Research On The Performance And Air-void Structure Of Foam Concrete By The Slurry Of Wet Grinding

Foam concrete is a new type of energy-saving and thermal insulation material,which has the characteristics of light weight,thermal insulation.It has been widely applied in wall materials,thermal insulation materials,municipal engineering,and filling of foundation cavities.The specific strength(the ratio of compressive strength to dry density)of lightweight foam concrete currently used in wall materials is relatively low;compared with organic thermal insulation materials,such as expanded polystyrene board(EPS),the burning grade of ultra-light foam concrete is Class A,and it has a good fire resistance performance.However,there are still problems with ultra-light foam concrete,such as the high density,high coefficient of thermal conductivity,and low compressive strength.In order to optimize the performance of the foam concrete,this paper introduces a new kind of experiment.Using ordinary Portland cement,fly ash,admixtures and fiber as the main raw materials,we adopt physical foaming,the slurry of wet grinding,and steam curing,to make lightweight foam concrete(dry density is 600 kg/m~3)and ultra-light foam concrete(dry density range from 300kg/m~3to 150kg/m~3).using the research methods of controlled variables and comparative experiments with the water-binder ratio and wet grinding time as variables,we systematically study the change law of its forming performance and compressive strength and coefficient of thermal conductivity;According to the changes in the fluidity of the slurry,the particle size,the compressive strength of the matrix phase and the air-void structure,we comprehensively analyze the reinforcement effect of lightweight foam concrete by the slurry of wet grinding.In addition,we investigate the influence of water-binder ratio(corresponding to the optimal wet grinding time)on the formability and macroscopic properties(compressive strength,volumetric water absorption rate,softening coefficient and coefficient of thermal conductivity)of ultra-light foam concrete and its influence on air-void structure.In the following are conclusions:(1)The representation methods of air-voids of various air-void diameters in cement-based materials are analyzed,and the reliability of the image representation method of foam concrete air-void is mainly discussed and we determine the method of taking photos with an optical microscope and analyzing the pore structure with Image-Pro plus.(2)The compressive strengths of lightweight foam concrete(about 600kg/m~3)by the slurry of wet grinding with water-binder ratios of 0.45,0.60,0.70 and 0.80(corresponding to the optimal wet grinding time of 40min,50min,60min and 70min)are respectively 4.7MPa,5.0MPa,5.4MPa and 5.1Mpa and the compressive strengths of the comparative test group(non-wet grinding of the slurry)are 2.8MPa,3.7MPa,4.1MPa and 3.6MPa respectively.The compressive strength of lightweight foam concrete by the slurry of wet grinding increase by 68%,35%,32%,and 42%respectively compared with the reference tests.(3)Compared with the reference tests,wet grinding slurry increase the particle content(≤20um)of cement-based slurry,and the increase of matrix phase hydration products results in a denser microstructure and improves the compressive strength of the matrix phase.The fluidity and consistency of slurry of wet-grinding are more suitable for mixing foam and slurry(that is,the foam is not easy to defoam and grow together),and the air-void size is more uniform,mainly distributed between the air-void diameter of 100～300um,and the large air-voids are reduced.There are fewer connected air-voids,and These excellent air-void structure characteristics are conducive to the compressive strength of foam concrete.Therefore,wet grinding slurry can greatly improve the compressive strength of lightweight foam concrete.The reason is the comprehensive results of the improvement of the matrix strength of wet grinding slurry and the optimization of the air-void structure.(4)Using ordinary portland cement(P·O 52.5),fly ash(gradeⅠ),admixtures,polymer emulsion,fiber and water as raw materials,we adopt physical foaming,slurry of wet grinding and steam curing to make ultra-light foam concrete.It has a dry density of 150kg/m~3,a compressive strength of 0.35MPa,a volumetric water absorption rate of 8.5%,a softening coefficient of 0.70,and a coefficient of thermal conductivity of0.045W/(m·K).The coefficient of thermal conductivity is close to the thermal conductivity of a conventional organic thermal insulation board(EPS board)(0.042 W/(m·K)).