Preface

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Accelerated carbonation of recycled concrete aggregates (RCA) could be an efficient way to reduce the carbon footprint. High CO2-concentration under optimal relative humidity could accelerate the CO2 binding capacity of the hydrated cement paste in the RCA. The latter is the topic of this paper. The study looks into the forced carbonation of crushed cement pastes as a basis to understand the CO2 uptake in relation to various binders containing supplementary cementitious materials (SCM) such as fly ash (FA) and ground granulated blast furnace slag (GGBS). Samples include three cement pastes: ordinary Portland cement, substitution rate of 30 % FA and 50 % GGBS respectively at a water/binder ratio of 0.45. All binders were graded to 0/2, 2/4 and 4/8 mm fraction sizes and preconditioned before exposed to CO2 concentration of 10 % under controlled temperature at 20 °C and 65 % RH. All tested binders presented a high CO2 uptake within the first hours of exposure with clear differences concerning the fraction sizes and the composition. The phase content before and after carbonation was observed by X-ray diffraction and the portlandite and calcite were quantified by thermogravimetric analyses and their derivative curves for fraction size 4/8 mm.
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University of Borås, RISE Research Institutes of Sweden, Infrastructure and Concrete, Technology, Material Design

Prof., Ph.D. M.Sc. Department R&D Manager and Professor

Ph.D. M.Sc. and Adjunct Professor, Luleå University of Technology

Accelerated Carbonation of Binders Containing SCM at High CO2 Concentration

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Pumping is the preferred placement method for concrete. The pumping process influences fresh properties of concrete. Competent producers handle these issues when composing the mix design. However, sudden changes in workability sometimes appear, both in the form of increased and decreased workability. Both changes might be handled on-site. However, even the situations that are sufficiently handled, cause delays and extra costs. Sometimes the final result’s quality is compromised, resulting in repairs and economic compensation claims. The extent and causes of incidents with sudden changes in workability are still to be investigated.
It is suggested that around 1 100 000 m3 or 30% of concrete experience sudden change in workability annually in Norway, and that 200 000 kg of chemical admixtures is used on-site. It appears that the most relevant cause is to find within variations in the fine aggregate. Increase in workability might also be caused by lack of compatibility between superplasticiser and binding materials in low-carbon concrete, enhanced by the extra mixing process caused by the pumping process.
To approach these questions, the Quality Assessment system of a medium-sized Norwegian concrete producer has been investigated. It comprises documentation of 1 500 000 m3 of concrete, over 10 years.
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Technology manager, Ribe Betong AS and PhD Candidate, Department of Engineering Sciences, Faculty of Engineering and Science

Professor, Department of Engineering Sciences, Faculty of Engineering and Science

Sudden Changes in Workability during Concrete Pumping – An Industrial Approach

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This study investigates the links between the non-steady-state chloride migration coefficient, the bulk electrical conductivity and the formation factor of blended cement paste specimens. 18 different binders were tested: two Portland cements (low- and high-alkali) in combination with limestone filler, fly ash, calcined clay, two biomass ashes, sewage sludge ash and crushed brick, as well as two Portland composite cements. In addition, the latter and the low-alkali Portland cement were tested in concrete as well for comparison.
Mixes with high-alkali cement showed better resistance to chloride transport, and the effect of supplementary cementitious materials was found to be strongly linked with their reactivity. Moreover, the results showed a clear correlation of the migration coefficient with the bulk electrical conductivity and, to a lesser extent, with the formation factor. However, these relationships are strongly influenced by the methods used to determine conductivities and they need to be validated for higher maturities. Finally, the results suggested a fairly good correspondence between the results obtained on paste and concrete.
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MSc, Industrial PhD student, Technical University of Denmark

Department of Environmental and Resource Engineering

Relationship between Chloride Migration, Bulk Electrical Conductivity and Formation Factor of Blended Cement Pastes

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Concrete cover is the thickness of the concrete layer that protects the reinforcing steel bars (rebar) within a reinforced concrete structure. It acts as a barrier against external elements such as moisture, chemicals, and environmental factors, safeguarding the rebar from corrosion. Concrete cover measurement is performed by using various nondestructive tests such as GPS (Ground Penetrating Radar), electromagnetic test and ultrasonic. The main benefit of the concrete cover thickness measurement is to explain the causes of corrosion and identify areas that have the capability to corrode faster.
This paper discusses the possibilities to measure the concrete cover depth and determine the location of steel bars of a thick-walled concrete structure by using different nondestructive testing methods. The methods studied are a concrete cover meter, Ground Penetrating Radar, which is based on propagation radar waves in concrete, and Ultrasonic Pulse Echo tomography based on stress waves produced by ultrasonic pulses. The paper demonstrates the use of these methods for in-situ measurements on a thick-walled reinforced concrete structure. The concrete cover depth and the location for the reinforcement bars received by different methods are compared and the strong and weak points of the methods are discussed.
The results indicate that the concrete cover meter is suitable for measuring the thickness of concrete cover, while the Ground Penetrating Radar and the Ultrasonic Pulse Echo device were able to identify and locate the reinforcement bars position in the concrete structure.
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Professor, Aalto University School of Engineering

Determining the Location of Steel Reinforcement in Thick Concrete Walls by Non-Destructive Inspection

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Today, the world is facing an enormous challenge where the emissions of greenhouse gases must be reduced significantly to stop the increasing mean temperature. For the construction industry, this challenge means that structures must be designed more carefully, and materials must be used and produced more efficiently. Concrete is one of the most widely used materials, and cement production alone contributes to around 8 % of the world’s total CO2 emissions. This paper presents a pilot study in which part of the cement clinker content in accelerated shotcrete is replaced with ground granulated blast furnace slag (GGBS). Shotcrete is widely used as part of the rock support for tunnels in hard rock and has a large cement content. Thus, the environmental impact must be reduced significantly to meet future demands. However, introducing GGBS will slow down strength development, which is a crucial part of shotcrete. Thus, this paper aims to investigate the early strength development, i.e., after one and seven days. The results show that an average compressive strength of 18 MPa can be reached after 24 hours when 35 % of the cement clinker content is replaced with GGBS. Finally, some important topics for further studies are pointed out.
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MSc, Researcher Assistant, Eastern Switzerland University of Applied Sciences

The Use of Slag in Accelerated Shotcrete for Rock Support: A Pilot Study on the Influence on the Early Compressive Strength

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In concrete structures, material performance is typically determined at the level of the concrete mix (the microscale) and the overall shape and dimensions of a building element (the macroscale). However, recent developments in the field of 3D Concrete Printing (3DCP) are demonstrating that the design of concrete now also can take place at a previously impossible intermediate scale involving the shaping and placement of the material at the level of the printing nozzle (the mesoscale). By focusing directly on the design of print paths, advanced surface effects and internal porous material distributions can be achieved that significantly affect the aesthetic experience and structural performance of 3DCP structures. This ability to design the distribution of concrete according to local architectural, structural, and functional design criteria is an especially interesting application of 3DCP that could be exploited to customise material performance while at the same time optimising material use and reducing the self-weight of building elements. This paper specifically examines how four different three-dimensional print patterns produce distinct material structures at the mesoscale (mesostructures) and presents an experimental procedure for evaluating their load-bearing capacity.
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Dept. of Civil & Architectural Engineering, Div. of Concrete Structures

Towards the Application of Mesostructures in 3D Concrete Printing – Evaluating Load-bearing Performance

AHEAD OF PRINT

Volume 69 (2023): Issue 2 (December 2023)

Volume 68 (2023): Issue 1 (July 2023)

Volume 67 (2022): Issue 2 (December 2022)

Volume 66 (2022): Issue 1 (July 2022)

Volume 65 (2021): Issue 2 (December 2021)

Volume 64 (2021): Issue 1 (June 2021)

Volume 63 (2020): Issue 2 (December 2020)

Volume 62 (2020): Issue 1 (June 2020)

Volume 61 (2019): Issue 2 (December 2019)

Volume 60 (2019): Issue 1 (June 2019)

Volume 59 (2018): Issue 1 (December 2018)

Volume 58 (2018): Issue 1 (June 2018)

Nordic Concrete Research

 The aim is to publish reviewed papers on research, recent experiences, and education within the broad concrete field. The scope covers all aspects of concrete and other cementitious materials, e.g., materials, design, construction, assessment, maintenance, repair, strengthening, dismantling, and recycling. The scope is limited to papers that have a Nordic connection, e.g., through the environment conducting the investigation, affiliation of any of the authors, or if the subject of the paper is devoted to any specific Nordic circumstances such as geographical, geological, or organizational ones.The Nordic Concrete Federation (NCF) which is publishing the bi-annually publications Nordic Concrete Research (NCF), is a collaboration organization of the concrete associations in the five Nordic countries, Denmark, Finland, Iceland, Norway and Sweden. Read more about NCF on www.nordicconcrete.net.  "Nordic Concrete Research” has no article processing chargers (APCs) nor article submission charges.  Archiving  Sciendo archives the contents of this journal in Portico - digital long-term preservation service of scholarly books, journals and collections.  Plagiarism Policy  The editorial board is participating in a growing community of Similarity Check System's users in order to ensure that the content published is original and trustworthy. Similarity Check is a medium that allows for comprehensive manuscripts screening, aimed to eliminate plagiarism and provide a high standard and quality peer-review process. 