Pre-treated Fly Ash-based Multi-element Solid Waste Cementing Material And Its Hydration Performance

Aiming at the disposal dilemma of hazardous waste domestic waste incineration fly ash,this thesis focuses on the feasibility of preparing cementitious materials by incineration fly ash and preparing pre-treated fly ash precursors by washing pretreatment.From revealing the original properties of pre-treated fly ash to clarifying the mechanism of binary hydration of pre-treated fly ash and cement,the research and development of multi-element solid waste materials based on pre-treated fly ash are finally realized,and the strength formation mechanism and application scenarios of pre-treated fly ash are gradually expanded and enriched.The main conclusions of this thesis are as follows.（1）The physical and chemical properties of pretreated fly ash show that the rich Ca O and Si O₂ in pretreated fly ash have specific potential gelling activity.The analysis of the hydration characteristics of pretreated fly ash found that compared with cement,the heat release rate of pretreated fly ash is higher at the moment of contact with water.The hydration products are mainly Ca（OH）₂,the primary source of its strength,and the hydration reaction is concentrated in the first 2 hours.Therefore,it is feasible to prepare cementitious materials from pretreated fly ash.（2）The study on the evolution of the strength of the pre-treated fly ash-cement system and the mechanism of binary hydration shows that the strength of the pre-treated fly ash-cement system gradually decreases with the increase of the content of the pre-treated fly ash.The strength of the system is affected by the positive increase of the hydration rate of cement by the pre-treated fly ash and the reverse shortening of the hydration time.A large amount of Ca（OH）₂ introduced by pre-treated fly ash can promote the hydration of C₃S and C₂S in cement and stimulate the secondary hydration of active oxides.However,trace heavy metal elements can quickly form an amorphous"passive film"in an alkaline environment and attach to the surface of hydrated cement particles.This prevents the hydration from continuing,so the hydration time cannot be guaranteed.（3）Ca（OH）₂ introduced into the pre-treated fly ash creates a suitable alkaline environment conducive to the secondary hydration of active oxidation substances in slag.Titanium gypsum participates in the hydration process and promotes cement hydration,enriching the number of hydration products in the system and optimizing the internal structure.The materials and proportion of pre-treated fly ash-based multi-element solid waste cementing material is 25%pre-treated fly ash,35%slag,35%PI cement,5%titanium gypsum,and 1%alum.Compared with standard curing and low heat curing at35℃,room temperature curing has the advantages of economy,environmental protection,and strength development.At this time,the 28d strength can reach 29MPa.（4）The 7-day unconfined compressive strength and heavy metal leaching concentration of stabilized macadam mixture stabilized by pretreated fly ash-based multi-element solid waste cementing material increase with the pretreated fly ash-based multi-element solid waste cementing material content.The strength of the stabilized macadam mixture mixed with 10%-30%pretreated fly ash-based solid waste cementing material is excellent,and the leaching concentration of all heavy metals is lower than the standard limit,so the solidification effect of heavy metals is reliable and meets the requirements of relevant environmental assessment.