Research on the pore size distribution and durability improvement mechanism of magnetic slurry

The internal pore structure of cement-based materials plays a key role in medium migration and directly impacts the material’s durability performance. This study proposes a method of regulating magnetic particle slurry using magnetic fields in order to systematically investigate the optimisation mechanism of pore structure under the influence of a magnetic field. Accelerated durability tests were conducted, including freeze-thaw cycles (50 cycles), chloride ion penetration and sulphate erosion (SO₄²⁻), combined with nuclear magnetic resonance (NMR) technology to analyse the pore structure evolution quantitatively. The results show that the magnetic field significantly improves the pore characteristics of the slurry, as evidenced by a reduction in the number of capillary channels and porosity. With a magnetic powder content of 20%, the strength loss rate after 50 freeze-thaw cycles was found to be 2.14%. Increasing the magnetic powder content to 25% improves resistance to sulphate erosion by 14.4% compared to the control group. Analysis of the microstructural mechanism revealed that the magnetic field drives magnetic particles to form ordered arrangements, generating a volume exclusion effect that promotes bubble escape while densifying micro-regions through magnetic forces between particles. NMR testing confirmed that, under a 0.5 T magnetic field, the micro-pore throat volume of samples containing 15% magnetic powder decreased by 23.35%. This study overcomes the limitations of traditional pore modification technologies by providing theoretical support and technical solutions for optimising the durability of functional cement-based composite materials.