多层复配微胶囊的制备及其在混凝土裂缝自修复中的应用

Preparation of multi-layer compound microcapsules and their application in self-healing of concrete cracks

摘要:

混凝土广泛应用于房屋土建工程以及道路桥梁等，其开裂问题一直是工程界的一大难题。为了开发有效、可行的混凝土修复技术，本研究结合微生物技术与微胶囊技术采用锐孔法制备了一种多层复配微胶囊，并以微胶囊的包埋率与机械性能为评价标准，优化了微胶囊的配方和干燥方式。而后表征了微胶囊钙转结晶过程以及产物晶型，并与游离细胞钙转过程进行对比。最后，测试了微胶囊的掺入对试件的机械性能、抗渗性能以及自修复效果的影响。结果表明：配方为蜡样芽胞杆菌湿菌体1.0%、氯化钙1.5%、海藻酸钠3.0%、营养物质5.0%、丙三醇6.0%、壳聚糖0.6%、尿素2.0%的风干多层复配微胶囊，其包埋率为95.3%，破裂力为59.7 N，硬度为150.8 N。该微胶囊能够在囊内的微生物发生钙转反应时，由固态转变为流动的胶态。微胶囊与游离细胞钙转反应产生的碳酸钙都是较稳定的方解石晶型，但微胶囊产的颗粒大小更加均匀，更有利于在裂缝中累积，从而增强修复的稳固性。将微胶囊投入混凝土试件，当掺量为0.45%时，试件的抗折强度提高了17.3%，试件的抗压强度提高了12.3%。在抗渗水试验中，添加了微胶囊的试件较掺入游离细胞的试件对水泥混凝土有更好的抗渗性补偿。裂缝自修复效果证明多层复配微胶囊能够对0.7 mm宽度以下的裂缝实现完全修复，对0.8 mm宽度裂缝修复率为95%。本研究开发了一种能够在混凝土中保护微生物并提供其生长所需营养的多层复配微胶囊，为微生物诱导碳酸钙沉淀在混凝土裂缝修复提供了新的思路。

关键词:微生物矿化;混凝土;多层微胶囊;蜡样芽胞杆菌;自修复;钙转结晶

Abstract:

Concrete is widely used in building construction, civil engineering, roads, bridges, etc., but concrete cracking remains a major issue in the engineering industry. To develop an effective and feasible concrete repair technology, this study combined microbial and microencapsulation technologies to prepare a multi-layer compound microcapsule using the piercing method. The formulation and drying method of microcapsules were optimized by taking their embedding rate and mechanical properties as evaluation criteria. The calcium transcrystallization process of microcapsules and the crystal form of products were characterized and compared with the calcium transcrystallization process in free cells. Finally, the effects of microcapsule incorporation on mechanical properties, impermeability, and self-healing performance of concrete specimens were then tested. The results showed that the air-dried multi-layer compound microcapsules, formulated with 1.0% wet cells of Bacillus cereus, 1.5% calcium chloride, 3.0% sodium alginate, 5.0% nutrients, 6.0% glycerol, 0.6% chitosan, and 2.0% urea, achieved an embedding rate of 95.3%, a rupture force of 60.0 N and a hardness of 150.8 N. These microcapsules can transform from a solid state to a flowing colloidal state when the microorganisms inside undergo a calcium formation reaction. Both the microcapsules and free cells produced stable calcite crystal forms of calcium carbonate through the calcium conversion reaction, with the microcapsules producing more uniform-sized particles, which are more conducive to accumulation in cracks, thereby enhancing the stability of repair. When microcapsules were incorporated into the concrete specimen at a content of 0.45%, the flexural strength of the specimen increased by 17.3%, and the compressive strength increased by 12.3%. In the water impermeability test, specimens with microcapsules demonstrated better impermeability compensation for the cement concrete than those with free cells. The self-healing effect of cracks proved that multi-layer compound microcapsules could completely repair cracks up to 0.7 mm wide, and a repair rate of 95% for 0.8 mm wide cracks. In this study, a multi-layer compound microcapsule was developed to protect microorganisms in concrete and provide nutrients required for their growth, which provided a new idea for microbial induced calcium carbonate precipitation in concrete crack repair.

Key words:microbial mineralization;concrete;multi-layer microcapsules;Bacillus cereus;self-healing;calcium transcrystallization