Study On Carbonation Reaction Of Fly Ash And Carbide Slag And The Characteristics Of The Reaction Products

Under the background of energy-saving emission reduction and comprehensive utilization of solid waste resources,how to achieve mineralize and fix CO₂ in industrial waste gas during building materials utilization of industrial solid waste has become a new research subject.Building materials utilization of industrial solid waste are usually based on the pozzolanic reaction between Ca O,SiO₂ and Al2O3 which produces calcium silicoaluminate hydrate gelling substances.Besides,Ca O is generally excessive in the pozzolanic reaction system.Excessive Ca O existing in the form of Ca?OH?2 in the cementing material is easy to react with CO₂ in the air in later stage which causes damage of the structure of cementing material and affects its durability.If CO₂ is introduced into the cementitious system during the process of preparation of the cementing material,the enhancement of strength and durability of cementing material can be simultaneously achieved and CO₂ can be mineralized and fixed to achieve carbon emission reduction which has great theoretical significance and industrial application prospects.However,there are few theoretical and practical application studies on using calcium carbide slag as a calcium source?providing Ca O component?and fly ash as a silicon and aluminum source?providing SiO₂ and Al2O3 components?to compound formula and for the preparation of cementing by the materialization reaction with CO₂.Therefore it is necessary to carry out systematic research in this area.Based on this,the main research contents and results of this paper are as follows:?1?The pH of the reaction slurry which contained fly ash,carbide slag and fly ash-carbide mixture was tested online,respectively.The raw materials and products from the reaction system were characterized by X-ray diffraction,thermogravimetric analysis and SEM.The results indicated that the average carbonation reaction rate of a fly ash when pH decreased to 7.0 was 51 times that of carbide slag.Compared with the carbide slag carbonation,the average carbonation reaction rate of the fly ash and carbide slag mixture?4:1,g/g?increased by nearly 5.6 times when the pH decreased to 7.0,and the reaction time for the mixture was shortened by 31.6% than that of calcium carbonate-carbide slag mixtures,indicating that there is a synergistic effect between carbide slag and fly ash in the carbonation reaction.The result of TGA showed that the carbon sequestration rate for fly ash and carbide slag was about 2% and 61.3% respectively.The carbon sequestration rate for the fly ash--carbide slag mixture increased by 19.6% than the sum of fly ash and carbide slag.The Ca CO3 produced by carbonation of Fly ash and carbide slag mixture attached on the surface of Fly ash particle in a state of dispersion,while the Ca CO3 produced by the carbide slag carbonation attached on the surface of carbide slag particle in a state of agglomerate,which were verified by the SEM results.This is likely the main reason for the increase of carbon sequestration for the Fly ash-carbide slag mixtures.?2?The effects of calcium carbide slag ratio,curing temperature and mineralization reaction time on the compression strength of the gelled test block were investigated.The results show that when the calcium carbide slag ratio is 30% and the curing temperature is 60 °C,a gel strength test block with better strength for 3 days can be obtained.With increasing of the mineralization reaction time,The 3-day strength and 28-day strength of the test block increased first and then decreased Under the conditions of the carbide slag ratio of 20% and the mineralization time of 30 min,the compression strength of 3-day and 28-day were increased by 62.2% and 89.1%,respectively,compared with that of the non-mineralization reaction.The study also found that the highest 3 days strength obtained at condition of calcium carbide slag ratio 40% with the mineralization reaction time of 50 min,in the range of calcium carbide slag ratio of 20% and 50% and of the mineralization reaction time of 30min-60 min,and the strength increased by 82.1%,compared with that of the non-mineralization reaction.XRD analysis showed that the calcium hydroxide diffraction peak of the gelled test block which from reaction for 30 min between the slurry with CO₂ disappeared completely and the Ca CO3 diffraction peaks appeared obviously.The TGA test results showed that there was obvious Ca CO3 decomposition weight loss peak for the gelation samples.In the condition of this experiment,for obtaining the best 3days strength,the degree of Ca?OH?2 carbonization by CO₂ in the gelation should keep in the range of 5%-10%,and the amount of mineralized fixed CO₂ per ton of gelled test block is about 7 kg-31 kg.?3?The effects of carbonation reaction time on the compressive strength of foamed concrete under the conditions of soaking water and lime water or not were investigated.The mineral composition,thermogravimetric characteristics and microstructure characteristics of the blocks were characterized by XRD,TGA and SEM,respectively.The results showed that the compressive strength of the foamed concrete first increased with carbonation reaction time and then decreased,the maximum strength of the block with carbonation reaction 4h was up to 6.5 MPa,which increased by 80.6% than that of the without carbonized reaction block.The results of SEM analysis showed that the change process was from sheet densification to granulous loosened structure for the block wall of hole with increasing of carbonation reaction time,this may lead to the compressive strength change.The TGA curve results showed that the amount of CO₂ fixation was about 37 kg per ton of foamed concrete block for the highest compressive strength,and CO₂ fixation of 61 kg per ton of foamed concrete block for the same strength before carbonation.