A New Mechanism for Inhibiting Alkali Efflorescence Dominated by Ettringite

doi:10.16552/j.cnki.issn1001-1625.2025.0772

Abstract

Abstract:

Efflorescence poses a critical challenge to the stability of cement-based decorative materials. Traditional methods have limitations such as low efficiency and strength damage. This study proposed and verified a new hypothesis： through the regulation of exogenous Ca²⁺， ettringite （AFt） can be transformed from an efflorescence promoting phase to an efficient efflorescence inhibition phase. Using sulphoaluminate cement （SAC） as the matrix and adding CaCl₂ as calcium sources， the efflorescence inhibition mechanism of AFt was systematically studied by multi-scale characterization methods such as XRD， SEM， TG-DSC and MIP. The results show that the optical density （OD） value of the SAC sample with 10% CaCl₂ （mass fraction） admixture is reduced by 39.2% compared to the sample without CaCl₂， indicating that it can significantly reduce the degree of efflorescence. The core mechanism lies in： 1） AFt crystal structure （3CaO·Al₂O₃·3CaSO₄·32H₂O） fixes free Ca²⁺， reducing the source of migratory ions. 2） AFt crystals can bind a large amount of crystalline water， reducing the carrier of ion migration. 3） A large amount of AFt interlaced growth forms a dense skeletonon， total porosity as low as 2.78%， blocking the ion migration channels. The three work together to achieve the "fixed ion source， bound migration carrier， and blocking migration channel" alkali inhibition effect. This study reveals the new function of AFt in active alkali inhibition and provides a new idea for the design of long-lasting anti-alkali efflorescence cement-based decorative materials.

Key words: CaCl₂, Ca（NO₃）₂, sulphoaluminate cement, ettringite, efflorescence inhibition, ion immobilization, channel blocking

CLC Number:

TU528

LI Lang, ZHANG Yuwei, GAO Yuhui, LIU Yue, CHENG Yan, ZHENG Weiguo. A New Mechanism for Inhibiting Alkali Efflorescence Dominated by Ettringite[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(2): 482-489.

Figures/Tables 12

Table 1 Formulations of SAC cement paste with different CaCl2 dosages

Sample No.	Mass ratio
Sample No.	SAC	Water	Iron black	CaCl₂	Optical density
1#	1	0.33	0.17	0	39.72
2#	1	0.33	0.17	0.10	24.17
3#	1	0.33	0.17	0.20	17.75
4#	1	0.33	0	0	—
5#	1	0.33	0	0.05	—
6#	1	0.33	0	0.10	—
7#	1	0.33	0	0.20	—

Table 2 Formulations of SAC mortar with different CaCl2 dosages

Sample No.	Mass ratio				Compressive strength/MPa
Sample No.	SAC	Water	Sand	CaCl₂	1 d	3 d	28 d
8#	1	0.5	3	0.10	42.3	49.4	57.6
9#	1	0.5	3	0	32.6	41.5	65.1

Table 3 Formulation of comparative test

Sample No.	Mass ratio
Sample No.	SAC	Water	Iron black	Ca（NO₃）₂	NaCl	Optical density
10#	1	0.27	0	0	0	—
11#	1	0.27	0	0.2	0	—
12#	1	0.27	0.2	0.2	0	20.45
13#	1	0.27	0	0	0.2	—
14#	1	0.27	0.2	0	0.2	36.39

Fig.1 XRD pattern of SAC

Fig.2 Efflorescence degree of SAC paste samples with different CaCl2 dosages

Fig.3 XRD patterns of SAC paste with different CaCl2 dosages

Table 4 Results of Rietveld refinement quantitative phase analysis of SAC with different CaCl2 dosages

Sample No.	Mass fraction/%							Refined reliable factor R_wp/%
Sample No.	AFt	CaSO₄	β-C₂S	SiO₂	CaCO₃	C₃S	Ca₄Al₂O₆CO₃·11H₂O	Refined reliable factor R_wp/%
5#	1.4	17.4	26.7	28.3	22.4	3.8	—	7.7
6#	10.5	21.0	8.4	26.8	27.7	1.8	3.8	9.4
7#	13.2	15.5	16.6	25.2	20.6	4.9	4.0	5.5

Fig.4 SEM images of hydration products of SAC paste samples

Fig.5 TG-DSC curves of SAC paste with 10% CaCl2

Fig.6 Efflorescence degree of SAC paste samples withCa（NO3）2 and NaCl dosages

Fig.7 Pore structure parameters of SAC paste samples with 0% and 10% CaCl2

Fig.8 Pore distribution parameters of SAC paste sample with 10% Ca（NO3）2

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