rss_2.0Nordic Concrete Research FeedSciendo RSS Feed for Nordic Concrete Research Concrete Research Feed 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 of Effective and Minimal Slab Widths for Evaluating the Shear Capacity of RC Overhang Slabs<abstract> <title style='display:none'>Abstract</title> <p>The effective width is a relevant parameter for the design of bridge overhang slabs under concentrated loads. Experimental tests have been used to assess expressions for its calculation. However, the load capacity increases with the width until a transition area is reached. Test specimens may have lacked enough width to reach full shear capacity, affecting thus the evaluation of the results. On the other hand, within the transition area, a threshold value has been hypothesized to match the effective width. This paper aims to provide recommendations for minimal widths that guarantee the full capacity of overhang slabs and to assess the calculation of the effective width by means of the threshold value and other formulations. The effect of the edge beam is also considered. A campaign of validated non-linear FE-simulations based on experiments on range of width-span ratios was performed. The results suggest using a width-span ratio of at least 4.0 for slabs without an edge beam and 5.3 for slabs with an edge beam for the experimental practice. The efficiency of the formulation for the effective widths is diffuse and the use of threshold value leads to unsafe predictions. Instead, linear-elastic FE-analyses are recommended for the design practice.</p> </abstract>ARTICLEtrue Review on Fatigue Performance of Concrete Structures Part II, Material Parameters and Environmental Factors<abstract> <title style='display:none'>Abstract</title> <p>Fatigue is a critical issue for concrete structures subjected to repetitive and varying loads, particularly in infrastructure and transportation systems. This review paper presents a comprehensive overview of the current state of knowledge on concrete fatigue and identifies areas for further research. Material and size factors that influence fatigue performance and life estimation of concrete such as concrete composition, internal moisture content and reinforcement are explored, along with environmental conditions such as presence of external moisture and seawater exposure. The paper also acknowledges the challenges associated with predicting concrete fatigue life accurately due to the heterogeneous nature of concrete and its complex behavior under cyclic loading.</p> </abstract>ARTICLEtrue Effects of ASR-induced Expansion in Reinforced Concrete and Their Consequences for Structural Assessment<abstract> <title style='display:none'>Abstract</title> <p>This paper describes the structural effects of ASR expansion in reinforced structures. It proposes models and procedures for calculating the strains in the concrete caused by the reinforcement, the load effects in statically indeterminate structures and the cross-sectional capacities. Three models are described to include variations of the ASR expansion in a section. Model 1 for constant or linearly varying ASR expansion, Model 2 for an expansion variation in different parts of a cross-section and Model 3 for a particular case of different expansion in subsections of the cross-section. The models are exemplified by calculations based on input data from one relevant bridge, the 70 years old Elgeseter bridge in Trondheim, Norway. This is done to illustrate various aspects of the calculation methods and show the structural consequences of the ASR expansion. The results correlate with the bridge’s observed structural behavior and assumed expansion. This paper also illustrates the importance of coordinating inspection, material testing and structural strength analysis to obtain reliable assessment.</p> </abstract>ARTICLEtrue Mechanisms of Fibre Reinforced Shotcrete: Numerical Simulations Considering Local Variations in Thickness and Bond Strength<abstract> <title style='display:none'>Abstract</title> <p>Fibre-reinforced shotcrete is the most common support method for hard rock tunnels in the Nordic countries. The design of shotcrete is often based on empirical methods or simplified analytical equations, which neglect variations in mechanical properties and shotcrete thickness. Data collected from the field shows that significant variations in shotcrete thickness and bond strength should be expected during tunnel construction. However, how this affects the structural behaviour and capacity of the shotcrete lining is unknown. Moreover, the design philosophy for shotcrete assumes that the primary failure modes of shotcrete, i.e. bond and flexural failure, can be treated separately. This was derived based on observations of experiments in a laboratory environment. Therefore, the focus of a finalized doctoral project was to develop a numerical framework to simulate the structural behaviour of fibre-reinforced shotcrete in interaction with hard rock and rock bolts. The effect of variations in shotcrete thickness and bond strength was studied through numerical simulations to increase the understanding of its effect on the failure load of the lining. The results indicate that the most important parameter is the mean value of the shotcrete thickness and bond strength around a narrow perimeter of the block.’</p> </abstract>ARTICLEtrue Modelling of Lithium Mitigation for Alkali-Silica Reactivity<abstract> <title style='display:none'>Abstract</title> <p>The Alkali-Silica Reaction (ASR) is a deleterious concrete chemical reaction that has been studied a lot since its discovery in 1940. The reaction produces a highly hygroscopic silica gel that swells into the pores of concrete, resulting in the critical decrease of the mechanical performances of the affected structures. Some methods have been investigated to limit expansion under a certain limit, among them lithium mitigation. However, the mechanisms are not really understood yet and determining the right amount of lithium is still arduous. An attempt for a method in coherence with experience is presented in this study, using the chemo-mechanical model of Larive and curve-fitting. The results provide accuracy to experimental measurements from several protocols, and call for further research.</p> </abstract>ARTICLEtrue Cement Paste Modified with Carbon Nanomaterials Capable of Self-Repair after a Fire?<abstract> <title style='display:none'>Abstract</title> <p>This manuscript presents preliminary results on the cement paste potential, with and without carbon nanomaterials, to heal high-temperature cracks. Cement paste beams were subjected to thermal loading of 200°C and 400°C after 28 days of water curing. High temperature caused the formation of microcrack networks on the specimen’s surface. Self-healing was achieved by exposing the cracked samples to cyclic water immersion. The efficiency of the process was evaluated based on the crack closure and mechanical properties recovery after 24 days. The results indicated a distinct dependence of the healing on the loading temperature. Carbon nanotubes had a positive effect on self-repair efficiency.</p> </abstract>ARTICLEtrue of Crushed Fine Materials<abstract> <title style='display:none'>Abstract</title> <p>As natural resources of sand and fine material used in the concrete industry are becoming more scarce, crushed materials are being used to a greater extent. Shape and texture of machine crushed materials differ from aggregates naturally ground, layered and sorted under the course of millions of years. It is assumed that crushed aggregates are more angular and of less smooth texture than natural aggregates, which will affect the flow behaviour of a suspension containing crushed material. In the mix design process of cementitous suspensions, an adequate rheology of the micro mortar (all constituents in the concrete being able to pass a 0.125 mm sieve, including the cement) is crucial. In this paper, the shape of fine particles is linked to the micro mortar plastic viscosity of the filler suspension including cement. The plastic viscosity here serves as an important quality assessment of the filler, since the micro mortar workability features are vital for the final mix design quality of the concrete workability.</p> </abstract>ARTICLEtrue of High-Pressure Washing on Chloride Ingress in Concrete – Development of an Accelerated Test Method<abstract> <title style='display:none'>Abstract</title> <p>Bridges constitute an important part of the infrastructure. For bridges to have the longest possible service life with minimum repairs, the maintenance is of great importance. One type of bridge maintenance that is rarely researched is the continuous preventive maintenance. The continuous preventive maintenance consists of removal of vegetation, cleaning of bridge joints and drainage systems as well as high-pressure washing of the structure. The effect of washing is discussed but not properly researched. A study on the effectiveness of high-pressure washing on concrete is therefore being conducted. An accelerated test method is being developed to mimic field testing. The method has been developed through tests on small concrete specimens subjected to fluctuating temperature, fluctuating moisture, and repeatable exposure to de-icing salt during several cycles. The specimens are of two recipes where one represents an old concrete bridge with rather high water-cement ratio (0.6) and the other one represents a new concrete bridge with a low water-cement ratio (0.4). The first two versions of the method are described. The second version shows promising results, but the method needs further development to incorporate additional factors.</p> </abstract>ARTICLEtrue