Effects of Red Mud-Based Composite Hydration Seeds on Properties of Portland Cement Mortar

doi:10.16552/j.cnki.issn1001-1625.2025.1317

Abstract

Abstract:

To enhance the efficient resource utilization of red mud in cement-based materials， this study prepared red mud-based composite hydration seeds （RM-CAW） via acid leaching pretreatment combined with hydrothermal synthesis， and incorporated them into cement mortar to systematically investigate their effects on cement hydration behavior， microstructure， and mechanical properties. Mechanical performance tests together with X-ray diffraction（XRD）， thermogravimetric analysis（TG）， scanning electron microscopy（SEM）， and specific surface area and pore size distribution analyses were conducted to elucidate the strengthening mechanism of RM-CAW. The results indicate that the incorporation of RM-CAW significantly improves the mechanical properties of cement mortar at both 7 and 28 d. In particular， compared with reference cement mortar， the mortar with 5.0%（mass fraction） RM-CAW （HARM-5.0） specimen exhibits increases of 11.1% and 6.9% in flexural strength and compressive strength at 28 d， respectively. The addition of RM-CAW promotes the formation of hydration products such as calcium silicate hydrate（C-S-H）， has a pronounced improvement in the interfacial transition zone and an overall densification of the matrix， and promotes pore structure refinement and a reduction in the proportion of large pores.

Key words: red mud, red mud-based composite hydration seed, ordinary Portland cement, humic acid, hydrothermal synthesis, resource utilization

CLC Number:

TQ172

LI Fuyun, HUANG Shengjing, JIAO Weili, DENG Xiaowei, CHEN Chunheng, WEI Chi, LAI Fang, LI Jing. Effects of Red Mud-Based Composite Hydration Seeds on Properties of Portland Cement Mortar[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(7): 2237-2249.

Figures/Tables 18

Table 1 Main chemical composition of RM and cement

Sample	Mass fraction/%
Sample	CaO	SiO₂	Al₂O₃	SO₃	Fe₂O₃	MgO	Na₂O
RM	15.61	15.35	17.53	1.16	29.68	0.18	10.40
Cement	59.23	15.80	3.30	3.35	2.65	2.41	0.26

Table 2 Mix ratio of cement mortar

Sample	Mass/g
Sample	Cement	Sand	Water	RM-CA	RM-CAW
RCM	450	1 350	225	0	0
ARM-2.5	450	1 350	225	11.25	0
ARM-5.0	450	1 350	225	22.50	0
ARM-7.5	450	1 350	225	33.75	0
HARM-2.5	450	1 350	225	0	11.25
HARM-5.0	450	1 350	225	0	22.50
HARM-7.5	450	1 350	225	0	33.75

Fig.1 XRD patterns of RM， RM-CA， and RM-CAW

Fig.2 FT-IR spectra of RM， RM-CA， and RM-CAW

Fig.3 SEM images of raw red mud and RM-CAW

Fig.4 EDS images of RM-CA and RM-CAW

Table 3 Comparison of Zeta potential between RM and RM-CAW at different pH values

Sample	Zeta potential（pH=11）/mV	Zeta potential（pH=13）/mV
RM	-48.25	-27.03
RM-CAW	-52.57	-29.38

Fig.5 Fluidity of different cement mortars

Fig.6 Mechanical properties of different cement mortars

Fig.7 XRD patterns of RCM-28 d， ARM-5.0-28 d， and HARM-5.0-28 d samples

Fig.8 TG and DTG curves of RCM and HARM-5.0 curing for 28 d

Table 4 Mass loss of RCM-28 d and HARM-5.0-28 d at different temperature ranges

Temperature/℃	Mass loss（RCM-28 d）/%	Mass loss（HARM-5.0-28 d）/%
50~300	4.252 5	6.288 5
420~470	1.078 2	2.197 0
580~780	1.825 2	3.014 4

Fig.9 SEM images of different cement mortars curing for 28 d

Fig.10 Adsorption-desorption isotherms and pore size distribution curves of RCM-28 d， ARM-5.0-28 d， and HARM-5.0-28 d samples

Table 5 BJH desorption average pore size of three types of cement mortars

Sample	BJH desorption average pore size/nm
RCM-28 d	21.406 3
ARM-5.0-28 d	24.304 3
HARM-5.0-28 d	19.037 6

Fig.11 Distribution diagrams of pore volume distribution of three types of cement mortars

Fig.12 Mechanism diagram of red mud modified by humic acid

Fig.13 Schematic diagram of RM-CAW as nucleation site of hydration products

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