硅酸盐学报

偏高岭土对再生水泥碳化反应活性的影响及其机理

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温小栋 ¹ , 季启龙 ¹ , 冯蕾 ¹ , 高小建 ² , 江源 ¹

硅酸盐学报 | 低碳水泥与固废资源化利用专题—研究论文 2026,54(5): 1576-1592

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硅酸盐学报 |低碳水泥与固废资源化利用专题—研究论文 2026 , 54 (5) : 1576 -1592

偏高岭土对再生水泥碳化反应活性的影响及其机理

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温小栋¹, 季启龙¹, 冯蕾¹, 高小建², 江源¹

作者信息

^1．宁波工程学院建筑与交通工程学院，浙江宁波 315211

^2．哈尔滨工业大学土木工程学院，哈尔滨 150090

通讯作者:

江源（1992—），男，博士。

作者简介:

温小栋（1976—），男，博士，教授。

Effect of Metakaolin on Carbonation Reactivity of Recycled Cement

Xiaodong WEN¹, Qilong JI¹, Lei FENG¹, Xiaojian GAO², Yuan JIANG¹

Affiliations

^1.School of Civil and Transportation Engineering, Ningbo University of Technology, Ningbo 315211, Zhejiang, China

^2.School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

Corresponding Author:

JIANG Yuan (1992-), male, Ph.D. E-mail: yuan.jiang@nbut.edu.cn

WEN Xiaodong (1976-), male, Ph.D., Professor. E-mail: Wenxiaodong8@163.com

出版时间: 2025-08-26 doi: 10.14062/j.issn.0454-5648.20250380

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摘要

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利用再生水泥制备固碳胶凝材料为绿色建筑发展提供了新的方向，但其较低的碳化反应活性和力学性能依然是制约其广泛应用的关键技术瓶颈。基于此，本工作引入偏高岭土（MK）对该体系进行改性，系统评价了不同MK掺量对煅烧活化再生水泥浆体的碳化行为、碳化程度及微观结构的影响。结果表明：掺入10%（质量分数）MK显著提高了材料的抗压强度及碳化程度，7 d碳化后的强度及碳化程度较对比组分别提升了119.2%和70.0%，这一提升主要归因MK的火山灰活性及其对孔结构和碳化反应动力学的积极影响。MK因其高火山灰活性和层片状结构加速了水化及碳化产物的生成，并推动了亚稳态碳酸钙向稳定晶相方解石的形成，同时促进了碳酸钙的均匀沉积，从而有效填充了基体中较大的孔隙。在7 d碳化后，10% MK掺量使样品的毛细孔占比从49.88%显著降低至36.56%，而凝胶孔占比则由8.98%提升至17.81%，形成了更加致密的微观结构。然而，过量（20%）掺入MK虽进一步细化了孔隙，但28 d碳化程度（51.72%）略低于10%掺量组（52.88%），表明过度致密化可能会抑制CO₂的后期扩散，从而限制最终的碳化效率。本工作表明，适量的MK掺入能够显著提升再生水泥材料的碳化反应、微观结构及力学性能，为新型绿色固碳水泥的开发提供了科学依据。

关键词

偏高岭土 / 再生水泥 / 碳化 / 微观机理

Abstract

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Introduction

The construction industry is a primary contributor to global CO₂ emissions, making the development of novel low-carbon building materials a critical scientific and engineering challenge. A promising strategy involves the valorization of waste concrete fines, which are generated in vast quantities. The thermal activation of these fines at 600-800 ℃ transforms the hydrated cement paste into a recycled cement rich in dicalcium silicate (i.e., β-C₂S), a clinker phase with a high intrinsic carbonation reactivity. This makes thermally activated recycled cement an ideal precursor for carbon-sequestering materials where CO₂ is utilized as a curing agent to enhance mechanical properties. However, its practical application is hindered by a key technical bottleneck, i.e., relatively low reaction kinetics and insufficient mechanical strength development. Therefore, identifying an effective modifier to stimulate its carbonation potential and optimize the final microstructure is of significant urgency. Metakaolin (MK) as a highly reactive pozzolan is a promising candidate due to its known ability to promote hydration and serve as a nucleation site. This study was to systematically investigate the role of MK as a synergistic component to overcome the performance limitations of carbonated recycled cement, providing a scientific basis for the development of high-performance, green building materials.

Methods

The raw materials used were a waste concrete powder (WCP) and a commercial metakaolin (MK). A thermally activated recycled cement (TARCP) was produced via first pressing a mixture of WCP and MK (0%, 10%, and 20% by mass, denoted as TARCP, MK10, and MK20, respectively) and then calcining it in a muffle furnace at 800 ℃ for 1 h. After cooling and grinding, the resulting powders were mixed with water at a water-to-binder ratio of 0.55 to prepare paste specimens. The pastes were cast and cured for 24 h before being demolded and subjected to one of two curing regimes for 7 d and 28 d, i.e., (1) water curing (25 ℃, 75% RH) and (2) accelerated carbonation curing (25 ℃, 75% RH, 20% CO₂).

The compressive strength of 20 mm cubic specimens was tested at each age. The phase evolution was comprehensively characterized by X-ray diffraction (XRD) with Rietveld quantitative analysis, Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). The pore structure distribution was analyzed by low-field nuclear magnetic resonance spectroscopy (NMR). The microstructure and morphology of the reaction products were determined by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX).

Results and discussion

The experimental results demonstrate that the incorporation of an optimal amount of MK significantly enhances the performance of the carbonated recycled cement. The addition of 10% MK (MK10) yields the optimum results, with the 7-d compressive strength under carbonationof 37.7 MPa, which is increased by 119.2%, compared to the carbonated control sample (TARCP). This superior performance is attributed to a combination of physical and chemical effects induced by MK.

The phase analysis reveals that MK accelerates the consumption of the primary reactive phase like β-C₂S. After 7-d carbonation, the β-C₂S content in the sample MK10 is reduced to just 1.2%, compared to 29.8% in the TARCP control. This accelerated reaction leads to a much higher degree of carbonation. The 7-d carbonation degree for the sample MK10 is 50.79%, which is improved by 70%, compared to the sample TARCP (i.e., 29.87%). Furthermore, the MK promotes the transformation of metastable vaterite to the thermodynamically stable calcite. At 7 days, the sample MK10 is overwhelmingly composed of calcite (i.e., 72.7%), with only a negligible amount of vaterite (1.6%), whereas the sample TARCP contains a significant amount of vaterite (i.e., 8.5%). The FTIR analysis indicates the formation of a highly polymerized amorphous silica-alumina gel in the carbonated MK-modified systems, which is evidenced by the shift of the main Si—O vibration band to a higher wavenumber (~1080 cm^-1), indicating a fundamental restructuring of the silicate network.

The microstructural analysis provides the strengthening mechanism. The NMR results show that the addition of 10% MK significantly refines the pore structure. After 7-d carbonation, the proportion of large capillary pores (i.e., >50 nm) in the MK10 sample decreases from 49.88% (in the sample TARCP) to 36.56%, while the proportion of fine gel pores (i.e., <10 nm) nearly increases from 8.98% to 17.81%. This pore refinement, which is driven by the uniform deposition of carbonation products, results in a much denser matrix, which is the primary reason for the observed strength enhancement. However, the effect of MK is non-linear. An excessive dosage of 20% MK (the sample MK20), while further refining the pore structure (the capillary of pores reduces to 29.75% at 7 d), resulting in lower compressive strength than the sample MK10 at all ages. This is accompanied by a slightly lower final degree of carbonation at 28 d (51.72% for the sample MK20 vs. 52.88% for the sample MK10). This indicates that the excessive pore refinement can create a dense, impermeable microstructure that impedes the diffusion of CO₂ gas into the material core, thereby limiting the overall reaction rate and extent in the later stages. Moreover, the anomaly of lower strength despite a denser pore structure in the sample MK20 increases that the intrinsic properties of the solid phases play a critical role. It is hypothesized that the higher Al/Si ratio in the sample MK20 leads to the formation of an amorphous alumina-silica gel with a lower degree of polymerization, possessing the inferior intrinsic mechanical properties, compared to the gel formed at an optimal Al/Si ratio.

Conclusions

This study demonstratesd that incorporating an optimal amount of metakaolin (10% by mass) could be a highly effective strategy for enhancing the carbonation reactivity and mechanical performance of thermally activated recycled cement. The improvements could be attributed to the synergistic effects of MK, i.e., accelerating the consumption of β-C₂S, promoting the formation of stable calcite, and refining the pore structure via creating a denser, more uniform microstructure. However, an excessive dosage of MK (20%) could be detrimental. It led to a further pore densification, this could inhibit a later-stage CO₂ diffusion, limiting the final carbonation degree. Furthermore, the higher Al/Si ratio could negatively affect the intrinsic strength of the amorphous binder phase. These findings could highlight the non-linear effect of metakaolin and provide a scientific basis for optimizing the design of high-performance, carbon-sequestering building materials derived from recycled cement.

Key words

metakaolin / recycled cement / carbonation / microstructural mechanism

引用本文

温小栋, 季启龙, 冯蕾, 高小建, 江源. 偏高岭土对再生水泥碳化反应活性的影响及其机理. 硅酸盐学报, 2026 , 54 (5) : 1576 -1592 . DOI: 10.14062/j.issn.0454-5648.20250380

Xiaodong WEN, Qilong JI, Lei FENG, Xiaojian GAO, Yuan JIANG. Effect of Metakaolin on Carbonation Reactivity of Recycled Cement[J]. Journal of the Chinese Ceramic Society, 2026 , 54 (5) : 1576 -1592 . DOI: 10.14062/j.issn.0454-5648.20250380

基金

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浙江省“尖兵领雁+X”研发攻关计划(2024C03826-SD2)
宁波市重点研发项目(2023Z148; 2024Z258)

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2026年第54卷第5期

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文章信息

doi: 10.14062/j.issn.0454-5648.20250380

接收时间：2025-05-13
首发时间：2026-09-20
出版时间：2025-08-26

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收稿日期：2025-05-13
修回日期：2025-07-17

基金

浙江省“尖兵领雁+X”研发攻关计划(2024C03826-SD2)

宁波市重点研发项目(2023Z148; 2024Z258)

作者信息

^1．宁波工程学院建筑与交通工程学院，浙江宁波 315211

^2．哈尔滨工业大学土木工程学院，哈尔滨 150090

通讯作者:

江源（1992—），男，博士。

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https://castjournals.cast.org.cn/joweb/gsyxb/CN/10.14062/j.issn.0454-5648.20250380

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2种不同金属材料的力学参数

科 Family	属数 Number of genus	种数 Number of species	占总种数比例 Percentage of total species (%)	属 Genus	种数 Number of species	占总种数比例 Percentage of total species (%)
鹅膏菌科Amanitaceae	2	11	5.26	鹅膏菌属 Amanita	10	4.78
小菇科 Mycenaceae	2	12	5.74	丝盖伞属 Inocybe	5	2.39
多孔菌科 Polyporaceae	8	14	6.70	蜡蘑属 Laccaria	5	2.39
红菇科 Russulaceae	3	23	11.00	小皮伞属 Marasmius	6	2.87
				小菇属 Mycena	11	5.26
				光柄菇属 Pluteus	5	2.39
				红菇属 Russula	17	8.13
				栓菌属 Trametes	5	2.39

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