Study On Erosion-Corrosion Of Mortar In Sulfuric Acid

Sulfuric acid corrosion problem is a common problem in existing concrete structures, which is also an important component of the study on the durability of concrete structures. Studying on the problem of sulfuric acid corrosion is of relatively important significance to the enhancement of sulfuric acid corrosion resistance capacity of concrete materials, and the improvement of theory on durability of concrete structures. In this paper, combined with the concentration boundary layer and flow boundary layer theories, the sulfuric acid erosion-corrosion test of cement mortars was analyzed, and sulfuric acid corrosion was modeled and predicted by utilizing support vector machine (SVM) algorithm, the following tasks were mainly completed:(1)Starting from the theory of the boundary layer, the paper proposed that when the dilute sulfuric acid eroded and corroded the concrete, there would be two types of boundary layers existing simultaneously, namely, the concentration boundary layer and flow boundary layer. A theoretical model of acid consumption rate was derived based on the concentration boundary layer theory, and the velocity distribution pattern within the flow boundary layer as well as the shear stress at the solid wall in laminar flow state were given based on the flow boundary layer theory. The relationship between the concentration boundary layer and the flow boundary layer was discussed.(2) A100-day dilute sulfuric acid erosion-corrosion test was carried out on the cement mortar specimens by adopting self-made rotary erosion-corrosion test equipment. The apparent characteristics of corroded specimens were analyzed, the specimens were weighed before and after the test through electronic balance and vernier caliper, respectively, and the mass loss rate and corrosion depth of cement mortar specimens were obtained. The acid consumption rate and total acid consumption of specimens were determined by the recorded dilute sulfuric acid titer. Based on the concentration boundary layer theory, the acid consumption rates of two batches of tests were fitted by using the theoretical acid consumption rate formula, and two important similar scale parameters (a, b), which reflected the corrosion rate, were obtained. Combined with the flow boundary layer theory, the flow boundary layer thickness and the function of velocity distribution in the flow boundary layer of specimens under different erosion rates were obtained, based on that, the shear stress at the wall (ts) of specimens was calculated, which was then fitted with the corrosion depth and total acid consumption of cement mortar specimens, relevant fitted curve and fitting formula were given.(3) Relevant basic theory of SVM was briefly introduced, concepts such as VC dimension, generalization error bound, structural risk mrninimization and optimality hyperplane were elaborated, and methods for selection of key parameters in the RBF Kernel function were given. MATLAB platform-based SVM prediction program was written based on SVM algorithm, and the apparent diffusion coefficient DOH of specimens, which was obtained in the tests of dilute sulfuric acid mortars (erosion corrosion20groups, immersion corrosion18groups), concrete (concrete with fly ash30groups, concrete with silica ash30groups) and pervious concrete (30groups), was predicted in this program. Specific modeling steps and prediction accuracy measures (RMSE, MAPE) of the corrosion prediction model were given. Corrosion prediction model was built for above tests, respectively, and the predicted results were analyzed. The results showed that:the five prediction models had relatively good prediction accuracy, which could convert the sulfuric acid corrosion mechanism problem into the parameter identification problem of SVM prediction model.This dissertation is part of the project sponsored by the Natural Science Foundation of China, Grant No.51078175.