The Preparation And Application Of Bio-microcapsules

Microbe is a good repairing agent for concrete cracks, as some bacteria are able to metabolize calcium ion and excrete lime carbonate to fill the fracture. So self-healing concrete could be made by embedding microencapsules which contained these bacteria inside. In consideration of biocompatibility, the shell materials of bio-microcapsules are normally selected from natural polymers, such as algin, chitin, glutin, etc. Unfortunately, all the polymers are hydrophilic, can be dissolved or swellen in water, hence not suitable for application in the self-healing concrete. In this thesis, epoxy E-51 was empolyed as shell material in the formation of water-proof bio-mcroencapsules, and Koch’s bacillus DSM6307 was contained as core material in the bio-mcroencapsules. The effect on spores’ activity of microencapsulation was studied. In succession, the self-healing process of the encapsulated spores was examined. It’s found these microcapsules can be easy mixed with cement slurry to form concrete without spore germination. This result is very important for realization of ―biological self-healing concrete‖.To keep the spores in dormancy, the microencapsulation must be carried out without the incooperation of water. In this thesis, an o/o suspension method was proposed to make the bio-microencapsule, where o/o means both continuous phase and dispersed phase were oil. The process was as follows: spores, germinant and nutritions were granulated with carrier material, the particles were then soaked in epoxy resin, pre-cured for bodying till the resin can enwrapped on the particle surface stickily, transfer these particles into polydimettlylsiloxane, agitated for dispersal and heated for the further consolidation. Once the shell hardened, the microencapsule was formed. Systemic experiments shows, the conditions, such as core/wall ratio, stirring rate, curing agent, pre-curing time, secondary curing temperature etc, effect on microencapsules. The optimal process parameters are: core/wall ratio=1:1, stirring rate =300rpm, curing agent= DMP-30, dose: 10g/100 g E-51, pre-curing time=40 mins, curing temperature = 50℃, 2nd curing time = 2~3 hrs. After microencapsulation, spores survival rate reaches to 90%. There were no change observed after the microcapsules soaked in water for 1 week, indicating the epoxy shell is very good at watertightness.Compression tests shows, the epoxy E-51 shelled bio-microcapsules can be triggered mechanically for spores release in common Portland cement matrix. Self-healing experiments, in which Koch’s bacillus DSM6307 was cultivated in a concrete crack at 37℃, makes clear the spores after microencapsulation are highly active in crack-repairing. Only in 30 days, a 100mm-width crevice was almost filled out by the bacteria with calcium carbonate metabolite.