High-volume CO2 capture, utilization and alkali-silica reaction mitigation in lightweight concrete through artificial aggregates–a case study with carbonated wollastonite granules

The production of artificial aggregates for concrete production by mineral carbonation is a promising way to utilize large quantities of CO2. In this study, porous artificial aggregates based on wollastonite were manufactured, carbonated and used as fine and coarse aggregates in the production of lightweight concrete. Strength, chemical properties and their effect on mortar and concrete were studied. Mortar bars containing 0–20 wt.% metakaolin were used to study alkali-silica reaction mitigation of the aggregates in Portland cement through expansion tests. The microstructural phase assemblage in the specimens was studied using scanning electron microscopy, thermogravimetry and X-ray diffraction. Thermodynamic modelling was used to ascertain the long-term effects of these aggregates. The study showed that 1000 kg aggregates stored 96 kg CO2, which could be improved with a more efficient carbonation process during manufacturing of the aggregates. During alkali–silica reaction mitigation with metakaolin, microstructural studies suggested similarity with limestone–calcined–clay cement (LC3) but also formation of Ca–modified silica gels due to excess amorphous silica. The aggregates were chemically stable in the concrete samples containing metakaolin, and no severe expansion was observed in mortar bar samples containing 10 and 20 % metakaolin. The study demonstrated that porous aggregates are promising for high volume CO2 capture and storage in lightweight concrete.

采用矿物碳酸化技术制备混凝土用人工骨料，是大规模资源化利用二氧化碳的极具潜力的方案。本研究以硅灰石（wollastonite）为原料制备多孔人工骨料，经碳酸化处理后分别作为细骨料与粗骨料应用于轻集料混凝土的生产，并对其力学性能、化学特性及其对砂浆与混凝土的影响展开了研究。本研究制备了掺量为0~20wt.%偏高岭土的砂浆试棒，通过膨胀试验探究该骨料在硅酸盐水泥体系中对碱硅酸反应（alkali-silica reaction）的抑制效果。采用扫描电子显微镜（scanning electron microscopy）、热重分析（thermogravimetry）与X射线衍射（X-ray diffraction）对试样的微观物相组成进行了表征分析，并借助热力学建模（thermodynamic modelling）手段研判了此类骨料的长期性能效应。研究结果表明，1000 kg该骨料可固存96 kg二氧化碳，通过优化制备过程中的碳酸化工艺效率，该固碳量可进一步提升。在通过偏高岭土抑制碱硅酸反应的过程中，微观结构研究显示，该体系与石灰石-煅烧黏土水泥（LC3）具有相似性，但同时因过量无定形二氧化硅的存在，生成了钙改性二氧化硅凝胶。在掺加偏高岭土的混凝土试样中，该骨料表现出良好的化学稳定性；且在掺加10%、20%偏高岭土的砂浆试棒试样中，未观测到显著膨胀现象。本研究证实，多孔人工骨料在轻集料混凝土中实现大规模二氧化碳捕集与固存方面具有良好的应用前景。