| Waste incineration fly ash（WIFA,hereinafter referred to as fly ash）is a solid waste produced after waste incineration,which contains many toxic heavy metals that exceed the standard,and direct landfill will produce great pollution.It is found that the composition of fly ash is similar to that of ordinary Portland cement and has potential coagulation characteristics,but the heavy metals in fly ash can be solidified in concrete,thus reducing the pollution of heavy metals.In order to recycle WIFA,this paper considers the application of WIFA as an alternative to cement in the field of building materials,and adds fly ash as another auxiliary cement material to prepare a high amount of WIFA and fly ash composite cement material,in which the ratio of WIFA,fly ash and cement is fixed at 40%:40%:20%.In this paper,the activity of WIFA and fly ash is activated by silica ash,nana-montmorillonite,calcium oxide to improve the mechanical properties of materials by promoting hydration and pore filling,and finally make it possible to use fly ash instead of cement in the field of building materials.The experiment preliminarily explored the influence of silica ash,stripping and calcium oxide on the mechanical:（1）According to the orthogonal test of three factors and four levels,the compressive and folding strength was tested,and the results were analyzed and the optimal ratio of the test was as follows:silicon ash/（WIFA+fly ash）is 15%,nana-montmorillonitel/（WIFA+fly ash）is 0.3%,and calcium oxide/（WIFA+fly ash）is 3%.Under this ratio,the compressive strength of 28 days is up to 22.36MPa,which can meet the basic material strength.Among them,silicon ash has a significant influence on the compressive strength of the test block,followed by nana-montmorillonitel,and calcium oxide has the least influence on the bending strength of the compression.（2）In the exploration of the influence of silica ash on high content WIFA and fly ash composite cementitious materials,it is found that the addition of silica ash can significantly reduce the pore size inside the material,which can make the material have a denser microstructure and generate more calcium silicate hydrate（C-S-H）,thereby improving the macroscopic characteristics of the material;Silica ash can also activate WIFA and fly ash to generate Al2O3to promote hydration reaction;In addition,the addition of silica ash can not only increase the amount of water and product generation,but also improve the polymerization degree of hydrate,making the entire structure of the material more stable.（3）Exploring the effect of nana-montmorillonite on high content WIFA and fly ash composite cementitious materials,experimental analysis found that nano-montmorillonite can stimulate hydration,fill pores,reduce the internal micropores of the solidified body,nano-montmorillonite can also activate WIFA and fly ash,promote the overall hydration reaction of the mixture more fully,provide more hydration reaction possibilities,it can also react with OH-in the hydration product Ca（OH）2to form a hydrated silicate gel,reducing the production of Ca（OH）2.（4）Experimental analysis found that calcium oxide can also reduce the internal pore size of the solidified body,so that the solidified body has a denser structure,but the impact on the internal pores is much smaller than that of silica ash and nano-montmorillonite;Calcium oxide also has a certain activating effect on the hydration activity of WIFA and fly ash,which can enhance their hydration activity and further improve the mechanical properties of the material.（5）The optimal ratio is carried out for heavy metal toxic leaching test,the experiment mainly detects the concentration of three heavy metals of Cr,Cu and Pb,and the test finds that the three heavy metal leaching concentrations meet the national normative limits,Among them,the leaching concentration of Cu is much lower than the limit value,indicating that this ratio can be used in the field of building materials. |
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