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Journal of Zhejiang University SCIENCE A
ISSN 1673-565X(Print), 1862-1775(Online), Monthly
2023 Vol.24 No.10 P.898-911
Geo-environmental properties and microstructural characteristics of sustainable limestone calcined clay cement (LC3) binder treated Zn-contaminated soils
Abstract: Limestone calcined clay cement (LC3) is an environment-friendly and sustainable cementitious material. It has recently gained considerable attention for the stabilization/solidification (S/S) of soils contaminated by heavy metals. However, the existing studies on S/S of Zn-contaminated soils using LC3 in terms of hydraulic conductivity and microstructural properties as compared to ordinary Portland cement (OPC) are limited. This study focuses on the evaluation of the mechanical, leaching, and microstructural characteristics of Zn-contaminated soils treated with different contents (0%, 4%, 6%, 8%, and 10%) of low-carbon LC3. The engineering performance of the treated Zn-contaminated soils is assessed over time using unconfined compressive strength (UCS), hydraulic conductivity (k), toxicity characteristic leaching procedure (TCLP), and synthetic precipitation leaching procedure (SPLP) tests. Experimental results show that the UCS of Zn-contaminated soils treated with LC3 ranged from 1.47 to 2.49 MPa, which is higher than 1.63%–13.07% for those treated with OPC. The k of Zn-contaminated soils treated with LC3 ranged from 1.16×10-8 to 5.18×10-8 cm/s as compared to the OPC treated samples. For the leaching properties, the leached Zn from TCLP and SPLP is 1.58–321.10 mg/L and 0.52–284.65 mg/L as the LC3 contents ranged from 4% to 10%. Further, the corresponding pH modeling results indicate that LC3 promotes a relatively suitable dynamic equilibrium condition to immobilize the higher-level Zn contamination. In addition, microscopic analyses demonstrate that the formations of hydration products, i.e., Zn(OH)2, Zn2SiO4, calcium silicate hydrate (C–S–H), calcium silicate aluminate hydrate (C–A–S–H) gel, ettringite, and CaZn(SiO4)(H2O), are the primary mechanisms for the immobilization of Zn. This study also provides an empirical formula between the UCS and k to support the application of LC3-solidified Zn-contaminated soils in practical engineering in the field.
Key words: Limestone calcined clay cement (LC3); Stabilization/solidification (S/S); Zn-contaminated soils; Microstructural characteristics
机构：1中山大学，土木工程学院，广东省海洋土木工程重点实验室，中国广州，510275，中国；2南方海洋科学与工程广东省实验室（珠海），中国珠海，519082；3四川轻化工大学，土木工程学院，中国自贡，643002；4东南大学，交通学院，中国南京，211189
目的：传统水泥材料普通硅酸盐水泥（OPC）处置总金属污染土面临高碳排及长期环境安全性的问题。本文旨在利用新型低碳探讨多尺度的形式获取新型绿色低碳固化剂石灰石煅烧粘土水泥（LC3）修复锌污染土的关键环境岩土工程参数，揭示LC3固化稳定化锌污染土的微观机理。
创新点：1.探明LC3固化多浓度梯度Zn污染土的物理化学特性、力学强度和环境安全性特征规律；2.揭示LC3固化土重金属固定及强度增长的关键机理。
方法：1.通过无侧限抗压强度（UCS）和渗透试验，获取LC3固化多浓度梯度Zn污染土的力学参数发展规律（图3）；2.通过毒性特征浸出试验（TCLP）和合成沉降浸出试验（SPLP），得到LC3固化剂符合毒性浸出安全指标的浓度（图6）；3.采用X射线衍射（XRD）、扫描电子显微镜-能谱仪（SEM-EDS）等微观测试技术，明确LC3固化Zn污染土的微观机理（图7和8）。
结论：1.证明了LC3替代OPC处理锌污染土壤的可行性；2.LC3和OPC固化污染土的UCS和渗透率k之间为负增长关系；3.LC3固化土壤中的锌离子及提高污染土强度的主要取决于水化产物的形成。
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DOI:
10.1631/jzus.A2200531
CLC number:
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On-line Access:
2023-10-18
Received:
2022-11-06
Revision Accepted:
2023-01-26
Crosschecked:
2023-10-19