Abstract:

In order to promote the efficient utilization of industrial solid waste such as silica fume and fly ash in the field of building materials and promote the green and low-carbon development of concrete materials， this paper used slump， slump flow， uniaxial compressive strength， impermeability test and SEM-EDS microscopic analysis method. Four groups of concrete with different admixture systems were systematically studied， including the reference group JZ （C30 concrete）， the single-doping silica fume group D1 （8% （mass fraction） silica fume） and the composite group D2 （8% silica fume+10% （mass fraction） fly ash） and D3 （8% silica fume+20% fly ash）. The results show that the D1 group exhibits the highest uniaxial compressive strength at both 1 and 3 d. In particular， its 3 d uniaxial compressive strength reaches 17.9 MPa， representing an increase of approximately 15% compared with 15.6 MPa for JZ group. The D2 group achieves the highest 28 d uniaxial compressive strength， at 38.6 MPa， and also has the lowest water penetration height， indicating the best overall performance. Although the D3 group workability is superior to the D2 group， its uniaxial compressive strength and impermeability are both inferior to those of the D2 group. The co-doping of silica fume and fly ash promotes the secondary hydration reaction， which is conducive to the further formation of hydration products and the densification of matrix. In general， silica fume dominates the early structural densification and uniaxial compressive strength formation， while fly ash improves the durability of concrete mainly through the reconstruction of pore structure and the blocking of infiltration channel in the later stage. The synergistic improvement of mechanical properties and impermeability can be achieved by the combination of silica fume and fly ash.

Key words: fly ash, silica fume, early strength, mechanical property, impermeability, microscopic analysis