Mechanisms of encapsulation of bacteria in self-healing concrete: review

Abstract

Fissures in concrete structures result from structural deterioration and inadequate building processes, among other factors. Traditional in situ repair is often expensive and complex. For this reason, self-healing techniques have been developed, such as the use of bacteria that precipitate calcium carbonate and seal fissures. However, adding bacteria directly to the concrete matrix reduces bacterial survival. We present a review of different methods of bacterial encapsulation and their effects on fissure repair and concrete resistance. We argue that encapsulation of Bacillus subtilis in clay is the most promising method for this type of concrete, increasing concrete strength by 12% and repairing fissures of up to 0.52 mm.

A review of the efficiency of self-healing concrete technologies for durable and sustainable concrete under realistic conditions

“…Bacteria are susceptible in their enzymatic and metabolic activity to changes in pH and temperature, the presence of salts or acids, or cold climates. The survival of bacteria inserted in cement matrices is a concern [48,208] and deserves more intense research efforts. However, there are indications that spores can survive in extreme conditions for a long time [197,200,209].…”

Performance of Capsules in Self-Healing Cementitious Material

“…Hence, autonomous healing, which can be achieved by adding cementing materials, microorganisms, or other healing agents that react chemically with the cementitious matrix, has been suggested and studied as a potential remedy [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 ]. The encapsulation of the healing agents has been used to protect microorganisms from the harsh conditions during mixing and cement hydration, and to protect cementitious and polymeric materials from early activation [ 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ]. The capsules, which are in most cases spherical in shape and range from μm to mm [ 56 ], can be effective in sealing and/or healing cracked concrete, provided they are uniformly distributed [ 41 ] and are bonded to the cement paste, and the crack opening is limited to 200 μm [ 20 ].…”

Relationship between Bacterial Contribution and Self-Healing Effect of Cement-Based Materials

“…At first, some researchers practiced the addition of sporogenic bacteria directly into cement paste, but they quickly realized that the number of active cells was reduced to a minimum due to the influence of unfavourable environmental conditions [ 7 , 56 ]. Briefly, adding bacteria and nutrients directly to the concrete matrix can improve some mechanical properties, but bacterial survival was between 1.9 and 7% after 10 days of curing [ 70 ]. This could have occurred due to different environmental impacts, such as long-term stress on cells which started immediately after addition to concrete, but also might be a consequence of the unpredictable and highly variable hydration of cement.…”