Research On The Preparation And Performance Of Cemented Paste Backfill Of Coarse Tailings

Cemented paste backfill(CPB) is to an optimized combination of one or more kinds of coarse and fine aggregates, cementing materials and water and configure into a cement base material with a good working performance and strength. The main technical indicators of CPB are the slurry’s slump is larger than or equal to 180 mm, the exudation rate is less than or equal to 5%, and compressive strength of 28 d solidified body is 2 MPa ~ 5 MPa.This thesis studied the influence of cementing agent, fly ash, lime stone powder and water reducing agent on the slurry’s working performance and the compressive strength of the solidified body, and used the scanning electron microscope to observe the microstructure, and adopted the mercury intrusion method to analyze the porosity and bore diameter of the solidified body. Through the analysis of experimental results, it got the following conclusions:(1) When the slurry’s solid concentration is fixed(containing 5% of cementing agent), with the increase of the adding amount of limestone powder, the slump of cemented paste backfill declines, and if the limestone powder mesh is bigger(that is, the thinner), the slump will decline more significantly. If the limestone powder particles are finer, the exudation rate of cemented paste backfill will decline more remarkably; If the limestone powder is finer, the setting ratio of 28 d cemented paste backfill solidified body will decline more remarkably.(2) After being mixed with 0.05% of water reducing agent and 20% of limestone powder(800 mesh), both granular coarse tailings and powdery coarse tailings can meet the slurry required by the cemented paste backfill, and they can make the pore diameter distribution of 28 d solidified body become more refined, which will significantly increase the compressive strength. Results show that mixing water reducing agent and limestone powder of 800 mesh with coarse tailings is an effective way to prepare cemented paste backfill.(3) When the solid concentration of coarse tailings is fixed(containing 5% cementing agent), the adding amount of Ⅱ level fly ash reaches 40%, and the slurry’s exudation rate is 19.54%, which cannot meet the requirements of cemented paste backfill; The early strength of solidified body of mixing with fly ash is lower, and the curing age required by the pozzolanic reaction is greater than 28 d. Results show that mixingⅡgrade fly ash into coarse tailings cannot prepare the cemented paste backfill.(4) When the adding amount of cementing agent is between 5% and 20%, the slump of granular coarse tailings backfill is greater than 200 mm, and the exudation rate is greater than 5%, which cannot meet the requirements of cemented paste backfill; But the compressive strength of 28 d solidified body increased with the increase of the adding amount of cemented paste backfill. Results show that mixing cementing agent into the coarse tailings also cannot prepare the cemented paste backfill.(5) Under the condition that the adding amount of cementing agent is lower(5%), the hydration products of silicate cementing agent has a tendency of producing self gathering, and the hydration products of slag composite cementitious material has a relative uniform distribution in CPB; Under the condition that the adding amount of cementing agent content is higher, compared with P ? I42.5 cementing agent, the cementing property of slag composite cementing agent has no advantage, but it is higher than P. C32.5 cementing agent.(6) Taking lead-zinc mine(containing 12.95% of sulfur) coarse tailings as the aggregate, and under the condition of keeping 180 mm of the slump, mixing 3% ~ 5% slag composite cementing agent with 10% of 800 mesh limestone powder and 0.25% of water reducing agent can prepare the slurry that meets the requirements of cemented paste backfill. The compressive strength of 28 d solidified body is between 2.7 MPa and 4.4 MPa, and the late strength(60 d) develops stably.