Estudo da biomineralização aplicada a argamassas de construção civil e sua viabilidade tecnológica PirassunungaPalavras-chave: Concreto, fissuras, bactérias, biomineralização, hidrogéis.

The biomineralization technique of crack remediation in construction mortar can be achieved through the incorporation of calcifying bacteria within the mortar matrix. However, the thermal and autogenous shrinkage associated with the hydration of cement can be detrimental to the survival of the bacterial spores. Encapsulation of the spores in a matrix such as superabsorbent hydrogels, specifically sodium alginate, can provide protection from such detrimental conditions while also serving as a water reservoir for the metabolic activity of the bacterial cells. This paper investigated the addition of sodium alginate capsules prepared through spherification in construction mortars, aiming to preserve and optimize rheological, physical and mechanical properties, and to release bacteria when cracks occur. Mortar formulations with capsules containing Lysinibacillus sphaericus were calculated in order to maintain the granulometric distribution of standard formulation, thus obtaining products with excellent rheological, physical and mechanical properties, and allowing the addition of up to 1% capsules. Multivariate analysis of variance was applied at each age, showing that formulations with capsules kept the same properties as the original formula. After cracking, it was possible to observe the action of the released bacteria, through the formation of crystalline structures at the cracks. The capsules were prepared through a simple and cheap process, and it was proved that not only they do not affect concrete properties, but also are effective in both protecting the bacteria during mixing and hardening and releasing it after cracking.

Concrete used in civil engineering is a composite obtained from the combination of coarse and fine aggregates, cement and water, and its cost and quality are normally associated to the proportion of its constituents (ceramic formulation), as well as the reduction of water consumption. The aggregates used in concrete may have diverse origins, and the syenite extracted at Pedra Branca Alkaline Massif is one of the materials that can be used for this substitution. In order to do so, a reference formulation of concrete was calculated and optimized using the mathematical models of Andreasen, and syenite was added substituting 25, 50, 75 and 100% of the fine aggregate. In order to maintain the original granulometric distribution, an algorithm was developed to compensate the different particle size distributions. The grain size correction guaranteed the maintenance of the original properties of the concrete, reaching values of mechanical strength above 35 MPa.

The use of calcium carbonate for closing cracks in concrete by the action of biomineralizing bacteria has been investigated. However, these bacteria are fragile and susceptible to the reaction medium, and they must be protected by encapsulation, until the moment they must carry out the biomineralization process. This research covered the study and optimization of the production of sodium alginate capsules for subsequent encapsulation of biomineralizing bacteria. The research also investigated the effect of these capsules (added in different percentages) in concrete masses using a CP II – E Portland cement (ABNT NBR Standard), formulated from the Andreassen equation. The samples were characterized in their fresh and hardened state. The swelling tests indicated that the sodium alginate capsules provided good conditions to receive the bacteria, to keep them alive and to be mixed in the concrete, presenting enough mechanical strength. Among the investigated conditions, the composition formulated using the Andreassen coefficient equal to q=0.37 and with the addition of 1.5% of sodium alginate capsules was the one that presented the most promising results; and after 28 days of curing, the mechanical strength to compression was 45.4 MPa, with the value within ABNT NBR 11578, since it establishes a minimum of 32 MPa.