New Spraying Construction and Crack Repair Performance of Ultra-Rapid Setting Magnesium Phosphate Cement Coating

doi:10.16552/j.cnki.issn1001-1625.2025.0676

Abstract

Abstract:

Aiming at the construction problem caused by the rapid setting and hardening of magnesium phosphate cement （MPC） under the condition of no retarder， this study adopted the new mixing-stirring-spraying integrated spraying construction to carry out the mechanized construction of ultra-rapid setting MPC coating， which effectively solved the bottleneck of jet construction of rapid setting cement coating and reduced the cost of raw materials. Based on this， this paper focused on the influence of spraying ultra-rapid MPC coating on the chloride ion penetration resistance of concrete matrix， and evaluated the improvement effect of ultra-rapid MPC coating on the mechanical properties and chloride ion penetration resistance of cracked mortar members. The results show that after 90 d seawater immersion， the chloride ion content of coated concrete in the depth 0~<5 mm is significantly reduced by 24.8% （mass fraction） compared with that of uncoated concrete， and the chloride ion penetration resistance is effectively improved. The permeability behavior of chloride ion in coated concrete obeys the law of decreasing with the increase of structural depth. In the depth 0~<5 mm， the chloride ion content increases with the increase of seawater immersion age， and gradually tends to be saturated， reaching saturation at 454 d， and the content is 0.193 %. The 28 d flexural strength of the cracked concrete members after coating repair is increased by 131.3%， and the chloride ion content in the depth 0~<5 mm is reduced by 12.9%. This study provides a theoretical basis for the application of spraying ultra-rapid MPC coating in the protection， repair and reinforcement of concrete structures in marine environment.

Key words: magnesium phosphate cement coating, mixing-stirring-spraying integrated spraying, ultra-rapid setting, flexural strength, chloride ion penetration resistance, crack repairing

CLC Number:

TU525.9

YU Qiuchun, LI Wei, LIANG Yun, DENG Yongjie, HUANG Hanhan, LI Weihong, LI Dongwei. New Spraying Construction and Crack Repair Performance of Ultra-Rapid Setting Magnesium Phosphate Cement Coating[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(1): 21-29.

Figures/Tables 16

Table 1 Main chemical composition of dead-burned MgO and fly ash

Material	Mass fraction/%
Material	MgO	SiO₂	Fe₂O₃	Al₂O₃	CaO	SO₃	TiO₂	Loss
Dead-burned MgO	92.66	2.37	1.38	0.79	1.44	—	—	0.22
Fly ash	1.71	51.97	5.27	28.77	6.27	1.46	1.66	2.89

Table 2 Main chemical composition of seawater

Composition	MgCl₂	NaCl	Na₂SO₄	CaCl₂	KCl	NaHCO₃
Concentration/（g·L^-1）	5.200	24.530	4.090	1.160	0.695	0.201

Fig.1 Schematic diagram of test blocks

Fig.2 Specific steps of concrete specimen chloride

Fig.3 Schematic diagram of flexural strength test loading ion content test

Fig.4 Composition of jet system

Fig.5 Operating principle of mixing-stirring-spraying integrated rapid-setting concrete mist spraying system

Fig.6 Flow chart of spraying construction process

Fig.7 Flexural strength of different types of cement mortar

Fig.8 Cross-sectional morphology at cracks of ultra-rapid MPC coating repaired structure

Fig.9 Chloride ion content of each specimen immersed in seawater after 30 d

Fig.10 Chloride ion content of concrete immersed in seawater at different ages

Fig.11 XRD patterns of ultra-rapid MPC coating immersed in seawater after 90 d

Fig.12 SEM images of ultra-rapid MPC coating-concrete bond interface immersed in seawater after 90 d

Fig.13 Fitting curve of chloride ion content of ultra-rapid MPC coating concrete at different depths

Fig.14 Fitted curve of chloride ion content of ultra-rapid MPC coating concrete at 0~<5 mm depth for each corrosion age

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