Biomineralização em concretos de alto desempenho

Abstract

The use of cementitious materials has been worrying scientists and organizations around the world. The growing demand for minerals in concrete production is responsible for one-tenth of the global emission of CO2 (carbon dioxide). Cementitious materials, such as conventional concrete and mortar, are exposed to the formation of cracks, requiring repairs and/or reconstruction, and consequently, demanding more of mineral resources. Ultra-high-performance concretes, such as reactive powder concrete (RPC), since they do not contain coarse aggregate in its formulation and make use of differentiated additives, they allow the achievement of greater microstructural homogeneity and superior mechanical properties when compared to traditional concretes; however, they are not immune to the formation of fissures. There are several repair alternatives; however, most of them generate harmful products to humans and the environment. To overcome this situation, an alternative has been gaining notoriety in recent decades: the use of microorganisms in the process of self-healing cementitious matrices through the biomineralization of calcium carbonate (CaCO3). To better understand the phenomenology associated with the use of this technique and its applicability in ultra-high-performance concrete matrices, this research aims to investigate how processing variables related to the biomineralization process affect the self-healing process of these concretes. For this, sodium alginate capsules were produced and characterized and Lysinibacillus spharaericus bacteria were successfully encapsulated in sodium alginate. After characterization of the raw materials constituting the RCP, three formulations (with additions of 0.5%, 1.0% and 1.5% of capsules) and a reference (without addition of capsules) were characterized, proving that the addition of capsules does not significantly affect any of the properties of the concrete, either in the fresh and hardened state. The fluidity of the concrete remained high, without any kind of segregation; low voids index (5.0~5.5%) and water absorption (2.2~2.5%) were obtained for all formulations; the maximum values reached for compression and flexural strength after 28 days were 83 and 20.8 MPa, respectively. Specimens containing the encapsulated bacteria were mechanically tested and the fractured surface was analyzed by optical microscopy, where the biomineralization process was proven through the action of the bacteria after rupture of the capsules.