Research on strength evolution law and ratio optimization of expansive backfill based on RSM-BBD

Aiming at the problems of low roof-contacted filling rate and poor roof-contacted filling effect in an iron mine stope, plastic expansive agent is introduced to realize active roof-contacted filling. In the paper，response surface methodology is adopted to design the strength ratio test of expansive backfill based on RSM-BBD, and the influence rules of slurry mass fraction, cementitious powder content and plastic expansive agent dosage on the compressive strength of expansive backfill are studied. The results show that the single factor and the interaction between various factors have significant influence on the compressive strength of expansive backfill. Cementitious powder content has the greatest influence, followed by plastic expansive agent dosage, and slurry mass fraction is the least in the single factor. The interaction between slurry mass fraction and cementitious powder content has the most significant influence on the compressive strength of the early and middle stage, and the interaction between cementitious powder content and plastic expansive agent dosage has the most significant effect on the later compressive strength. The optimal ratio of expansive backfill determined by goal programming method is 69% of slurry mass fraction, 10% of cementitious powder content, and 3? of plastic expansive agent dosage. The analysis of XRD and SEM show that the plastic expansive agent can loosen the internal structure of the backfill and cause expansion, and improve roof-contacted filling rate.