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The production of concrete for construction purposes is a major source of anthropogenic CO 2 emissions. One promising avenue towards a more sustainable construction industry is to make use of naturally occurring mineral-microbe interactions, such as microbial-induced carbonate precipitation (MICP), to produce solid materials. In this paper, we present a new process where calcium carbonate in the form of powdered limestone is transformed to a binder material (termed BioZEment) through microbial dissolution and recrystallization. For the dissolution step, a suitable bacterial strain, closely related to Bacillus pumilus , was isolated from soil near a limestone quarry. We show that this strain produces organic acids from glucose, inducing the dissolution of calcium carbonate in an aqueous slurry of powdered limestone. In the second step, the dissolved limestone solution is used as the calcium source for MICP in sand packed syringe moulds. The amounts of acid produced and calcium carbonate dissolved are shown to depend on the amount of available oxygen as well as the degree of mixing. Precipitation is induced through the pH increase caused by the hydrolysis of urea, mediated by the enzyme urease, which is produced in situ by the bacterium Sporosarcina pasteurii DSM33. The degree of successful consolidation of sand by BioZEment was found to depend on both the amount of urea and the amount of glucose available in the dissolution reaction.

The production of concrete is one of the most significant contributors to global greenhouse gas emissions. This work focuses on bio-cementation-based products and their potential to reduce global warming potential (GWP). In particular, we address a proposed bio-cementation method employing bacterial metabolism in a two-step process of limestone dissolution and recrystallisation (BioZEment). A scenario-based techno-economic analysis (TEA) is combined with a life cycle assessment (LCA), a market model and a literature review of consumers’ willingness to pay, to compute the expected reduction of global GWP. Based on the LCA, the GWP of 1 ton of BioZEment is found to be 70–83% lower than conventional concrete. In the TEA, three scenarios are investigated: brick, precast and onsite production. The results indicate that brick production may be the easiest way to implement the products, but that due to high cost, the impact on global GWP will be marginal. For precast production the expected 10% higher material cost of BioZEment only produces a marginal increase in total cost. Thus, precast production has the potential to reduce global GWP from concrete production by 0–20%. Significant technological hurdles remain before BioZEment-based products can be used in onsite construction scenarios, but in this scenario, the potential GWP reduction ranges from 1 to 26%. While the potential to reduce global GWP is substantial, significant efforts need to be made both in regard to public acceptance and production methods for this potential to be unlocked.

<p>A feasibility study has been performed by Dr. Techn. Olav Olsen, Reinertsen, Norconsult and the Norwegian Public Road Administration (NPRA) for a Submerged Floating Tube Bridge (SFTB) crossing the Bjørnafjord strait. Design of flexible floating structures with lengths above 5 kilometers has previously not been developed to a detailed level. This article will discuss the approach the design team used to achieve a solution that was robust, reliable and economically viable for a SFTB for crossing the Bjørnafjord. The proposed approach was found to be an efficient and safe approach to reduce the total cost of the project. The experience is based mainly on work for the NPRA with the Bjørnafjord strait crossings on the west coast of Norway. This paper will address three main issues; 1) Design challenges, 2) Practical challenges and 3) SFTB sensitivities.</p> <ol><li> <p>No complete standards was applicable and existing methods of predicting dynamic behavior proved to be too crude to be applicable in design. A significant work was therefore put into improving the above mentioned. This lead to a large amount of time domain simulations, which is an uncommon challenge in concept design. A solution to use this as an advantage is discussed along with the guidelines for concept screening and optimization with economic impact analyses.</p></li><li> <p>A 100 year life time with minimal maintenance is requested by the NPRA. Technical solutions, with emphasis on landfalls and flexible parts of the structure is discussed.</p></li><li> <p>A significant work with screening of response variations relative to changes in environmental loads has been performed. This was possible due to the methodical and analytical progress mentioned in 1)</p></li></ol> <p>The concluding remarks of the experience reported in the article show that the SFTB is both robust and flexible, with low sensitivity to change in environmental loads. Previous experience indicated that the SFTB was not suitable for harsh environments, whereas the new solutions indicate that even swell loading is more of a design issue rather than a feasibility issue.</p>