Study on the electromagnetic transmission properties and mechanical properties of calcium aluminate cement paste by silica fume

The effects of different contents of silica fume (SF) on the electromagnetic transmission performance (ETP) and mechanical properties of calcium aluminate cement (CAC) paste were studied. The dielectric loss of the main hydrated phases in the CAC paste was compared and analyzed for the first time by synthesizing various phases, and the electromagnetic transmission mechanism of SF in the CAC paste was explored. The results show that after adding SF, the porosity and pore tortuosity of CAC paste decrease, C₂ASH₈ is densely packed in the pores, and long-term strength is significantly improved. With the increase of SF content, the dielectric constant and loss tangent decrease, and ETP becomes better. When the SF content is 30%, the ETP is increased by 40.51%, and the 90d compressive strength is increased by 18.50%. The degree of electromagnetic wave loss in CAC paste from large to small is: C₃AH₆ > AH₃ > C₂AH₈ > C₂ASH₈ > CAH₁₀ > CA and CA₂. Finally, the reasons for the improvement of long-term strength and ETP of CAC paste by SF were comprehensively elucidated from the aspects of crystal content, pore structure, and microstructure through a variety of microscopic test methods. This SF-CAC composite material is expected to be used in the basement or the partition wall of the house to enhance the signal of electronic devices, such as mobile phones in the above places.