ZHANG H B, SUN H T, CHAI H C, et al. Effect of silica fume content on the properties and microstructure of foam filling materials [J]. Journal of Henan Polytechnic University (Natural Science) , 2025, 44(4): 188-196.

doi: 10.16186/j.cnki.1673-9787.2023120020

Received: 2023/12/08

Revised: 2024/02/18

Published: 2025/06/19

Effect of silica fume content on the properties and microstructure of foam filling materials

Zhang Haibo, Sun Huiting, Chai Hucheng, Hu Yikang, Zhou Yuntong, Xie Baien, Tian Yanchao

School of Materials Science and Engineering， Henan Polytechnic University， Jiaozuo 454000， Henan，China

Abstract: Objectives The high porosity of cement-based foam concrete used as a filling material significantly reduces its strength. Methods In this study， silica fume （SF） was used to partially replace ordinary Portland cement （OPC） to prepare a high-strength， low-density foam concrete （SF-OPC）. The effects of different SF replacement levels （0%， 5%， 10%， 15%， and 20%， by weight） on the fluidity， setting time， compressive strength， and dry density of SF-OPC were systematacially investigated. Additionally， low-field nuclear magnetic resonance （LF-NMR） was employed to characterize pore structure， nanoindentation was used to evaluate the hardness of the hardened slurry skeleton， X-ray diffraction （XRD） was applied to analyze hydration products， and scanning electron microscopy （SEM） was conducted to observe microstructural morphology. Results The results showed that increasing SF content initially improved the fluidity of the slurry and then caused a decline， while the setting time decreased continuously. The compressive strength of the specimens first increased and then decreased. The maximum fluidity （223.1 mm） was observed at 5% SF content， whereas the highest compressive strength was achieved at 15% SF content， with 3-， 7-， and 28-day strengths of 3.8 MPa， 4.2 MPa， and 4.9 MPa， respectively—representing increases of 123.5%， 100.0%， and 75.0% compared to the control group. The proportion of macropores decreased by 75.8%， while the proportion of nanopores increased by 208.4%. Conclusions The addition of silica fume promoted the formation of low calcium C—S—H gel， effectively optimizing the pore structure distribution， enhancing the structural hardness of the slurry skeleton， and resulting in a denser microstructure. Under the same foaming ratio， SF significantly improved the compressive strength of SF-OPC foam concrete. This makes it a promising material for high-strength， low-density backfilling applications in coal mine caving zones and offers a useful reference for fire prevention and control materials used in mine goafs. 

Key words: filling material; foam concrete; silica fume; pore structure; pozzolanic effect