| As a recyclable material,building waste aggregate can be treated as paste filling material,fill into goaf,to control the earth surface subsidence induced by mining.However,it is still uncertain that how these filling bodies would be affected by the carbonation of air,the corrosion of mine water and the effect of ground stress after filled into the goafs,and what mixture ratio should be while mixing building waste aggregates with other materials.This paper summarized the study of a long-term evolution of building waste aggregate mechanical properties under the impact of carbonization,corrosion and geostress,which will be of great significance to recyclable building waste utilization.In the study,construction waste was treated as coarse aggregate and natural sand was treated as fine aggregate,cement was treated as the cementing material,mixed with fly ash,mass concentration.The orthogonal design method was adopted to determine water cement ratio,sand ratio and dosage of fly ash on construction waste aggregate filling body slump,strength and elastic modulus.Based on the orthogonal tests,it is concluded that the mass concentration of 83%,water cement ratio 2.5,sand rate was 65%,the dosage of fly ash is 250 kg/m3 is the optimal mixture ratio;The influence of the size,shape and curing condition of the backfill specimen on the mechanical properties of the backfill was analyzed.The triaxial creep test of the backfill was carried out,and the creep deformation law of the backfill and the influence of confining pressure on the creep law were analyzed.Carbonation tests of backfill under different conditions were carried out,and the evolution of carbonation depth,carbonation rate and strength of backfill after carbonation with carbonation time,different CO2 concentrations,humidity and temperature were explored,and a mathematical model was established.The results show that the depth of carbonation of backfill increases with time,but the rate of carbonation decreases.At 7 d of carbonation,the depth of carbonation is already large.Carbonization depth and carbonization rate are positively correlated with CO2 concentration,negatively correlated with humidity at carbonization,and positively correlated with temperature at carbonization.After the carbonation time exceeds 3 d,the strength of backfill has little relation with CO2 concentration,the strength loss rate is positively correlated with CO2 concentration,and the carbonation humidity has little effect on backfill strength,showing a negative correlation trend.There is no correlation between carbonation temperature and backfill strength.The creep deformation of the backfill after carbonization exceeds that of the uncarbonized backfill,and the accelerated creep time is shorter and the stress level is lower.The effects of salt and acid solution corrosion on the strength and creep characteristics of backfill were studied by the dry-wet cycle accelerated corrosion test.The effects of different solution types and concentration on the strength of backfill were analyzed and the mechanism of corrosion was explored.The results show that the strength of the backfill increases first and then decreases,and the strength loss rate is positively correlated with the concentration.After the acid solution corroded,the strength of the backfill showed a significant downward trend,and with the decrease of PH value,the magnitude of strength decline increased,and its strength degradation was more severe than that of the salt solution after corrosion.The creep deformation increased after the corrosion of the backfill,the stress level threshold of accelerated creep decreased and the deformation modulus decreased obviously.Numerical simulation of filling mining in panjiaxigou coal mine was carried out.The numerical simulation results show that the use of paste filling can control the surface subsidence induced by mining and the backfilling is weakened after carbonization. |
PDF Full Text Request