地下电缆系统的有限元方法模型，并提供了优化的回填尺寸，以最大程度地减少使用地质聚合物热回填的材料成本，并使地下电力电缆系统的性能最大化。本文的主要结果是，与传统的回填（砂-水泥混合物）相比，地质聚合物的应用导致地下电缆系统的成本降低。原因是导热系数较高，因此可以选择横截面积较小的电缆。此外，还讨论了将地质聚合物应用于电缆敷料的环境效益。与传统回填（砂浆混合物）相比。原因是导热系数较高，因此可以选择横截面积较小的电缆。此外，还讨论了将地质聚合物应用于电缆敷料的环境效益。与传统回填（砂浆混合物）相比。原因是热导率值较高，因此可以选择横截面积较小的电缆。此外，还讨论了将地质聚合物应用于电缆敷料的环境效益。

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