The Influence Of Corroded Product Surface Layer On The Rate Of The Concrete Corroded By The Sulfuric Acid

As one of the important building materials,concr ete has been widely used all over the world.Concrete can be corroded easily by the acidic solution,s ince it is alkaline.It can produce sulfuric acid and corrode concrete,such as Atmospheric pollution,weathering of sulfur-containing minerals,industria l production,etc.resulting in the aging speed of the concrete structure is far exceed than its expected speed,endangering the safety of building.Therefore,it has important practical significance for the research of sulfuric acid corrod ing concrete.This paper reviewed the existed 24 groups of concrete long-term immersion test data,finding that the degree of influence of the parameters such as water-cement ratio,p H value of the sulfuric acid solution,and admixture on the corrosion process can change greatly,due to the amount of calcium sulfate precipitation.In order to further study the effects of corroded products,water-cement ratio and p H on the corrosion of concrete by sulfuric acid,this paper designed 18 groups of concrete long-term immersion test on the three control conditions:soaking method,water-cement ratio and p H value,with soaking duration of 1524h.After the test,the curve of sulfuric acid consumption with soaking time was obtained,and the micro morphology,elemental composition an d mineral components of the surface material of each group of test specimens were analyzed by SEM,EDS and XRD.The type of sulfuric acid eroded concrete is classified,according to whether the surface of the test piece contains the corroded product layer and the mineral composition of the product layer.In order to explore the influence of the product surface layer of different mineral compositions on the speed of sulfuric acid attack on concrete,the relationship between the acid consumption of each corros ion type and the p H value of the sulfuric acid solution and the soaking time was analyzed.And on the basis of the experiment,the effect of the product layer and the water-cement ratio on the rate of sulfuric acid corrosion of concrete was further analyze d from the perspective of micro ion diffusion.Using the above research methods to analyze test results and draw the following conclusions:（1）The lost of Ca SO₄ and the cleanout of the corroded concrete surface layer during the immersion process would sign ificantly impact th e chemical components and decelerate effect of the corroded concrete surface layers.In the condition of replacement of immersion sulfuric acid,the mainly chemical ingredient are Si O₂ and other residue materials of cement stone after eroding.In those non-replacement cases,the chemical products contain gypsum（Ca SO₄·2H₂O）.Both types of corroded concrete surface layers can decrease the corrosion rate and the corroded concrete surface layer containing gypsum can decrease greatly.When the concrete surface does not contain gypsum layer,the amount of concrete corrosion will increase in a stable proportion with the decrease of the p H value of the sulfuric acid solution.The corroded concrete surface layer with gypsum is the main factor that destroys the similarit y between different experiments.With reference to the empirical model of concrete corrosion depth（d=kc^mtⁿ）proposed by Pavilik,empirical models of the corrosion amount of two corrosion types of concrete surface without gypsum layer related to the H⁺concentration of sulfuric acid corrosion solution and corrosion time were established,these models can obtain a better fitting effect in a wider range of sulfuric acid concentration changes.In addition,Fe（OH）₃ also affects the rate of sulfuric acid corrode concrete,but its impact is much less than Ca SO ₄.（2）Before the precipitation of Ca SO ₄ in the corrosive liquid,the pure leaching damage occurred in the concrete,and the main destruction mode is calcium leaching destruction.Numerical simulation of calciu m leaching for concrete of 3 groups test of pure leaching damage and different soaking methods by using concrete calcium leaching model,which established by the one-dimensional diffusion transport equation of calcium ions and the solid-liquid equilibrium equation between the soluble solid phase calcium in concrete and the concentration of calcium ions in the pore fluid proposed by Gerard.By analyzing the simulation results,it is found that the sulfuric acid consumption of the concrete specimen in the sul furic acid environment has a linearly increas ed relationship with the addition of initial porosit y and cement dosage of concrete,and the earlier the corrosion product layer is removed,the more obvious the promotion effect of the rate of sulfuric acid erodes concrete.