Study On Air Void Parameters Of Fresh Concrete And Hardened Concrete

Freeze-thaw damage is the main failure mode of concrete structures in cold climateregions. Air entraining is the most effective technology approach to solve freeze-thawdamage of concrete. Air void parameters measurement of the hardened concrete whichcan characterize the frost resistance of concrete had been stipulated in the standards. Butit does not get rid of the lag in the fast freezing method and slow freezing method; itcannot be used on site. So, fresh concrete is taken as the research object innovatively inthis article. The main parameters which influence the air void measurement of freshconcrete are studied; the correlation of air void parameters between fresh concrete andhardened concrete is analyzed based on the durability of concrete. The main researchconclusions are:①A new method(Air-Void Analyzer) which can measure air void parameters offresh concrete is validated. The air content, spacing factor, specific surface and airbubbles pore size distribution can be obtained in30min by AVA. The frost resistance ofconcrete and the quality of air entraining agent can be evaluated by AVA rapidly.②The important parameters which affect Air-Void Analyzer test mostly aredetermined. That is, the sample time and the viscosity of the analyze liquid. The sampletime of fresh concrete should be from1h to the initial setting time of concrete. Theviscosity of the viscous analyze liquid should be in the range of75~110mPa s. Theviscous analyze liquid can be replaced by the compound of glycerol and ethylene glycol(glycerol: ethylene glycol=1:1.36).③The spacing factors of fresh concrete and hardened concrete decrease firstly andthen increase, but the specific surface increase firstly and then decrease with theincrease of air content. Viscosity of the concrete decreases with the increase of slumpwhen the slump is similar, which makes the spacing factors of fresh concrete andhardened concrete decrease firstly and then increase, the specific surface increase firstlyand then decrease. The grade of powder could be optimized due to the micro-aggregateeffect of mineral admixture, the spacing factor of fresh concrete can be reduced bymineral admixtures, but have little effect on air void parameters of hardened concrete.When the air content and slump is similar, the spacing factor can be reducedsignificantly by the air entraining agent which can entrain smaller air bubbles.④The correlation between the parameters of fresh concrete and hardened concrete is studied. There is a good linear correlation of air content between fresh concrete andhardened concrete. Air content measured by AVA and air content of hardened concretecured for56days are smaller than air content measured by Pressure method. There is agood linear correlation of spacing factor between fresh concrete and hardened concrete,the correlation coefficient is0.731. But the correlation of specific surface is bad.⑤The evaluate index of air void parameters of concrete based on durability indexis proposed. When the criterion of the durability index of60%was applied, air contentof hardened concrete should be4%-7%，spacing factor should be smaller than300μm.Air content of fresh concrete measured by AVA should be2.4%-4.6%, spacing factorshould be smaller than360μm.