A Review on the Performance Evaluation of Autonomous Self-Healing Bacterial Concrete: Mechanisms, Strength, Durability, and Microstructural Properties

The development of cracks, owing to a relatively lower tensile strength of concrete, diverse loading, and environmental factors driving the deterioration of structures, is an inescapable key concern for engineers. Reparation and maintenance operations are thus extremely important to prevent cracks from spreading and mitigating the lifetime of structures. However, ease of access to the cracked zone may be challenging, and it also needs funds and manual power. Hence, autonomous sealing of cracks employing microorganisms into the concrete sans manual intervention is a promising solution to the dilemma of the sustainable improvement of concrete. ‘Ureolytic bacteria’, key organism species in rumen-producing ‘urease’ enzymes such as Bacillus pasteurii or subtilis—when induced—are capable of producing calcium carbonate precipitations into the concrete. As their cell wall is anionic, CaCO3 accumulation on their surface is extensive, and the whole cell, therefore, becomes crystalline and ultimately plugs pores and cracks. This natural induction technique is an environmentally friendly method that researchers are studying intensively. This manuscript reviews the application process of bacterial healing to manufacture autonomous self-healing bacterial concrete. Additionally, it provides a brief review of diverse attributes of this novel concrete which demonstrate the variations with the auto-addition of different bacteria, along with an evaluation of crack healing as a result of the addition of these bacteria directly into concrete or after encapsulation in a protective shell. Comparative assessment techniques for autonomous, bio-based self-healing are also discussed, accompanied by progress, potential, modes of application of this technique, and its resultant benefits in the context of strength and durability. Imperatives for quantitative sustainability assessment and industrial adoption are identified, along with the sealing of artificially cracked cement mortar with sand as a filling material in given spaces, as well as urea and CaCl2 medium treatment with Bacillus pasteurii and Sporosarcina bacteria. The assessment of the impact on the compressive strength and rigidity of cement mortar cubes after the addition of bacteria into the mix is also considered. Scanning electron microscope (SEM) images on the function of bacteria in mineral precipitation that is microbiologically induced are also reviewed. Lastly, future research scope and present gaps are recognised and discussed.

Development of Single-Phase Microbial Cementation Method and to Investigate its Efficacy on Bearing Capacity, UCS, and Permeability of Sandy Soils

Microbially induced calcite precipitation (MICP) is a method based on collaborative knowledge of microbiology, chemistry and geotechnical engineering. The objective of this study was to investigate the increase of the bearing capacity and the unconfined compressive strength (UCS) as well as the reduction of the permeability of sandy soil using MICP. Experiments were carried out using Bacillus Pasteurii, on three different types of sand. The admixture of bacterial culture and cementation (BCC) solution all-in-one with sand by single-phase injection was applied to induce cementation. Three samples of the selected sand were treated with varied concentrations of BCC solution, ranging from 0.05 to 0.2 L/kg, with a curing period of 3, 7 and 14 days. The test results indicated an enhancement of 55% in UCS for sand treated with a BCC content of 0.05 to 0.2 L/Kg and a reduction of 40% in permeability for untreated sand with an effective diameter of 0.5 mm treated with 0.2 L/kg of BCC solution after 14 days of curing. The results of a plate load test (PLT) on MICP treated sand showed an increase in the ultimate bearing capacity (qu) by about 2.95 to 5.8 times and a 1.7 to 3.31-fold reduction in settlement corresponding to the same load applied on untreated footing. Further investigation of the size and shape of the bearing plate on bearing capacity and settlement was carried out through a plate load test. The higher and more favorable results shown by a rectangular plate compared to a circular plate indicate that the first is preferable.

Research on the Preparation of Microbial Capsules by Epoxy Resin-Coated Bacillus pasteurii

With the increasing number of underground engineering construction projects such as coal mining, tunnel, and subway, water inrush disasters occur more and more frequently. Inspired by the phenomenon of microbial mineralization and diagenesis, microbial-induced calcium carbonate precipitation (MICP) is used to repair cracks in cement-based materials, which provides a new idea to solve the problem of water inrush. To investigate the self-healing properties of microbial capsules, this paper selected epoxy resin E-51 cured by DMP-30 as the wall material and Bacillus pasteurii as the core materials for experiments. In this paper, a single-factor method was adopted to determine the optimal preparation process of microbial capsules and the oil-phase separation method to prepare the microbial capsules. The effects of various factors on the experimental results under different core-wall ratios, reaction time, reaction temperatures, and agitation rates were analyzed. Microbial capsules were analyzed by Fourier transform infrared spectroscopy and optical microscopy to explore the functional groups and features of microbial capsules. The experimental results showed that the microbial capsules achieved the best performance with a core-to-wall ratio of 1 : 3, a reaction temperature of 50°C, a reaction time of 40 min, and a stirring rate of 300 rpm. Meanwhile, we determined the spore survival rate of microbial capsules and finally studied the waterproofness, storage stability, and rupture under the pressure of microbial capsules. We concluded that microbial capsules have high-efficiency and self-healing properties.

Effects of Biostabilization on Engineering Properties of Geomaterials

Biostabilization is a newly proposed method to improve the strength and durability of geomaterials, and it can serve as an alternative to chemical and mechanical stabilization. The objectives of this study are to perform biostabilization treatments for selected roadway construction geomaterials and to evaluate the biostabilization effects on engineering properties of the geomaterials. Three types of geomaterials were selected, and two of them were compacted soil from unpaved road surface. Bacillus pasteurii, the biostabilization bacterium, was used to induce mineral precipitates within the geomaterial pore spaces, where the biostabilization effects were performed. Two types of liquid incubation media, containing NH4Cl or (NH4)2 SO4, were applied for bacteria culturing. Unconfined compression, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) measurements were conducted to evaluate the biostabilization results. From unconfined compression, sample strength performance was improved by the biostabilization treatments; the benefits of biostabilization were pronounced by a relatively long culturing time and an oven-dry procedure; the liquid culturing medium containing NH4Cl performed better than the medium containing (NH4)2 SO4. After biostabilization, SEM photographs provided direct evidence for the precipitates induced by bacteria within the geomaterial pore space. The precipitates either connected the adjoined particles or partially covered the particle surface, which increased the surface roughness. EDS and XRD results indicated that calcite, dolomite, and albite were the major precipitates produced during biostabilization treatments. In conclusion, biostabilization ameliorated the microstructures of the geomaterials and improved their strength. Future research topics should include the applications of biostabilization for in situ road construction.

Performance of Bio Concrete by Using Bacillus Pasteurii Bacteria

In concrete, cracking is a common phenomenon due to its relatively low tensile strength‎ ‎, which occurs due to external loads and imposed deformations‎‎. The main research objective is to create a kind of self-healing concrete by employing mineral producing bacteria Bacillus pasteurii‎ to locate the rift in the most favourable circumstances for autogenous healing to take place. Self-healing concrete containing bacteria has been generated for this study through the application of bacterial self-healing elements as ‎spores ‎and nutrients with different percentages of bacteria ranging from (10% - 25%) as a replacement of mixing water is added at the time of pouring. The bacteria influence was observed by Scanning Electron Microscope (SEM) and with Energy ‎Dispersive X-ray Spectrometer. The mechanical properties and durability of a thirty-five mixture were ‎examined. The optimal blending content proportion was ‎10SF20BC, which showed an increment in compressive strength and flexural strength compared to the control mixture ‎to ‎reach 79.16%, 50% respectively and 24.38% enhancement in sulfate resistance. The highest percentage of calcium carbonate precipitations was ‎9.49% of a weight of ‎mixtures ‎elements, which, in turn, revealed the highest area repair rate, which was able to fill the ‎crack with widths leads to 0.80 mm.

Self-Healing Microbial Concrete - A Review

The cracks naturally exist in concrete and make it weak to the deleterious environment, ending with structure degradation. According to this fact, concrete requires to be improved and remediated. Self-healing methods are considered as a helpful way to mitigate the propagation and development of the cracks in the concrete. Bio-mineralization methods can heal the concrete by using bacteria suchlike Bacillus subtilis and Bacillus pasteurii, which can seal the cracks by CaCO3 precipitation. The literature represents the MICP method of using bacteria in concrete, which can improve the concrete durability by increasing the compressive strength. Furthermore, the different kinds of bacteria used in the concrete structure and the methods of employing as a self-healing agent review. Moreover, it illustrates B. Pasteurii and B. Sphaericus has more efficient results between other bacteria due to increasing the compressive strength and lifespan of the concrete.

Lead Molecules for Targeted Urease Inhibition: An Updated Review from 2010 -2018

The field of enzyme inhibition is a tremendous and quickly growing territory of research. Urease a nickel containing metalloenzyme found in bacteria, algae, fungi, and plants brings hydrolysis of urea and plays important role in environmental nitrogen cycle. Apart from this it was found to be responsible for many pathological conditions due to its presence in many microorganisms such as H. Pylori, a ureolytic bacteria having urease which elevates pH of gastric medium by hydrolyzing urea present in alimentary canal and help the bacteria to colonize and spread infection. Due to the infections caused by the various bacterial ureases such as Bacillus pasteurii, Brucella abortus, H. pylori, H. mustelae, Klebsiella aerogenes, Klebsiella tuberculosis, Mycobacterium tuberculosis, Pseudomonas putida, Sporosarcina pasteurii and Yersinia enterocolitica, it has been the current topic of today’s research. About a wide range of compounds from the exhaustive literature survey has been discussed in this review which is enveloped into two expansive classes, as Inhibitors from synthetic origin and Inhibitors from natural origin. Moreover active site details of enzyme, mechanism of catalysis of substrate by enzyme, uses of plant urease and its pathogenic behavior has been included in the current review. So, overall, this review article diagrams the current landscape of the developments in the improvements in the thriving field of urease inhibitory movement in medicinal chemistry from year 2010 to 2018, with an emphasis on mechanism of action of inhibitors that may be used for more development of recent and strong urease inhibitors and open up new doors for assist examinations in a standout amongst the most lively and promising regions of research.

Self-Healing Concrete by Biological Substrate

At present, the commonly used repair materials for concrete cracks mainly include epoxy systems and acrylic resins, which are all environmentally unfriendly materials, and the difference in drying shrinkage and thermal expansion often causes delamination or cracking between the original concrete matrix and the repair material. This study aimed to explore the feasibility of using microbial techniques to repair concrete cracks. The bacteria used were environmentally friendly Bacillus pasteurii. In particular, the use of lightweight aggregates as bacterial carriers in concrete can increase the chance of bacterial survival. Once the external environment meets the growth conditions of the bacteria, the vitality of the strain can be restored. Such a system can greatly improve the feasibility and success rate of bacterial mineralization in concrete. The test project included the microscopic testing of concrete crack repair, mainly to understand the crack repair effect of lightweight aggregate concrete with implanted bacterial strains, and an XRD test to confirm that the repair material was produced by the bacteria. The results show that the implanted bacterial strains can undergo Microbiologically Induced Calcium Carbonate Precipitation (MICP) and can effectively fill the cracks caused by external concrete forces by calcium carbonate deposition. According to the results on the crack profile and crack thickness, the calcium carbonate precipitate produced by the action of Bacillus pasteurii is formed by the interface between the aggregate and the cement paste, and it spreads over the entire fracture surface and then accumulates to a certain thickness to form a crack repairing effect. The analysis results of the XRD test also clearly confirm that the white crystal formed in the concrete crack is calcium carbonate. From the above test results, it is indeed feasible to use Bacillus pasteurii in the self-healing of concrete cracks.