Effect of Natural Gypsum Content on Hydration and Performances of High-Alumina Ladle Slag Based Compound Cementitious Materials

doi:10.16552/j.cnki.issn1001-1625.2025.1291

Abstract

Abstract:

High-alumina ladle slag is a solid waste generated during the secondary refining process of crude steel. Its composition， structure， and properties are similar to those of aluminate cement， suggesting its potential use as a low-grade aluminate cement. In this study， a compound cementitious material was prepared using high-alumina ladle slag and natural gypsum， and the effect of natural gypsum content on its hydration and performances was investigated. The results show that the incorporation of natural gypsum reduces the water requirement for normal consistency of the compound cementitious material. Specifically， for compound cementitious material containing 40% to 60% （mass fraction， same below） natural gypsum， the water requirement for normal consistency decreases to approximately 27.6%. The setting and hardening of the compound cementitious material are accelerated compared to pure high-alumina ladle slag. For compound cementitious material with 10% to 40% natural gypsum， the initial setting time ranges from 18 min to 24 min， and the final setting time from 64 min to 71 min. Further increasing the natural gypsum content prolongs the setting time. As the natural gypsum content increases， the compressive strength of the compound cementitious material mortars increases first and then decreases. The compound cementitious material mortar containing 50% natural gypsum exhibits the highest 28 d compressive strength， reaching 29.8 MPa， although it remains lower than that of the pure high-alumina ladle slag mortar. An appropriate amount of natural gypsum mitigates the flexural strength regression observed in high-alumina ladle slag mortars. The compound cementitious material mortars with 40% and 50% natural gypsum show no flexural strength regression， achieving a 28 d flexural strength of approximately 6.0 MPa， which is higher than that of the pure high-alumina ladle slag mortar. The 28 d drying shrinkage of the compound cementitious material mortars increases first and then decreases with increasing natural gypsum content. The compound cementitious material mortar with 10% natural gypsum exhibits the highest 28 d drying shrinkage rate of 0.073 2%. In contrast， the compound cementitious material mortars with 30% to 60% natural gypsum show lower drying shrinkage than the pure high-alumina ladle slag mortar. Natural gypsum significantly influences the hydration of high-alumina ladle slag. It preferentially reacts with calcium aluminate in the high-alumina ladle slag and its hydration products to form ettringite （AFt）， reducing the content of metastable hydration phases and leading to a more stable hydration structure in the compound cementitious material system.

Key words: high-alumina ladle slag, natural gypsum, compound cementitious material, hydration characteristic, hydration product, drying shrinkage

CLC Number:

TU52

ZHANG Liu, GONG Ming, DING Pan, ZHOU Fei, YANG Fengyuan, LU Zhongyuan, LI Jun. Effect of Natural Gypsum Content on Hydration and Performances of High-Alumina Ladle Slag Based Compound Cementitious Materials[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(7): 2389-2396.

Figures/Tables 11

Table 1 Main chemical composition of raw materials

Material	Mass fraction/%
Material	MgO	Al₂O₃	SiO₂	SO₃	CaO	Fe₂O₃	K₂O	Na₂O	Loss
High-alumina ladle slag	0.68	50.35	7.67	0.67	29.19	1.62	0.28	0.09	7.40
Natural gypsum	3.13	1.05	3.74	42.65	41.09	0.38	0.27	0.07	7.28

Fig.1 XRD pattern of high-alumina ladle slag

Fig.2 Particle size distribution of raw materials

Fig.3 XRD pattern of natural gypsum

Table 2 Mix proportion of compound cementitious materials

Sample No.	Mass fraction/%
Sample No.	High-alumina ladle slag	Natural gypsum
LF0	100	0
LF1	90	10
LF2	80	20
LF3	70	30
LF4	60	40
LF5	50	50
LF6	40	60

Table 3 Water requirement for normal consistency， setting time， and soundness of compound cementitious materials

Sample No.	Water requirement for normal consistency/%	Setting time/min		Soundness
Sample No.	Water requirement for normal consistency/%	Initial	Final	Soundness
LF0	29.8	60	255	Qualified
LF1	29.3	22	67	Qualified
LF2	28.8	24	64	Qualified
LF3	28.2	22	71	Qualified
LF4	27.6	18	67	Qualified
LF5	27.7	29	88	Qualified
LF6	27.6	29	111	Qualified

Fig.4 Mechanical properties of compound cementitious material mortars

Table 4 Drying shrinkage rate of compound cementitious material mortars

Sample No.	LF0	LF1	LF2	LF3	LF4	LF5	LF6
Drying shrinkage rate/%	0.052 4	0.073 2	0.059 2	0.048 8	0.022 0	0.022 0	0.002 4

Fig.5 Heat of hydration of high-alumina ladle slag-natural gypsum compound cementitious materials

Fig.6 XRD patterns of hydration products

Fig.7 TG-DTG analysis of hydration products

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