Relationship between Bacterial Contribution and Self-Healing Effect of Cement-Based Materials

Comparison of calcium carbonate production by bacterial isolates from recycled aggregates

The new technology of microbially induced calcium carbonate precipitation (MICP) has been applied in construction materials as a strategy to enhance their properties. In pursuit of solutions that are more localized and tailored to the study's target, this work focused on isolating and selecting bacteria capable of producing CaCO3 for posterior application in concrete aggregates. First, eleven bacterial isolates were obtained from aggregates and identified as genera Bacillus, Lysinibacillus, Exiguobacterium, and Micrococcus. Then, the strains were compared based on the quantity and nature of calcium carbonate they produced using thermogravimetric analysis, X-ray diffraction, and scanning electron microscopy with energy dispersive spectroscopy. Bacillus sp. dominated the cultured isolates and, along with Lysinibacillus sp., exhibited the highest CaCO3 conversion (up to 80%). On the other hand, Exiguobacterium and Micrococcus genera showed the poor ability to MICP (21.3 and 20.3%, respectively). Calcite and vaterite were the dominant carbonate polymorphs, with varying proportions. Concrete aggregates have proven to be a source of microorganisms capable of producing stable calcium carbonates with a high conversion rate. This indicates the feasibility of using microorganisms derived from local sources for application in construction materials as a sustainable way to enhance their characteristics.

Feasibility of Using New Sustainable Mineral Additions for the Manufacture of Eco-Cements

Due to a continuously developing population, our consumption of one of the most widely used building materials, concrete, has increased. The production of concrete involves the use of cement whose production is one of the main sources of CO2 emissions; therefore, a challenge for today's society is to move towards a circular economy and develop building materials with a reduced environmental footprint. This study evaluates the possibility of using new sustainable supplementary cementitious materials (SCMs) from waste such as recycled concrete aggregates (RCAs) and mixed recycled aggregates (MRAs) from construction and demolition waste, as well as bottom ash from olive biomass (BBA-OL) and eucalyptus biomass ash (BBA-EU) derived from the production of electricity. A micronisation pre-treatment was carried out by mechanical methods to achieve a suitable fineness and increase the SCMs' specific surface area. Subsequently, an advanced characterisation of the new SCMs was carried out, and the acquired properties of the new cements manufactured with 25% cement substitution in the new SCMs were analysed in terms of pozzolanicity, mechanical behaviour, expansion and setting time tests. The results obtained demonstrate the feasibility of using these materials, which present a composition with potentially reactive hydraulic or pozzolanic elements, as well as the physical properties (fineness and grain size) that are ideal for SCMs. This implies the development of new eco-cements with suitable properties for possible use in the construction industry while reducing CO2 emissions and the industry's carbon footprint.

Research Progress of Self-Healing Polymer for Ultraviolet-Curing Three-Dimensional Printing

Ultraviolet (UV)-curing technology as a photopolymerization technology has received widespread attention due to its advantages of high efficiency, wide adaptability, and environmental friendliness. Ultraviolet-based 3D printing technology has been widely used in the printing of thermosetting materials, but the permanent covalent cross-linked networks of thermosetting materials which are used in this method make it hard to recover the damage caused by the printing process through reprocessing, which reduces the service life of the material. Therefore, introducing dynamic bonds into UV-curable polymer materials might be a brilliant choice which can enable the material to conduct self-healing, and thus meet the needs of practical applications. The present review first introduces photosensitive resins utilizing dynamic bonds, followed by a summary of various types of dynamic bonds approaches. We also analyze the advantages/disadvantages of diverse UV-curable self-healing polymers with different polymeric structures, and outline future development trends in this field.

The roles of calcium signaling and calcium deposition in microbial multicellularity

Calcium signaling is an essential mediator of signal-controlling gene expression in most developmental systems. In addition, calcium has established extracellular functions as a structural component of biogenic minerals found in complex tissues. In bacteria, the formation of calcium carbonate structures is associated with complex colony morphology. Genes promoting the formation of biogenic minerals are essential for proper biofilm development and protection against antimicrobial solutes and toxins. Here we review recent findings on the role of calcium and calcium signaling as emerging regulators of biofilm formation in beneficial bacteria, as well as essential mediators of biofilm formation and virulence in human pathogens. The presented analysis concludes that the new understanding of calcium signaling may help to improve the performance of beneficial strains for sustainable agriculture, microbiome manipulation, and sustainable construction. Unraveling the roles of calcium may also promote the development of novel therapies against biofilm infections that target calcium uptake, calcium sensors, and calcium carbonate deposition.

Toward Self-Healing Concrete Infrastructure: Review of Experiments and Simulations across Scales

Cement and concrete are vital materials used to construct durable habitats and infrastructure that withstand natural and human-caused disasters. Still, concrete cracking imposes enormous repair costs on societies, and excessive cement consumption for repairs contributes to climate change. Therefore, the need for more durable cementitious materials, such as those with self-healing capabilities, has become more urgent. In this review, we present the functioning mechanisms of five different strategies for implementing self-healing capability into cement based materials: (1) autogenous self-healing from ordinary portland cement and supplementary cementitious materials and geopolymers in which defects and cracks are repaired through intrinsic carbonation and crystallization; (2) autonomous self-healing by (a) biomineralization wherein bacteria within the cement produce carbonates, silicates, or phosphates to heal damage, (b) polymer-cement composites in which autonomous self-healing occurs both within the polymer and at the polymer-cement interface, and (c) fibers that inhibit crack propagation, thus allowing autogenous healing mechanisms to be more effective. In all cases, we discuss the self-healing agent and synthesize the state of knowledge on the self-healing mechanism(s). In this review article, the state of computational modeling across nano- to macroscales developed based on experimental data is presented for each self-healing approach. We conclude the review by noting that, although autogenous reactions help repair small cracks, the most fruitful opportunities lay within design strategies for additional components that can migrate into cracks and initiate chemistries that retard crack propagation and generate repair of the cement matrix.

New non-ureolytic heterotrophic microbial induced carbonate precipitation for suppression of sand dune wind erosion

The detrimental effects of sand storms on agriculture, human health, transportation network, and infrastructures pose serious threats in many countries worldwide. Hence, wind erosion is considered a global challenge. An environmental-friendly method to suppress wind erosion is to employ microbially induced carbonate precipitation (MICP). However, the by-products of ureolysis-based MICP, such as ammonia, are not favorable when produced in large volumes. This study introduces two calcium formate-bacteria compositions for non-ureolytic MICP and comprehensively compares their performance with two calcium acetate-bacteria compositions, all of which do not produce ammonia. The considered bacteria are Bacillus subtilis and Bacillus amyloliquefaciens. First, the optimized values of factors controlling CaCO₃ production were determined. Then, wind tunnel tests were performed on sand dune samples treated with the optimized compositions, where wind erosion resistance, threshold detachment velocity, and sand bombardment resistance were measured. An optical microscope, scanning electron microscope (SEM), and X-ray diffraction analysis were employed to evaluate the CaCO₃ polymorph. Calcium formate-based compositions performed much better than the acetate-based compositions in producing CaCO₃. Moreover, B. subtilis produced more CaCO₃ than B. amyloliquefaciens. SEM micrographs clearly illustrated precipitation-induced active and inactive bounds and imprints of bacteria on CaCO₃. All compositions considerably reduced wind erosion.