Abstract: In order to analyze the mechanical properties of alkali-activated fly ash cementitious materials,the compressive strength tests of fly ash cemented backfill under different alkali-activated conditions were carried out in the laboratory,and the effects of the type of activator,the dosage of activator and the dosage of fly ash on the strength of backfill were systematically analyzed. The results show that when the fly ash content is 10% ~ 20%,the compressive strength of fly ash based cemented backfill increases with the increase of fly ash content,and the addition of alkaline activator can effectively improve the strength index. The strength growth rate of fly-ash cemented backfill with activator is obviously higher than that of the backfill without activator. The compressive strength of fly ash-based cemented backfill firstly increases and then decreases with the increase of the content of activator,and reaches the maximum value when the content of activator is 3%. In addition,the strength of backfill supplemented with NaOH is significantly higher than the compressive strength of backfill supplemented with Na2SiO3,and the improvement effect of compressive strength at 28 d is more prominent. With the increase of curing time,gel substances generated by hydration reaction also gradually increase,and hydration products fill the pore structure,thus promoting the filling body to have good bearing capacity.

Key words: alkali excitation,filling body,fly ash,backfill,compressive strength