Corrosion characteristics of basalt-polypropylene hybrid fiber concrete under the compound salt and drying-wetting cycles

Abstract

Concrete is widely used in civil engineering due to its superior properties, however, due to its crack-prone nature, its application in marine engineering will generate a large number of micro-cracks, which will affect the durability and service life of the concrete structure. Basalt-polypropylene hybrid fibers have been added to concrete as a new type of hybrid fiber to improve tensile strength. However, the long-term erosion resistance of basalt-polypropylene hybrid fiber concrete (BPHFC) in marine tidal environments has not been well studied. Therefore, the corrosion degradation behavior of BPHFC under the combined action of compound salt (NaCl+Na2SO4) and drying-wetting cycles was investigated using indoor simulation experiments, and analyzed the effects of fiber content and form on the macroscopic properties and sulfate concentration of concrete. In addition, the corrosion deterioration mechanism of BPHFC was revealed using a concrete surface pore structure analyzer, X-ray diffractometer, and field emission scanning electron microscopy. The research results showed that after 60 cycles, the mass loss rate of BPHFC began to increase, and the specimens mixed with 0.1% BF exhibited the smallest mass loss rate. The relative compressive strength (Kn) and relative dynamic elastic modulus showed a tendency to increase and then decrease. Compared with the control specimens, the addition of 0.1% BF, PF, or BF-PF reduced the Kn loss rate of concrete by 24.04%, 13.28%, and 8.10%, respectively, whereas 0.2% BF-PF hybrid fibers increased the Kn loss rate of concrete by 1.62%. The sulfate concentration of BPHFC increased with the number of cycles, and the addition of 0.1% single or hybrid fibers increased the magnitude of the decrease in sulfate concentration during the later stages of erosion. The addition of BF, PF, or hybrid BF-PF reduced the percentage of super-large pores in concrete by 0.67–28.91% after 90 cycles, and addition of BF and PF attenuated the deterioration of concrete pores after erosion. There was a difference in the bonding properties of BF and PF with the concrete matrix, and the corrosion products of BPHFC were mainly ettringite and gypsum. The results of this study contribute to the development and application of BPHFC in marine engineering.