Study on the Mechanical Properties and Thermal Conductivity of Cotton Stalk Fiber Heat-Insulating Shotcrete

Abstract

In this study, heat-insulating shotcrete with excellent performance was developed to effectively reduce the thermal conductivity and meet the strength requirements of shotcrete in high ground temperature roadways. Ceramsite and pottery sand were used to replace 5% and 10% of sand and stone, respectively. The shotcrete was composed of cotton rod fiber treated with polyvinyl alcohol solution (SH adhesive) and other materials in a certain mix ratio. The working, mechanical, and heat insulation properties of the shotcrete were investigated by compressive strength, splitting tensile, thermal conductivity, electron microscope scanning, and X-ray diffraction tests. The results showed that the optimum content of the cotton stalk fiber was 2 kg/m3. The compressive strength and the splitting tensile properties were excellent, and the strength attained the maximum value. The performance of shotcrete increased with an increase in the cotton stalk fiber content. The thermal conductivity curve decreased smoothly when the cotton stalk fiber content exceeded 2 kg/m3. Furthermore, when the cotton stalk fiber content was 0–2 kg/m3, the internal cotton stalk fiber was tightly wrapped by the hydrate, and the mechanical properties were enhanced. Moreover, when the cotton stalk fiber content was 2-3 kg/m3, a clustering phenomenon occurred, and the compressive and tensile strengths were reduced. The hydration reaction of the cement mixed with cotton stalk fiber was normal, and the reinforced reticulated porous structure was formed with ceramsite in the concrete matrix, improving the strength of the concrete and reducing the thermal conductivity.