Optimization of Magnesium Potassium Phosphate Cements Using Ultrafine Fly Ash and Fly Ash

Yongshan Tan; Laura J Gardner; Brant Walkley; Oday H Hussein; Hao Ding; Shikuan Sun; Hongfa Yu; Neil C Hyatt

doi:10.1021/acssuschemeng.2c04987

Optimization of Magnesium Potassium Phosphate Cements Using Ultrafine Fly Ash and Fly Ash

ACS Sustain Chem Eng. 2023 Feb 10;11(8):3194-3207. doi: 10.1021/acssuschemeng.2c04987. eCollection 2023 Feb 27.

Authors

Yongshan Tan^{1

2}, Laura J Gardner², Brant Walkley³, Oday H Hussein², Hao Ding², Shikuan Sun^{2

4}, Hongfa Yu⁵, Neil C Hyatt²

Affiliations

¹ College of Civil Science and Engineering, Yangzhou University, Yangzhou 225127, China.
² NucleUS Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK.
³ Department of Chemical and Biological Engineering, University of Sheffield, Sheffield S1 3JD, UK.
⁴ School of Material Science and Energy Engineering, Foshan University, Foshan, Guangdong 528000, China.
⁵ Department of Civil and Airport Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China.

Abstract

The effect of ultrafine fly ash (UFA) and fly ash (FA) on the physical properties, phase assemblage, and microstructure of magnesium potassium phosphate cement (MKPC) was investigated. This study revealed that the UFA addition does not affect the calorimetry hydration peak associated with MKPC formation when normalized to the reactive components (MgO and KH₂PO₄). However, there is an indication that greater UFA additions lead to an increased reaction duration, suggesting the potential formation of secondary reaction products. The addition of a UFA:FA blend can delay the hydration and the setting time of MKPC, enhancing workability. MgKPO₄·6H₂O was the main crystalline phase observed in all systems; however, at low replacement levels in the UFA-only system (<30 wt %), Mg₂KH(PO₄)₂·15H₂O was also observed by XRD, SEM/EDS, TGA, and NMR (³¹P MAS, ¹H-³¹P CP MAS). Detailed SEM/EDS and MAS NMR investigations (²⁷Al, ²⁹Si, ³¹P) demonstrated that the role of UFA and UFA:FA was mainly as a filler and diluent. Overall, the optimized formulation was determined to contain 40 wt % fly ash (10 wt % UFA and 30 wt % FA (U10F30)), which achieved the highest compressive strength and fluidity and produced a dense microstructure.