Hydration Characteristics of Slag-Fly Ash Cementitious System Activated by Lime-Sodium Sulfate Composite

doi:10.12068/j.issn.1005-3026.2025.20230270

Abstract

Abstract:

In order to solve the problems of quick setting time and poor safety when using strong alkali activator such as sodium hydroxide in alkali-activated slag-fly ash cementitious system， a compound activator with the amount of substance ratio of lime to sodium sulfate of 1∶1 was used to activate the slag-fly ash cementitious system. The effects of activator dosage and fly ash content on the properties of lime-sodium sulfate compound-activated slag-fly ash cementitious system were analyzed. The hydration products and hydration process of the cementitious system were explored by XRD and other detection methods. The results show that the composite activator composed of lime and sodium sulfate can replace sodium hydroxide to activate the cementitious system of slag-fly ash， and the fluidity and setting time of the cementitious system can be controlled. The optimal dosage of the composite activator in the cementitious system is 10%， and when the fly ash content is less than 50%， the 28 d compressive strength of the cementitious system is above 36MPa. Lime-sodium sulfate compound activator can effectively destroy the shell of fly ash， promote fly ash to participate in the hydration reaction of cementitious system， and enhance the later compressive strength of cementitious system. C-（A）-S-H gel and ettringite cement slag and fly ash with different reaction degrees and particle sizes to form a compact matrix structure， which provides the main compressive strength for the cementitious system. This study provides a reference for the preparation of noval low-carbon cementitious materials.

Key words: lime-sodium sulfate, slag-fly ash cementitious system, compressive strength, hydration characteristics

CLC Number:

TU 526

Ying WANG, Xiao-wei GU, Xiao-chuan XU, Qing WANG. Hydration Characteristics of Slag-Fly Ash Cementitious System Activated by Lime-Sodium Sulfate Composite[J]. Journal of Northeastern University(Natural Science), 2025, 46(4): 87-96.

Figures/Tables 16

Table 1 Chemical composition of raw materials

原材料	SiO₂	Al₂O₃	Fe₂O₃	MgO	CaO
粉煤灰	54.94	34.86	5.52	0.81	0.63
矿渣	34.50	17.70	0.03	7.01	34.00

Fig.1 Particle size distribution of raw materials

Fig.2 Phase composition of raw materials

Table 2 Test proportions of slag-fly ash cementitious system activated by lime-sodium sulfate composite

序号	石灰	硫酸钠	粉煤灰	矿渣	水
T0	12.4	23.6	36	324	144
T1	12.4	23.6	72	288	144
T2	12.4	23.6	108	252	144
T3	12.4	23.6	144	216	144
T4	12.4	23.6	180	180	144
T5	6.2	11.8	108	252	144
T6	18.5	35.5	108	252	144
T7	24.7	47.3	108	252	144

Fig.3 Experimental process of slag-fly ash cementitious system activated by lime-sodium sulfate composite

Fig.4 Compressive strength of slag-fly ash cementitious system with varying content of activator

Fig.5 Compressive strength of slag-fly ash cementitious system with varying fly ash content

Fig. 6 Flowability of cementitious system

Fig.7 Setting time of cementitious system

Fig.8 Hydration products of slag-fly ashcementitious system（a）—3 d；（b）—28 d.

Fig. 9 Chemical structure of slag-fly ash cementitious system

Fig.10 Micro-morphology of slag-fly ash cementitious system under different fly ash contents

Fig.11 Calcium hydroxide and ettringite in slag-fly ash cementitious system

Fig.12 EDS of C-(A)-S-H gel in gelling system

Fig.13 Fly ash in slag-fly ash cementitious system

Fig.14 Hydration mechanism of slag-fly ash cementitious system activated by lime-sodium sulfate composite

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