Research On The Influence Factors Of The Compressive Strength Of Cemented Paste Backfill

Iron tailingsCemented Paste Backfill is shorted for iron tailings CPB,a kind oflow strength cement-based materials. It is mixed with total tailings, cement, water,additives and is stired pumped to a specified location, In this thesis, we researched thewater reducing agent.binders properties (one kind cement is silicate cement, referredto as cement; another cement is slag cement which is consist of20%silicate cement80%slag cement), fly ash and limestone powder on the influence laws of theCompressive strength of Cemented Paste Backfill. We measured the total porosityand pore size distribution of the solidified using (Autopore Ⅳ9500) Mercuryporosimetry analyzer.Through the analysis of experiment results, we can drawing these followingconclusions:（1）The reducing agent can improve the fluidity of the slurry,and whenmaintaining the same flow phase it can improve the compressive strength of the curedbody,The total porosity and pore size of iron tailings paste solidified decline withreducing agent becomes small, it is the main reason of the compressive strengthincrease of the solidified which the pore become thinner.（2）With the increasing of slurry solids concentration (such as cement contentwith10%and the concentration of slurry with70%,78%, and86%), the compressivestrength of the two kinds of cement solidified are constantly improving,the two kindcements are slag cement and cement, When the mix is same, the compressive strengthofsolidified whose cement is slag cement is greater than the compressive strengthofsolidified whose cement is cement. With the increasing of slurry solidsconcentration, the raise rates and total porosity of the former continue to reduce, andwhat is the same to average pore diameter.（3）With the increasing of their`s age (such as whose concentration is86%andthe cement content is5%), both of the two slurry`s compressive strength areincreasing. When the age is same, the compressive strength of the cured cementwhose cement is slag cement is greater than the compressive strength ofthe solidified whose cement is cement. With the increasing of age, compared with the compressivestrength of latter, the raise rates of the former is increasing and its`average porediameter continuously reduced.（4）When the water-cement ratio is greater than0.65, the compressive strengthof the solidified whose cement is slag cement is greater than that whose cement iscement. When the water-cement ratio is less than0.65, the compressive strength ofthe solidified whose cement is slag cement is less than the that whose cement iscement. Analysisingby scanning electron microscopy (SEM) and mercuryporosimetry (MIP), we can concluded that in high water-cement ratio (>0.65)environment, the aggregate of the solidified is not completely wrapped by the cementhydration products, and the pore of the solidified mixed with slag cement is finer thanthan the cured cement (ie hydration products is more and less dispersed), resulting inan increase in the aggregate cross-sectional area of the solidified, and the increase ofthe aggregate cross-sectional area result the increasing of the compressive strength. Inthe low water-cement ratio (<0.65) material, the aggregate of the solidified iscompletely wrapped by the cement hydration products, the porosity of the solidifiedmixed slag cement increases significant. And it decreases the bond strength of thesolidified aggregate which could reduce the compressive strength of solidified.（5）Ⅱ fly ash can improve the fluidity and compressive strength of theirontailings CPB slurry.It can reduce the amount of water, and the more it content, thebetter its water-reducing effect and strength. Analysising by mercury porosimetry, wecan concluded thatthe average pore diameter is gradually reduced with ageincreasing,The reducing of pore size is the reason of the compressive strengthimproving.（6）Limestone powder whose maximum particle size is less than40μm canimprove the fluidity of the slurry and the compressive strength of the curedbody.When the grounded limestone powder content is5%,the total porosity iscontinuosly reducing, and the average pore diameter is continuously decreasing.Thesephenomena can increase the compressive strength of the cured body.