Effect of SAP on Autogenous Shrinkage and Thermodynamic Properties of Alkali-Activated Foam Concrete

doi:10.16552/j.cnki.issn1001-1625.2026.0127

Abstract

Abstract:

Alkali-activated foam concrete （AAFC） possesses multiple advantages， including low density， high strength， and excellent thermal insulation. However， its inherent susceptibility to shrinkage cracking remains a critical drawback that hinders widespread practical application. This study systematically investigated the effects of the morphology and water absorption/release behavior of superabsorbent polymer （SAP） on the workability， autogenous shrinkage， compressive strength， and thermal conductivity of AAFC using ground granulated blast-furnace slag as the primary binder. The underlying mechanisms were elucidated through thermogravimetric analysis （TG）， scanning electron microscopy （SEM）， low-field ¹H nuclear magnetic resonance （¹H NMR）， and capillary pressure measurements. The results demonstrate that the addition polyacrylate SAP （SAP-A）， characterized by a high-water absorption capacity and irregular morphology， significantly increases the yield stress and plastic viscosity of the paste， markedly raises the proportion of pores larger than 500 μm in diameter， and ultimately leads to a 30.5% reduction in the 28 d compressive strength of AAFC compared to the control group without SAP. In contrast， the incorporation of acrylic acid-acrylamide copolymer SAP （SAP-M）， which exhibits a moderate water absorption capacity and spherical structure， facilitates uniform dispersion of bubbles. This optimizes the pore structure， thereby enabling the steady development of strength while reducing the thermal conductivity of AAFC to 0.089 W/（m·K）. Furthermore， SAP-M rapidly releases its absorbed water after final setting， achieving a 32.6 percentage point higher cumulative water release at 3 d compared to SAP-A. This behavior effectively alleviates the development of capillary pressure and enhances the autogenous shrinkage mitigation efficiency by 28.7%.

Key words: alkali-activated foam concrete, superabsorbent polymer （SAP）, autogenous shrinkage, compressive strength, thermal conductivity, microstructure

CLC Number:

TU528.2

LI Mingming, JIANG Dongbing. Effect of SAP on Autogenous Shrinkage and Thermodynamic Properties of Alkali-Activated Foam Concrete[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(8): 2686-2698.

Figures/Tables 16

Table 1 Main chemical composition of GGBS

Chemical composition	CaO	SiO₂	Al₂O₃	MgO	SO₃	Na₂O	Fe₂O₃	Other	LOI
Mass fraction/%	30.54	33.98	18.80	12.24	2.11	0.67	0.20	0.40	1.06

Fig.1 Micromorphology and particle size distribution of SAP

Table 2 Foaming agent parameters

Parameter	Dilution multiple	Foaming multiple	Bleeding water/g	Settlement distance/mm	Half-life/h
Value	1∶60	20.6	39.4	2.0	8.5

Table 3 Synthetic parameters of SAP-M

Sample No.	AA mass/g	NaOH mass/g	AM mass/g	KPS mass/g	MBA mass/g	Span60 mass/g	HJW volume/mL
SAP-M	0.600	0.250	5.400	0.054	0.006	2.772	90

Fig.2 Absorption capacities of SAP in different solutions and macroscopic images after water absorption

Table 4 Mix proportion of AAFC

Sample No.	Mass/kg
Sample No.	GGBS	NaOH	Na₂SiO₃	Water	Foam	SAP-A	SAP-M
C	351.60	20.22	110.46	63.16	52.74	—	—
CSA	351.60	20.22	110.46	63.16	52.74	1.76	—
CSM	351.60	20.22	110.46	63.16	52.74	—	1.76

Fig.3 Rheology of alkali-activated pastes with SAP and fluidity of AAFC

Fig.4 Effect of SAP on setting time of AAFC

Fig.5 Effect of SAP on autogenous shrinkage of AAFC

Fig.6 Effect of SAP on compressive strength and thermal conductivity of AAFC

Fig.7 TG/DTG curves of AAFC cured 28 d

Table 5 Mass loss of C（N）-A-S-H gels （Mg）， hydrotalcite-like phases （Mh） and CaCO3 （Mc） in each sample

Sample No.	Mass loss/%
Sample No.	Mg （50~250 ℃）	Mh （275~425 ℃）	Mc （600~900 ℃）
C	13.97	5.48	3.07
CSA	13.29	5.34	2.65
CSM	13.91	5.63	1.78

Fig.8 Effect of SAP on pore structure of AAFC

Fig.9 SEM images of SAP-modified AAFC

Fig.10 Evolution law of T2 distribution and signal fractions of different types of water versus hydration time for alkali-activated pastes

Fig.11 SAP on capillary pressure of AAFC

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