Study On The Mechanical Properties And Durability Of Alkali-Activated Coal Gangue Concrete

Coal gangue is one of the principal associated waste of coal resources,accounting for about 15%～20%of the coal output.It is one of the most massive industrial waste worldwide.In China,its emission and growth rates roughly exceed 7 billion and 150million tons per year,respectively.Raw coal gangue occupies territory and even induces geological disasters,such as instability,landslide,and collapse.Moreover,the abandoned coal gangue can also pollute the atmosphere,water,and soil due to spontaneous combustions and soluble substances.Therefore,how to make the most use of coal gangue as resources has become a global issue.Based on identifying the mineral composition,chemical composition,and microstructure of coal gangue in the Ordos area,a composite activation strategy combining mechanical activation,thermal activation,and chemical activation was employed to enhance the reactivity of coal gangue as a primary cementitious material in this paper.An orthogonal test was designed and carried out to determine the optimal combination of composite activation parameters.The coal gangue after composite activation was used as a cementitious material to replace cement by 100%in the preparation of alkali-activated coal gangue concrete.Finally,the mechanical properties and durability of alkali-activated coal gangue concrete were systematically studied.The main conclusions are as follows:(1)The reactivity of coal gangue was significantly enhanced by the proposed composite activation technique.The compressive strength of the optimum combination group of alkali-activated coal gangue cementitious materials could reach 58.8 MPa.Among them,the optimal combination of composite activation parameters is that the M=1.3,A=10%,W/B=0.3,H=2 h,and T=700℃.(2)The mechanical properties of alkali-activated coal gangue mortar are better than ordinary cement mortar.The flexural strength,compressive strength,and impermeability of alkali-activated coal gangue mortar are 1.19 times,1.23 times,and1.15 times those of ordinary cement mortar,respectively.In addition,the freeze-thaw resistance of alkali-activated coal gangue mortar is also better than ordinary cement mortar.After 100 freeze-thaw cycles,the mass loss rate,flexural strength,and compressive strength loss rate of ordinary cement mortar are 1.85 times,3.09 times,and 5.54 times that of alkali-activated coal gangue cement mortar,respectively.(3)The mechanical properties of alkali-activated coal gangue concrete are better than ordinary concrete.The compressive strength,splitting strength,flexural strength,and axial compressive strength of alkali-activated coal gangue concrete are 1.17 times,1.04 times,1.03 times,and 1.42 times that of ordinary concrete,respectively.In addition,the freeze-thaw resistance of alkali-activated coal gangue concrete is also better than ordinary concrete.After 200 freeze-thaw cycles,the mass loss rate,relative dynamic modulus loss rate,and axial compressive strength loss rate of ordinary concrete are 1.26 times,1.19 times,and 1.15 times higher than that of alkali-activated coal gangue concrete,respectively.(4)The bonding performance between alkali-activated coal gangue concrete and reinforcement is better than that of ordinary concrete.The ultimate bond strength,ultimate load,and bond energy of alkali-activated coal gangue concrete are 1.62 times,1.58 times,and 2.07 times that of ordinary concrete,respectively.In addition,the constitutive relationship of bonding stress–slip between alkali-activated coal gangue concrete and reinforcement is established,and the bond failure mechanism between alkali-activated coal gangue concrete and reinforcement is analyzed.Finally,the bonding performance between alkali-activated coal gangue concrete and reinforcement was simulated by ABAQUS finite element software.(5)The flexural performance of alkali-activated coal gangue concrete reinforced beam is better than that of ordinary concrete reinforced beam.Compared with the latter,the ultimate bearing capacity of the former is increased by 3.60%,the ductility ratio is increased by 10.60%,the cracking moment is increased by 2.88%,the deflection value under ultimate load is reduced by 2.30%,the average crack spacing is reduced by10.30%,and the average crack length is reduced by 2.10%.In addition,the crack propagation law and failure mechanism of alkali-activated coal gangue concrete beams are expounded,and the calculation model of the cracking moment and ultimate moment of alkali-activated coal gangue concrete beams is proposed.(6)The fracture mechanical properties of alkali-activated coal gangue concrete are better than those of ordinary concrete.Compared with the latter,the ultimate load,fracture energy,and initiation fracture toughness of the former are increased by 10.00%,7.21%,and 15.71%,respectively.While the CMOD_c and CTOD_c are reduced by 6.95%and 2.99%,respectively.In addition,the crack propagation law of alkali-activated coal gangue concrete beam is summarized.