<abstract xmlns="http://www.w3.org/1999/xhtml">Concrete waste as crushed concrete aggregates (CCA) in structural concrete prolongs the technical life of the reference concrete accomplishing closed loop recycling. CCA concrete reaches the reference concrete compressive strength and workability by the densification of CCA and cement paste. Our previous study demonstrates CCA densification by mechanical pre-processing, aggregate quality improvements discerned by increased packing density giving reference concrete strength and workability. This study addresses paste densification with blast furnace slag (GGBS) to replace 30 (wt.%) of Portland cement at reference concrete w/b ratio 0.5 and a lower w/b 0.42. Two CCA replacements are investigated: fine aggregates, CCA50; overall aggregate replacement, CCA100.Compressive strength results show that both CCA50, CCA100 mixes achieve reference values at w/b 0.42, only CCA100 achieves reference value at w/b 0.5 as a climate-optimized concrete. The CCA50 mix-w/b 0.5 reaches reference strength when paste densification by GGBS is combined with CCA densification from mechanical pre-processing of aggregates. The 7-day strength of CCA100 with GGBS increases by 11% by mixing with pre-soaked GGBS. Statistical analysis of CCA100 strength results shows significant improvements with GGBS compared to mechanical pre-processing. Significant improvements are possible in CCA50 mix for a combination of mechanical pre-processed aggregates and GGBS replacement.</abstract>

Ph.D., Department of Resource Recovery and Building Technology

Adjunct Professor, Ph.D., Department of Resource Recovery and Building Technology

Ph.D.,Senior Lecturer, Department of Resource Recovery

Ph.D.,Senior Lecturer, Department of Resource Recovery and Building Technology

Effects of Slag Addition and Mechanical Pre-Processing on the Properties of Recycled Concrete in Terms of Compressive Strength and Workability

<abstract xmlns="http://www.w3.org/1999/xhtml">Thickness (<italic>T</italic>), Length (<italic>L</italic>), Width (<italic>W</italic>) and size distribution of scaled concrete particles in frost testing were measured. <italic>T</italic> (mm) increases with particle size surprisingly similarly for different concrete qualities and frost test methods. 2<italic>T</italic>/(<italic>L</italic>+<italic>W</italic>) reduces as function of size and is lowest for the largest particles of the salt scaling test: 0.1 – 0.15 but increases if large aggregate particles scale. Particle size distributions from salt frost testing peak for particles of 1-2 mm. The particles are flakier compared to particles from freeze/thaw in water which also have flatter size distribution no matter type of concrete or degree of damage. Scaling in water is not so efficiently reduced by air voids despite protecting very efficiently against internal damage and scaling in salt frost testing. Comparisons with <italic>T</italic> predicted by the glue spall model (≈3/4 × ice thickness) and the air void dependent (≈3× critical air void spacing) model proposed by Fagerlund are difficult due to the size dependent flake thickness. Image analysis could well describe shape. Further studies of concrete flake thickness scaled at varying thickness of ice layers are proposed.</abstract>

Professor, Norwegian University of Sc.&Techn.

Shape and Size of Particles Scaled from Concrete Surfaces during Salt Frost Testing and Rapid Freeze/thaw in Water

<abstract xmlns="http://www.w3.org/1999/xhtml">Widely used crack width calculation models and allowable crack width limits have changed from time to time and differ from region to region. It can be identified that some crack width calculation models consist with limitations for parameters like cover thickness. The current Norwegian requirement for cover thickness is larger than these limitations. The applicability of existing crack width calculation models and the allowable crack width limits must be verified for structures with large cover thickness. The background of crack width calculation models in Eurocode, Model Code 2010, Japanese code, American code and British code have been examined. By comparing the experimental crack widths with the predictions of the aforementioned models, the existing codes can be identified as requiring modification. Considering the durability aspect, it can be identified a long-term study proving that the allowable crack width can be increased with the increase in cover thickness. When considering the aesthetic aspect, the authors suggest categorizing the structures based on their prestige level and deciding the allowable crack widths accordingly. The paper proposes potential solutions for future research on how to improve both crack width calculation methods and allowable crack width limits to be used effectively in structures with large cover thickness.</abstract>

Department of Mechanical and Structural Engineering and Material Science

Associate Professor., University of Stavanger

Adjunct Professor., University of Stavanger

Department of IMBM. Manager Concrete Technology

Applicability of Existing Crack Controlling Criteria for Structures with Large Concrete Cover Thickness

<abstract xmlns="http://www.w3.org/1999/xhtml">Ultra-high performance concrete might be a competitive alternative to normal concrete for some purposes. But despite research efforts during decades, utilisation is still not widespread. Reasons include limited competence and material availability. This paper presents one step of a research initiative aimed at facilitating the use of UHPC in Norway. The step presented here comprises the accumulated results from investigations on the influence steel fibres (content, type, and hybrid combination) have on material strength and deformation behaviour of locally produced UHPC, made with constituents found in southern Norway. 231 specimens were tested, spanning nine UHPC mixes. Digital Image Correlation (DIC) was successfully used to study crack propagation. Compressive strength of 166 MPa and E-modulus of 46 GPa were obtained, not being influenced by fibre content. The flexural tensile strength was found to be strongly dependent on variations in steel fibre properties and mix design. The highest flexural tensile strength was obtained for prisms with micro straight steel fibres alone, or in 50% combination with macro hooked-end fibres. The experimental results are considered in a theory-informed discussion. Suggestions are made on the use of steel fibres in locally produced UHPC, potentially lowering the cost by 30%.</abstract>

M.Sc, PhD Research Fellow, Department of Engineering sciences, Faculty of Engineering and Science

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

Locally Produced UHPC: The Influence of Type and Content of Steel Fibres

<abstract xmlns="http://www.w3.org/1999/xhtml">Predicting the stress increase of an unbonded tendon in a post-tensioned continuous concrete beam at ultimate capacity is more difficult than when bonded tendons are used. The failure mechanisms of the continuous beam are also different to that of the simple-span beam. The loading type, ductility of the support area and moment redistribution influence the behaviour of the continuous structures. In this research, the simplified nonlinear analysis was used for predicting the unbonded tendon stress increase at ultimate capacity in continuous two-span beams. The model is based on the moment-curvature relationships of the reinforced concrete cross-sections under different compressive forces and deformations of the continuous beam under loading. The results have been compared with the experimental results of recent studies found in the literature. In addition, 92 unbonded post-tensioned two-span beams with different reinforcements have been examined by using the model and compared to the results obtained from empirical equations from the literature. The results from the nonlinear analysis correspond well to the results from the other models up to the reinforcement ratio of 0.35. The calculated values of the maximum moment capacity at the centre support were close to the results from the test beams.</abstract>

Determination of the Stress Increase of the Unbonded Tendon in a Continuous Concrete Beam at Ultimate Capacity Using Nonlinear Analysis

<abstract xmlns="http://www.w3.org/1999/xhtml">Construction business along with other businesses have set carbon neutrality goals in the following years. To reach these goals a lot needs to be done fairly quickly. The high impact of concrete production on carbon emissions has been known for years and solutions for this problem are studied in this paper through supplementary cementing materials.Ordinary Portland cement can be replaced partly but not completely with cement replacing materials since the strength properties are lost at replacement level higher than 80%. These replacing binders can be pulverized fly ash, blast furnace slag or silica fume.The use of the new low-carbon products can half the embodied carbon for the bearing frame of the building. The total area of a certain structure type is important since replacing its cement can have much higher impact on the total carbon footprint than replacing it for a single structure type that has fairly small area in the building.</abstract>

Decreasing Carbon Footprint of Block of Flats – Concrete Technology Possibilities

<abstract xmlns="http://www.w3.org/1999/xhtml">Service life of nine wind power unit pedestals, which concrete grades between C45 and C55, were studied with four different service life models. The exact service life could be calculated only with two of them with the initial data.The service life models that were used in calculations:
<list list-type="bullet"><list-item>• Factor method</list-item><list-item>• Deterioration and service life prediction of concrete subjected to freeze-thaw cycles in Na2SO4 Solution-method</list-item></list>Service life models that were considered only at theoretical level:
<list list-type="bullet"><list-item>• FIB Bulletin 34 – Model Code for Service Life Design, and</list-item><list-item>• An equation for determining freeze-thaw fatigue damage in concrete and a model for predicting the service life.</list-item></list>The latter two methods are more theoretical, and they require laboratory tests to obtain more information before the calculations can be properly executed.This article concludes that damage to concrete due to freeze-thaw cracking is still poorly known and a sufficiently accurate service life model has not yet been developed for its computational modeling. Therefore, there is a need to develop a service life model suitable for Finnish climate and concrete grades, which could be used for estimating the damage rate of an existing concrete structure.</abstract>

Service Life of Concrete Pedestal without Air Entrainment

<abstract xmlns="http://www.w3.org/1999/xhtml">The need for better natural resource use is currently increasingly recognised, and high emphasis is given to the circularity of building materials and the reduction of activities with negative environmental impact. Legislation, guidelines, and other documentation play an important role in improving demolition activities and construction and demolition waste (CDW) management. Good practices in CDW handling is not achievable without knowledge about CDW recovery techniques described in guidelines and other documents.Demolition activities in arctic regions could be more challenging due to harsh climate conditions, and therefore the cooperation between Russia, Norway and Finland was established to boost the uptake of good practices in demolition activities and CDW management. The main subject of this article is an overview of presently used demolition practices, CDW management, and verification of areas where practices with lower environmental impact and increase of material circularity could be utilised. Two fundamental documents, namely “EU Construction &amp; Demolition Waste Management Protocol” and “Guidelines for the waste audits before demolition and renovation works of buildings” [1, 2], were published by the European Union (EU) in 2019 and serve as a foundation for changes in demolition activities and CDW management in EU and adventitiously also in the Russian Federation and Norway.</abstract>

M.Sc., Northern (Arctic) Federal University named after M.V. Lomonosov

Dr., Doc., Senior research fellow, University of Oulu

Northern (Arctic) Federal University named after M.V. Lomonosov

Dr., Postdoctoral researcher, University of Oulu

A Comprehensive Summary of Available Legislation and Practices in Demolition and Construction &amp; Demolition Waste Management in the Arctic Region

<abstract xmlns="http://www.w3.org/1999/xhtml">A new admixture is available, to reduce the sludge produced from the cleansing of production and transportation equipment in the fresh concrete industry. The result is agglomerations of hardening concrete, that might be utilised for aggregate. Utilisation depends on adequate properties. This paper reports from investigations on the physical and mechanical properties of the aggregate and discussions on the performance relative to natural and recycled aggregates and towards requirements for utilisation. The findings indicate substantial potential for utilisation, supporting the reduction of waste for deposit and development of the concrete industry towards a circular economy.</abstract>

From Waste to Resource – Utilising Residue from Ready-Made Concrete as New Aggregate

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. 