Research On Hydration And Early Strength Mechanism Of Wet-grinding Fly Ash With High Content In Cementitious Material

With the issuance of the ‘Directives on the Development of Assembled Buildings’ issued by the General Office of the State Council,fabricated structure has ushered in unprecedented opportunities for development.From the perspective of material design and preparation,fabricated concrete component is a key part of the fabricated structure.At present,in order to ensure production efficiency(sufficient demolding strength),the substitution content of fly ash for auxiliary cementitious materials is generally less than 20%,and the degree of material ‘greenness’ is far below the average level of the concrete industry(30%).How to improve the utilization of fly ash admixtures in fabricated components and moreover ensure the demolding strength of component has become the focus of researchers.This paper relies on the sub-topic of the National ‘Thirteenth Five-Year’ Plan for Scientific and Technological Support Project ‘Research and Application of Chloride Ion Fixation and New Type Retaining Technology in Sea Sand Concrete’ and Hubei Provincial Technical Innovation Project(major project)in 2018 ‘Preparative Component Based on Nanoparticle-Functional Polymer Coupling Effect Green preparation technology’,with the aim of the contradiction between fly ash with large amount of auxiliary cementitious material and super early strength in fabricated components,this paper adopts comparative test methods.The main experiment content is to test the cement mortar strength of each system and X-rays Diffraction analysis(XRD),Thermogravimetric Analysis-differential scanning calorimetry(TG-DSC),field emission scanning electron microscopy(SEM),mercury intrusion hole(MIP),plasma emission spectrometry(ICP)and other microscopic analysis methods have been used to study the hydration mechanism of the wet-grinding FA-cement system at different temperatures.Simultaneously the early-strength technology of alcohol amines to promote the elution of fly ash ions and the nano-effect induced hydration were used to study the early-strength mechanism of alcohol amines and nano-silica sols on high content wet-grinding superfine FA-cement systems.The main innovations achieved in this paper are as follows:(1)The addition of raw fly ash FA0 or wet-grinding fly ash FA1 reduces the strength of cement mortar.However,the incorporation of wet-grinding superfine fly ash FA2 can significantly improve the early strength of cement mortar.And with the increase of steam curing temperature,this positive effect is stronger,but the excessive steam curing temperature inhibits the growth of the later strength of FA2-cement mortar,whose strength is less than that of FA0-cement mortar with the same FA content.Increasing the steam curing temperature and wet grinding greatly increase the dissolution rate of fly ash Al and Si ions in the pore solution,which is conducive to the early use of the pozzolanic activity of fly ash,and at the same time enhances the degree of play of the pozzolanic activity of fly ash.The formation of a dense microstructure,and thus improve the early strength of high volume fly ash cement mortar.(2)At the standard temperature(20°C),the addition TEA and TIPA will do harm to the early strength of high content FA2-cement mortar,but have an increasing effect on the later strength,and TEA is more effective than TIPA.Increasing the steam curing temperature(40°C)can improve the adverse effects of TEA and TIPA on the strength cement mortar with large amount of FA2.At the same time,the increasing effect of TEA is further strengthened.When increasing the steam curing temperature to 60°C,the addition of TEA and TIPA can all improve the strength of cement mortar with large amount of FA2.Increasing the steam curing temperature will accelerate the dissolution of active components of fly ash by TEA and TIPA,increase the pozzolanic activity of fly ash,and the microstructural defects caused by TEA and TIPA’s own air entraining effect are improved,and then the strength of large amount of FA2 cement mortar is improved.(3)At the standard temperature(20°C),it is not obvious that the addition of NS has an enhancement on the early strength of high content FA2-cement mortar,which even has a certain degree of decline,but it can improve the late strength.Increasing the steam curing temperature(40°C)can promote the enchancement effect of NS on the early strength of cement mortar with high content of FA2,but when the steam curing temperature is too high(60°C),the enchacement effect of NS on early strength of cement mortar with a high content of FA2 is not as good as that of 40° C.It was found that the strength of cement mortar with a large content of FA2 come to the highest when 0.5% NS was added at 40°C.This paper has clarified the hydration mechanism of a large amount of wet-grinding FA-cement system,and laid a theoretical foundation for the material design of green fabricated components,At the same time,the mechanism of early-strength action of alcohol amines and nano-silica sol on large amount of wet-grinding superfine fly ash-cement was studied,which provided theoretical support for the large amount of fly ash waste in fabricated components.It has important scientific significance and enormous social,economic,and environmental benefits.