Abstract

Struvite, the stable hydration product and primary strength phase in magnesium ammonium phosphate cement (MAPC), derived from wastewater treatment, has recently been utilized as a sustainable additive to Portland cement (PC). However, its impacts on cement hydration kinetics, pore refinement, rheology, and the mechanisms underlying these processes have not been comprehensively studied. This study developed Portland cement-struvite (PCS) systems by replacing PC with 3–20 % struvite (ST wt.%: PCS3–PCS20) and evaluated these processes using isothermal calorimetry, 3D micro-computed tomography (μXCT), time-dependent rheometry, X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR), and the Krstulović-Dabić (K-D) model. The FTIR/XRD confirmed the coexistence of typical PC hydrates and struvite, while μXCT showed a 41.7 % porosity reduction for PCS10 after 28 days. Static yield stress (SYS) increased significantly with ST; PCS10 and PCS15 exhibited 200 % and 351 % higher SYS than the control after 30 min. Plastic viscosity decreased with increasing ST, extending placement windows and improving workability. At the optimal 10–15 % substitution rate, PCS10 (and PCS15) achieved a 5.6 % (6.7 %) and 72.1 % (86.8 %) increase in compressive and flexural strengths, respectively, after 28 days. The K–D modeling showed that all systems followed the NG–I–D mechanisms, with slightly declining rate constants and crystal growth index (n) as ST increased, indicating retardation and a shift in hydrate morphology. The PCS systems rely on filler effects and ST-mediated Ca2+ surface adsorption, promoting early flocculation and reducing porosity. The PCS systems require less water to maintain workability and mechanical strength, without needing flow-modifying additives.

Department(s)

Chemical and Biochemical Engineering

Publication Status

Full Text Access

Comments

Missouri University of Science and Technology, Grant CMMI #2239511

Keywords and Phrases

3D μ-XCT; Filler effects; Krstulović-Dabić kinetic model; Portland cement; Struvite; Time-dependent rheology

International Standard Serial Number (ISSN)

0958-9465

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2026 Elsevier, All rights reserved.

Publication Date

01 Feb 2026

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