rss_2.0Nordic Concrete Research FeedSciendo RSS Feed for Nordic Concrete Research Concrete Research 's Cover Waste to Resource – Utilising Residue from Ready-Made Concrete as New Aggregate<abstract><title style='display:none'>Abstract</title><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Service Life of Concrete Pedestal without Air Entrainment<abstract><title style='display:none'>Abstract</title><p>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.</p><p>The service life models that were used in calculations: <list list-type="bullet"><list-item><p>• Factor method</p></list-item><list-item><p>• Deterioration and service life prediction of concrete subjected to freeze-thaw cycles in Na2SO4 Solution-method</p></list-item></list></p><p>Service life models that were considered only at theoretical level: <list list-type="bullet"><list-item><p>• FIB Bulletin 34 – Model Code for Service Life Design, and</p></list-item><list-item><p>• An equation for determining freeze-thaw fatigue damage in concrete and a model for predicting the service life.</p></list-item></list></p><p>The latter two methods are more theoretical, and they require laboratory tests to obtain more information before the calculations can be properly executed.</p><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Determination of the Stress Increase of the Unbonded Tendon in a Continuous Concrete Beam at Ultimate Capacity Using Nonlinear Analysis<abstract><title style='display:none'>Abstract</title><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Locally Produced UHPC: The Influence of Type and Content of Steel Fibres<abstract><title style='display:none'>Abstract</title><p>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%.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Shape and Size of Particles Scaled from Concrete Surfaces during Salt Frost Testing and Rapid Freeze/thaw in Water<abstract><title style='display:none'>Abstract</title><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Applicability of Existing Crack Controlling Criteria for Structures with Large Concrete Cover Thickness<abstract><title style='display:none'>Abstract</title><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Decreasing Carbon Footprint of Block of Flats – Concrete Technology Possibilities<abstract><title style='display:none'>Abstract</title><p>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.</p><p>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.</p><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00A Comprehensive Summary of Available Legislation and Practices in Demolition and Construction & Demolition Waste Management in the Arctic Region<abstract><title style='display:none'>Abstract</title><p>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.</p><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Effects of Slag Addition and Mechanical Pre-Processing on the Properties of Recycled Concrete in Terms of Compressive Strength and Workability<abstract><title style='display:none'>Abstract</title><p>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.</p><p>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.</p></abstract>ARTICLE2021-07-17T00:00:00.000+00:00Salt-Frost Scaling of Concrete with Slag and Fly Ash - Influence of Carbonation and Prolonged Conditioning on Test Results<abstract><title style='display:none'>Abstract</title><p>According to Swedish experience the slab method in CEN/TS 12390-9 is successful in predicting the salt-frost resistance of Portland cement concrete. However, doubts have been raised whether the same can be said when used on concrete with supplementary cementitious material, e.g. fly ash or ground granulated blast furnace slag (GGBS). Test results from concrete mixes with up to 35 % fly ash 65 % GGBS, with two different Portland cements and a water-to-binder ratio of 0.45 are presented in this paper. The tests were carried out with the standard method and with five modifications concerning the pre-conditioning of the specimens before freeze-thaw cycling. The age of the specimens at sawing was increased, the time in 65 % RH was prolonged and exposure to 1 % CO<sub>2</sub>-environment was used. The results show that for air-entrained concrete with fly ash or GGBS both prolonging the exposure to 65 % RH and exposure to CO<sub>2</sub> diminishes the salt-frost resistance. The influence increases with increasing amount of fly ash or GGBS. However, the type of cement also has a certain influence. The influence of exposure to CO<sub>2</sub> on the salt-frost resistance of concrete without entrained air was totally different from the influence on concrete with entrained air.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Preface Bauxite Residue as Novel SCM<abstract><title style='display:none'>Abstract</title><p>Bauxite residue is a major waste stream available in large volumes globally that can cause risks to the surrounding environment (e.g. ecotoxicity) when disposed and stored by conventional methods. There is yet no large-scale application and the utilization as supplementary cementitious material might be the best way to re-use bauxite residue. The main obstacle for the utilization of bauxite residue in the construction industry is the high alkalinity. This paper presents first results of a study on alkali reduction of bauxite residue by acetic acid treatment and the potential application of this alkali reduced bauxite residue as pozzolan in cementitious binders. A process of alkali reduction is presented that can help solving waste management problems of alumina refineries by transforming bauxite residue to a less hazardous waste, while producing a reactive pozzolan and Na-acetate that can find application in the construction and infrastructure market. 90% alkalinity reduction of bauxite residue could be achieved by simply washing with diluted acetic acid. Alkali-reduced bauxite residue showed good pozzolanic reactivity regarding portlandite consumption, bound water and 28-day compressive strength of mortars with 20% replacement of OPC.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Review of Sprayability of Wet Sprayed Concrete<abstract><title style='display:none'>Abstract</title><p>Wet sprayed concrete quality is affected by more production factors than cast concrete, particularly due to the propulsion through the nozzle and the flash set caused by the set accelerator. Practitioners often use the term “sprayability” to describe these factors. We propose a definition of “sprayability” that relates the application to the final properties of the hardened sprayed concrete and review factors affecting it: concrete constituents, proportioning, and application mechanics. These factors affect the hardening and the structure of the hardened sprayed concrete – the porosity, permeability and durability. We consider improving sustainability through proportioning with increased share of supplementary cementitious materials, calculate the placed composition and focus on factors that affect water transport, and hence durability. Due to the spray application and flash-set, irregular compaction voids dominate the macro pore structure of sprayed concrete. Studies of permeability of sprayed concrete have shown that it is possible to obtain low permeabilities given adequate composition and curing. Presumably these samples have been well-cured, uncracked and with non-percolating macro voids. Given observations of cracks in sprayed concrete linings and the macro voids, important further studies will be on the effect of accelerator, compaction porosity and cracking on permeability.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Concrete and Sustainability – Some Thoughts from a Swedish Horizon<abstract><title style='display:none'>Abstract</title><p>Concrete production, especially the cement production, stands for 5-8 percent of the global CO<sub>2</sub> emissions. Since concrete is the most frequently used man-made construction materials, this fact is not surprising. Concrete is also the only realistic alternative in order to improve the living circumstances in many countries around the world. Due to its size, the concrete sector has a great responsibility for limiting the consequences of the on-going climate change. The Swedish cement producer Cementa has an ambitious zero vision stating zero CO<sub>2</sub> emissions in year 2030. The measures include energy efficiency, bio mass instead of fossil fuels, blended cements, CO<sub>2</sub> uptake through carbonation and Carbon Capture Storage (CCS). This paper discusses these measures but also others such as optimization of the concrete mix, optimization of the structural geometry and prolongation of the service life. The paper is ended by a section on adaptation since concrete will also have an important role concerning protection of the built environment for climate change. Protection structures against flood, reconstruction of dams, new waste-water systems and bright permeable concrete pavements reflecting sunlight and improving drainage after heavy rain constitute some examples.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Environmental Assessment of Frost-resistant Concrete with Superabsorbent Polymers<abstract><title style='display:none'>Abstract</title><p>Air-entraining agents (AEA) are normally used to improve the frost resistance of concrete. However, it is not possible to accurately control the air void system in concrete with AEA. Thus, a significant loss of concrete strength is caused by over-dosing voids, and this increases the environmental impact from concrete structures. Superabsorbent polymer (SAP) can also be used to produce frost-resistant concrete. Compared to AEA, it can be used to precisely engineer the air void structure of concrete, promote cement hydration, and mitigate self-desiccation cracks. In this study, life cycle assessment methodology is applied to evaluate the overall environmental impact of frost-resistant concrete based on AEA and SAP, respectively. The results illustrate that frost-resistant concrete with SAP has a lower environmental impact than frost-resistant concrete with AEA if the strength and durability of concrete are considered in the defined functional unit. In addition, frost-resistant concrete with SAP reduces the environmental burdens of the vertical elements such as columns, but it increases the environmental load of the horizontal elements such as slabs, where the strength increase cannot be utilized. Moreover, the inventory data for AEA and SAP can affect the impact assessment results.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Utilization of Bio Ashes in Cement-based Materials: A Case Study in Cooperation with Pulp and Paper and Energy Production Industries in Sweden<abstract><title style='display:none'>Abstract</title><p>Worldwide increased concern of the CO<sub>2</sub> emissions has led to the replacement of coal by biomass in combustion-based power plants. However, this would cause the scarcity of fly ash, one of the most well-known rest products from coal combustion, which is used as supplementary cementitious materials (SCM) in construction sector to reduce the large environmental footprint of cement production. Seeking to find alternative SCMs, this article aims to demonstrate the viability of using bio ashes in Sweden as SCM, which, due to lack of studies validating their value, are landfilled today. According to the obtained results, bio ashes produced at pulp and paper industries have a considerably consistent chemical composition and exhibit a satisfactory pozzolanic behaviour. Nevertheless, according to the conclusions of this study, the pozzolanicity of these alternative binders is not reflected equally with respect to the most known reactivity tests for common SCMs. The results imply that although “R3” tests method infers the pozzolanic characteristics of the bio ashes in focus of this study, the “activity index test” as well as “calcium consumption test” indicate otherwise.</p></abstract>ARTICLE2020-12-31T00:00:00.000+00:00Reduction of Radon Gas in Concrete Using Admixtures and Additives<abstract><title style='display:none'>Abstract</title><p>The second largest cause of lung cancer is related to radon (<sup>222</sup>Rn) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of <sup>238</sup>U from its constituents. The Swedish Cement and Concrete Research Institute (CBI) has examined three concrete recipes where only an additive as well as fly ash were added as single constituents to a reference recipe and compared to a reference concrete. The inputs of an additive as well as a supplementary cementitious material (fly ash) were made as a mean to investigate their potential influence on the radon exhalation rates of the concrete. Measurements were performed with an ATMOS 33 ionizing pulsation chamber for at least five different occasions for each recipe during a 22 month period. The results indicate a reduction of the exhalation rate by approximately 30-35 % for each altered recipe. This means roughly 1.5-2 mSv per year decrease in effective dose to a human using an additive or a supplementary cementitious material such as fly ash in relation to the investigated standard concrete.</p></abstract>ARTICLE2018-12-01T00:00:00.000+00:00The Influence of Supplementary Cementitious Materials on Climate Impact of Concrete Structures Exposed to Chlorides<abstract><title style='display:none'>Abstract</title><p>Addition of fly ash or GGBS in concrete has shown to increase the durability and thus the service life of concrete structures exposed to chlorides. Currently, the durability relies on regulations, which beside a minimum cover thickness also put constraint on amount and type of SCM in different environments. Swedish regulations do not, however, consider the actual durability of different binders. As a consequence, a LCA might be misleading. This paper investigates the climate impact of concrete with SCM in chloride environment. Current prescriptive design approach is compared with a performance based service life approach and applied to bridge parts.</p></abstract>ARTICLE2018-12-01T00:00:00.000+00:00Long-term Influence of Concrete Surface and Crack Orientation on Self-healing and Ingress in Cracks – Field Observations<abstract><title style='display:none'>Abstract</title><p>This paper presents results from investigations on the long-term influence of concrete surface and crack orientation on ingress in cracks. Five reinforced concrete structures from Norway exposed to either de-icing salts or seawater have been investigated. Concrete cores were taken with and without cracks from surfaces with vertical and horizontal orientation. Carbonation in cracks was found on all de-iced structures, and a crack on a completely horizontal surface appeared to facilitate chloride ingress. Ingress of substances from seawater was found in all cracks from marine exposure. However, the impact of cracks on chloride ingress was unclear. Horizontal cracks on vertical surfaces appeared to facilitate self-healing.</p></abstract>ARTICLE2018-12-01T00:00:00.000+00:00Dynamic Measurements for Determining Poisson’s Ratio of Young Concrete<abstract><title style='display:none'>Abstract</title><p>Knowledge of the elastic properties of concrete at early age is often a pre-requisite for numerical calculations. This paper discusses the use of a laboratory technique for determining Poisson’s ratio at early concrete age. A non-destructive test set-up using the impact resonance method has been tested and evaluated. With the method, it has been possible to obtain results already at 7 hours of concrete age. Poisson’s ratio is found to decrease sharply during the first 24 hours to reach a value of 0.08 and then increase to approximately 0.15 after seven days.</p></abstract>ARTICLE2018-12-01T00:00:00.000+00:00en-us-1