Construction Material
Bauer´s Competency regarding Construction Materials is established and has been constantly progressing, as a result of:
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In-house scientific research supported through academic cooperation with partner universities, investigating and assessing materials’ influence on the installation process and their influence on the final, integral quality of the wall or pile.
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BAUER Spezialtiefbau GmbH cooperates worldwide with various organisations to specify standards and regulations. Amongst others we participate in the following groups:
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We are a member of the German delegation for the Technical Committee TC288 of CEN in charge of European Standards for Execution of Special Geotechnical Works (EN 1538 Diaphragm Walls). We were also a member of the tremie concrete task group of the Piling and Foundation Specialists Federation (which compiled the “Guideline on Tremie Concrete for Deep Foundations”, published in 2012, by the Concrete Institute of Austral
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Furthermore we have been chairing the joint Concrete Task Group of the EFFC, the European Foundation Contractors, and of the DFI, the Deep Foundation Institute (USA), established in January 2014. In 2018 the 2nd edition of the Guide to tremie Concrete for Deep Foundation was released. It recommends to adjust the design and quality control of tremie concrete in accordance with to latest developments and introduces these results to the European and international market, applicable for the revision of the concrete specifications for the next generation of CEN standards.
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Consulting in operational works, hence giving project-specific advice in concrete design, raw materials and concrete testing, as well as quality assessment, in all construction phases from planning, calculating or finally executing the dam rehabilitation project.
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Bauer aims to support own projects in all matters and steps of materials’ use for deep foundation works. Regarding concrete for dam rehabilitation principal demands have to be specified in order to proof both sufficient fresh and hardened concrete properties:
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According to Bauer’s experiences gathered in own research, standards and consulting works the concrete, prior to its application in a project, must be properly designed, specifically tested and optimized. For placing concrete in deep excavations, the fresh concrete behavior must be understood and required properties must consequently be controlled throughout the concreting process.
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It is Bauer’s experience that the cut-off wall construction safety for both the ultimate and service limit state, in terms of its function as a water barrier, should not be based on the strength of the plastic concrete used but on its deformation capacity in or-der to gain from the material‘s plastic properties.
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Permeability and erodibility, both must, within defined ranges, ensure the demanded serviceability of the wall
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Construction materials
The materials used for dam construction and remediation have to meet the demands arising from the design and functionality aspects, as well as to fulfil the specific requirements imposed by the used construction methods and the project’s boundary conditions. The following section describes the most common water cut-off materials and their application respectively.
Plastic concrete is used preferably for permanent D-wall installation under main dams and for temporary approaches at cofferdams. Compared to structural concrete, plastic concrete is characterized by lower strength, below 5 MPa, lower cement content, the use of a clayey component, such as bentonite and lower young modulus. It is most suitable for dams which need to sustain higher hydraulic gradient, but still exposed to deformations due to upcoming loads. Besides the design strength level, the durability of the plastic concrete with respect to erosion is supported by suitable grading curve. Cement content and bentonite dosage can be set and adjusted, depending on the required strength and maximum allowable permeability. Workability properties and duration of plastic concrete can be set to site requirements with available admixtures.
The Lean concrete is an intermediate option between the highly deformable plastic concrete and the conventional structural concrete, with higher resistance towards mechani- cal and hydraulic impacts. Compared to plastic concrete, this concrete has a higher strength, with up to 15 MPa and a higher cement content. The stability of such concrete is enhanced by a higher fines content, achieved, whererequired, with inert, pozzolanic and/or clayey additions, such as fly ash, selected stone powders and/or adding calcium or sodium bentonite. Similar to plastic or structural concrete, lean concrete contains sand and gravel, composed to a well adjusted grading curve, together with a required design strength to guaranty erosion stability. Flowability and workability duration are controlled similarly to other concretes with available admixtures.
Bentonite-cement slurry
In application fields with less existing water pressure, like construction pits or dikes and lower dams, the use of hardening bentonite-cement slurry is a practicable option. Here the well-retarded slurry, produced on-site by slurry plants, is pumped to the trench with remotely con- trolled pumps. Compared to plastic concrete, the major advantage is the significantly increased productivity and the higher independency from on-time concrete deliveries. The hardened bentonite-cement mix does not have a stiff grain structure like concrete, which gives such materials higher plasticity and allow better accommodation of intro- duced strains. Cement content and bentonite dosage can be set and adjusted depending on the required strength and maximum allowable permeability or required elasticity. Required open working time of slurry can be set to site requirements up to 36 hrs with suitable admixtures
Soil-slurry mix is favourable due to its lower ecological impact. It uses major parts of the existing ground and therefore requires less transportation for materials and spoil, as well as a smaller mixing plant. By preparing a bentonite-cement slurry and mixing it into the ground, strength and permeability properties of the soil-slurry-mix can be set similar to plastic concrete by adjustment of cement and bentonite content. Workability of slurry and the liquefied soil mix can be fit to required working con- ditions with suitable admixtures.
