Study on physical and mechanical properties of complex-phase conductive fiber cementitious materials
Authors: Li Jiuyang , Wang Zhenwei , Guo Jinpeng , Luo Jingwei , Fan Xinmei , Zhu Yuepeng 
Published: July 2024

Abstract
With the continuous upgrading of infrastructure construction and the gradual development of theoretical research about engineering construction, higher performance requirements have been put forward for concrete materials. Therefore, to meet the engineering quality requirements of various concrete structures, the research direction of engineering materials has shifted towards developing new concrete with high strength, high ductility, high toughness, and other multifunctional properties. Mixing two or more types of fibers with conductive properties with the cement matrix material allows various fibers to leverage their strengths and weaknesses, thereby utilizing their respective characteristics. This results in the formation of a complex-phase conductive fiber cementitious material (CFCM), which enhances the safety, durability, and toughness of the structure. It enables the engineering structure to exhibit intelligence and resourcefulness, thereby improving its service life and reducing the full life cycle cost of the cementitious material structure. Additionally, this approach relatively eases the demand for concrete materials and reduces material consumption. This method represents one of the research directions for new concrete. Complex-phase CFCMs are essentially smart materials capable of sensing not only compressive or tensile stresses but also temperature. The emergence of CFCM represents a significant step forward in enhancing the mechanics, functionality, and sustainability of modern infrastructure. In this experiment, an orthogonal test involving 16 working conditions with three factors and four levels was designed, with steel fiber (SF) type, SF content, and carbon fiber (CF) content as the factors. The study focused on the physical and mechanical properties of composite conductive fiber cement-based materials containing both SF and CF. Performance indicators such as flexural strength, volume resistivity, and energized temperature rise of the composite conductive fiber cement-based materials were tested. The analysis of orthogonal tests produced the following results regarding the degree of influence of each factor on the mechanical and physical properties: the order of influence on flexural strength was SF doping > SF type > CF doping. Further analysis revealed that the best combination was A4B4C4. The relationship between the effect of each factor on resistivity is as follows: carbon fiber doping > SF doping > SF type. Comparing the weights between the levels, it can be observed that the optimal combination of conductivity schemes is also A3B4C4. SF and CFs, respectively, enhanced the mechanical and physical properties of complex-phase conductive fiber cementitious materials. The results of the temperature rise test on cementitious materials concluded that there is a certain relationship between the temperature rise and electrical conductivity. Specifically, the higher the electrical conductivity, the greater the temperature rise observed. Through orthogonal analysis of electrical conductivity, disregarding the effect of the non-significant influence factor SF type on the conductive heating test, the impact of two factors, CF doping and SF doping, on the heating test was investigated under 16 sets of conditions, and the data were analyzed visually. The optimal mix ratio for the test is A3B4C4, determined through comprehensive optimization of orthogonal and intuitive analyses. This means that the optimal physico-mechanical properties are achieved when using copper-plated SFs, with a SF dosage of 1.25% and a CF dosage of 0.48%. As a preceding study in the field of intelligent concrete, this experiment explores the research path of intelligent concrete, which holds positive significance for subsequent, more intricate research endeavors.