Macro–microscopic experimental and numerical simulation study of fiber‒mixed concrete under the salt–freezing effect

Abstract

Mixing an appropriate amount of fiber in concrete can enhance its strength and durability. Macroscopic and microscopic tests of fiber-mixed concrete under the action of salt freezing cycles are conducted to investigate the macroscopic mechanical properties and the evolution of the microscopic pore structure of unadulterated, single-adulterated and fiber-mixed concrete under a sulfate solution with a mass fraction of 5 % and freeze‒thaw cycles. The macro‒microscopic damage model of fiber-mixed concrete is constructed and verified. The model is applied to one concrete slab rockfill dam to reveal the deformation, stress and damage evolution of the slab after the cracks are repaired with fiber‒mixed concrete. The results show that compared with the unadulterated fiber concrete, the fiber concrete resistance to salt freezing and erosion ability is enhanced, and the macromechanical properties of the mixed fiber concrete reach the optimum when the mixing amount of basalt fibers and polypropylene fibers is 0.15 % and 0.1 %, respectively. With the increase in the number of salt freezing cycles, the pore size distribution of fiber concrete is lognormal; the porosity, pore volume, and pore surface area gradually increase, and the pore fractal dimension gradually decreases. Mixing fiber can effectively improve the unstable toughness of concrete and exert its anti-cracking performance. The maximum displacements, compressive stresses and tensile stresses of the slab repaired with fiber concrete without experiencing salt freezing are reduced compared with those of the case without fibers; at 300 salt freezing cycles, they decrease by 4.44 %, 15.65 % and 9.23 %, respectively; and the area of salt freezing damage displays a significant decline.