rss_2.0Nordic Concrete Research FeedSciendo RSS Feed for Nordic Concrete Research Concrete Research 's Cover Concrete Research workshop: “Accelerated freeze-thaw testing of concrete”, Lyngby, 20 April 2022<abstract> <title style='display:none'>Abstract</title> <p>A one-day Nordic Concrete Research workshop on “Accelerated freeze-thaw testing of concrete” attracted approx. 30 participants. The workshop included presentations on various aspects, such as observed frost damage in the field and the importance of the temperature curve during testing as well as other interactions with the surroundings of the concrete. The workshop also included examples of recent research, which can improve our knowledge about the frost damage mechanism and therefore provide input to improving the standardised test methods. The present paper is a summary of the nine presentations and the discussion arising from the presentations.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00When and How Should Chloride Profiles be Calibrated for Paste Fraction?<abstract> <title style='display:none'>Abstract</title> <p>Due to stochastic and systematic variations in the paste fraction, data for total chloride content are occasionally calibrated using parallelly measured calcium content as a measure of the actual paste fraction − assuming non-calcareous aggregates and no calcium leaching. Data from concrete exposed at the marine Fehmarn Belt Exposure Site questions the latter assumption. In the outer zone experiencing calcium leaching (ten mm after ten years), errors will be introduced by calcium calibration. To account for the wall effect, calcium profiles from cores taken before exposure might be used to correct for the systematically higher paste fraction at cast surfaces.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Nonlinear Cyclic Analysis of Reinforced Concrete Columns Using Fiber Section Approach<abstract> <title style='display:none'>Abstract</title> <p>This study investigates nonlinear modeling and verification of a reinforced concrete element using the fiber section method. At first, the theory related to the fiber section approach and hysteresis models used for cyclic analysis is given. Then, a reinforced concrete column tested previously in the literature is modeled and simulation results are compared with the test results. An acceptable approximation is made utilizing only a few input parameters: Uniaxial stress-strain curves of the materials, location and length of the plastic hinge, and geometry of the model. Moreover, the axial force-moments interaction curve from Eurocode is compared with the one obtained from the nonlinear model. It is shown that by conducting nonlinear analysis a larger capacity of the element is considered which results in a more realistic and economic design.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Preface Management of Existing Concrete Bridges Using Digital Twins and BIM: a State-of-the-Art Literature Review<abstract> <title style='display:none'>Abstract</title> <p>The need to optimize investments in bridge maintenance has created a demand for improved bridge management systems (BMS). Outdated practices in bridge inspection and constant advances in information technology have also contributed to this demand. The use of Digital Twins (DT), although well established in other industries, is still incipient for asset management and structural analysis of bridges. There is a great deal of research on Building Information Modelling (BIM) for bridge inspection, but its post-construction potential is still under-explored. This study presents a state-of-the-art review of the literature on asset management for bridges using digital models such as BIM and digital twins. The review was conducting using a systematic approach. Despite the rapid increase in research on DT and the amount of existing research on BIM, several gaps remain to be addressed, such as the lack of consensus about the definition of digital twins, which has led to wrongful categorisation of digital models as DT. The complex data flow and software compatibility required to develop a functional DT have hindered the exploitation of their full potential so far. The integration of BIM post-construction to BMS and existing automation technologies can also significantly improve current practices of bridge management.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Grading Material Properties in 3D Printed Concrete Structures<abstract> <title style='display:none'>Abstract</title> <p>Functionally graded materials (FGMs) describe composite materials with a gradual change in properties along one or several axes. A major advantage with this approach is the avoidance of discontinuities between different layers of material. 3D Printing offers the possibility to control the material composition and spatial placement along the printing process to create structures with graded properties. However, there are very few examples of the application of this approach to 3D concrete printing (3DCP). This paper presents a review of the current approaches of and methods to grade the material properties of a 3DCP structure, as well as a review of similar methods used in other 3D printing processes. Finally, the potential applicability of these principles into concrete are presented and discussed.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Effect of Set Accelerator on Properties of Wet Sprayed Concrete<abstract> <title style='display:none'>Abstract</title> <p>This paper describes sprayed concrete experiments varying the set accelerator dose. Literature on the hydration of cement with modern alkali-free set accelerators is reviewed and two full scale wet spraying experiments have been conducted, varying the dose of set accelerator in each. The effects on the properties of the hardening and hardened sprayed concrete were investigated by field and laboratory testing. Increasing the set accelerator dose was found to increase the rate of early age strength development but reduce density, long term strength and increase suction porosity of hardened sprayed concrete.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks<abstract> <title style='display:none'>Abstract</title> <p>Concrete cracks in structures such as water tanks and nuclear power stations cause anxiety to owners, contractors and engineers. These cracks may significantly increase the structure’s permeability and thus increase leakage, reduce durability, and eventually lead to loss of structural functionality. Therefore it is important to minimize their occurrence and size. To identify effective ways of minimizing cracking in young concrete segments, a parametric study was conducted using the finite element method (FEM). Parameters considered include casting sequence, joint position, wall height, and cooling. The study examined continuous and jumped casting approaches to the casting of a cylindrical reinforced concrete tank for a sewage-treatment plant, with and without the application of the ‘kicker’ technique in which the lower part of the wall is cast with the slab. The main cause of cracking is thermal change and restraint imposed by adjacent older structures, and the FEM predictions agree well with experimental observations. Continuous casting is most effective at minimizing cracking because it creates only two contact edges between newly cast and existing structures producing the lowest level of restraint. The kicker technique is shown to be very effective for reducing restraint and consider rephasing.</p> </abstract>ARTICLE2022-07-11T00:00:00.000+00:00Application of an Improved Empirical Model for Rheology Prediction of Cement Pastes Modified with Filler from Manufactured Sand<abstract> <title style='display:none'>Abstract</title> <p>There is a need for simple but precise prediction models for proportioning concrete with manufactured sand, for use in ready-mix concrete production. For the last two decades, the particle-matrix model has been used in Norway for proportioning and prediction of concrete flow based on the properties and proportions of two concrete phases: coarse particles and filler modified cement paste (matrix). This paper presents experimental testing of 117 cement pastes of which 107 contain filler, i.e. particles &lt; 125 microns, from manufactured sand. Based on compositions and properties of ingoing materials in these mixes, an empirical equation is developed that predicts the rheological properties plastic viscosity, yield stress, flow resistance ratio and mini slump flow. Optimization by regression analysis provides a practical microproportioning equation that readily can be used as input in concrete proportioning with the particle-matrix model. The equation provides a coefficient of determination <italic>R<sup>2</sup></italic> = 0.98 for plastic viscosity, <italic>R<sup>2</sup></italic> = 0.95 for mini slump flow, <italic>R<sup>2</sup></italic> = 0.91 for flow resistance ratio and <italic>R<sup>2</sup></italic> = 0.80 for yield stress.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Nonlinear Analysis of Reinforced Concrete Shear Walls Using Nonlinear Layered Shell Approach<abstract> <title style='display:none'>Abstract</title> <p>This study discusses nonlinear modelling of a reinforced concrete wall utilizing the nonlinear layered shell approach. Rebar, unconfined and confined concrete behaviours are defined nonlinearly using proposed analytical models in the literature. Then, finite element model is validated using experimental results. It is shown that the nonlinear layered shell approach is capable of estimating wall response (i.e., stiffness, ultimate strength, and cracking pattern) with adequate accuracy and low computational effort. Modal analysis is conducted to evaluate the inherent characteristics of the wall to choose a logical loading pattern for the nonlinear static analysis. Moreover, pushover analysis’ outputs are interpreted comprehensibly from cracking of the concrete until reaching the rupture step by step.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Resonant Frequency Ultrasonic P-Waves for Evaluating Uniaxial Compressive Strength of the Stabilized Slag–Cement Sediments<abstract> <title style='display:none'>Abstract</title> <p>Marine sediments can be stabilized by ultra high-strength binders: cement, Cement Kiln Dust (CKD) and slag. The properties of the stabilized soil indicate potential to their reuse. This study investigated the performance of the unconfined compressive strength (UCS) in the marine sediments stabilized by binder (cement, CKD, slag), tested by ultrasonic P-waves. Materials include 194 specimens collected from the port of Gothenborg. The experiment was performed in Swedish Geotechnical Institute (SGI). The UCS of specimens stabilized by different ratio of binders (cement, CKD, slag) was tested by resonance frequencies of the elastic P-waves. The significant increase in the UCS (&gt;1500 kPa) was recorded for the highest values of CKD and cement, and low values of slag. The correlation profiles of low water/high binder (L<sub>W</sub>/H<sub>B</sub>) cement/slag (40/60%) were controlled by curing time. The slag–cement–CKD simplex tests demonstrated UCS of samples with low/high water content and various binder ratio of cement (kg/m<sup>3</sup>). The ratio of cement binder and curing time play a critical role in the increase of UCS followed by mechanical properties of specimens and intensity of stress. The highest values exceed 1000 m/s in P-waves. The results shown high accuracy (97%) and non-contacting approach for testing UCS of sediments. Seismic methods can be applied to test the UCS of the stabilized sediments, and also <italic>in-situ</italic> via seismic CPT, surface testing or cross hole seismic testing.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Visible Corrosion Damage in Carbonated Reinforced Concrete<abstract> <title style='display:none'>Abstract</title> <p>This study discusses visible corrosion damage due to carbonation in concrete balconies and facades. The focus of the study was to find out how the age of the structure, cover depth of concrete, carbonation coefficient, capillarity of concrete and the climate affect visible corrosion damage. The research data consist of condition investigation reports of existing concrete balconies and facades built between 1948 and 1996.</p> <p>Balcony slabs and brushed painted facades were the most prone to visible corrosion damage. None of the researched panels met the required minimum cover depth of reinforcement even at the time of construction. However, most of the visible damage on the database was localized damage and there was not much visible corrosion damage. The carbonation coefficient of balconies was higher than the carbonation coefficient of facades. Brushed painted facade panels had clearly higher carbonation coefficient than other facade panels. The carbonation coefficient was considerably lower on white concrete panels compared to other panel types.</p> <p>When capillarity of concrete raises, the carbonation rate of concrete increases slightly. However, no correlation can be seen. The capillarity of concrete and the carbonation rate of concrete had a major range.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Towards Efficient Use of Cement in Ultra High Performance Concrete<abstract> <title style='display:none'>Abstract</title> <p>This paper presents an investigation on substituting the cement content with an inert material, in a typical locally produced UHPC mix. A structured literature review was performed to enrichen the discussion and to benchmark the results towards already reported investigations in the research society. Investigations on cement substitution in UHPC are frequently reported. However, usually the cement is substituted with other binding materials – often pozzolanic by-products from other industries. Reports from investigations on the use of inert materials for cement substitution in UHPC seem scarce.</p> <p>An experimental program that included a total of 210 test specimens was executed. This program included evaluating several questions embedded to the problem on how to substitute cement while keeping all other variables constant.</p> <p>It is concluded that up to 40% of the cement can be substituted with an inert material, without significantly changing the flexural tensile strength or compressive strength of the hardened UHPC. Two preconditions were caretaken: the particle packing was maintained by securing that the substitution material had a Particle Size Distribution (PSD) near identical to the cement and that the water balance was maintained through preconditioning of the substitution material. Suggestions are made for improving benchmarking.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Static and Dynamic Four-Point Flexural Tests of Concrete Beams with Variation in Concrete Quality, Reinforcement Properties and Impact Velocity<abstract> <title style='display:none'>Abstract</title> <p>This paper discusses the results from three experimental test series previously conducted. The tests consist of quasi-static monotonic and dynamic four-point flexural tests on reinforced concrete beams. The effect of varying material and load parameters on the plastic strain distribution and energy absorbed by the reinforcement is discussed. The main findings are the significant effect of the post-elastic region of the steel reinforcement and the impact velocity during dynamic loading. The results will be used to validate and construct numerical models in future work, where the findings presented can be investigated further.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Evaluation of Rapid Repair of Concrete Pavements Using Precast Concrete Technology: A Sustainable and Cost-Effective Solution<abstract> <title style='display:none'>Abstract</title> <p>Concrete and asphalt are the two competitive materials for a highway. In Sweden, the predominant material for the highway system is asphalt. But under certain conditions, concrete pavements are competitive alternatives. For example, concrete pavements are suitable for high-traffic volume roads, roads in tunnels, concentrated loads (e.g., bus stops and industrial pavement). Besides the load-carrying capacity, the concrete pavement has many advantages such as durability (wear resistance), resistance against frost heave, environment (pollution, recycling, and low rolling resistance leading to fuel savings), fire resistance, noise limitations, brightness, evenness and aesthetics.</p> <p>Concrete pavements are long-lasting but need final repair. Single slabs may crack in the jointed concrete pavement due to various structural and non-structural factors. Repair and maintenance operations are, therefore, necessary to increase the service life of the structures. To avoid extended lane closures, prevent traffic congestions, and expedite the pavement construction process, precast concrete technology is a recent innovative construction method that can meet the requirement of rapid construction and rehabilitation of the pavement. This paper evaluates rapid repair techniques of concrete pavement using precast concrete technology by analysing three case studies on jointed precast concrete pavements. The study showed that the required amount of time to re-open the pavement to traffic is dramatically reduced with jointed precast concrete panels.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00Numerical Modelling of Heat Transport in Freezing Mortars with an External Liquid Reservoir<abstract> <title style='display:none'>Abstract</title> <p>Several studies indicate that the temperature distribution in concrete may affect the extent of frost scaling. This study presents a numerical model that describes the thermal response of freezing mortars in the presence of an external liquid reservoir, where the external liquid is either pure water or 3% sodium chloride solution. The phase transformation of supercooled external liquid is modelled in two stages: quick freezing, when the supercooled liquid starts to form crystals and slow freezing. The model is developed in two parts. In part I, the focus is the modelling of external liquid, and therefore a non-porous body with an external liquid reservoir is modelled and validated. In part II, the model developed in part I is developed further for a porous body containing different phases, i.e., unfrozen liquid and ice, in the pores. A comparison of simulated and experimentally measured temperature distributions shows a good agreement.</p> </abstract>ARTICLE2021-12-30T00:00:00.000+00:00From 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+00:00en-us-1