The Study On Frost Resistance And Fractal Characteristics Of The Pore Of Concrete Under Dry-Wet Circulation

Frost resistance of concrete is an important indicator of its durability,especially for large engineering projects,high frost resistance means high durability of concrete,design specifications in hydraulic concrete are often used frost resistance index instead of its durability index.Especially in the vicinity of ice water about 20cm,where is under dry-wet and freeze-thaw cycles conditions,the surface of concrete often has partial loss phenomenon,This not only weakens the strength and dimensional stability of the concrete structure,but also has brought great risks to the safety and durability of the project,Therefore,researching on this issue in-depth is very necessary.This paper studies the concrete frost resistance of concrete under dry-wet and freeze-thaw cycles conditions,in the premise of the basically same slump and concrete strength,focused on the influence of fly ash,silica fume admixture,air-entraining agents for the frost resistance of concrete under dry-wet and freeze-thaw cycles conditions,measured the compressive strength and mass loss of the specimen,do mercury test,test the pore structure of concrete under different conditions by useing mercury intrusion,study the relevance between the pore fractal dimension and frost resistance of concrete under dry-wet and freeze-thaw cycles conditions by useing fractal.Experimental research and theoretical analysis showed that:(1)Appropriate fly ash can improve the frost resistance of concrete under dry-wet and freeze-thaw cycles conditions,with the increase of mixing amount of fly ash,compressive strength loss and weight loss of concrete are reduced,but when the mixing amount of fly ash is more than 20%,concrete compressive strength loss and weight loss increased,so the mixing amount of fly ash should be less than 20%for the concrete under dry-wet and freeze-thaw cycles conditions;(2)When the mixing amount of fly ash is 20%,appropriate silica fume can improve the frost resistance of concrete under dry-wet and freeze-thaw cycles conditions,after dry-wet and freeze-thaw cycles,strength loss,mass loss of concrete were lower than fly ash concrete,with the increase of mixing amount of silica fume,compressive strength loss and weight loss of concrete are reduced,but when the mixing amount of silica fume is more than 5%,concrete compressive strength loss and weight loss increased,so the mixing amount of fly ash should be 5%for the concrete under dry-wet and freeze-thaw cycles conditions;(3)The incorporation of air-entraining agents have a significant effect on frost resistance of concrete under dry-wet and freeze-thaw cycles conditions,appropriate air-entraining agents can improve the frost resistance,but mixing amount of air-entraining agents is increased,the mass loss of concrete increased,when the mixing amount of air-entraining agents is 0.08%,compressive strength loss is smallest and weight loss of concrete are little;(4)With the increase of the mixing amount of fly ash and silica fume content,the pore fractal dimension increased first,then decreased.When mixed with 20%fly ash,mixed with 20%fly ash and 5%silica fume,the fractal dimension of concrete is the highest,pore structure has been a certain amount of refinement and optimization,surface of pores become more complex,by test of Chapter ?,frost resistance of concrete has been improved under dry-wet and freeze-thaw cycles conditions;(5)With the increase of the mixing amount of fly ash and silica fume content,the pore fractal dimension increased first,then decreased,the average pore size decreases,increased macropores reduce the number of micropores,air-entraining agent refines the pores of concrete,improve the frost resistance of concrete under dry-wet and freeze-thaw cycles conditions.When mixed with 0.08%air-entraining agent,its fractal dimension is highest,the frost resistance of concrete is best under dry-wet and freeze-thaw cycles conditions.