Ion Transport and Mineral Phases Composition Evolution in Recycled Aggregate Concrete with Fly Ash-Metakaolin Exposed to Mg2+-SO42--Cl- Solution

doi:10.16552/j.cnki.issn1001-1625.2025.0945

Abstract

Abstract:

Saline soils widely distributed in western China contain aggressive ions of magnesium， sulfate and chloride， severely threatening the durability of recycled aggregate concrete （RAC） structures. A solution simulating the primary aggressive media of these soils—comprising 7.5% MgSO₄， 7.5% Na₂SO₄， and 5.0% NaCl （mass fraction）— was utilized for RAC salt attack experiments. Water-soluble contents of magnesium， sulfate， chloride， and calcium， and pH values were measured by solid-liquid extraction， potentiometry， and chemical titration methods to investigate the effect of metakaolin replacement ratio on ion content and transport behavior. Analysis of mineral composition of exposed RAC elucidates evolutionary patterns and influencing mechanisms. Results indicate that aggressive ion contents increase gradually with higher metakaolin replacement ratios， whereas calcium content and pH values decrease continuously. At equivalent exposure times， chloride exhibites the widest migration range within RAC， compared to the most restricte migration shown by magnesium. Changes in calcium concentration and pH are significantly influenced by magnesium and sulfate diffusion. Higher metakaolin replacement ratios result in a rapid decrease in the mineral composition of insoluble corrosion products and an increase in that of soluble corrosion products. Prolonged exposure times and greater exposure depths cause the mineral composition of corrosion products to transform from simple to complex， followed by progressive simplification. Simplified mineral compositon of corrosion products， or those consisting solely of hydration product phases， is observed in RAC subjected to either short-term exposure time or deeper exposure depths.

Key words: recycled aggregate concrete, saline soil envoronment, Mg²⁺- $S O 4 2 ? -$ -Cl^- erosion, replacement ratio of metakaolin, ions transport, mineral composition

CLC Number:

TU528

LIU Dongming, YANG Guanfei, ZHU Huiguo, WANG Jiabin, HAN Huiyang. Ion Transport and Mineral Phases Composition Evolution in Recycled Aggregate Concrete with Fly Ash-Metakaolin Exposed to Mg²⁺-SO₄^2--Cl^- Solution[J]. BULLETIN OF THE CHINESE CERAMIC SOCIETY, 2026, 45(4): 1282-1295.

Figures/Tables 14

References 34

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Cementitious material	Mass fraction/%
Cementitious material	CaO	SiO₂	Al₂O₃	Fe₂O₃	MgO	Na₂O	K₂O	P₂O₅	SO₃	MnO	Cl	R₂O
Cement	64.77	18.90	4.66	3.38	2.18	1.28	0.97	0.48	3.75	0.05	0.05	0.35
Fly ash	6.98	50.95	29.01	4.21	1.10	2.97	2.03	0.93	1.37	0.07	0.06	1.87
Metakaolin	1.44	45.05	40.32	2.80	0.13	0.13	0.16	0.09	0.06	—	—	2.21

Cementitious material	Mass fraction/%
Cementitious material	CaO	SiO₂	Al₂O₃	Fe₂O₃	MgO	Na₂O	K₂O	P₂O₅	SO₃	MnO	Cl	R₂O
Cement	64.77	18.90	4.66	3.38	2.18	1.28	0.97	0.48	3.75	0.05	0.05	0.35
Fly ash	6.98	50.95	29.01	4.21	1.10	2.97	2.03	0.93	1.37	0.07	0.06	1.87
Metakaolin	1.44	45.05	40.32	2.80	0.13	0.13	0.16	0.09	0.06	—	—	2.21

Aggregate type	Water absorption/%		Needle and flake particle content/%	Crushing index/%
Aggregate type	8 h	24 h	Needle and flake particle content/%	Crushing index/%
Natural coarse aggragate	0.45	0.56	4.90	6.10
RCA	4.50	5.40	3.45	11.51

Aggregate type	Water absorption/%		Needle and flake particle content/%	Crushing index/%
Aggregate type	8 h	24 h	Needle and flake particle content/%	Crushing index/%
Natural coarse aggragate	0.45	0.56	4.90	6.10
RCA	4.50	5.40	3.45	11.51

Mixture	Mass fraction/%
Mixture	Cement	FA	MK	Sand	Natural coarse aggregate	RCA	Water	Water reducer
F0P0	443	0	0	717	569	506	155	5.54
F20P10	310	89	44	704	559	497	155	5.54
F15P15	311	66	66	705	560	498	155	5.54
F10P20	310	44	89	706	561	499	155	5.54

Ion Transport and Mineral Phases Composition Evolution in Recycled Aggregate Concrete with Fly Ash-Metakaolin Exposed to Mg²⁺-SO₄^2--Cl^- Solution

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		Replacement ratio of fly ash-metakaolin				Dry-wet cycle				Exposure depth/mm
		F0P0	F20P10	F15P15	F10P20	0	30	90	180	2	4	10	20	30
Aggragate	A	√	√	√	√	√	√	√	√	√	√	√	√	√
	C	√	√	√	√	√	√	√	√	√	√	√	√	√
	D	√	√	√	√	√	√	√	√	√	√	√	√	√
	Q	√	√	√	√	√	√	√	√	√	√	√	√	√
Hydrationproducts	P	√				√	√					√	√	√
	Ms					√								√
	Z					√
	Es					√							√	√
Insolublecorrosionproducts	E_f	√	√				√	√	√		√	√
	F	√	√				√	√	√		√	√
	G	√	√	√				√	√	√	√
	N	√	√	√	√		√	√	√	√	√	√
	Y							√			√	√
Solublecorrosionproducts	Gl			√	√
	H			√	√
	K	√	√	√	√		√	√	√	√	√	√
	L	√	√	√	√			√	√	√	√

		Replacement ratio of fly ash-metakaolin				Dry-wet cycle				Exposure depth/mm
		F0P0	F20P10	F15P15	F10P20	0	30	90	180	2	4	10	20	30
Aggragate	A	√	√	√	√	√	√	√	√	√	√	√	√	√
	C	√	√	√	√	√	√	√	√	√	√	√	√	√
	D	√	√	√	√	√	√	√	√	√	√	√	√	√
	Q	√	√	√	√	√	√	√	√	√	√	√	√	√
Hydrationproducts	P	√				√	√					√	√	√
	Ms					√								√
	Z					√
	Es					√							√	√
Insolublecorrosionproducts	E_f	√	√				√	√	√		√	√
	F	√	√				√	√	√		√	√
	G	√	√	√				√	√	√	√
	N	√	√	√	√		√	√	√	√	√	√
	Y							√			√	√
Solublecorrosionproducts	Gl			√	√
	H			√	√
	K	√	√	√	√		√	√	√	√	√	√
	L	√	√	√	√			√	√	√	√