rss_2.0Nordic Concrete Research FeedSciendo RSS Feed for Nordic Concrete Research Concrete Research Feed Testing Non-air Entrained High-performance Fly-ash Concrete Part II: Parameter Study of Effect of Internal Cracking on Glue Spall Stress<abstract> <title style='display:none'>Abstract</title> <p>A parametric analysis of glue spall stress (concrete surface tensile stress at ice-discontinuities by differential thermal expansion ice-concrete) as affected by internal cracking in concrete in the CEN/TS 12390-9 salt-frost slab-test was made. Increasing differential thermal expansion ice-concrete (∆α) and reduced E-modulus and Poisson ratio (ν) due to internal cracking were used based on data from Part 1 of this study. For the concrete specimens in Part 1 of this study [<xref ref-type="bibr" rid="j_ncr-2023-0016_ref_001">1</xref>] glue spall stress increased by 14 % due to internal cracking whereas reduced ice thickness of 1 – 2 mm due to accelerated Liquid Uptake (LU) in wet freeze/thaw reduced glue spall stress by 34 to 65 %. LU should hence be accounted for in modelling scaling, both due to reduced ice thickness and increased ∆α due to internal cracking. Increased crack penetration depth and its effect on scaled particle size due to internal cracking were also analyzed.</p> </abstract>ARTICLEtrue and Joint Evaluation of Importance, Redundancy and Robustness Indicators Applied to Aging Prestressed Concrete Bridges<abstract> <title style='display:none'>Abstract</title> <p>A bridge failure can result in significant social, economic, and environmental problems; therefore, its reliability and risk management are essential. Bridges’ system reliability and risks are governed mainly by their redundancy and robustness, which currently are not adequately included in most design code specifications. Thus, in this study, a comprehensive comparison between relevant importance, redundancy, and robustness indicators found in the literature with different levels of complexity is carried out. The indicators under analysis have been used separately in different studies but have never been addressed together. Therefore, this study presents a joint evaluation of deterministic, reliability- and risk-based indicators to evaluate the differences in interpretation and information provided by the indicators. The approach is exemplified by analyzing a prestressed concrete bridge subjected to continuous degradation due to chloride ingress. A procedure is implemented to couple a metamodel-based reliability approach with a Nonlinear Finite Element Analysis (NLFEA). Based on the analysis performed, the comparison between indicators showed how different interpretations can be obtained depending on the implemented approach. Thus, creating more uniform formulations and agreeing on target values is necessary to help with redundancy and robustness interpretation.</p> </abstract>ARTICLEtrue Testing Non-air Entrained High-Performance Fly-ash Concrete. Part I: Relations Liquid uptake - Internal Cracking – Scaling<abstract> <title style='display:none'>Abstract</title> <p>The surface scaling of low CO<sub>2</sub>-emission High Performance Concretes (HPC) was studied in freeze/thaw performance tests with a 3 mm layer of 3% NaCl on the surface to investigate whether such concretes can be made frost durable without air entrainment. Four different non-air entrained silica fume (SF)-fly ash concrete mixes with w/b = 0.30 – 0.35 with 91d strengths &gt;100 MPa were investigated after 3 different curing conditions (Normal, Dried, Wrapped). The w/b=0.30 CEM IIA reference mix without additional FA had lowest scaling following all curing conditions. However, all 4 mixes at all 3 curing conditions had severe internal damage. Liquid Uptake (LU) during freeze/thaw related best to internal damage. The correlation between LU-scaling and strain-scaling was very good for wrapped curing which also showed high internal damage. We therefore suggest proceeding in modelling simultaneous salt scaling and internal damage.</p> </abstract>ARTICLEtrue of the Result of a Traditional Salt-Frost Scaling Test<abstract> <title style='display:none'>Abstract</title> <p>Frost damage on the concrete surface might be aggravated when freezing occurs in the presence of a salt solution, like sea water or de-icing salt. A possible mechanism behind this combination of frost and salt is discussed. When freezing takes place in pure water, ice formed at the surface will block inflow of water to the concrete, but it will cause drying of the concrete. When freezing occurs in salt solution, unfrozen water (brine) can enter the concrete surface and make the concrete completely saturated. When pore water freezes, it exerts pressure. The effect of air-entrainment is favourable since it reduces the stresses. A calculation is made of the air requirement for concrete with w/c-ratio 0.45.</p> </abstract>ARTICLEtrue Options for Corrosion-damaged Prestressed Concrete Bridges<abstract> <title style='display:none'>Abstract</title> <p>Prestressing of bridges allows construction of long spanned bridges made from thin structural members with high flexural and shear capacity. Studies have shown that some of the existing prestressed bridges are not meeting their designed service life due to corrosion of the tendons. The main reasons are poor construction practices in combination with inadequate inspection and maintenance plans. This paper provides a summary of repair options for corrosion-damaged prestressed concrete structures with focus on the individual components of the prestressed system. The applicability of identified repair options to Norwegian conditions is discussed.</p> </abstract>ARTICLEtrue of Composite Cements Containing Novel SCMs<abstract> <title style='display:none'>Abstract</title> <p>The impact of novel supplementary cementitious materials (SCMs) on the phase assemblage and the pore structure in cement pastes was studied and linked to their impact on the compressive strength in mortar. The composite cements analysed had a composition of 78 wt.% Portland cement, 18 wt.% SCM and 4 wt.% limestone filler, and the samples were cured sealed for 91 days at 20°C. The investigated SCMs comprise natural materials such as clays and volcanic rocks (rhyolite and hyaloclastite), and industrial products such as fly ash, slag, oil shale ash, bio-fuel ash or bio-coal fly ash. The results revealed that all the SCMs except oil shale ash contribute to the phase assemblage in a similar way, when clinker is replaced with 18 wt.% SCM. The pore structure of the different cement pastes was similar. Even when the composite cement pastes showed a higher total intruded pore volume compared to the Portland cement paste sample, these samples showed higher compressive strength. This indicates that total intruded porosity is not the only contribution to strength.</p> </abstract>ARTICLEtrue the Influence of Curing Temperature and SCMs on C-A-S-H Composition Using SEM-EDS Hypermaps<abstract> <title style='display:none'>Abstract</title> <p>Calcium-alumina-silicate-hydrate (C-A-S-H) is the main hydration product formed in Portland composite cement pastes. C-A-S-H is a key phase with regard to the strength and durability of concrete. Proper characterization of C-A-S-H is difficult due to intermixing with other phases, thus limiting the applicability of point scan analyses using scanning electron microscopy (SEM). Recent advances have enabled the use of hypermaps from energy dispersive spectroscopy (EDS) to investigate hydrate phases with better statistics. This study investigated how increased curing temperature and the inclusion of pozzolanic SCMs change the composition of the C-A-S-H, using the edxia plugin and SEM-EDS hypermaps. Composite cement pastes were cured at 20, 38, and 60°C for 180 days before analysis. We discuss the interpretation of the data from hypermaps in comparison to the traditional point scan approach.</p> </abstract>ARTICLEtrue for Assessing Concrete Segregation Due to Compaction<abstract> <title style='display:none'>Abstract</title> <p>Segregation in concrete significantly affects its durability and structural integrity by introducing local variance in both the strength distribution and the modulus of elasticity within a structural element. Additionally, segregation can lead to durability complications, such as shrinkage induced cracking. Recent observations have identified such segregation issues in already existing structures, underscoring the importance of assessing segregation. In this study, we evaluate the extent of segregation in normally vibrated concrete specimens, which were subjected to different vibration durations and vibrated using either table or poker vibrators. The research introduces three segregation indices to assess this phenomenon. One index relies on the standard deviation of densities across multiple slices of each specimen, while the other two utilize Digital Image Processing (DIP) to analyse the distribution of aggregates in horizontal and vertical slices, respectively. High correlations were found between the density-based index and vibration time for both poker-vibrated and table-vibrated specimens. The DIP-based indices showed strong correlations with the density-based approach, offering quicker alternatives for assessing segregation. The study further proposes classification levels for segregation based on these methods and reveals the negative impact of increased air entrainment on segregation. These findings provide insights for optimizing concrete compaction processes and understanding segregation.</p> </abstract>ARTICLEtrue Use of Slag in Accelerated Shotcrete for Rock Support: A Pilot Study on the Influence on the Early Compressive Strength<abstract> <title style='display:none'>Abstract</title> <p>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 CO<sub>2</sub> 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.</p> </abstract>ARTICLEtrue the Location of Steel Reinforcement in Thick Concrete Walls by Non-Destructive Inspection<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>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.</p> <p>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.</p> </abstract>ARTICLEtrue the Application of Mesostructures in 3D Concrete Printing – Evaluating Load-bearing Performance<abstract> <title style='display:none'>Abstract</title> <p>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.</p> </abstract>ARTICLEtrue Changes in Workability during Concrete Pumping – An Industrial Approach<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>It is suggested that around 1 100 000 m<sup>3</sup> 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.</p> <p>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 m<sup>3</sup> of concrete, over 10 years.</p> </abstract>ARTICLEtrue between Chloride Migration, Bulk Electrical Conductivity and Formation Factor of Blended Cement Pastes<abstract> <title style='display:none'>Abstract</title> <p>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.</p> <p>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.</p> </abstract>ARTICLEtrue Carbonation of Binders Containing SCM at High CO Concentration<abstract> <title style='display:none'>Abstract</title> <p>Accelerated carbonation of recycled concrete aggregates (RCA) could be an efficient way to reduce the carbon footprint. High CO<sub>2</sub>-concentration under optimal relative humidity could accelerate the CO<sub>2</sub> 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 CO<sub>2</sub> 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 CO<sub>2</sub> concentration of 10 % under controlled temperature at 20 °C and 65 % RH. All tested binders presented a high CO<sub>2</sub> 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.</p> </abstract>ARTICLEtrue Experiments on Concrete Containing Ground Granulated Blast-Furnace Slag: Influence of Temperature, Air Entrainment And Salt<abstract> <title style='display:none'>Abstract</title> <p>Frost deterioration of concrete is an important durability issue for structures exposed to high degree of saturation, low temperatures and de-icers. The material can then be severely damaged with internal cracking and/or scaling of the surface, which can lead to e.g. reduced protection of the reinforcement and loss of load bearing capacity. Experiments with liquid uptake in concrete using different temperature cycles was made to study cryosuction. The material used was concrete with different air content and different replacement levels of ground granulated blast-furnace slag (GGBS). The concrete samples were preconditioned by capillary suction. Three temperature conditions were used: constant temperatures of +20 °C and -20 °C, and temperature that cycled between -20 °C and +20 °C. As liquid medium, deionized water and a 3% NaCl salt solution were used. Air entrainment generally increased the liquid uptake. The amount of GGBS and the NaCl concentration in the liquid did not have any significant impact on the liquid uptake in these experiments.</p> </abstract>ARTICLEtrue Review on Fatigue Performance of Concrete Structures Part I: Loading Parameters, Current Prediction Models and Design Approaches<abstract> <title style='display:none'>Abstract</title> <p>This review paper highlights the most fundamental state of knowledge regarding the fatigue of concrete that is available through the literature over the last decades and reveals the areas that are needed for further investigation. The loading factors influencing the fatigue performance and the fatigue life estimation of concrete structures are taken into consideration. This review explores the impact of eight loading parameters on the fatigue life of concrete structures, and we aimed to be succinct in our investigation. Besides, we present a review on the deterministic and probabilistic approaches for fatigue life prediction. For example, in more recent studies, the utilization of machine learning techniques has been shown to outperform the traditional methods. The review gives adequate insight into the approach of some of the main current design codes for fatigue life prediction of concrete.</p> </abstract>ARTICLEtrue Ion Diffusion Resistance of Bulk Hydrophobic Concrete: Comparison of w/c and Dosages<abstract> <title style='display:none'>Abstract</title> <p>Post-cast application of hydrophobic agents onto hardened concrete is successful at reducing external ion diffusion into cement paste, this work examines pre-cast application of hydrophobic admixtures in fresh concrete. Concretes, with water to cement ratios (w/c) 0.45 and 0.50 (CEM I; low C3A), were mixed. Adding alkyltrialkoxysilane or triacylglycerol admixtures ranging from 1 to 3 wt%cem in these concretes were evaluated. Increasing the dosage of hydrophobic admixtures decreased the compressive strength. The usage of these admixtures did not hinder the further development of the microstructure as all concretes gained strength after one year, but not in the same percentage increase as the reference concrete. Chloride ion diffusion, after exposure to 3 wt% NaCl solution at 20 °C for 91 days, in concretes with 1 wt%cem admixture showed slight reductions in diffusion rate (8-17%) compared to the reference. At 3 wt%cem, triacylglycerol admixtures showed better hindering effects of inward chloride diffusion, this was especially evident in w/c = 0.45. Equivalent addition of alkyltrialkoxysilane-based admixtures increased the diffusion of chloride ions transferred into the cement matrix.</p> </abstract>ARTICLEtrue for Test Series for Relative Humidity Measurements to Calibrate Drying Time Simulation Model<abstract> <title style='display:none'>Abstract</title> <p>There is a great need for an easy-to-use tool to simulate drying of concrete floors. In order to model practical situations, the tool should take into account changing conditions, especially wetting at worksite, but also temperature. For this purpose, a simulation program was developed for drying time estimations for concrete floors, which was published in 2021 and is named as the “by2020 Concrete drying time estimate”. This study presents the results of the laboratory test series conducted to calibrate the drying time estimations of the by2020 software. As all possible scenarios for practical situations were not possible to study in the test series, results from the literature were partly used for calibration and validation of the tool. A methodology for test series for calibration of the drying time estimation model is proposed based on this study. It was found that a model suitable for practical applications can be implemented based on relative humidity measurements only. However, the tests series of relative humidity measurements should take into account the influence of various factors such as wetting period and different temperature conditions.</p> </abstract>ARTICLEtrue