Potencial de autocicatrização dos materiais cimentícios promovida pela biomineralização de carbonato de cálcio por diferentes linhagens bacterianas em uma matriz com ar incorporado

Abstract

Historical data and future projections indicate a growing use of concrete worldwide, while its production and that of other cementitious composites is linked to a large consumption of inputs and energy. Cracking is a constant pathological manifestation in these materials, contributing to the deterioration of buildings and causing various damages. In this scenario, studies seek to provide cementitious materials the ability to self-heal their cracks, with some of them focused on the use of bacteria for this purpose. It is common to encapsulate bacteria for protection against the aggressiveness of the cementitious matrix, and recent publications suggest incorporating air pores into the matrix to serve as protection for bacteria. Thus, this study seeks to evaluate different bacterial strains, collected in the metropolitan region of Porto Alegre - RS, isolated and molecularly identified, regarding their potential for the formation of healing products in a mortar with incorporated air. Optical microscopy was performed to verify the occurrence of self-healing, in addition to scanning electron microscopy (SEM) associated with energy dispersive X-ray spectroscopy (EDS) for morphological and elemental characterization of the crystals, and X-ray diffraction (XRD) for its mineralogical characterization. The influence of different strains on the compressive strength of the mortar was verified. The isolation steps performed resulted in the obtaining of 6 distinct isolates, characterized as belonging to the genera Bacillus, Pseudomonas, Cronobacter and Citrobacter. All isolates provided an increase in compressive strength compared to air-entrained and bacteria-free mortar, with increases between 10 and 108% at 28 days. Regarding the analysis by optical microscopy, 1 of the isolates showed no formation of healing products, while the others showed healing between 7 and 14 days of analysis, but only in the lower regions of the specimens, in addition to an observed loss of part of the crystals formed. XRD and EDS analyzes indicate that the crystals are calcite, being visualized by SEM calcite, but also aragonite. The results indicate that all isolates were able to promote selfhealing and that their encapsulation in incorporated air bubbles was effective.