| 1. |
- Al-Gburi, Majid, et al.
(author)
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Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks
- 2022
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In: Nordic Concrete Research. - : Walter de Gruyter. - 0800-6377 .- 2545-2819. ; 66:1, s. 41-54
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Journal article (peer-reviewed)abstract
- 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.
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| 2. |
- Andersson, Louise, et al.
(author)
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Continuous Preventive Bridge Maintenance of Swedish Municipalities : A Survey on Common Practice
- 2018
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In: Nordic Concrete Research. - Oslo : Walter de Gruyter GmbH. - 2545-2819 .- 0800-6377. ; 58
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Journal article (peer-reviewed)abstract
- As part of a report [1] on continuous preventive bridge maintenance, a survey was conducted with Swedish municipalities. The survey’s focus was on bridges and preventive maintenance, as well as the demands and performance control stated by the municipalities. The preventive maintenance the survey focused on was the annual maintenance concerning washing, cleaning of drainage system and removal of vegetation. The survey showed both similarities and differences within the municipalities but also in comparison with Swedish Transport Agency (STA).
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| 3. |
- Andersson, Louise, et al.
(author)
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Effect of High-Pressure Washing on Chloride Ingress in Concrete : Development of an Accelerated Test Method
- 2022
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In: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 67:2, s. 35-50
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Journal article (peer-reviewed)abstract
- 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.
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| 4. |
- Baba Ahmadi, Arezou, 1985, et al.
(author)
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Utilization of Bio Ashes in Cement-based Materials: A Case Study in Cooperation with Pulp and Paper and Energy Production Industries in Sweden
- 2020
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In: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 63:2, s. 63-78
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Journal article (peer-reviewed)abstract
- Worldwide increased concern of the CO2 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.
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| 5. |
- Cyron, Wojciech, et al.
(author)
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Bonded Concrete Overlays: A Brief Discussion on Restrained Shrinkage Deformations and Their Prediction Models
- 2019
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In: Nordic Concrete Research. - : Walter de Gruyter. - 0800-6377 .- 2545-2819. ; 61:2, s. 107-129
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Journal article (peer-reviewed)abstract
- Bonded concrete overlays (BCO) on bridge decks are beneficial solutions due to their superior properties as compared to the typical asphalt pavement. A significant number of overlays suffer however, from occurrence of cracks and delamination due to poor bond, and restrained shrinkage and thermal dilation. Over the past years different appraisals for estimation of the restrained deformations have been developed, from micro-scale models, based on poromechanics, to empirical equations as given in B3 or B4 models suggested by Baiant. This paper provides a short overview of calculation models along with a brief theoretical explanation of shrinkage mechanism.
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| 6. |
- During, Otto, et al.
(author)
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Rice Husk Resource for Energy and Cementitious Products with Low CO2 contributions
- 2018
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In: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 59:2, s. 45-58
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Journal article (other academic/artistic)abstract
- Rice Husk Ash (RHA) is a well-known supplementary cementitious materials (SCMs) that can be used for concrete with reduced CO2 contributions. In 2016, only Nepal produced 5.2 million tonnes rice that gave about 1.14 million tonnes rice husk. The rice husk can also be used directly in a cement kiln as a fuel. This study analysis the potential CO2 reductions from three scenarios and emphasis strengths, weaknesses, opportunities and treats in the production systems for initiate a decision process with possibilities to get an industry project financed from the green climate found. The highest CO2 benefits were from rice husk used in a cement kiln were half of the yearly rice husk production in Nepal could reduce the climate impact with 808000 tonnes CO2.
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| 7. |
- Döse, Magnus, et al.
(author)
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Effect on Radon Exhalation Rate Due to Cracks in Concrete
- 2019
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In: Nordic Concrete Research. - : NORDIC CONCRETE FEDERAT. - 0800-6377 .- 2545-2819. ; 61:2, s. 79-90
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Journal article (peer-reviewed)abstract
- The second largest cause of lung cancer in the World is related to radon (Rn-222) and its progenies in our environment. Building materials, such as concrete, contribute to the production of radon gas through the natural decay of U-238 from its constituents. The Swedish Cement and Concrete Research Institute (CBI), part of RISE (Research Institute of Sweden AB), has examined the effects of cracks in concrete on two different concrete recipes where an Ordinary Portland Cement, OPC-CEM-I concrete (REF) and an OPC concrete including a hydrophobic additive (ADD) were addressed. Two concrete prisms from each concrete recipe were examined. The radon exhalation rate was measured in the pristine state and after concrete cracks had been induced into the concrete prisms. Measurements were performed with an ATMOS 33 ionizing pulsation chamber. The results indicate a strong influence of cracks on the radon exhalation rate. An increase in radon exhalation rate was calculated for every test prism. The increase in radon exhalation rate varied between 80 and 260 %. The crack apertures may play a significant role on the exhalation rate. The concrete prisms with the largest apertures (ADD) also generated the highest radon exhalation rates. The results imply that there could be a substantial variation in the exhalation rate, due to numerous factors, but nonetheless, the results should, raise the awareness of the impact cracks in concrete structures, may have on the final exhalation rate of radon. The exhalation rate of the recipe with an additive (ADD) also showed a lower exhalation rate than for the reference recipe (REF), when compared in a pristine state. This was in part expected. However, the effect of induced cracks and its aperture, seemingly trumps the effect that an additive may play on the radon exhalation rate, when cracks are induced.The hypothesis is in part verified in view of the results of the prism for the ordinary Portland recipe (REF-prisms), were an increase of approximately 100 % would be expected due to the total surface increase. The results also indicate this. The major increase in the radon exhalation rate of the ordinary Portland recipe including an additive, implies however other factors, such as minor internal cracks, that may substantially contribute to the final exhalation rate.
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| 8. |
- Flansbjer, Mathias, et al.
(author)
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Meso Mechanical Study of Cracking Process in Concrete Subjected toTensile Loading
- 2018
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In: Nordic Concrete Research. - Oslo : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 59:2, s. 13-29
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Journal article (other academic/artistic)abstract
- This project focused on how the cracking process in concrete is influenced by both the micro and meso structures of concrete. The aim was to increase knowledge pertaining to the effect of critical parameters on the cracking process and how this is related to the material's macroscopic properties. A methodology based on the combination of different experimental methods and measuring techniques at different scales was developed. Crack propagation during tensile loading of small-scale specimens in a tensile stage was monitored by means of Digital Image Correlation (DIC) and Acoustic Emission (AE). After testing, crack patterns were studied using fluorescence microscopy.
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| 9. |
- Geiker, Mette Rica, et al.
(author)
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Screening of Low Clinker Binders, Compressive Strength and Chloride Ingress
- 2017
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In: Nordic Concrete Research. - : Nordic Concrete Federation. - 0800-6377 .- 2545-2819. ; 57:2, s. 23-38
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Journal article (peer-reviewed)abstract
- This paper reports an initial screening of potential new binders for concrete with reduced CO2-emission. Mortars cured saturated for 90 days are compared with regard to a) compressive strength of mortars with similar water-to-binder ratio, and b) chloride ingress in similar design strength mortars exposed to seawater. The reference used was a binder composition typical for a Danish ready mixed concrete for aggressive environments and strength class C35/45. Based on the present investigation and assumptions up to around 15% reduction in CO2 emission from binder production might be obtained without compromising the 90 days compressive strength and resistance to chloride ingress in marine exposure by using selected alternative binders.
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| 10. |
- Gram, Annika, et al.
(author)
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Evaluation of Crushed Fine Materials
- 2022
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In: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 67:2, s. 65-77
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Journal article (peer-reviewed)abstract
- 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.
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