# Research on the Hydration Mechanism and Mechanical Properties of Stainless Steel Slag–Fly Ash Recycled Concrete in Pavements

## TL;DR

This study explores how combining industrial by-products like stainless steel slag and fly ash with recycled aggregates can create strong, sustainable concrete for pavements.

## Contribution

The novel contribution is the discovery of synergistic hydration reactions between AOD slag and fly ash that enhance concrete strength when combined with recycled aggregates.

## Key findings

- Concrete with 50% recycled aggregate replacement and 10–20% AOD slag and fly ash replacement achieves optimal mechanical performance.
- Compressive strength reaches 33.9 MPa, significantly higher than using AOD slag or fly ash alone.
- Flexural and tensile strengths also improve, meeting pavement requirements while promoting resource reuse.

## Abstract

This study systematically investigates the effects of slag from the argon–oxygen decarburization (AOD) process, fly ash, and recycled aggregate (RA) replacement ratios on the mechanical properties of mortar samples and AOD slag–fly ash recycled concrete. The sustainable reuse of industrial by-products and construction waste is significant for reducing environmental impact and resource consumption during pavement construction. Experimental results demonstrate that when AOD slag and fly ash are used in combination, they undergo synergistic hydration reactions, producing calcium hydroxide (CH), calcium silicate hydrate (C-S-H) gel, and ettringite (AFt), resulting in superior strength compared to the individual use of either material. This research reveals that concrete strength decreases significantly when the recycled aggregate replacement ratio exceeds 50%; therefore, RA = 50% was selected as the optimal replacement ratio for subsequent studies. On this basis, when the combined replacement ratio of AOD slag and fly ash is 10–20%, concrete performance reaches its optimum level: maximum compressive strength is 33.9 MPa, which is 8.57% and 36.2% higher than using fly ash or AOD slag alone, respectively; maximum flexural strength is 4.6 MPa, which is 6.08% and 14.44% higher than using fly ash or AOD slag alone, respectively; and peak axial compressive and splitting tensile strengths are 24.9 MPa and 3.4 MPa, respectively. These findings demonstrate that the synergistic use of AOD slag, fly ash, and recycled aggregates can produce concrete that meets pavement application requirements, while effectively promoting the resource utilization of industrial by-products and construction waste, aligning with circular economy principles.