Analysis Of Salt Freezing Mechanism And Performance Optimization Of Concrete With Multi-admixtures

Durability is the most important index of cement concrete,and the deterioration of durability will directly affect the reliability and safety of the concrete structure.The process of salt-freezing damage of concrete is a complex process of physics,chemistry and mechanics,which is one of the important contents of concrete durability research.When concrete is exposed to salt solution and the freeze-thaw environment at the same time,the freeze-thaw damage of concrete will be intensified,and concrete surface will produce a serious loss,at the same time,concrete dynamic elastic modulus and the durability of concrete will be reduced.In northeast and northwest areas of China,the deicing salt is often used during the winter,which formed the environment of salt-freezing and thaw cycle,leading to severe salt-freezing damage of cement concrete pavement and bridge,causing huge economic loss and safe hidden trouble.Therefore,it is significant and urgent to improve the durability of concrete.Concrete admixture and mineral admixture have been considered to be the fifth and sixth components of modern concrete,under the proper dosage,they can effectively improve the internal structure,mechanical properties and durability of concrete.This paper mainly studied the influence of air-entraining agent and silica fume,fly ash,slag powder on salt-freezing resistance of concrete,and the performances of concrete under different materials in different dosage were analyzed with the genetic algorithm.Considering both the mechanical properties and salt-freezing resistance of concrete requirements,the optimal dosage of each material was selected.The main research work and conclusions of this paper are as follows:(1)Firstly,the effects of mineral admixtures such as fly ash,slag powder and silica fume on the anti-salt properties of cement concrete were studied.By testing the strength,resistivity and electric flux of concrete,the salt-freezing resistance of concrete was analysed.It was concluded that the salt-freezing resistance of concrete is better when only mixed with slag powder or silica fume,while the strength,resistivity and electric flux of concrete were improved with the three admixtures mixed together.Then,the effect of adding different amounts of air agent on the salt-freezing resistance of concrete was studied.And it was found that the air agent can improve the anti-salt resistance of concrete significantly,but also reduce the strength of concrete.(2)Then the air content was then taken as the first order parameter and the mineral admixture as the second order parameter.The levels of air content were 2%-3%,4%-5% and 6%-7%.At each level of the air content,with 3 factors 3 levels orthogonal test design content of slag powder and fly ash,silicon ash,on every level 9 groups of concrete were tested for mechanical properties,physical properties and salt-freezing resistance.Respectively using least squares equation for each level index to fitting,using the genetic algorithm to optimize quadratic function of salt-freezing resistance of concrete with fly ash,slag powder and silica fume dosage.Each level of concrete mechanical properties and physical properties was obtained.In the salt-freezing resistance of concrete and economy as the main control parameters,both the mechanical and physical properties of concrete,the three air content levels of mineral admixtures for integrated will choose the best dosage.Concrete should be controlled by adding air-entraining agent concrete's air content is 4%-5%,and the best mix proportion of admixture is recommended: 5.06% dosage of fly ash,slag powder content is 6.75%,silicon ash content is 7.77%.