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%e40%, 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.

Introduction

Tailings and construction waste are inevitable products of accelerated urbanization construction and rapid economic development. Due to the immaturity of regeneration technology, a large number of tailings ponds and construction waste treatment plants exist, which not only occupy land, waste resources, and pollute the environment but also pose a substantial threat to the property and personal safety of the surrounding residents (Li al., 2018; Kox et al., 2019; Lu et al., 2018). Currently, making recycled concrete from tailings and construction waste is the most effective approach. However, at present, most studies worldwide have been focused on concrete with tailings or recycled aggregate concrete (RAC). In these investigations, the effects of aggregates, such as tailings, and natural coarse aggregates (NCA) on dam concrete were compared, their mechanical properties and frost resistance were discussed. The studies demonstrated the feasibility of using tailings as the aggregate to completely replace an ordinary aggregate in dam concrete (Lv et al., 2019). Cheng et al. (2016) studied the mechanical and chemical activation of iron tailings and the performance of concrete after the partial replacement of cement. The results showed that the compressive strength of concrete decreased gradually with the replacement rate. Shettima et al. (2016) used iron tailings to replace river sand in concrete, and studied its compressive strength, splitting tensile strength, elastic modulus and durability, the results showed that the strength and elastic modulus of the modified concrete were higher than that of ordinary concrete due to the addition of tailings.