Steel Fiber Reinforce Concrete Durability In The Atmospheric Environment Based On Multi-factor Effects

Currently, steel fiber reinforced concrete (SFRC) has been used more and more widely in some large-span structures, large tunnel linings, dam structures, military engineering and some other major projects. These major structural engineering is an important national social and economic infrastructure, and the security work for the sustainable development of society plays a very important role. But as the same with the ordinary concrete structures, durability problem appears in SFRC in the service process when subjected to the corrosive media in environment. The neutralization of concrete and the steel corrosion are the main aspects in the durability of concrete structures,and the neutralization of concrete is the prerequisite for steel corrosion. The neutralization of concrete in practical projects is the result of interaction of physical, chemical and mechanical factors. Therefore, the neutralization of SFRC under multiple factors should be investigated, which is significant for the durability design and assessment and for the further investigation reinforcement corrosion and service life prediction of SFRC structures.In this paper, through the theoretical analysis and laboratory combination of rapid test method, the effects of single, double and multiple influencing factors on the neutralization of SFRC were investigated, and the action mechanism and the rule of performance degradation were revealed. Finally, a predicting model of neutralization depth of SFRC in the atmospheric environment was proposed. The main contents of this paper are as follows:Firstly, the result of Mercury and SEM test of pore structure of SFRC showed that the pore structure of concrete turn to better with the number of large pore reduced when the steel fiber content from 0 to 1.5%. But when the fiber content increased to 2%, the pore structure of concrete direct to worse and the number of large pore increased. According to the theoretical analysis and experimental results, the calculation method of the porosity of SFRC was established which lay the foundations for the predicting model of neutralization depth of SFRC.Secondly, laboratory accelerated carbonation tests of SFRC were carried out. The carbonation rule of SFRC was obtained considering the influencing factors. The test result showed that the rate of concrete carbonation turn to slowest when the steel fiber content is 1.5%. The porosity change of SFRC which caused by the carbonation mostly depending on the amount of cement per unit volume of concrete, but the impact was not significant in the content of steel fiber.Thirdly, the method to simulating acid rain solution in laboratory was proposed ,on the basis of the survey and analysis on the components of acid rain around China. Parameters such as mass loss, erosion rate, splitting tensile strength and neutralization depth of SFRC were used to evaluate the acid rain resistance of SFRC. Then the degree of the different influencing factors on the evaluating index was analyzed. The damage process and the reinforced mechanism of SFRC under the action of acid rain are analyzed. The corrosion of Acid rain to SFRC is the combined action of H⁺ and SO₄^2-.Fourthly, test modes of acid rain and carbonation working together were built up on the basis of the mechanism and the characteristics of acid rain and carbonation separately. Then, durability tests of acid rain and carbonation working together on SFRC were carried out. The coupling effects were further and the mechanism of acid rain and carbonation working together was obtained. There has a neutral contribution to the neutralization under the action of the carbonation and acid rain, which result in the coupling effects greater than the role of individual, and carbonization can accelerate the erosion of SFRC in acid rain solution.Fifthly, accelerated carbonation test, acid rain attack test, and simultaneous attack test of acid rain and carbonation of concrete under load were carried out. The neutralization and corrosion mechanism of SFRC under load was investigated in different corrosive media. Through analyzed, the relationship between neutral bending stress coefficient and stress level of SFRC under load can be expressed in quadratic polynomial.Finally, a neutralization model for SFRC subjected to acid rain attack was proposed on the basis of the theoretical model on the carbonation of ordinary concrete. On an experimental basis, the main parameters including water-cement ratio, fiber content, acid rain concentration and the casting surface of SFRC were considered, a neutralization predicting model of SFRC was established when subjected to acid rain attack. With the carbonation primarily, the neutralization predicting model of SFRC in the atmospheric environment was established for the first time on the basis of carbonation model. The effects of acid rain and bending loads were taken into account in this model. Through comparing verification between model calculation value and test result,the model is reasonable as the results calculated by the model agree well with test results.