Study of the basic mechanical properties and degradation mechanism of recycled concrete with tailings before and after carbonation

Abstract

Based on the fine powder and the activation characteristics of iron tailings, the basic mechanical properties and deterioration mechanism of the recycled concrete with tailings before and after carbonization were macroscopically and microscopically analyzed via rapid carbonization tests. The macroscopic results showed that the cubic compressive strength increased first and then decreased with the tailings addition at different dosages, with a peak value of 30%. The values of the splitting tensile strength and axial compressive strength fluctuated differently, and the tailings content ranged from 20% to 40% at the peak point before and after carbonization. The peak strain and elastic modulus of recycled concrete were reduced to different extents, and the longer the carbonization age was, the greater the reduction range was. Simultaneously, the carbonization age also increased the brittleness of recycled concrete, causing the descending section of the constitutive curve to greatly fluctuate. Microscopically, the influence of tailings on the matrix structure of the recycled concrete was verified by energy dispersive spectrometer (EDS) and scanning electron microscope (SEM) analysis. The results proved that the appropriate tailings content could improve the interface transition zone (ITZ) and the compactness of the concrete, also optimize the mechanical properties of the recycled concrete. However, excessive tailings could reduce the integrity of the matrix structure, increase the number of harmful pores. According to the research, when the tailings content was 20%–40%, the recycled concrete had high mechanical properties and reasonable microstructure. This study provided a theoretical basis for the popularization and application of the recycled concrete with tailings.