Effect of Activation Process on Properties of Kaolin-Based Low-Carbon Cement

doi:10.16552/j.cnki.issn1001-1625.2025.1116

Abstract

Abstract:

This study utilized activated kaolin， limestone powder， and a small amount of cement clinker to prepare low-carbon cement. The effects of two activation methods， mechanochemical activation and thermal activation on the microstructure of kaolin， the properties of the low-carbon cement， and the composition and structure of its hydration products were systematically examined. The results indicate that kaolin transforms into an amorphous state after activation treatment. Mechanochemical activation is more effective in enhancing the reactivity of kaolin than thermal activation. When 40% （mass fraction） mechanochemically activated kaolin and 20% （mass fraction） limestone powder are incorporated， together with an external addition of 5% by mass of calcium hydroxide， the prepared low-carbon cement achieves compressive strengths of 14.8 MPa at 3 d and 39.4 MPa at 28 d. The main hydration products are calcium silicate hydrate （C-S-H） gel， ettringite （AFt）， and calcium sulfoaluminate hydrate （AFm）. Furthermore， the external addition of calcium hydroxide enhances the pozzolanic reaction of kaolin， increases the formation of hydration products， and improves pore structure of the paste and enhances its mechanical properties. This study explores a technical pathway for producing low-carbon cement with activated kaolin， achieving favorable performance development at a 60% clinker replacement rate by mass， thereby providing an effective approach for the development of low-carbon cement.

Key words: kaolin, low-carbon cement, mechanochemical activation, thermal activation, hydration mechanism

CLC Number:

TU525

LIAO Yuntian, PENG Wenjie, LI Bo, CHEN Wei, ZHENG Xuhang. Effect of Activation Process on Properties of Kaolin-Based Low-Carbon Cement[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(6): 1979-1987.

Figures/Tables 14

Fig.1 XRD pattern of kaolin

Table 1 Chemical composition of kaolin and cement clinker

Material	Mass fraction/%
Material	CaO	Al₂O₃	MgO	SiO₂	P₂O₅	K₂O	SO₃	LOI	Other
Cement clinker	61.40	6.00	1.38	21.06	0.19	0.81	2.79	2.02	4.35
Kaolin	1.22	30.16	0.57	54.09	0.06	2.08	0.09	7.16	4.57

Fig.2 Particle size distribution of raw kaolin and activated kaolin

Table 2 Particle size and specific surface area distribution of raw kaolin and activated kaolin

Sample	D₅₀/μm	Specific surface area/（m²·g^-1）
Kaolin	5.302	1.130
CK	6.100	0.984
MK	1.897	3.160

Fig.3 XRD patterns and amorphous content of activated kaolin

Table 3 Mix proportion of low carbon cement paste

Sample	Mix proportion /（kg·m^-3）								W/B
Sample	Cement clinker	CK	MK	Limestone	Gypsum	Ca（OH）₂	Water	PCE	W/B
CAL-MK	35	0	40	20	5	5	40	0.7	0.4
CAL-MK-CH	35	0	40	20	5	0	40	0.7	0.4
CAL-CK	35	40	0	20	5	0	40	0.4	0.4
CAL-CK-CH	35	40	0	20	5	5	40	0.4	0.4

Table 4 Effect of activated kaolin on setting time and standard consistency of low carbon cement

Sample	Initial setting time/min	Final setting time/min	Standard consistency/%
CAL-CK	168	206	28.2
CAL-CK-CH	160	187	30.1
CAL-MK	194	236	35.6
CAL-MK-CH	184	223	38.4

Fig.4 Effect of activated kaolin on compressive strength of low carbon cement

Fig.5 NMR relaxation analysis of samples at 28 d

Table 5 Porosity calculation results of samples

Sample	CAL-MK	CAL-MK-CH	CAL-CK	CAL-CK-CH
Porosity/%	18.22	13.98	21.66	16.31

Fig.6 XRD patterns of hydration products of low carbon cement at 3 and 28 d

Fig.7 TG-DTG curves of hydration products of low carbon cement at different ages

Fig.8 CH content in samples determined by thermogravimetric analysis at 3， 7， and 28 d

Fig.9 27Al and 29Si MAS NMR spectra of hydration products at 28 d

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