Sulfate Erosion Resistance of Composite Alkali-Reducing Modified Ecological Porous Concrete

doi:10.16552/j.cnki.issn1001-1625.2025.1298

Abstract

Abstract:

In order to improve the service durability of ecological porous concrete （EPC） in a sulfate dry-wet cycling environment， a composite alkali-reduction system was established using diatomaceous earth （DE）， oxalic acid （OA） and ferric sulfate （FS）. EPC specimens with different alkalinity gradients were prepared， and the evolution of macroscopic property and the variation of microstructure under sulfate dry-wet cycles were systematically investigated. The macroscopic deterioration behavior of EPC was characterized by relative compressive strength and mass loss rate， while hydration products and microstructural features were analyzed by XRD， FTIR， and SEM. The results show that moderate alkali reduction significantly improves the sulfate erosion resistance of EPC. Among the specimens， the group with 1.2% （mass fraction） OA-FS composite system （pH=9.0 to 10.0） still maintains the highest relative compressive strength （72.59%） after 24 sulfate dry-wet cycles. Microstructural characterization shows that the DE-OA-FS composite system optimizes the pore structure and chemical stability of EPC by promoting the formation and structural stabilization of C-S-H gel， slowing the rapid consumption of Ca（OH）₂， and inhibiting the concentrated precipitation of sulfate-attack products such as ettringite （AFt）， thereby delaying the process of crack propagation and carbonation-induced deterioration. The findings provide a technical reference for durability optimization design and engineering applications of EPC in complex aggressive environments.

Key words: ecological porous concrete, sulfate dry-wet cycle, alkalinity gradient, macroscopic mechanical property, microstructure

CLC Number:

TU528

OUYANG Qi, YIN Jian, LI Sijiao, CHEN Yihao, QIN Yuhang, ZENG Yi. Sulfate Erosion Resistance of Composite Alkali-Reducing Modified Ecological Porous Concrete[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(7): 2290-2298.

Figures/Tables 10

Table 1 Chemical composition of OPC and DE

Material	Mass fraction/%
Material	CaO	SiO₂	Al₂O₃	SO₃	Fe₂O₃	MgO	Na₂O
OPC	62.55	21.89	5.58	2.89	2.86	2.26	0.83
DE	—	≥85.00	≤3.35	—	≤1.30	—	—

Table 2 Properties of chemical admixtures

Name	Molecular formula	Molecular weight	Standard value	Property
OA	C₂H₂O₄·2H₂O	90.034 9	≥99.5	White crystalline powder
FS	Fe₂（SO₄）₃·7H₂O	399.88	21.0~23.0	Light yellow powder

Table 3 Mix ratio of EPC under different alkalinity gradients and compressive strength at 28 d

Sample No.	Mix ratio/（kg·m^-3）								28 d compressive strength/MPa
Sample No.	Alkali gradient	Aggregate	Cement	DE	Water	SP	OA	FS	28 d compressive strength/MPa
B	11.0~12.0	1 533	438	―	110	―	―	―	7.9
A1	10.0~11.0	1 533	443	38.5	120	1.44	2.4	2.4	11.2
A2	9.0~10.0	1 533	443	38.5	120	1.44	6.0	6.0	13.5
A3	8.0~9.0	1 533	443	38.5	120	1.44	9.6	9.6	14.7

Fig.1 Relative compressive strength of EPC with different alkalinity gradients under sulfate dry-wet cycle action

Fig.2 Mass loss rate of EPC with different alkalinity gradients under sulfate dry-wet cycle action

Fig.3 XRD patterns of EPC with different alkalinity gradients under sulfate dry-wet cycle action

Fig.4 FTIR spectra of EPC with different alkalinity gradients under sulfate dry-wet cycle action

Fig.5 SEM images of EPC before sulfate dry-wet cycle action

Fig.6 SEM images of group B samples after 12 times of sulfate dry-wet cycle action

Fig.7 SEM images of group A2 samples after 24 times of sulfate dry-wet cycle action

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