# Synergistic Effects of Steel Slag Powder and Ground Granulated Blast Furnace Slag on the Hydration and Performance of Alkali-Activated Magnesium Phosphate Cement

## TL;DR

This study explores using steel slag and blast furnace slag to improve the performance and reduce the cost of magnesium phosphate cement.

## Contribution

A novel approach to enhance MPC using steel slag and GGBS with an alkaline activator for better strength and durability.

## Key findings

- Modified MPC with 10% SSP and GGBS achieved 7-day and 28-day compressive strengths of 37.2 MPa and 50.2 MPa, respectively.
- Adding an alkali activator with a modulus of 1.3 increased 28-day strength to 62.3 MPa while maintaining high flowability.
- C-(A)-S-H gel formation from SSP and GGBS improved the pore structure and water resistance of MPC.

## Abstract

Magnesium phosphate cement (MPC) is widely used in rapid repair applications due to its fast setting, high early strength, and high-temperature resistance. However, the high cost of magnesium oxide (MgO) and the rapid hydration reaction make it challenging to control the setting time. In this study, steel slag powder (SSP) and ground granulated blast furnace slag (GGBS) were incorporated to partially replace MgO. The reactivity of SSP and GGBS was enhanced by an alkaline activator, promoting the dissolution of their glassy phases, which facilitated the formation of C-(A)-S-H gels and improved the performance of MPC. Experimental methods, including compressive strength testing, water resistance measurements, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), mercury intrusion porosimetry (MIP), and thermogravimetric analysis (TG), were used to evaluate the 28-day compressive strength and the microstructural characteristics of the modified MPC. When both SSP and GGBS were incorporated at 10 wt.%, the modified MPC achieved a 7-day compressive strength of 37.2 MPa, with the 28-day strength increasing to 50.2 MPa. The addition of an alkali activator with a modulus of 1.3 significantly boosted the 28-day strength to 62.3 MPa, while maintaining high flowability (215 mm). Microscopic characterization revealed that C2S and C3S in SSP undergo continuous hydration under alkaline conditions, while reactive silica-aluminum in GGBS reacted with phosphate to form a water-resistant C-(A)-S-H gel phase, optimizing the pore structure of MPC. This study provides a novel approach to developing low-cost, high-durability modified MPC with improved performance.