通过圆形钢管对膨胀混凝土形成三向约束，采用扫描电镜（SEM），研究约束膨胀混凝土的显微结构与普通混凝土显微结构的差异，进而揭示约束膨胀混凝土的显微工作机理。实验证明：由于约束膨胀的填充作用，大幅度降低空隙率及孔径，定将有效地提高混凝土的弹性模量及强度。 Three-way restraints are formed on the expanded concrete by circular steel tubes. Scanning electron microscopy (SEM) is used to study the differences between the microstructures of the confined expansive concrete and the ordinary concrete microstructures, and the microscopic working mechanism of the confined expansive concrete is revealed. Experiments have shown that due to the confinement expansion filling effect, the porosity and pore diameter are greatly reduced, and the elastic modulus and strength of the concrete will be effectively improved.