# Mechanical Properties and Failure Mechanism of Recycled Concrete with Different Coal Gangue Powder Contents

## TL;DR

This study examines how adding coal gangue powder affects the strength and crack formation in recycled concrete.

## Contribution

The study identifies optimal coal gangue powder content for improving mechanical properties and reducing cracks in recycled concrete.

## Key findings

- Recycled concrete strength decreases with higher recycled coarse aggregate replacement rates.
- Adding 15% coal gangue powder maximizes peak strength and minimizes cracks.
- Crack ratios stabilize when coal gangue powder content exceeds 15%.

## Abstract

In this study, the mechanical properties and failure characteristics of concrete with 10–20 mm recycled coarse aggregate at 0%, 25%, 50%, 75%, and 100% substitution rates were studied. In addition, the influence of coal gangue powder (CGP) on the mechanical properties of concrete was studied under the dosages of 5%, 10%, 15%, and 20%. The research results show that the peak strength of recycled concrete decreases with the increase in the replacement rate of 10–20 mm recycled coarse aggregate. When the replacement rate is 25%, the decrease in strength is the smallest. When the content of CGP increases from 0 to 20%, the peak strength of recycled concrete increases first and then decreases. When the content of CGP is 15%, the peak strength reaches the maximum value. The peak strength increases slightly. The density of pores and cracks in recycled concrete increases with the increase of 10–20 mm recycled coarse aggregate replacement rate. When the substitution rate exceeds 25%, the proportion of cracks increases by nearly 1.7 times. After adding CGP to recycled concrete, the pore density and crack ratio inside a specimen are significantly reduced. When the CGP content exceeds 15%, the crack ratio tends to be stable. When the CGP content is 15%, the crack ratio is 0.519%, which is 23.5% lower than that of the RAC-25 specimen. When the content exceeds 15%, the crack ratio tends to be stable.