Abstract: To investigate the relationship between macro swelling and micro characteristics of red mudstone fillers, we conducted loaded and unloaded swelling tests to analyze the swelling rate and time curves of different red mudstone fillers. Additionally, we performed systematic tests on these fillers using X-ray diffraction (XRD) and scanning electron microscopy (SEM) to examine their mineral fractions and microstructures. Our aim was to establish a quantitative relationship between macro swelling and microstructure, with micro characteristic parameters as intermediate variables. The results reveal that under unloaded conditions, the swelling rate of the mudstone filler was 28.3 times that of pure mudstone, and this rate increased exponentially with the addition of montmorillonite. Upon loading, the swelling rate decreased significantly compared to the unloaded state, with a slower decrease observed for fillers with higher montmorillonite content. After the tests, clay mineral content increased by 4.57%. Furthermore, as montmorillonite content increased, the crystallinity and average crystal diameter decreased by 18.1% and 16.5 nm, respectively. The geometric characteristic parameters exhibited a linear relationship with montmorillonite content. Additionally, the number of pores with a diameter of 1-2 μm increased with higher montmorillonite dosage. Finally, we established an exponential growth relationship between swelling rate and micro characteristic parameters.

Key words: red mudstone filler, swelling deformation, XRD, SEM, porosity, microscopic characteristic parameters