Study On The Micro-structure And Physical-mechanical Performance Of Concrete With Coal Gangue As Aggregate

Coal gangue is currently one of the largest industrial wastes in annual emissionsand the cumulative stocks in China. Therefore, utilizing coal gangue as buildingmaterials is an effective way to realize renewable use of it.The dissertation selectedcoal gangue as concrete aggregates,by using the theoretical mathematical model,physical-mechanical experiments and optical fiber sensing technology and so on. Theinfluences on the micro-structure and physical-mechanical performance of concretewith coal gangue as aggregate incorporation were studied. And the fundamentalmechanical and early shrinkage performance were analysis; evaluation model of coalgangue aggregate’s quality was obtained. The research conclusions would offertheoretical basis for further application and promotion of coal gangue concrete.Combined with phase analytical method and materials micro-morphology, theinfluence of coal gangue aggregate activity on the micro-structure of concrete wasstudied.The phase analysis indicated that new substances such as gismondine andandradite were generated after secondary hydrated reaction of active coal gangueaggregate. In the microstructure analysis, the compact structure can’t form afterhydration due to that hydration products cross-linked each other to form large poremesh skeleton system which filled in the microscopic pores and fractures. So theactivity of coal gangue couldn’t improve the microstructure characteristics of cementpaste. The influence of the macroscopic mechanical properties were that hydratedreaction can promot its early compressive strength, but had little effect on the latercompressive strength. The strength coordination between coal gangue and cementmatrix was also a key factor for macro-properties development of cement mortarBy using XRD, SEM, EDXA, MIP, the interface microstructure, chemicalelements distribution、migration and enrichment in ITZ, micro-hardness analysis andpore structure were studied. Based on the theory of material pore science andmicroscopic structure of concrete, the physical and chemical mechanism among thecoal gangue aggregate and the cement paste was revealed and the ITZ’s structuremodel of coal gangue aggregate concrete was built.The mechanical performance of288test blocks were performed by material testwith considering the influence of coal gangue types, grain composition, pretreatment,curing condition and two kinds of W/C. Combined with the development of itsmechanical performance, the inner connection between the microstructure and macro -mechanical performance was established. Besides the selection principle of coalgangue aggregate and the design method of coal gangue aggregate concreteWith concrete materials testings, the fundamental mechanical performances oftwo kinds of coal gangue aggregate concrete were experimented. With regressinganalysis, the empirical equations describing the relationship between axialcompressive strength, plitting strength and cubic compressive strength were obtained;and coal gangue aggregate concrete’s complete curves of stress-strain were gained byexperiments. The strength and deformation index’s relationship as: peak strain,ultimate strain, elastic modulus and poisson ratio which were reflected in thestress-strain curves had built through the relationship with ordinary concrete, and theconstitutive model of coal gangue aggregate concrete was established. The specimenswere312blocks totally.By using the fiber grating sensing technology, coal gangue aggregate concrete’searly shrinkage performance were examined which mainly include concrete’s plasticshrinkage, autogenously shrinkage, chemical condensation and dry shrinkage. And thetesting results showed that active and inactive coal gangue aggregate incorporationwill exacerbate early shrinkage of concrete. The primary causes include that gangue‘swater-absorbing, bleeding resorption, activity and chemical reaction.Based on multiple factors affected the mechanical performance and theproperties diversified of coal gangue,12kinds of coal gangue specimens wereselected from7different coal mine in Xuzhou. Based on the gray correlation analysis,the influencing factors on concrete mechanical performance were obtained and theireffect from large to small in turn is rock strength, the contents of needle-like particles,water absorption, fractal dimension of grain grading, bulk density and moisturecontent. The comprehensive evaluation model of coal gangue aggregate quality basedon GM (1,4) was built, and assessment and prediction of coal gangue aggregatequality were proposed.