Performance and Strength Formation Mechanism of High Dosage Phosphogypsum-Cement-Curing Agent Stabilized Crushed Stone Base Layer Material

doi:10.16552/j.cnki.issn1001-1625.2025.0660

Abstract

Abstract:

This study investigated the use of high dosages of phosphogypsum in combination with cement and a self-developed curing agent for the stabilization of graded crushed stone， with the objective of preparing pavement base layer material. The study encompassed a comprehensive investigation into the effects of varying dosages of cement， phosphogypsum and curing agent on the unconfined compressive strength and pavement performance of base layer material at various ages. The hydration mechanism and microscopic properties of the materials were investigated by XRD， FTIR， SEM-EDS and other testing method， and its leaching toxicity was also tested. The results indicate that increasing the mass ratio of cement to phosphogypsum enhances the mechanical properties of the base layer material. Moreover， the mechanical properties of the base layer material are further optimised through the incorporation of a geopolymer curing agent， self-developed， replacing 20%（mass fraction， the same below） of the cement. The 7 d unconfined compressive strength is selected as the evaluation index， and the optimal mix ratio of high dosage phosphogypsum-cement-curing agent stabilized crushed stone base layer material is determined by combining this with the actual engineering requirements. The proposed optimal mix ratio is 35% phosphogypsum + 4% cement + 1% ternary alkali activated curing agent + 60% graded crushed stone， and the ratio of 7， 28 and 60 d unconfined compressive strengths increases by 69.2% （reaches 6.6 MPa）， 106.7% （reaches 9.3 MPa） and 88.3% （reaches 11.3 MPa）， respectively， in comparison with the control group without a curing agent. The primary hydration products are calcium silicate hydrate （C-S-H） gel and ettringite （AFt）， which are formed by the hydration of cement. The alkaline curing agent not only activated the cement but also reacted with the Ca²⁺ from the phosphogypsum via a pozzolanic reaction， further promoting the formation of C-S-H and calcium silicate （aluminate） hydrate （C-（A）-S-H） gels， the collective formation of these gels contributes to the overall strength of the base layer material. In addition， the toxic leaching concentrations of F^-， PO $4 3 -$ ， and heavy metal elements in base layer material are in accordance with the current standards established by China for sewage discharge.

Key words: phosphogypsum, road base, curing agent, hydration characteristic, unconfined compressive strength, formation mechanism

CLC Number:

U414

HE Zhaoyi, ZOU Meng, YAO Qiwen, CAO Dongwei, QIN Meng. Performance and Strength Formation Mechanism of High Dosage Phosphogypsum-Cement-Curing Agent Stabilized Crushed Stone Base Layer Material[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(1): 346-358.

Figures/Tables 17

Fig.1 Macro and micro morphology of raw materials

Table 1 Chemical composition of PG and cement

Material	Mass fraction/%
Material	SO₃	CaO	SiO₂	F	P₂O₅	Al₂O₃	Fe₂O₃	Na₂O	MgO	Other
PG	52.64	38.36	4.15	1.73	1.51	0.57	0.21	0.21	0.19	0.43
Cement	1.25	54.43	22.71	—	—	9.86	4.75	0.86	2.28	3.86

Fig.2 XRD patterns of raw materials

Fig.3 Moisture content of PG versus time

Fig.4 Particle size distribution of PG

Table 2 Gradation design of aggregates

Sieve aperture size/mm	19.00	16.00	13.20	9.50	4.75	2.36	1.18	0.60	0.30
Pass rate of each sieve aperture in gradation design/%	100	90.5	81.0	65.5	40.0	24.8	14.5	8.0	1.5

Table 3 Mix proportions of high dosage phosphogypsum stabilized crushed stone base layer material without curing agent

Number	Mass fraction/%			Cement-PG mass ratio
Number	Graded crushed stone	Cement	PG	Cement-PG mass ratio
A1	80.0	5.0	15.0	1∶3
A2	80.0	4.0	16.0	1∶4
A3	80.0	3.3	16.7	1∶5
A4	80.0	2.9	17.1	1∶6
A5	80.0	2.5	17.5	1∶7
A6	80.0	2.2	17.8	1∶8
A7	80.0	2.0	18.0	1∶9
A8	70.0	7.5	22.5	1∶3
A9	70.0	6.0	24.0	1∶4
A10	70.0	5.0	25.0	1∶5
A11	70.0	4.3	25.7	1∶6
A12	70.0	3.8	26.3	1∶7
A13	70.0	3.3	26.7	1∶8
A14	70.0	3.0	27.0	1∶9
A15	60.0	10.0	30.0	1∶3
A16	60.0	8.0	32.0	1∶4
A17	60.0	6.7	33.3	1∶5
A18	60.0	5.7	34.3	1∶6
A19	60.0	5.0	35.0	1∶7
A20	60.0	4.4	35.6	1∶8
A21	60.0	4.0	36.0	1∶9
A22	50.0	12.5	37.5	1∶3
A23	50.0	10.0	40.0	1∶4
A24	50.0	8.3	41.7	1∶5
A25	50.0	7.1	42.9	1∶6
A26	50.0	6.3	43.7	1∶7
A27	50.0	5.6	44.4	1∶8
A28	50.0	5.0	45.0	1∶9

Table 4 Mix proportion of high dosage phosphogypsum stabilized crushed stone base layer material with curing agent

Number	Curing agent type	Mass fraction/%
Number	Curing agent type	Graded crushed stone	Actual cement	Curing agent	PG
B0（control group）	—	60.0	5.0	0	35.0
B1	CA1	60.0	4.0	1.0	35.0
B2	CA1	60.0	3.0	2.0	35.0
B3	CA1	60.0	2.0	3.0	35.0
B4	CA1	60.0	1.0	4.0	35.0
B5	CA1	60.0	0.0	5.0	35.0
B6	CA2	60.0	4.0	1.0	35.0
B7	CA2	60.0	3.0	2.0	35.0
B8	CA2	60.0	2.0	3.0	35.0
B9	CA2	60.0	1.0	4.0	35.0
B10	CA2	60.0	0.0	5.0	35.0

Table 5 Proctor compaction test results of samples

Number	Optimum water content/%	Maximum dry density/（g·cm^-3）
A1	7.08	2.245
A2	7.45	2.233
A3	7.72	2.217
A4	7.93	2.209
A5	8.21	2.201
A6	8.52	2.197
A7	8.69	2.191
A8	9.54	2.154
A9	9.67	2.135
A10	9.81	2.118
A11	10.07	2.101
A12	10.23	2.087
A13	10.43	2.069
A14	10.60	2.053
A15	11.33	1.989
A16	11.60	1.976
A17	11.94	1.959
A18	12.20	1.948
A19	12.37	1.941
A20	12.49	1.926
A21	12.62	1.923
A22	13.68	1.804
A23	13.88	1.782
A24	14.01	1.760
A25	14.25	1.741
A26	14.48	1.728
A27	14.60	1.723
A28	14.75	1.712
B1	11.71	2.077
B2	11.67	2.080
B3	11.59	2.086
B4	11.55	2.091
B5	11.48	2.099
B6	11.74	2.073
B7	11.68	2.079
B8	11.63	2.083
B9	11.58	2.086
B10	11.51	2.095

Fig.5 Unconfined compressive strength of samples without curing agent at 7， 28 and 60 d

Fig.6 Unconfined compressive strength of samples with curing agent at 7， 28 and 60 d

Fig.7 Splitting strength of samples

Fig.8 Dry shrinkage test results of samples

Fig.9 FTIR spectra of samples at 28 d

Fig.10 XRD patterns and quantitative analysis of samples at 28 d

Fig.11 SEM-EDS images of samples at 28 d

Table 6 Leaching toxicity of raw PG and samples and related standard limits

Sample	Leaching concentration/（mg·L^-1）
Sample	F^-	PO $4 3 -$	Pb²⁺	Cr⁶⁺	Total Cr	As³⁺	Ba²⁺	Ni²⁺
Raw PG	144.143	315.923	0.019	—	0.046	1.628	0.069	0.054
B0	8.878	0.257	0.018	—	0.037	0.012	0.031	0.008
B1	7.120	0.196	0.012	—	0.041	0.003	0.033	0.013
B6	5.434	0.085	—	—	0.023	—	0.019	0.008
GB 8978—1996（Class A）	10.0	0.5	1.0	0.5	1.5	0.5	—	1.0
GB 5085.3—2007	100	—	5	5	15	5	100	5

Table 6 Leaching toxicity of raw PG and samples and related standard limits

Sample	Leaching concentration/（mg·L^-1）
Sample	F^-	PO $4 3 -$	Pb²⁺	Cr⁶⁺	Total Cr	As³⁺	Ba²⁺	Ni²⁺
Raw PG	144.143	315.923	0.019	—	0.046	1.628	0.069	0.054
B0	8.878	0.257	0.018	—	0.037	0.012	0.031	0.008
B1	7.120	0.196	0.012	—	0.041	0.003	0.033	0.013
B6	5.434	0.085	—	—	0.023	—	0.019	0.008
GB 8978—1996（Class A）	10.0	0.5	1.0	0.5	1.5	0.5	—	1.0
GB 5085.3—2007	100	—	5	5	15	5	100	5

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