Strength and Microscopic Mechanism of Fly Ash-Slag-Red Mud-Based Cementitious Materials Solidified Soil

doi:10.16552/j.cnki.issn1001-1625.2025.0758

Abstract

Abstract:

In order to solve the problems of high cost and high carbon emission in the production process of traditional cementitious materials in subgrade reinforcement engineering， and to realize the recycling and high-value utilization of industrial solid waste， sodium hydroxide was used as alkali activator to prepare fly ash-slag-red mud ternary composite cementitious materials. Through the unconfined compressive strength （ UCS ） test， the effect of mix ratio of solid waste-based cementitious materials and sodium hydroxide content on the 7 d UCS of solidified soil was studied. The correlation analysis of UCS results was carried out by SPSS software， and the solidification mechanism of solid waste-based cementitious materials on soil was discussed by means of SEM-EDS and XRD. The results show that the solidified soil specimens with different mix ratios show three types of splitting failure， shear failure and tensile-shear composite failure. The interaction between solid waste-based raw materials and alkali activator has a significant effect on the UCS of solidified soil. When the mass ratio of fly ash， slag， and red mud is 1∶3∶1， the 7 d UCS of solidified soil is the highest， up to 1.795 MPa. There is a significant positive correlation between sodium hydroxide content and UCS， and the correlation coefficient reaches 0.76. With the hydration reaction in the solidified soil， a large number of hydrated calcium silicate and hydrated calcium aluminate gel phases is generated to wrap the soil particles and fill the pores between the particles， thereby significantly improving the strength of solidified soil. With the increase of sodium hydroxide content， its promotion effect on the hydration reaction is more significant. The proportion of the sum of micropores and small pores in solidified soil gradually increases， and the proportion of the sum of mesopores and macropores gradually decreases.

Key words: solid waste-based cementitious material, solidified soil, unconfined compressive strength, correlation analysis, microscopic morphology

CLC Number:

TU447

YUE Pengfei, GUO Sibiao, DING Xiujuan, WANG Yusong, WANG Dazhou, HU Yue, ZHANG Rongrong, ZHANG Gang, DING Jinmeng. Strength and Microscopic Mechanism of Fly Ash-Slag-Red Mud-Based Cementitious Materials Solidified Soil[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(1): 336-345.

Figures/Tables 14

Table 1 Physical performance index of undisturbed soil

Parameter	Value
Natural water content/%	26.2
Specific gravity of soil particle	2.7
Maximum dry density/（g·cm^-3）	1.7
Liquid limit/%	42.5
Plastic limit/%	19.3
Plasticity index	23.2
Optimum moisture content/%	18.0

Fig.1 Granular gradation curve of undisturbed soil

Table 2 Main chemical composition of fly ash， slag and red mud

Matreial	Mass fraction/%
Matreial	CaO	SiO₂	SO₃	Al₂O₃
Fly ash	5.6	45.1	2.1	24.2
Slag	39.3	33.1	1.9	15.0
Red mud	1.7	15.1	0.2	26.8

Fig.2 Macro-morphology of test raw materials

Table 3 Mix proportion of solidified soil specimen

Specimen No.	Mass fraction/%			NaOH content/%
Specimen No.	Fly ash	Slag	Red mud	NaOH content/%
15FA-55SL-30RM	15	55	30	0，4，8
15FA-60SL-25RM	15	60	25	0，4，8
20FA-50SL-30RM	20	50	30	0，4，8
20FA-55SL-25RM	20	55	25	0，4，8
20FA-60SL-20RM	20	60	20	0，4，8
25FA-45SL-30RM	25	45	30	0，4，8
25FA-50SL-25RM	25	50	25	0，4，8
25FA-55SL-20RM	25	55	20	0，4，8
25FA-60SL-15RM	25	60	15	0，4，8
30FA-45SL-25RM	30	45	25	0，4，8
30FA-50SL-20RM	30	50	20	0，4，8
30FA-55SL-15RM	30	55	15	0，4，8
30FA-60SL-10RM	30	60	10	0，4，8

Fig.3 20FA-55SL-15RM solidified soil specimen

Fig. 4 Stress-strain curves of solidified soil specimen

Fig.5 7 d UCS of solidified soil specimen with various mix proportion

Fig.6 Correlation coefficient matrix diagram

Fig.7 T2 spectra of 20FA-60SL-20RM specimen

Fig.8 Pore size distribution of 20FA-60SL-20RM specimen

Fig.9 SEM images of 20FA-60SL-20RM solidified soil specimen under various magnifications

Fig.10 SEM image and EDS point scan diagram of 20FA-60SL-20RM solidified soil specimen

Fig.11 XRD pattern of 20FA-60SL-20RM solidified soil specimen

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