Fractal characteristics of fiber lithium slag concrete cracks under sulfate attack

Natural corrosion of concrete structure due to sulfate poses a serious threat to people's lives and property. Therefore, it is of great practical significance to study the phenomenon of sulfate corrosion on concrete. In order to explore the mechanical properties of a new type of concrete corroded by sulfate, a full immersion accelerated erosion method was used with 5% sulfate solution. Erosion tests were performed on 11 groups of polypropylene fiber reinforced concrete (PC) specimens, 11 groups of polypropylene fiber lithium slag concrete (PLiC) specimens, 8 PC columns with large eccentricity, and 8 PLiC large eccentric columns. The mechanical properties of concrete under different erosion times are obtained. Based on the fractal theory, the fractal characteristics of surface crack distribution of specimens and columns are analyzed. In addition, the relationship between the fractal dimension of surface crack and erosion time, compressive strength, and ultimate bearing capacity is discussed. Results show that the compressive strength of PC and PLiC initially increases and then decreases with increased erosion days, reaching a maximum of 120 days. The distribution of surface cracks is observed to be fractal when they are broken. With increased erosion days, fractal dimension of surface cracks initially increases, then decreases, and finally increases again. On the other hand, a decreasing trend of fractal dimension of surface cracks is observed with increased compressive strength. The ultimate bearing capacity of PC and PLiC columns with large eccentricity increases first and then decreases with erosion days. Addition of lithium slag is observed to improve the sulfate resistance of polypropylene fiber reinforced concrete columns. With broken members, fractal dimension of surface cracks presents a rising trend of shock with sulfate erosion days. Results signify that fractal characteristics of concrete surface cracks can be used as one of the indexes to determine the damage degree of members, which can provide reference for the prediction of bearing capacity and service life of concrete structures in the future.