The effect of temperature on bacterial self-healing processes in building materials

This paper is focused on the bacterial induced calcitation for the crack healing. The bacteria applied for this purpose are from group which is adapted for growth in the high pH environment as a concrete in hydration phase and their metabolic activity leads to create of calcite. In this study, three different bacteria strains (Sporosarcina pasteurii, Bacillus cohnii, Bacillus pseudofirmus) were applied and the influence of various temperatures on their microbial properties was investigated. Our previous experiment indicated that one of the applied bacterial strain in spores form (Bacillus pseudofirmus) are able to survive the temperatures in the range from −20 °C to 140 °C. The xperiment described in this paper extends the previous study and determines the effect of different temperatures on the change in growth activity. In this experiment, bacterial activity was determined based on the change of absorbance in 640 nm by spectrophotometric measurements. The experiment was performed at optimal temperature (30 °C) and lower temperature (10 °C) and it used suitable broth for calcitation. The results showed that the beginning of metabolic activity was shifted by 40 to 50 hours. Only Bacillus cohnii showed different results because its metabolic activity was nearly zero at 10 °C

Applicability of Bio-Based Self-Healing Concrete in Central European Conditions: a Preliminary Study

Durability of concrete structures is significantly affected by the microcracks formation. The manual remediation of cracks is time consuming and financially challenging, thus research of the self-healing potential is a promising topic. The basic principle of the biological self-healing concrete is to fill the cracks with calcium carbonate, which is the product of metabolism of specific microorganisms, when they are supplied with appropriate nutrients and a source of calcium. The paper deals with cultivation of the selected microorganism – bacteria Bacillus pseudofirmus, determines its survival and viability in various difficult conditions simulating the production and final environment of the cementitious material and examines different possibilities of encapsulation of bacteria in protective carries, namely polyvinyl alcohol nanofibres and lightweight ceramic aggregates. The objective of this study was a preliminary evaluation of applicability of the investigated method in Central European conditions

Impact of the self-healing agent composition on material characteristics of bio-based self-healing concrete

This paper investigates the composition of the biological self-healing agent based on its impact on material characteristics of concrete. A direct addition of the agent – a mixture of bacterial spores and nutrients – into concrete matrix has been investigated by many studies in recent decades. Under certain conditions, the applied microorganisms proved to be able to produce CaCO3, and researchers used this biocalcification process to autonomously seal microcracks in concrete. Thus, this bio-based material could potentially heal itself and lead to a more durable and economic structure. However, it has been shown that the self-healing agent, especially the indispensable nutrients, can positively or negatively influence the material characteristics. In this study, some of the most suitable and frequently proposed nutrients (calcium lactate, calcium nitrate, calcium formate, urea, and yeast extract) were directly added into cement mortar during the mixing process and their impact on material characteristics – compressive strength, flexural strength, and rheology – was evaluated and compared. Results show that calcium nitrate, calcium formate, calcium lactate, and urea have generally a potential to increase the compressive strength, especially in early ages. In contrast, the applied dose of yeast extract resulted in a drastic drop of compressive strength when compared to the control series, thus further optimization of the concentration is needed. The flexural strength was affected rather negligibly by the proposed nutritional admixtures