Preparation And Application Of Composite Cementitious Material Of Ash And Slag From Biomass Power Plant

At present,there was no enough large-scale environment-friendly utilization technology for the ash residue of biomass power plants which resulting in waste of resources,and environmental pollution.This thesis takes biomass power plant ash and slag as the object,physical and chemical properties of biomass power plant ash was analyzed,and the resource utilization potential of its preparation of cementitious materials and bricks was evaluated.The cementitious material was prepared from biomass power plant ash,slag and sulphoaluminate cement clinker.The best preparation process of the composite cementitious material was determined based on the result of compressive strength,flowability,and setting time,and then economy and environment effect of application of composite cementitious material of ash and slag from biomass power plant were analyed.The mineral phase composition,micromorphology,and functional group structure of the hydration product of the composite cementitious material were analyzed by XRD,SEM,TG,and FTIR,which combined with the strength test results,the hydration and hardening mechanism of the composite cementitious materials were obtained.Unburned bricks and permeable bricks were prepared from biomass power plant ash and composite cementitious material,and their mechanical properties and water permeability were tested.Based on the above research,a technical route for preparing composite cementitious materials and bricks from biomass power plant ash was formed,which can realize its green and large-scale utilization.The main results are as follows:The analysis of physical and chemical characteristics of ash and slag of biomass power plant shows that the content of Si,Ca,Al and Fe in ash and slag are rich,which meet the standard of C-class pozzolanic materials and have potential pozzolanic activity.However,the p H of slag was higher than that of ash with strong alkalinity and great alkali excitation potential,which is more suitable for the preparation of cementitious material.The slag particles were coarse and could be used as brick aggregate after the screening,while the ash could be used as an admixture of building materials,due to the average particle size of ash particles being 79μm.The composite cementitious materials were prepared from biomass power plant ash,slag and sulphoaluminate cement clinker respectively.The compressive strength of both hardened pastes decreased with the increase of ash and slag content within 28 days.When the the addition of 10 wt%ash and slag,the compressive strength reach 92.5%and 98.1%of the reference group at the same curing age respectively,and when the addition of 20wt%ash and slag,the compressive strength reach 80.6%and 85%respectively.The composite cementitious materials prepared from biomass power plant slag had better compressive strength.When the content is 20%,the compressive strength of 3 d and 28d reached 43 MPa and 68 MPa respectively.The flowability and setting time of the composite cementitious material prepared from washed biomass power plant slag increased slightly,but the compressive strength decreased significantly.Through comparative analysis,the content of biomass power plant slag without water washing is less than 20%,which was suitable for the preparation of high-value composite cementitious materials,and the strength grade is equivalent to 42.5 sulfoaluminate cement.The development mechanism of hydration strength of biomass power plant slag-sulfoaluminate composite cementitious material shows that its strength development is divided into two main stages.In the early stage,calcium sulphoaluminate hydrated and formed ettringite and aluminum glue.Ettringite crystal grows to form a network structure framework,which is filled with aluminum glue,which together with the physical filling of biomass power plant slag forms the early strength of composite cementitious materials;In the later stage,based on the development of hydration strength of sulphoaluminate cement clinker,the alkaline environment generated in the hydration process stimulates the pozzolanic reaction of biomass power plant slag to generate hydrated calcium silicate and hydrated calcium aluminate,which are continuously diffused and crystallized in the cementitious material and continue to fill in the early formed ettringite network structure framework,promoting the rapid growth of the strength of the composite cementitious material in the later stage.The ash and slag from the biomass power plant and composite cementitious materials were used to prepare the unburned brick and permeable brick.When the ash,slag and SAC clinker content were 50%,10%and 40%respectively,the compressive strength of unburned brick reached 12.10 MPa,while the flexural strength and the unit weight were 3.6 MPa and 1358.031 kg/m³.When the water cement ratio is 0.29,the bone cement ratio is 2.40 and the coarse to fine aggregate ratio is 7:3,the water permeability coefficient of the produced permeable brick can reach 1.0×10^-2 cm/s,compressive strength up to 20 MPa,in line with industry norms,meet market demand,and have a good prospect of economic benefits.