Strength and Expansion Properties of Hydrated Lime-Solidified CFB Ash-Slag-Based Controlled Low-Strength Material

doi:10.16552/j.cnki.issn1001-1625.2026.0216

Abstract

Abstract:

Controlled low-strength material （CLSM） was prepared through the synergistic activation of hydrated lime and circulating fluidized bed fly ash and slag （CFB ash-slag）. To clarify the development behavior， influencing factors， and mechanism of expansion properties in hydrated lime-solidified CFB ash-slag-based CLSM， the effects of ash-slag ratio， hydrated lime content， and water dosage on the unconfined compressive strength and linear expansion rate of the hardened CLSM specimens were investigated. XRD， SEM， and thermogravimetric analyses were employed to characterize the reaction products and elucidate their mechanisms. The results show that， within the tested range， the 28 d unconfined compressive strength reaches a maximum of 7.7 MPa at an ash-slag ratio of 40∶60， while increasing the ash-slag ratio causes only a slight rise in the linear expansion rate. Hydrated lime content is identified as the most significant factor. In the range from 0% to 25%， both the unconfined compressive strength and linear expansion rate of the hardened CLSM specimens increase markedly with increasing hydrated lime content. When the hydrated lime content increases from 0% to 5%， the 28 d unconfined compressive strength increases from 0.7 MPa to 6.2 MPa， and the linear expansion rate increases from 0% to 1.0%，showing the most remarkable growth. Increasing the water dosage significantly reduces the linear expansion rate of the hardened CLSM specimens； when the water dosage increases from 590 kg/m³ to 650 kg/m³， the linear expansion rate decreases by 62.5%. Microstructural analysis indicates that the main hydration products formed in the hydrated lime-solidified CFB ash-slag system are ettringite （AFt）， calcium silicate hydrate （C-S-H） gel， and hydrated calcium silicate aluminate （C-A-S-H） gel. AFt is mainly generated at the early stage， whereas the gel phases continue to develop at later ages. An increase in water dosage leads to a looser structure and higher porosity， thereby weakening both the strength and expansion properties of the hardened CLSM specimens.

Key words: CFB ash-slag, hydrated lime, controlled low-strength material, alkali-activation, compressive strength, expansion property

CLC Number:

U414

PENG Shuang, GAO Peng, ZHOU Mingkai, XUE Xiu, WANG Yuqiang, QIN Zhiqing. Strength and Expansion Properties of Hydrated Lime-Solidified CFB Ash-Slag-Based Controlled Low-Strength Material[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(9): 3140-3150.

Figures/Tables 17

Table 1 Main chemical composition of CFBFA

Composition	Al₂O₃	SiO₂	SO₃	CaO	Fe₂O₃	MgO	LOI	f-CaO	Anhydrite
Mass fraction/%	23.5	34.7	9.1	16.5	4.0	0.7	11.3	0.39	8.66

Fig.1 XRD pattern of CFBFA

Table 2 Particle gradation of raw CFBS

Sieve size/mm	9.50	4.75	2.36	1.18	0.60	0.30	0.15
Cumulative residue mass fraction/%	0	9	21	35	49	75	84

Fig.2 SEM image of CFBS

Table 3 Main chemical composition of CFBS

Composition	SiO₂	Al₂O₃	Fe₂O₃	CaO	MgO	SO₃	LOI	f-CaO	Anhydrite
Mass fraction/%	46.6	29.3	3.6	7.1	0.6	6.4	3.7	3.6	4.0

Fig.3 XRD pattern of CFBS

Table 4 Mix proportion of hydrated lime-solidified CFB ash-slag CLSM

Group	Mass fraction/%			Water content/（kg·m^-3）	W/S
Group	CFBFA	CFBS	Hydrated lime content	Water content/（kg·m^-3）	W/S
A30S70	30	70	15	620	0.62
A40S60	40	60	15	620	0.62
A50S50	50	50	15	620	0.62
L0	40	60	0	620	0.62
L1	40	60	1	620	0.62
L3	40	60	3	620	0.62
L5	40	60	5	620	0.62
L15	40	60	15	620	0.62
L25	40	60	25	620	0.62
W590	40	60	15	590	0.59
W620	40	60	15	620	0.62
W650	40	60	15	650	0.65

Fig.4 Unconfined compressive strength and linear expansion ratio of hardened CLSM specimens with different ash-slag ratios

Fig.5 Unconfined compressive strength and linear expansion ratio of hardened CLSM specimens with different hydrated lime content

Fig.6 28 d unconfined compressive strength and linear expansion ratio of hardened CLSM specimens with different hydrated lime content

Fig.7 XRD patterns and TG-DSC curves of hardened CLSM specimens with different hydrated lime content

Fig.8 SEM image and EDS elemental analysis of hardened CLSM specimen of L5 group at 28 d

Fig.9 XRD patterns of hardened CLSM specimen of L5 group at 7 and 28 d

Fig.10 Unconfined compressive strength and linear expansion ratio of hardened CLSM specimens with different water content

Fig.11 TG-DSC curves of 28 d hardened CLSM specimens with different mixing water content

Fig.12 SEM images of hydration products of hardened CLSM specimens at 28 d under different water content

Fig.13 SEM images and EDS elemental analysis of hardened CLSM specimen in W620 group

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