Study On Mechanical Properties Of Spontaneous Combustion Coal Gangue Based Geopolymer Recycled Concrete

Spontaneous combustion gangue is a discarded solid waste in the process of coal mining and washing,and its combustible components are formed under the natural condition of oxidation and combustion.At present,the coal gangue in China has accumulated more than 50 million tons,and is still increasing at a rate of 3 to 3.5billion tons per year.It is expected that by 2020,the annual discharge of coal gangue will increase to 7.29 million tons,seriously polluting the ecological environment,which is contrary to the sustainable development,and its harmfulness can not be underestimated.The mineral components of spontaneous combustion gangue are mainly aluminum silicate minerals and carbon,and the coal gangue after high temperature heat treatment is also called calcined coal gangue,which greatly improves its volcanic ash activity and increases its application range.This determines the best choice of the spontaneous combustion coal gangue Shi Ke as a new green cementitious material-geological polymer raw material.It has many characteristics such as high strength,fast hardening,corrosion resistance and high temperature resistance.It can be used in combination with other solid wastes（slag and fly ash）.From the angle of resource utilization and environmental protection,it is the best choice for the new cementitious material.It is the change of the road of"high energy consumption"cement to"green"development.Concern at home and abroad has become a worldwide research hotspot.In accordance with the principle of"sustainable development,waste treatment and recycling",this research topic uses the main raw materials of the traditional industrial waste,the spontaneous combustion gangue,slag and fly ash as the geological polymer,and studies the coal gangue and the calcined coal gangue based on the spontaneous combustion of coal gangue and the activation of high temperature calcination.The mechanical properties and microstructure of the polymer recycled concrete should be used to apply the spontaneous combustion coal gangue in full coverage,multi angle and stereoscopic application to the geopolymer recycled concrete.The main contents of this paper are as follows:（1）The recycled coarse aggregate processed by the process of crushing,sieving and cleaning of waste concrete is compared with the physical and mechanical properties of natural coarse aggregate.The apparent density,water absorption and crushing value of natural coarse aggregate and recycled coarse aggregate were analyzed.The results show that the physical and mechanical properties of recycled coarse aggregate are lower than that of natural coarse aggregate.（2）Using self ignite gangue and calcined coal gangue as the main raw materials,geopolymers are prepared by comprehensively adding traditional bulk industrial solid waste slag and fly ash.The preparation of geopolymer instead of all cement was used to produce the green concrete,coal gangue based geopolymer recycled concrete,in twenty-first Century.By using the reliable technical indexes of mortar strength,2kinds of coal gangue（spontaneous combustion gangue and calcined coal gangue）base polymer recycled concrete mix ratio are designed,and 5 groups of different recycled coarse aggregate（0%,30%,50%,70%,100%）and 3 years of age（3d,7d,28d）and150 blocks of spontaneous combustion gangue are prepared.Stone and calcined coal gangue based geopolymer concrete specimens.（3）Recycled coarse aggregate,coal gangue and calcined coal gangue based geopolymer are used as cementitious material,and Coal Gangue Based Geopolymer recycled concrete is prepared on the basis of the mix ratio design method of mineral admixture application technology.And compared with the compressive strength and splitting tensile strength of natural coarse aggregate concrete,the influence of different recycled coarse aggregate on the mechanical properties of coal gangue based geopolymer concrete was analyzed,and the possibility of applying large amount of recycled coarse aggregate to coal gangue based geopolymer concrete was discussed.（4）Scanning electron microscopy（SEM）technique is used to analyze the microstructure of each age（3d,7d,28d）of regenerated concrete of spontaneous combustion coal gangue base and calcined coal gangue based geopolymer.The results show that there are micro cracks at the interface between the recycled coarse aggregate and coal gangue（spontaneous combustion gangue,calcined coal gangue）base geological polymer matrix,and the hydration reaction of 7d spontaneous combustion gangue base and calcined coal gangue based recycled concrete is mainly acicular hydrated sodium aluminosilicate（calcium）（N,C-A-S-H）and granular C-S-H coagulating With the increase of curing age,the pores in the 28d spontaneous combustion gangue base and the calcined coal gangue based geopolymer are gradually filled,making the structure of the geopolymer more compact and even,and strengthening the interface area of the geopolymer with the recycled coarse aggregate.On the other hand,the calcium dissolution reaction of the spontaneous combustion gangue Based Geopolymer and the interaction of silicon and aluminum formed the pore structure,and the polymerization reaction was further strengthened with time,and the pore was obviously more uniform and closed.The calcined coal gangue based geopolymer was in demand for the hydration reaction due to the growth of the nursing age.The higher the degree,the high ratio of silicon to aluminum and the deficiency of the alkali environment,there are a large number of unreacted free Si O₂in the system,and the geological polymer sclerosis is formed in the form of amorphous silicic acid root,which makes a large number of cracks on the surface of the regenerated concrete of the calcined coal gangue geological polymer base,and the regenerated mixture of the spontaneous combustion gangue based geopolymer is regenerated.The compressive strength and splitting tensile strength are reduced compared with the frozen soil.