Effects of Calcium Sulfate Whiskers on Hydration and Microstructure of Fly Ash-Cement Composites

doi:10.16552/j.cnki.issn1001-1625.2026.0080

Abstract

Abstract:

The high-value co-utilization of solid waste has become an important way to promote the green and low-carbon development of cement-based materials. This paper investigated the effects of 1%， 3%， and 5% （mass fraction） calcium sulfate whiskers on the microstructure， hydration reaction， and mechanical properties of fly ash-cement composites. Experimental results show that the addition of 1% calcium sulfate whiskers promote the hydration reaction of aluminate phases and the formation of ettringite， thereby optimizing the microstructure density and mechanical properties of fly ash-cement composite materials. However， when the calcium sulfate whisker content over 1%， with the increase of calcium sulfate whisker content， the excessive sulfate ions lead to the formation of a large amount of expansive ettringite in the later stage， causing cracks in the microstructure and thus reducing the strength of fly ash-cement composite materials. Comprehensive analysis shows that calcium sulfate whiskers exhibit optimal performance at 1% content in the fly ash-cement composite material system. This study provides a theoretical basis for the design of calcium sulfate whiskers in fly ash-cement composite materials.

Key words: calcium sulfate whisker, fly ash, fly ash-cement composite material, hydration, microstructure

CLC Number:

TU528

ZHANG Wencong, BAO Qinfan, WANG Yuqiu, MAN Baoliang, HUANG Guo, GUO Rongxin. Effects of Calcium Sulfate Whiskers on Hydration and Microstructure of Fly Ash-Cement Composites[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(7): 2428-2437.

Figures/Tables 12

Fig.1 Particle size distribution， XRD patterns， and SEM image of raw materials

Table 1 Chemical composition of raw material

Material	Mass fraction/%
Material	SiO₂	Al₂O₃	SO₃	CaO	TiO₂	Fe₂O₃	MgO	LOI^a
Cement	20.74	5.54	3.91	59.74	1.26	4.12	2.68	2.01
Fly ash	52.04	23.56	0.83	4.67	3.42	11.02	1.30	3.16
Gypsum	0.06	0.03	54.00	38.70	—	—	0.09	7.12
CSW	0.09	0.03	56.89	42.86	—	—	0.02	0.11

Table 2 Proportion of mixture

Sample No.	Mass fraction/%
Sample No.	Cement	Fly ash	CSW	Gypsum	Water
OPC	100	0	0	0	50
FA30	70	30	0	0	50
FA30-W1	70	30	1	0	50
FA30-W3	70	27	3	0	50
FA30-W5	70	25	5	0	50
FA30-G3	70	27	0	3	50

Fig.2 Compressive strength of samples at different ages

Fig.3 Linear relationship between compressive strength and accumulated hydration heat at 7 d of samples

Fig.4 Effects of different mineral admixtures on hydration heat of cement paste

Fig.5 Hydration heat and cumulative hydration heat of mixed paste normalized to cement

Fig.6 TG-DTG curves of samples at different ages

Fig.7 CH and Wb content of samples at different ages

Fig.8 XRD patterns of samples after 28 d of curing

Fig.9 FTIR spectra of samples after 28 d of curing

Fig.10 SEM images of samples after 28 d of curing

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