Study On Properties Of Interface Transition Zone Of Spontaneous Combustion Coal Gangue Aggregate Fly Ash Geopolymer Concrete

Using solid waste as raw material,the new concrete has many advantages,such as reuse of solid waste resources,energy saving and emission reduction.At present,studies on Geopolymer as cementing material to prepare concrete and coal gangue as aggregate to prepare concrete have been quite mature,but there are few studies on Geopolymer as cementing material and coal gangue as aggregate to prepare concrete.In particular,the research on its macroscopic mechanical properties and Interfacial Transition Zone(ITZ)at the micro level is relatively weak.In this paper,water-binder ratio(0.35,0.4,0.45,0.5),alkali content(4%,6%,8%,10%),prewetting time of coarse aggregate(0h,1h,24h)were used as variables,spontaneous combustion coal gangue as coarse aggregate,fly ash ground polymer as cementitious material,Sodium silicate and sodium hydroxide were used as alkaline activator solution to prepare spontaneous combustion coal gangue aggregate fly ash geopolymer concrete.The mechanical properties and microstructure properties of interface transition zone were studied respectively.The main research results are as follows:(1)When the water-binder ratio is 0.4,the amount of alkali is 6%,and the pre-wetting time is 24 h,the compressive strength of the spontaneous combustion coal gangue aggregate fly ash aggregate concrete is the highest after 28 days,which can reach 80% of the compressive strength of the control group(with the same ratio of natural aggregate fly ash aggregate concrete).Through orthogonal test,it is found that water-binder ratio and pre-wetting time have significant effects on 28 d compressive strength.(2)Based on the material morphology observed by scanning electron microscope and micro-hardness test analysis,it is shown that when the water-binder ratio is higher than 0.4,the -interface transition zone structure of spontaneous combustion coal gangue aggregate fly ash geoparborite concrete becomes loose and the micro-hardness value decreases.When the water-binder ratio is constant,the integrity of the interfacial transition zone of polymer concrete is better than that of Portland cement concrete,and the thickness of the interfacial transition zone decreases.With the increase of prewetting time,the structure of interfacial transition zone of geopolymer concrete becomes denser and the microhardness value on the surface of aggregate is higher.(3)The simulated porosity at the interface transition zone of concrete was obtained by using backscattering image analysis method,and compared with the measured porosity obtained by mercury injection method,it was found that the difference between the two was about 5%.(4)The simulated porosity and microhardness values are fitted to establish the mapping relationship between porosity and microhardness,so as to find a more economical,convenient and fast method to obtain the micromechanical properties of the corresponding position of the interface transition zone.