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Y. Zeng

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Characterization workflow and open dataset for fresh, physical, and mechanical properties

Although air lime is a carbonatable binder with high carbon sink potential, reproducible research remains hindered by the limited availability of lime-oriented standards and openly accessible datasets. These limitations prevent the consolidation of fundamental knowledge and reinforce the perception of lime mortars as highly variable and empirical materials. This study addresses this gap by implementing a FAIR-aligned (Findable, Accessible, Interoperable, Reusable) and reproducible workflow for the characterization of air lime-containing mortars. Four mixtures were monitored for up to 364 days to assess fresh, physical, and mechanical properties under defined conditions. All experimental metadata and datasets are openly published in a structured repository. Results show that air lime-containing mixtures exhibited longer setting times, higher open porosity, greater carbonation depths, and lower compressive strength. Length change measurements indicate hydration-carbonation interactions, particularly in lime-cement systems. By combining experimental characterization with a FAIR-aligned and reproducible workflow, this work supports more transparent, resource-efficient research practices. ...
Journal article (2026) - Yu Chen, Yao Li, Yiqun Xue, Zhipeng Li, Yu Zeng, Xusheng Chen, Yilin Zhao, Yamei Zhang
Seawater-mixed concrete for 3D printing offers a promising solution for marine infrastructure construction in coastal and island regions facing shortages of freshwater and labor. However, the high chloride concentration in seawater accelerates the initial setting of concrete, thereby hindering pumping and extrusion in one-component (1 K) printing. The two-component (2 K) printing approach, which combines retarded cementitious mixtures with aluminate-based accelerators, enables set-on-demand behavior and provides a potential solution for seawater-based printing. Nevertheless, the early-age behavior of seawater-mixed cementitious materials incorporating aluminate-based accelerators, such as aluminum sulfate (A$) and calcium aluminate cement with anhydrite (CAC-C$), remains largely unexplored, particularly regarding their interactions with seawater ions and Portland cement. This study systematically investigates the structural build-up and early-age hydration of seawater-mixed cementitious materials incorporating A$- and CAC-C$-based acceleration slurries. Structural build-up was quantified using constant shear rate rheometry, while water state evolution, hydration kinetics, and phase assemblages were characterized using low-field 1H NMR, isothermal calorimetry, thermogravimetric analysis, and X-ray diffraction. The results demonstrate that ettringite (AFt) precipitation governs structural build-up in both systems due to its high water-binding capacity and voluminous needle-like morphology. Seawater significantly enhances AFt formation in the A$-based system, leading to rapid stiffening but a narrowed printability window. In contrast, seawater initially suppresses AFt formation in the CAC-C$ system due to delayed sulfate dissolution and the preferential formation of Friedel’s salt; this effect is transient, and AFt formation resumes at later ages. Consequently, the CAC-C$ system exhibits superior robustness and greater suitability for seawater-mixed concrete 2 K printing. ...
Municipal solid waste incineration (MSWI) bottom ash (BA) is widely available and has been increasingly explored for sustainable concrete production. While it is commonly used in Ordinary Portland Cement (OPC)-based concrete, its application in alkali-activated concrete (AAC) remains rare. This study developed a new AAC using MSWI BA as coarse aggregate to evaluate whether this represents a more sustainable application pathway compared to its use in conventional concrete. To address issues associated with metallic aluminum (Al) in MSWI BA, a NaOH-based pre-treatment was applied to reduce its content and minimize surface cracking and volume expansion in AAC. The incorporation of treated MSWI BA increased the overall porosity of AAC. The interfacial transition zone (ITZ) surrounding MSWI BA exhibited characteristic microstructural features. While previous studies suggested that MSWI BA-induced porosity may enhance freeze-thaw resistance in OPC concrete, the opposite trend was observed in AAC. The increased pore volume, irregular pore shapes, and MSWI BA-related microcracking reduced freeze-thaw durability. Despite these challenges, the developed AAC retained mechanical performance within strength class C30/37 and achieved a substantially lower carbon footprint compared to OPC and CEM III/B concretes. Leaching assessments further confirmed that the developed AAC complied with environmental standards and did not release harmful contaminants. Overall, these findings demonstrate that MSWI BA is a promising coarse aggregate for AAC. ...
Journal article (2025) - Yu Chen, Yu Zeng, Minfei Liang, Shan He, Oğuzhan Çopuroğlu
Adding hydrated lime (CH) into blended cement incorporating high volume of Supplementary Cementitious Materials (SCMs) is a viable method to provide the necessary calcium hydroxide for the pozzolanic reaction, thereby improving the mechanical performance at later stages. However, the effects of relatively small dosages of CH on the rheological properties and resulting microstructure of limestone-calcined clay cement (LC3) remain unclear. This paper aims to investigate the influence of a small CH addition on the fresh and hardened properties of LC3 systems, in which Portland cement is largely replaced (80 wt%) by limestone and calcined clay. The results indicate that the additional CH notably reduces the water film thickness, leading to increased dynamic yield stress, plastic viscosity and re-flocculation. A delay in the elasticity development and static yield stress evolution within the first 1.5 h was observed with the addition of 2.5 wt% CH, attributed to the initial dissolution of CH, which is mitigated by using 10 wt% CH. Furthermore, additional CH accelerated early-age hydration and facilitated long-term pozzolanic reactions, resulting in the increased amount of C-(A)-S-H gel and AFm phases, and reduced porosities after 7 and 28 days. These chemical effects could well compensate the high air void content caused by the high viscosity, and therefore contributes to mortars with higher compressive strengths than plain LC3 at later ages. ...
Recent studies have been focusing on the carbon sink potential of carbonatable binders as an attempt to reduce CO2 levels. Air lime is a carbonatable binder that fully relies on CO2 absorption to harden and, thus, offers great carbon sink potential. Yet, CO2 absorption is favoured only after the evaporation of the excess water. Therefore, this study investigated the behaviour of air lime-containing mortars regarding water retention and evaporation. Four groups (with different contents of air lime) were monitored for up to 91 days after curing. Results showed that higher contents of air lime yielded greater water retention capacity. Yet, water retention did not prevent the carbonation front from further advancing – especially within lime-cement groups. In this case, greater porosity proved to be an open door for the simultaneous evaporation and ingress of CO2. Thus, hero or villain? It depends on the mixture. ...

Current measurement methods and limitations

Given the crucial role of carbonation in the hardening of lime-based binders, accurate measurements of carbonation depths are essential for analysing both carbonation kinetics and carbon sequestration capabilities. This study employed both the conventional phenolphthalein spray method and the profile-based method to determine carbonation depths in four types of binders. Unlike the distinct carbonation front observed in cementitious materials, lime-based binders displayed a transition zone between fully carbonated and uncarbonated areas. Meanwhile, the remaining portlandite content in some specimens did not necessarily increase with depth, and typical Liesegang patterns were observed. Compared to phenolphthalein spray method, profile-based methods provide more quantitative evidence for further analyses, but inevitable slice interval can also lead to errors in carbonation depth estimation. Therefore, developing a more precise and convenient method remains essential for a deeper understanding of the carbonation behaviour in lime-based binders. ...