Chloride ion permeability of concrete containing recycled composite powder from building demolition waste

Abstract

Buildings in the marine environment are vulnerable to chloride ion erosion, which threatens the service life of concrete structures. To facilitate the application of concrete containing construction demolition waste in the marine environment, recycled composite powder concrete (RCPC) was prepared using recycled composite powder as cement substitute. The chloride ion permeability of RCPC was evaluated by chloride ion diffusion test and rapid chloride ion migration test (RCM). The chloride ion permeability of RCPC continued to enhance with growing content of recycled composite powder. During the immersion age, the surface chloride ion content of the samples containing recycled composite powder increased by an average of 18.3–65.3% over the control group, with a corresponding average increase in chloride ion diffusion coefficients ranging from 17.0% to 31.5%. The chloride ion migration coefficients in the RCM test raised by 9.5–24.7%. A series of microscopic tests such as nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometer (SEM-EDS) suggested that the total porosity increased by 11.9–29.5% with the addition of recycled composite powder. The chloride ion diffusion coefficients exhibited a linear increase with growing total porosity and porosity of capillary pores, whereas an exponential increase with the porosity of transitional pores. The poor reactivity of the recycled composite powder resulted in a looser microstructure and weakened chloride binding capacity, and these factors boosted chloride ion transport. A chloride ion diffusion model of RCPC considering the time dependence of chloride ion transport was developed, and the reliability of the model was verified by experimental data.