Search

Urease production of calcifying bacterium, Bacillus megaterium SS3 was enhanced by using response surface methodology (RSM) in current study. The preliminary screening by Plackett-Burman's design revealed that among the tested factors, glucose, urea and NaHCO3 significantly ( p < 0.05) enhanced the urease production. Further optimization of urease production by B. megaterium through RSM was achieved as 879 U mL−1 in the presence of glucose (21.7 g L−1), urea (21.1 g L−1) and NaHCO3 (1.9 g L−1) compared to 640 U mL−1 in unoptimized medium. The effect of different factors seems to promote the growth of bacterial isolate leading to improvement in urease production. As production of carbonates by ureolytic bacteria is dependent on urease enzyme, improvement in enzyme production enhanced the carbonate precipitation efficacy to 1.7-fold in optimized medium. Carbonic anhydrase production also increased from 120 U mL−1 to 190 U mL−1 in optimized medium. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Modern civilization is facing the dichotomy of rapid development of infrastructure that makes concrete as most traded material on the earth other than water. However, the production of cement, key ingredient of concrete, releases roughly a tonne of CO 2 into the environment with each tonne of cement production. The environmental concerns and sustainability issues associated with cement and concrete necessitate alternative and better approach in the construction. Nature, on the other hand, has a plethora of examples of sustainable habitats such as coral reefs, silk webs and ant hills. Recent advances in biotechnology have great potential of emulating nature’s way of building in modern days infrastructures at a scale that would sustain increasing population. Further, many of the biological materials of nature, be it ceramics or polymeric composites formed in the process of biomineralization, provides basis for sustainable construction. This paper elaborates nature’s way of construction based on biomineralization and discusses the progress of different biological pathways for sustainable construction. Main milestones achieved have been identified and the effect of biological intervention on the properties of structural materials has been highlighted. Variety of applications of biomineralization based technology in the construction has been reported. The paper briefly documents the future directions of the technology. [ABSTRACT FROM AUTHOR]

Evidence of bacterial involvement in precipitation of calcium carbonates has brought a revolution in the field of applied microbiology, geotechnical sciences, environmental and civil engineering with its marked success in restoration of various building materials. For applications of these calcite binder-producing bacterial cultures, different expensive carrier materials have been used but their high costs have come in the way of their successful commercialization. In the present study, we have explored the potential of cheap industrial by-product fly ash as a carrier material for bacterial cells and investigated the viability of calcifying bacterial isolates: Bacillus megaterium, Bacillus cereus, and Lysinibacillusfusiformis in fly ash carrier at varying temperatures and moisture conditions along with biomineralization efficacy of these formulations. We used laser scanning confocal microscopy to analyze the viability of bacteria by florescent dye 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) along with the plate count method. Results revealed that fly ash successfully served as an effective carrier material and bacterial formulations stored at 4 °C provided longer shelf life than those stored at higher temperatures. Up to 10 6 cfu/g was found to sustain in all formulations at 4 °C compared to 10 4-10 5 cfu/g in case of higher temperatures up to 1 year. For 4 °C, higher moistures (50 %) were found to provide better survivability while for higher temperatures, lower moistures (30 %) favored higher viability. The biomineralization capability of fresh and formulated bacterial cells was compared on the basis of precipitation of carbonates and it was found that carbonate precipitation efficacy of formulated bacterial cells was comparable to fresh bacterial cells. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the results of an experimental study to investigate the flexural behavior of reinforced concrete (RC) beams that have reached their ultimate bearing capacities and then retrofitted with externally prestressed carbon fiber reinforced composite (CFRC) laminates. The effect of variation in prestressing force on CFRC laminates bonded to the RC beam is investigated in terms of the flexural strength, deflections, cracking behavior and failure modes. The results indicate that rehabilitation of significantly cracked beams by bonding CFRC laminates is structurally efficient. [Copyright &y& Elsevier]

Abstract: An investigation on the performance of reinforced concrete beam-column joints under cyclic loading is reported. Joints have been cast with adequate and deficient bond of reinforcements at the beam-column joint. FRP sheets and strips have been applied on the joints in different configurations. The columns are subjected to an axial force while the beams are subjected to a cyclic load with controlled displacement. The amplitude of displacement is increased monotonically using a dynamic actuator. The hysteretic curves of the specimens have been plotted. The energy dissipation capacity of various FRP configurations has been compared. In addition, the control specimens have been reused after testing as damaged specimens that are candidates for rehabilitation. The rehabilitation has been carried out using FRP and their performance has been compared with that of the undamaged specimens. [Copyright &y& Elsevier]

Microbially induced calcium carbonate precipitation (MICP) is emerging as a sustainable technology for improved construction materials. In this technique, calcium carbonate is deposited in the pores of substrates such as sand and concrete. As the technology moves from laboratory to field new metrics and field measurement techniques are required to ensure that the results achieved at the laboratory are replicated. In the scaled up technique it is not possible to collect samples from deep inside the substrate for direct measurement. This paper explores some indirect indicators of MICP that can be easily monitored in large scale applications. Bacterial fluid has been passed through sand columns of varying grain sizes. The rate of flow is monitored for ten days. The effluent has been tested for pH and electrical conductivity to evaluate their potential for ensuring MICP. The residual urea and calcium in the effluent has been monitored to have a quantitative estimate of MICP. At the end of the tests the quantity of carbonate deposited in the sand columns is measured. A correlation between the residual reactants and the carbonate deposition is developed. An approximate expression for different grain sizes has been developed. This study demonstrates the utility of indirect measurement techniques as flow rate, pH, conductivity, urea and calcium consumption as potential indicators of efficient MICP in sand media. [ABSTRACT FROM AUTHOR]

Microbially induced calcium carbonate precipitation is a biomineralization process that has various applications in remediation and restoration of range of building materials. In the present study, calcifying bacteria, Bacillus megaterium SS3 isolated from calcareous soil was applied as biosealant to enhance the durability of low energy, green building materials (soil–cement blocks). This bacterial isolate produced high amounts of urease, carbonic anhydrase, extra polymeric substances and biofilm. The calcium carbonate polymorphs produced by B. megaterium SS3 were analyzed by scanning electron microscopy, confocal laser scanning microscopy, X-ray diffraction and Fourier transmission infra red spectroscopy. These results suggested that calcite is the most predominant carbonate formed by this bacteria followed by vaterite. Application of B. megaterium SS3 as biogenic surface treatment led to 40 % decrease in water absorption, 31 % decrease in porosity and 18 % increase in compressive strength of low energy building materials. From the present investigation, it is clear that surface treatment of building materials by B. megaterium SS3 is very effective and eco friendly way of biodeposition of coherent carbonates that enhances the durability of building materials. [ABSTRACT FROM AUTHOR]

• The porous old attached mortar and weak ITZ of RCA are the primary reason behind its inferior behavior. • Qualitative and quantitative petrographic analysis is conducted to assess the inferior performance of RCA. • There is a mismatch with NA and RCA with respect to the geological background. Recycled concrete aggregate (RCA) shows more complex behavior in fresh and hardened concrete due to its higher water absorption, weak bonding capacity, poor interfacial transition zones (ITZs) and other uncertainties. The old attached mortar (AM) of RCA is the primary reason behind this. Petrographic analysis is normally assessed for construction aggregate to evaluate the physical and mineralogical characteristics, along with these the prediction of aggregate behavior in concrete. The same methodology is applied here for RCA and demanding to investigate the reason behind the inferior performance of it into fresh concrete. Optical microscopy, thin section, and Scanning Electron Microscopy (SEM) analysis are carried out in order to solve the addressed issue. Both the qualitative and quantitative petrographic analysis is conducted in order to identify the inferior properties of RCA. Micropores and microcracks are very common for RCA surface which propagates the failure of recycled aggregate concrete (RAC) under load. The experimental observation is suggested that the RCA is different kind of aggregate for sustainable construction material and cannot comparable with natural aggregate (NA) without proper understanding the type of parent aggregate or source of RCA. The range of aggregates between 20 and 10 mm can give good quality RCA after additional crushing and suitable treatment is required on RCA for strengthening the old ITZ and AM in order to achieve high-quality RCA. [ABSTRACT FROM AUTHOR]

Ureolytic microbial calcium carbonate precipitation technology has recently emerged as a sustainable, eco-friendly approach for protection and remediation of building materials. However, use of urea has some disadvantages such as production of ammonia, which has raised environmental concerns, as well as risks of damage to concrete materials. In the present investigation, urea is replaced with direct influx of carbon dioxide and studied the precipitation of carbonates by bacteria ( Bacillus megaterium SS3). The bacteria is able to grow well and precipitate carbonates well when CO 2 influx of 99.5% pure passed (20 ml/min) into the flasks for 60 s. The amount of CaCO 3 precipitated through CO 2 influx is comparable with that of 2% urea used for precipitation. The percentage improvement in strength with respect to the control specimens by accelerated carbonation curing was 117% while it was 47% in urea treated specimens. Sorptivity was significantly reduced in accelerated carbonation specimens treated with bacteria compared to other treatments. Though carbonation increased compressive strength in control samples, but bacterial treatment significantly reduced the water absorption in concrete specimens. Present study results suggested that utilization of CO 2 serves as an alternative to urea during CaCO 3 precipitation. [ABSTRACT FROM AUTHOR]

• Clear methodology for effective use of C&D waste in concrete is warranted. • Treatment methods for mitigation of weaknesses within RCA and RAC has discussed. • Performance enhancement methods on RCA considering sustainability has analysed. • Present review recommends for the strengthening of attached mortar not the removal. With global increase in construction and demolition, recycling of construction debris as an aggregate can be a vital step towards achieving sustainability in concrete construction. However, a clear methodology for reuse of construction and demolition (C&D) waste in concrete is warranted for its use in practice. This paper reviews the challenges revealed hitherto such as weak interfacial transition zone, high water absorption and presence of micro cracks in the use of C&D wastes as the recycled aggregate (RA). Methods of mitigation of these weaknesses through various treatments have been reported. This review has a special focus on India, a country that generates one of the world's highest quantity of C&D waste. After analysing all the treatment methods, the authors summarize that the strengthening of attached mortar (AM) technique is better than removing of AM, which is also cost-effective, eco-friendly and sustainable. Use of nano-materials and pozzolana along with different mixing methods and application of bio-cement is found to be superior and environmental friendly approach for improving the properties of recycled aggregates. [ABSTRACT FROM AUTHOR]