Study On Properties Of Nano-silica Modified Foamed Concrete

With the proposal of the national"double carbon"goal,new building energy saving materials have been widely concerned and applied.As one of them,foamed concrete has the characteristics of light weight,heat preservation,heat insulation,sound insulation,earthquake resistance,fire resistance,durability,safety,environmental protection and low cost,thus ushered in unprecedented development opportunities.But foamed concrete also has many shortcomings,especially low density foamed concrete is prone to shrinkage,cracking,low strength problems,so how to improve the performance of foamed concrete and ensure its popularization in practical engineering has a positive significance.In this paper,by studying the effect of water reducing agent,fiber and silica fume content on the performance of ordinary foamed concrete,the optimal mix ratio of ordinary foamed concrete with dry density of 400kg/m³was formulated.The stability of nano-sio₂foam before and after modification was evaluated by Ross Miles method and Waring Blender method.The influence and mechanism of nano-sio₂with different dosage and modified by KH550 on working performance,mechanical property and thermal insulation property of foamed concrete were explored.Scanning electron microscopy（SEM）,X-ray diffractometer（XRD）and X-ray microscope（XRM）were used to analyze the influence of nano-sio₂on hydration,microstructure and pore structure of foamed concrete before and after modification and the mechanism.It provides theoretical support for the wide application of foamed concrete in practical engineering.The results are as follows:（1）The content of water reducing agent,fiber and wollastonite has certain influence on the performance of ordinary foamed concrete.When the content of water reducing agent is 0.6%,the content of fiber is 0.95%,the content of wollastonite is10%,the performance of ordinary foamed concrete is the best,and the best construction mix of ordinary foamed concrete dry density is 400kg/m³is determined.（2）By adding nano-sio₂into the animal protein foaming agent,the foam prepared by Ross Miles method has good stability;In the test,0wt%,1wt%,2wt%,3wt%,4wt%and 5wt%nano-sio₂were added respectively.It was found that the addition of nano-sio₂would reduce the fluidity of foamed concrete and affect the working performance of foamed concrete.Compared with ordinary foamed concrete,the addition of nano-sio₂can improve the mechanical properties and thermal insulation properties of foamed concrete.SEM and XRD showed that nano-sio₂reacted with hydration product Ca（OH）₂to produce calcium silicate hydrate,which effectively filled the pores and enhanced the strength of the pore wall.（3）When the concentration of KH550 and KH570 is 5%,the contact angles of nano-sio₂particles are in the range of 50°～55°,and certain hydrophobicity is obtained.The half-life and volume change of foam prepared from KH550-modified nano-sio₂were better than that of KH570 by Waring Blender.（4）It is found that the modified nano-sio₂has improved the working performance,mechanical properties and thermal insulation properties of the foamed concrete,and its performance is better than that of the unmodified nano-sio₂foamed concrete.This is because the modified nano-sio₂hydroxyl group（-OH）is replaced,and certain hydrophobicity is obtained,which can be adsorbed at the gas-liquid interface of the foam.To reduce the disproportionation between foams and prolong the half-life of foam drainage,the foam stability is better and the performance of foamed concrete is better.Combined with SEM,XRD and XRM,it is found that the modified nano-sio₂reacts more thoroughly with hydration product Ca（OH）₂,and the content of hydration product Ca（OH）₂is less.The nano-sio₂before and after modification can reduce the size of pores,which is conducive to the uniform distribution of pores,but the modified nano-sio₂ has the best effect.