Mechanical and self-healing properties of cement paste containing incinerated sugarcane filter cake and Lysinibacillus sp. WH bacteria

Cement is the most widely used construction material due to its strength and affordability, but its production is energy intensive. Thus, the need to replace cement with widely available waste material such as incinerated black filter cake (IBFC) in order to reduce energy consumption and the associated CO2 emissions. However, because IBFC is a newly discovered cement replacement material, several parameters affecting the mechanical properties of IBFC-cement composite have not been thoroughly investigated yet. Thus, this work aims to investigate the impact of IBFC as a cement replacement and the addition of the calcifying bacterium Lysinibacillus sp. WH on the mechanical and self-healing properties of IBFC cement pastes. The properties of the IBFC-cement pastes were assessed by determining compressive strength, permeable void, water absorption, cement hydration product, and self-healing property. Increases in IBFC replacement reduced the durability of the cement pastes. The addition of the strain WH to IBFC cement pastes, resulting in biocement, increased the strength of the IBFC-cement composite. A 20% IBFC cement-replacement was determined to be the ideal ratio for producing biocement in this study, with a lower void percentage and water absorption value. Adding strain WH decreases pore sizes, densifies the matrix in ≤ 20% IBFC biocement, and enhances the formation of calcium silicate hydrate (C-S-H) and AFm ettringite phases. Biogenic CaCO3 and C-S-H significantly increase IBFC composite strength, especially at ≤ 20% IBFC replacement. Moreover, IBFC-cement composites with strain WH exhibit self-healing properties, with bacteria precipitating CaCO3 crystals to bridge cracks within two weeks. Overall, this work provides an approach to produce a "green/sustainable" cement using biologically enabled self-healing characteristics.

Insight into biomolecular interaction-based non-classical crystallization of bacterial biocement

In an attempt to draw a correlation between calcium carbonate (CaCO3) precipitation and biomacromolecules such as extracellular polymeric substances and enzyme activity in biomineralizing microbe, this report aims to elucidate the ureolytic and ammonification route in Paenibacillus alkaliterrae to explore the possible role of organic biomolecule(s) present on cell surface in mediating nucleation and crystallization of biogenic CaCO3. After 168 h of biomineralization in ureolysis and ammonification, 2.2 g/l and 0.87 g/l of CaCO3 precipitates were obtained, respectively. The highest carbonic anhydrase activity (31.8 µmoles/min/ml) was evidenced in ammonification as opposed to ureolysis (24.8 µmoles/min/ml). Highest urease activity reached up to 9.26 µmoles/min/ml in ureolytic pathway. Extracellular polymeric substances such as polysaccharides and proteins were found to have a vital role not only in the nucleation and crystal growth but also in addition direct polymorphic fate of CaCO3 nanoparticles. EPS production was higher during ammonification (3.1 mg/ml) than in ureolysis (0.72 mg/ml). CaCO3 nanoparticle-associated proteins were found to be 0.82 mg/ml in ureolysis and 0.56 mg/ml in ammonification. After 30 days of biomineralization, all the polymorphic forms stabilized to calcite in ureolysis but in ammonification vaterite predominated. In our study, we showed that organic template-mediated prokaryotic biomineralization follows the non-classical nucleation and varying proportions of these organic components causes selective polymorphism of CaCO3 nanoparticles. Overall, the findings are expected to further the fundamental understanding of enzymes, EPS-driven non-classical nucleation of CaCO3, and we foresee the design of fit-for-purpose futuristic biominerals arising from such renewed understanding of biomineralization. KEY POINTS: • Organic-inorganic interface of cell surface promote crystallization of biominerals • Carbohydrate and proteins in the interface results selective polymorphism of CaCO3 • Calcite stabilized at 30 days in ureolysis, vaterite-calcite mix in ammonification.

Bio-composites treatment for mitigation of current-induced riverbank soil erosion

Mitigation of erosion along the riverbanks is a global challenge. Stabilisers such as cement can control erosion, but it risks the river ecology. This paper presents the erosion characteristics of riverbank soil treated with two biological stabilisers that alleviate the ecological cost. The riverbank soil of one of the largest river systems, Brahmaputra, is treated by bio-polymeric and bio-cement binders and their composite. Moreover, a novel selective bio-stimulation technique has been employed to achieve bio-mineralisation. The soil stabilisation is assessed by needle penetration tests and CaCO₃ contents. The specimens were tested in a flow-controlled hydraulic flume subjected to a critical current profile ranging from 0.06 to 0.62 m/s. Soil samples treated up to four cycles of biocementation have been tested at three different slopes (30°, 45° and 53°). The eroded depth and erosion rate are evaluated with image analysis. Up to four-fold reduction in the erosion rate was observed with biocementation treatment. However, cementation beyond a threshold led to the formation of brittle chunks. A bio-composite was devised through a pre-treatment of low-viscosity biopolymer along with biocementation. The bio-composite was found to effectively mitigate the current-induced erosion with 36% lower ammonia production than the equally erosion resistant biocemented counterpart. The dual characteristics of the bio-composite were confirmed with the microstructural analysis. This study unravels the potential of biopolymer-biocement composite as a sustainable erosion mitigation strategy.

Elution properties of a resorbable magnesium phosphate cement

OBJECTIVE

This study tests the elution capabilities of a magnesium phosphate cement (MPC). Study objectives were to quantify the passive release of magnesium ions from MPC and to assess the effects of antibiotic-loaded MPC on bacterial growth and osteoblast viability.

METHODS

MPC constructs were created and incubated in fetal bovine serum (FBS). At 2, 4, and 17 weeks, a sample was collected for magnesium ion concentration analysis. Control and vancomycin-loaded (vanc) MPC beads were also created. Zone of inhibition was measured after incubating beads on Staphylococcus aureus agar plates for 24 h. Osteoblasts were seeded onto control and vanc beads and cultured for 9 days. Metabolic activity was measured via a resazurin assay. ANOVA with Tukey HSD post-hoc tests and t-tests were performed.

RESULTS

Magnesium ions were eluted at 2 and 4-week time points without significant difference, but demonstrated a significant spike at the 17-week time point. Zones of inhibition for the bacterial species was observed for Vanc-MPC beads, but not control beads. No cytotoxic effects on osteoblasts were noted.

CONCLUSION

MPC has potential to improve bone regeneration based on its ability to passively elute magnesium. Additionally, antibiotic-loaded MPC inhibits bacterial growth while avoiding osteoblast cytotoxicity.

Understanding and creating biocementing beachrocks via biostimulation of indigenous microbial communities

Bacterially induced precipitation of minerals leading to cementation of natural geological formations has been well recorded in a variety of environments. A range of microbial pathways and geochemical processes have been found to influence the cementation processes; but detailed formation mechanisms and biogeochemical relationships are still not very clear. There has been a growing demand for the application of bacterially driven biocementation in a number of geotechnical engineering applications recently. Here, we aimed to unpin the mechanisms behind the formation of actively mineralising beachrock sediments at Lucky Bay in Western Australia to understand the natural accretionary processes and potential of indigenous bacterial communities in biocementation. We observed ferruginous, aluminosilicate and carbonate cements along with extensive extra polymeric substances, borings with possible microbial activities in certain sections of native beachrock sediments. Cement precipitation under calcium- and iron-rich microenvironments sourced from seawater and iron creek seems to be driven by both biogenic and abiogenic processes in nature. Native microbial communities with a dominance of the genera Halococcus and Marinobacter were recorded. Enrichment of native bacterial communities under seawater media conditions was conducted which lead to successful biomineralisation of calcitic and ferruginous cements under in vitro conditions although the community composition changed significantly. Nanomechanical properties of natural and laboratory synthesised cement crystals showed that engineered biocement is highly promising. The results of this study clearly demonstrate biological influence in the formation of natural cements and hint significant potential of biostimulation which can be harnessed for different engineering applications including coastal erosion.

Environmental safety and biosafety in construction biotechnology

The topics of Construction Biotechnology are the development of construction biomaterials and construction biotechnologies for soil biocementation, biogrouting, biodesaturation, bioaggregation and biocoating. There are known different biochemical types of these biotechnologies. The most popular construction biotechnology is based on precipitation of calcium carbonate initiated by enzymatic hydrolysis of urea which follows with release of ammonia and ammonium to environment. This review focuses on the hazards and remedies for construction biotechnologies and on the novel environmentally friendly biotechnologies based on precipitation of hydroxyapatite, decay of calcium bicarbonate, and aerobic oxidation of calcium salts of organic acids. The use of enzymes or not living bacteria are the best options to ensure biosafety of construction biotechnologies. Only environmentally safe construction biotechnologies should be used for such environmental and geotechnical engineering works as control of the seepage in dams, channels, landfills or tunnels, sealing of the channels and the ponds, prevention of soil erosion and soil dust emission, mitigation of soil liquefaction, and immobilization of soil pollutants.

Biomineralization in metakaolin modified cement mortar to improve its strength with lowered cement content

The role of industrial byproduct as supplementary cementitious material to partially replace cement has greatly contributed to sustainable environment. Metakaolin (MK), one of such byproduct, is widely used to partial replacement of cement; however, during cement replacement at high percentage, it may not be a good choice to improve the strength of concrete. Thus, in the present study, biocement, a product of microbially induced carbonate precipitation is utilized in MK-modified cement mortars to improve its compressive strength. Despite of cement replacement with MK as high as 50%, the presented technology improved compressive strength of mortars by 27%, which was still comparable to those mortars with 100% cement. The results proved that biomineralization could be effectively used in reducing cement content without compromising compressive strength of mortars. Biocementation also reduced the porosity of mortars at all ages. The process was characterized by SEM-EDS to observe bacterially-induced carbonate crystals and FTIR spectroscopy to predict responsible bonding in the formation of calcium carbonate. Further, XRD analysis identified bio/minerals formed in the MK-modified mortars. The study also encourages combining biological role in construction engineering to solve hazardous nature of cement and at same time solve the disposal problem of industrial waste for sustainable environment.

Remediation of Cr(VI) from chromium slag by biocementation

Here we demonstrate a calcifying ureolytic bacterium Bacillus sp. CS8 for the bioremediation of chromate (Cr(VI)) from chromium slag based on microbially induced calcite precipitation (MICP). A consolidated structure like bricks was prepared from chromium slags using bacterial cells, and five stage Cr(VI) sequential extraction was carried out to know their distribution pattern. Cr(VI) mobility was found to significantly be decreased in the exchangeable fraction of Cr slag and subsequently, the Cr(VI) concentration was markedly increased in carbonated fraction after bioremediation. It was found that such Cr slag bricks developed high compressive strength with low permeability. Further, leaching behavior of Cr(VI) in the Cr slag was studied by column tests and remarkable decrease in Cr(VI) concentration was noticed after bioremediation. Cr slags from columns were characterized by SEM-EDS confirming MICP process in bioremediation. The incorporation of Cr(VI) into the calcite surface forms a strong complex that leads to obstruction in Cr(VI) release into the environment. As China is facing chromium slag accidents at the regular time intervals, the technology discussed in the present study promises to provide effective and economical treatment of such sites across the country, however, it can be used globally.