The Durability Analysis Of Concrete Subjected To Sulfate Attack

The durability of concrete structure researched by the subject of structural engineering is now a concerned problem. A lot of concrete structure failed before its normal using years due to durability failure It results in huge economic loss and bad social impact.There are many factors which can cause concrete structure durability destruction. Sulfate attack is one of important factors that influences the duration of concrete.Therefore it is a matter of great significance to research the durability problem of concrete structure under the circumstances of sulfate ions.The material work of the paper are as follows:Firstly,this paper introduced the current development of durability of concrete structure and sulfate attack in the country and abroad, and analysed the mechanism of sulfate attack.The producing process of expansive crystallization-ettringite was presented too.Secondly,the paper established the one-dimensional diffusion-reaction equation of concrete due to sulfate attack based on Fick's second law. A finite difference model of diffusion-reaction equation was set up using unconditionally stable Crank-Nicolson method,which can be used to gain the corrosive situation of concrete slab or wall subjected to sulfate attack under certain boundary and initial conditions.Thirdly,the paper presented the producing amount of ettringite in the concrete model according to the sulfate concentration distribution and the diffusion-reaction equation,which could be used to calculate the expansive strain caused by expansive crystallization in concrete model. The crystallization pressure of products can be calculated and the failing progress of the concrete model can be described based on. stress-strain response and yield law of concrete material.Finally,a finite difference model of two-dimension diffusion-reaction equation of concrete due to sulfate attack was set up using unconditionally stable alternating direction implicit scheme,which can get the corrosive situation of concrete component with rectangle section whose boundary and initial conditions are complex.Through the reseach above,the paper gave out the destructive mechanism of concrete. subjected to sulfate attack,established the diffusion-reaction equation of sulfate ions and destructive mechanical model,after that progress the numerical simulation was executed.The result indicates that the content of C₃A determines the producing content of ettringite and the ability of concrete to resist sulfate attack, the diffusion coefficient and reacting rate are important factors that influence the diffusion-reaction progress,the former's influence is more greater than the latter, the concrete component subjected to sulfate attack is destroyed layer by layer and the destroying rate is increasing by time.