Study On Mechanical Properties Of Full Tailings Cemented Backfills In Acidic Solution

In the acidic corrosion environment,the microstructure,mineral composition and porosity of the filling body will change,it deteriorate filling body mechanics performance seriously,then influence the stability of the filling body.This paper summarizes the research results of material mechanics experiment in the corrosion conditions at home and abroad achievements,and a cementsand ratio 1:4,a density of 75% and 28 day-curing cycle of the backfilling has made,it is soaked in sulfuric acid solution with pH of 1,3,5 respectively.Based on laboratory experiments,the change law of physics,chemistry,mechanical properties of cemented tailing backfill after corrosion is studied,the main research contents and results as follows:(1)The physical and chemical properties in acidic environment is studied.There has 19 groups of filling body with specimens of 50 mm x 100 mm to be 285 in number,and the sulfuric acid solution with pH value of 1,3,5 has prepared.The change rule of its physical and chemical properties is studied when filling soaked in sulfuric acid solution with pH of 1,3,5 respectively.Microscopic pore filling body is obtained by nuclear magnetic resonance experiment.With the acoustic detector test,the compressional wave velocity change is studied.The pH change of sulfuric acid solution after filling body soaked in it is tested by pH meter.With the help of X-ray diffraction(XRD)analysis study,the change of the filling body composition was found.The micro damage mechanism of filling is discussed.The results showed that: first,from the appearance of filling in p1(pH = 1,similarly hereinafter)environment,the surface of the filling body change is more obvious,with the increase of time,cementitious mineral of cementing filling body surface loss more and more serious,and pitting corrosion hole increases gradually,fine aggregate exsertion,if touch filling body,fine aggregate can fall off.In p3 and p5 environment,filling surface morphology had no obvious change;Before 30 days,the quality of filling body appears to periodic trends of first increased and then decreased,with the increase of corrosion time,showed obvious downward trend.In p1 environment,the quality of filling the fastest decline;The filling body compressional wave velocity increases with the increase of corrosion time before 30 days,and the change is bigger then later,after 30 days,we can see wave velocity of p3,p5 increases has slow down,after 40 days,wave velocity of p1 filling body began to decline;The volume of the filling body with the increase of corrosion time,showed a significant positive correlation;Filling volume with the extension of corrosion time,has a tendency to increase;Regardless of the initial solution is strong or weak acid,the pH of the solution are tend to be neutral trend,namely the system between sulfuric acid solution and filling will evolve to present the trend of balance over time;Sample in p5 environment,after corroded for 10 days,in addition to the hydration products,can also be found that the diffraction peak of ettringite.At this time,the mass of ettringite is limited,it filling the specimen micro pore,optimize the pore structure.With the increase of corrosion time,the diffraction peak of calcium hydroxide and Aft decreases,the number of diffraction peak of gesso rise;In the P1 environment,the diffraction peak of calcium hydroxide is very small,the diffraction peak of Aft decreases,and the number of gesso increase with the corrosion time.(2)The study of strength properties for filling in acidic conditions.Using specimen of 50 mm x 100 mm cylinder filling body,the mechanical parameters were measured at different period,like compressive strength,elastic modulus,cohesion,internal friction Angle.Damage mechanics knowledge is discussed in this paper to explain acid corrosion mechanism of filling body.The results show that the compressive strength,elastic modulus,cohesion,internal friction Angle all showed a similar rule which is first increased then decreased;Filling body damage variable D with the increase of corrosion time,showed the trend of growth,namely corrosion damage more and more serious;The increase of porosity on mechanical properties of filling body will produce adverse effect;If only considering the compressive strength,elastic modulus,cohesion,internal friction Angle of decline phase,we can found that compressive strength,elastic modulus,cohesion and Angle of internal friction present negative correlation with damage variables D;Under Corrosion and load conditions,the filling material damage degradation degree increases with the increase of strain.At the initial stage of load,the material micro pore,defect is compacted,as the strain increases gradually,the material internal microporosity and microcrack have a Continuous development and evolution,thus accelerating the material damage until macro crack,at that time,the strength of the specimen reaches its peak value,failure occurs.(3)Strength prediction and analysis of filling body in the acidic conditions.By using random forests to predict the strength of filling body,mainly considering two factors,which is pH value and the number of days.With the test data,the random forest model of strength was founded,and use the model to predict the strength of filling body.Value of pH is the important factor to the precision for prediction;Corrosion time is an important factor of filling body uniaxial compressive strength;Compared with Support Vector Machine model,it has better goodness of fit than support vector machine forecasting model,shows that random forest is more suitable for the filling body strength prediction.