Research On Performance Of Cement-fly Ash System Foamed Concrete Modified By Nano Materials

With the publication of the “Building Energy Conservation and Green Building Development Plan”,green building materials have been strongly supported.At the same time,the poor fire resistance of organic thermal insulation wall materials has serious potential risk.Therefore,the inorganic thermal insulation wall material foamed concrete has ushered in an unprecedented development opportunity.However,the foamed concrete,especially that with large volume of solid waste,has poor mechanical properties,which is not conducive to the demoulding and the improvement of production efficiency.How to improve the mechanical properties of large-volume solid waste foamed concrete and ensure the large-scale application of foamed concrete in green buildings has become the focus of researchers.Based on the enterprise project “High-performance foamed concrete based wall material”,this paper studies and solves the problem of high-volume fly ash foamed concrete wall material with low early strength.We studied the effect of fly ash content,water-binder ratio,water reducing agent dosage and mixing time of pre-formed foam and cementitious material slurry on the working performance and mechanical properties of cement-fly ash system foamed.Prepared optimal mix ratio of cement-fly ash system foamed concrete.With X-ray diffraction(XRD),comprehensive thermal analysis(TG-DSC),field emission environment scanning electron microscopy(SEM)and high resolution three-dimensional X-ray microscopic imaging system(XCT),this paper studied the effect and mechanism of nano-silica(NS)and nano-calcium carbonate(NC)on the working performance,mechanical properties,hydration,microstructure and pore structure of cement-fly ash system foamed concrete.This paper aimed to provide theoretical support for the large-scale application of largevolume fly ash foamed concrete in green building wall materials.The main results achieved in this paper are as follows:(1)Fly ash content,water-binder ratio,water reducing agent dosage and mixing time of pre-formed foam and cementitious material slurry have significant influence on the working performance and mechanical properties of cement-fly ash system foamed concrete.When the fly ash content is 50%,the water-binder ratio is 0.4,the powder water reducing agent is 0.017%,and the mixing time of pre-formed foam and cementitious material slurry is 3s,the sample has the better working performance,selflevelling ability,excellent mechanical properties and can be demoulded in one day.(2)The incorporation of NS will greatly reduce the fluidity of cement-fly ash system foamed concrete,and this paper carried out study with 1% content of NS.Compared with cement system foamed concrete,NS has a more significant improvement on the strength of cement-fly ash system foamed concrete.NS can promote the hydration of silicate minerals because NS with high pozzolanic activity reacts with Ca(OH)2 in secondary hydration and consumes a lot of Ca(OH)2.The crystal nucleation effect of NS makes the microstructure of sample hydration products more dense.XCT results show that NS can reduce the average pore diameter of foam concrete and make pores more homogeneous.Fly ash can reduce the proportion of macropores and improve the pore size and distribution of pores.(3)The incorporation of NC has little effect on the working performance of foamed concrete.The cement-fly ash system foamed concrete with 0.5% NC has the best working performance,excellent 7d compressive strength,and the best 28 d compressive strength.The study carried out with 0.5% content of NC.Microscopic test analysis show that NC with the effect of crystal nucleation make the hydration have more nucleation sites and accelerate the hydration of silicate minerals.The filling effect of NC makes the hydration products of sample more dense.