Alkali-activated Materials For Municipal Solid Waste Incineration Bottom Ash

With the rapid development of the economy and the rapid expansion of the urban living population,municipal solid waste incineration bottom ash is increasing.The ash and residue produced after incineration accumulated in large quantities,which greatly pressured the environment.Applying municipal solid waste incineration bottom ash as a new alkali-activated material to the construction industry could effectively alleviate the negative impact of bottom waste ash on urban ecology,which aligned with the eco-development concept of high efficiency,energy saving and green environmental protection.However,the low reactivity of the bottom ash affected the formation of polymerization products,and the high strength properties of the bottom ash alkali-activated materials could not be fully utilized.Moreover,the existing research mainly focused on the small batch of specimens in the laboratory.Its defects,such as high production cost and single maintenance mechanism,could not meet the actual utilization rate and economic benefits required for engineering projects and could not realize the batch production of bottom ash alkali-activated materials,which restricted the application and development of bottom ash alkali-activated materials.Therefore,exploring the mechanical property enhancement technology of bottom ash alkali-activated materials and realizing the resourcefulness and scale utilization has become the key to existing research.In this thesis,the composition design,theoretical research,and microscopic analysis of bottom ash alkali-excited materials were carried out using municipal solid waste incineration bottom ash as raw material.The effects of defoaming treatment,active silica content,active calcium content and maintenance mechanism on the mechanical properties of bottom ash alkali-activated specimens were investigated in depth.To provide experimental support and a theoretical basis for the practical application of bottom ash alkali-activated materials and to realize the "harmless," "resourceful," and "large-scale" treatment of municipal solid waste incineration bottom ash.At the same time,it would help the cement industry to achieve pollution and carbon reduction and accelerate the green development of the cement industry.The main research contents are as follows:(1)Improve the particle gradation and reactivity of municipal solid waste incineration bottom ash by physically activating it.The alkali-aged antifoaming pretreatment test of bottom ash was designed to eliminate the swelling of bottom ash with alkali foaming and solve the problem of foaming and deformation of bottom ash components.The results showed that the alkali-aging pretreatment of bottom ash with the appropriate amount of sodium hydroxide could eliminate the alkali foaming and swelling of bottom ash caused by aluminum.Furthermore,the alkali-aging pretreatment was simple to operate and complete defoaming,a kind of pretreatment with high economic efficiency.(2)The optimal dose of silicon and calcium enhancement in the bottom ash alkali-activated specimens was investigated by the composition design of the bottom ash alkali-activated materials.At the same time,various microscopic testing methods were combined to analyze the mechanism of increasing silicon and calcium.The mechanical properties of the bottom ash alkali-activated materials were enhanced.The results showed that the reactive silicon and calcium content in the reaction environment affected the strength of the bottom ash alkali-activated specimens.The strength of the specimens increased significantly with the increase of active silica,but when the proportion of sodium silicate in the alkali activator exceeds 66.6%,the excessive active silicon decreased the calcium-silicon ratio and increased the active sodium content,which led to a sharp decrease of the strength.When the content of granulated blast furnace slag(GBFS)exceeded 75%,the dissolution rate of active calcium drops sharply,and the compressive strength of the specimen increased no more.When the volume ratio of water glass solution to sodium hydroxide solution was 2:1,the degree of polymerization reaction gradually increased,and the compressive strength of the specimens gradually grew as the content of GBFS increased.(3)The tests on the maintenance mechanism of the bottom ash alkali-activated specimens were conducted to investigate the influence of sealing conditions and different maintenance temperatures on the strength development of bottom ash alkali-activated specimens and to realize the preparation of high-strength bottom ash alkali-activated specimens.The results showed that the composite maintenance temperature design under sealed conditions(after demoulding and sealing,the specimen was cured in an oven at 60℃for 24 h,then stood still at room temperature for 24 h,and then transferred to the standard curing temperature for curing until the test age)could maintain the moisture balance inside the specimens and prevent the formation of cracks.It could also provide a suitable temperature to promote the polymerization reaction process in the early stage and ensure a continuous and stable polymerization reaction in the later stage.At the same time,it made the polymerization reaction more complete and the internal compactness and compressive strength of the specimens higher.(4)By means of microscopic testing,the influence of the maintenance mechanism on the conversion law of free alkali to bound alkali inside the bottom ash alkali-activated specimens was investigated,and the influence of the internal alkali conversion law on the strength development of bottom ash alkali-activated materials was analyzed.The results showed that the composite maintenance temperature could effectively avoid the precipitation of free alkali and active substances and maintain the high alkalinity inside the specimens.At the same time,it could promote the polymerization reaction process and increase the conversion rate of binding alkali,which helped improve the compressive strength of bottom ash alkali-activated materials.