Ewende Silica fume can significantly improve the microstructure of concrete, mainly in the following aspects:

I. Filling effect

1. Micro silica powder particles are extremely small, the average particle size is only one tenth of the cement particles. These tiny particles can be fully filled into the pore space between the cement particles and the interface between the cement paste and aggregate, greatly reducing the porosity of the concrete, so that the concrete microstructure is more dense.

2. Reduce the existence of large pores, refine the pore size distribution, thereby improving the permeability and chemical erosion resistance of concrete.

II. Volcanic ash reaction

1. Micro silica powder has high activity and can react with calcium hydroxide produced by cement hydration. The generated hydrated calcium silicate gel with low calcium-silicon ratio is more dense and stable than ordinary cement hydration products.

2. This gel substance not only fills the pores, but also enhances the bond between cement stone and aggregate, improves the structure of the interface transition zone, and makes the overall microstructure of concrete more uniform and continuous.

III. The role of nucleation

1. Micro silica powder provides a large number of nucleation sites for the hydration of cement, accelerating the hydration process of cement. Promote the formation of more hydration products in the early stage of cement, improve the early strength of concrete. 

2. The nucleation effect also makes the distribution of hydration products more uniform, further optimizing the microstructure of concrete.

In summary, through the filling effect, volcanic ash reaction and nucleation, micro silica powder effectively improves the microstructure of concrete, thus improving the performance and durability of concrete.