Experimental study and mechanism analysis of functional nanocrystalline cellulose to improve the electromagnetic transmission performance of ordinary Portland cement

5G signal transmission can be seriously blocked by cement-based materials, so it is very important to improve the electromagnetic transmission performance (ETP) of cement-based materials. Carboxylated nanocrystalline cellulose (NCC) is used to prepare Ordinary Portland cement paste with high ETP. The water-cement ratio and NCC content of the cement paste are 0.5 and 0–4% respectively. The test results show that the ETP of cement paste increases by 13.9%–90.6%, but the compressive strength of the sample decreases by 7.3%–87.6%. The 2% of NCC content causes the ETP of cement paste increases by 75.6%, while the compressive strength only decreases by 14.6%. The reasons for improvement of ETP are that the electrostatic force between the globule, the polymerization degree and mean chain length of C–S–H, the total volume proportion of phases (calcium hydroxide, ettringite and unhydrated cement) with low dielectric loss and the volume proportion of the no harmful pore for electromagnetic energy loss are increased, the conductivity of cement pore solution and the content of water are decreased.