# Strength Enhancement of 3D-Printed Phosphogypsum Concrete Based on Synergistic Activation of Multi-Solid Wastes

## TL;DR

This paper proposes a new method to enhance the strength of 3D-printed concrete using phosphogypsum and other solid wastes, offering a sustainable construction solution.

## Contribution

The study introduces a novel approach for large-scale phosphogypsum utilization in 3D-printed concrete through synergistic activation of multiple solid wastes.

## Key findings

- 3DPPGC's mechanical properties peaked at a 70% cement replacement ratio.
- 3DPPGC showed a 1.52% increase in 28-day flexural strength compared to cast specimens.
- Using PG, BS, FA, and SF significantly enhanced the strength of 3DPPGC.

## Abstract

What are the main findings?
Proposes a novel route for large-scale phosphogypsum valorization in 3D-printed concrete.Achieves dual-function utilization of phosphogypsum as a binder and sulfate activator.Elucidates the synergistic mechanism between slag and phosphogypsum.

Proposes a novel route for large-scale phosphogypsum valorization in 3D-printed concrete.

Achieves dual-function utilization of phosphogypsum as a binder and sulfate activator.

Elucidates the synergistic mechanism between slag and phosphogypsum.

What are the implications of the main findings?
Resolves the inherent strength-deficiency of 3DPPGC.Integrates solid waste recycling with low-carbon construction goals.Paves the way for large-scale engineering deployment of phosphogypsum-based materials.

Resolves the inherent strength-deficiency of 3DPPGC.

Integrates solid waste recycling with low-carbon construction goals.

Paves the way for large-scale engineering deployment of phosphogypsum-based materials.

Phosphogypsum (PG) is the main by-product of wet-process phosphoric acid production. Its annual global production reaches about 200 million tons, yet its utilization rate remains low. Consequently, long-term stockpiling of large PG volumes poses immense pressure to the ecological environment. To mitigate negative environmental impacts, the utilization of PG is imperative. Despite progress in PG utilization and 3D-printing technology, there is still a significant lack of understanding about the synergistic activation mechanisms in multi-solid-waste systems. In particular, the composition design, microstructure evolution, and structure–property relationships of 3D-printed PG-based composites are not well-studied, which limits their high-value engineering applications. Three-dimensional-printed phosphogypsum concrete (3DPPGC) is proposed here, promoting PG resource utilization by leveraging the expanding applications of 3D-printed concrete (3DPC). However, the strength of 3DPPGC needs to be enhanced to meet engineering requirements. This study designed the mix proportion of 3DPPGC and fabricated the corresponding test specimens. The optimal Cement Replacement Ratio (CRR) was determined through experimental testing, and the mechanism behind the strength enhancement of the 3DPPGC was elucidated. The results indicated that the 3DPPGC’s mechanical properties peaked at the 70% CRR. Compared with cast specimens, 3DPPGC exhibited a 1.52% increase in 28-day flexural strength in the y-direction, reaching 4.69 MPa. The early-age compressive strength, flexural strength, and later-age compressive strength of 3DPPGC were significantly enhanced when PG, blast-furnace slag (BS), fly ash (FA), and silica fume (SF) were used to partially replace cement. This study provides a theoretical and experimental basis for the large-scale, high-value application of PG in intelligent construction.