Research On Preparation And Hydration Mechanism Of New Pattern Coal Gangue Based LC3 Cementitious Material

To cater to the challenges of energy saving,emission reduction and consumption reduction and to maintain sustained economic growth required by the global circular economy,the government makes great efforts to nurture and develop a more effective and sustainable low-carbon economy,which is guided by circular economy and make maximum use of the potential value contained in waste and by-products.Therefore,the efficient use of resources with low carbon dioxide emissions is a priority,decoupling economic growth from the use of resources and energy and greenhouse gas emissions.Scientific research and commercial production of eco-efficient cement based on industrial waste is a priority approach to promote the sustainability of cement industry.Coal gangue is a kind of solid waste with the largest discharge in the coal industry.Promoting the comprehensive utilization of abundant coal gangue resources and improving the utilization efficiency are of great significance to the sustainable development of economy and country.This study focuses on the development of a new type of low-carbon cementing material with coal gangue as auxiliary cementing material to realize the production of high-performance cementing material with coal gangue,provide a way to save energy,reduce emission,protect the environment and promote the resource utilization of industrial solid waste.Firstly,the physical and chemical properties of Huaibei coal gangue were studied,then the thermal activation treatment method was adopted and different calcination regulations were modified.After that,the optimal activation system was determined through the strength test of mortar.Next,the influence of coal gangue on the hydration of portland cement system was investigated by using the hydration kinetics model.According to the composition and properties of the materials,the design-expert software was used to design the mixture ratio of the new coal gangue-based LC3cementitious material,and the mixture model was used to determine the best mixture ratio.The hydration mechanism,mechanical properties,microscopic properties and durability of the new LC3 cementing system is explored by comparing the designed LC3 ratio with ordinary portland cement system and slag cement system.Experimental research results show that:1)The main chemical compositions of Huaibei coal gangue are SiO₂ and Al₂O₃,whose loss of combustion is up to 12.7%.The mineral compositions are quartz,kaolinite and a small amount of sodium mica.2)Heating rate of 10?/min,higher calcination temperature?i.e.850??,preservation time of 2 h and rapid cooling are the best way to stimulate the activity of coal gangue and are conducive to the improvement of the later strength of the mortar.3)The substitution of activated coal gangue for different proportion of cement will significantly reduce the matrix fluidity and improve the standard consistency value.The larger the substitution ratio is,the lower the matrix fluidity is and the higher the standard consistency is.The optimum content of activated coal gangue which has a certain delay effect on the initial setting time and final setting time of cement to replace portland cement clinker is 30%in this paper.Increasing the content of activated coal gangue will increase the resistance of crystal nucleus formation and crystal growth,and reduce the reaction rate constant of phase boundary reaction and diffusion process.4)The mechanical properties of the cementitious system can be effectively improved by low content of limestone powder or appropriate content of activated coal gangue.Preparation of low carbon cementitious material based on coal gangue LC3-45by compounding activated coal gangue,limestone powder and clinker.When the ratio of activated coal gangue to limestone powder is close to 2.33:1,the synergistic effect of the two can be maximum stimulated.5)Compared with ordinary Portland cement,slag Portland cement and self-made gangue-based low-carbon LC3-45 cement,it was found that mechanical properties of different cementitious material systems increased differently at different water-cement ratios.The mechanical properties of the self-made coal gangue-based low carbon LC3-45 cement has the largest increase with the decrease of water cement ratio,and the compressive strength of 28 days can reach 53.5 MPa at a low water cement ratio of 0.35.6)In terms of durability,compared with ordinary Portland cement,LC3-45cement and slag cement have good chloride ion permeability resistance,and LC3-45cement has higher chloride ion permeability resistance than slag cement;LC3-45cement can obviously reduce the autogenous shrinkage rate in the early stage of cement,while slag cement can improve the autogenous shrinkage rate in the early stage of cement.The relation of carbonation resistance of three different cementitious systems is:P.O52.5 cement>slag cement>LC3-45 cement.