| 1. |
- Al-Ayish, Nadia, et al.
(författare)
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Environmental impact of concrete structures reinforced with GFRP bars : A simplified study on columns
- 2019
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Ingår i: Proceedings of the fib Symposium 2019. - : International Federation for Structural Concrete. - 9782940643004 ; , s. 1998-2005
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Konferensbidrag (refereegranskat)abstract
- Concrete has a significant influence on the global warming due to its high usage in the construction industry. There are a few different strategies to increase the sustainability potential of concrete structures. Most of these strategies involve reduction of the total clinker content. One strategy, which is often neglected due to its complexity, is to increase the durability of the concrete structure. By increasing the durability, the need for repair and maintenance is reduced and thus less resources are consumed during the service life. One of the main deterioration mechanisms in concrete structures is the corrosion of steel reinforcement. A strategy to increase the service life of concrete structures in harsh environment would therefore be to increase the durability of concrete or to use low- or non-corrosive reinforcement instead of traditional steel reinforcement. This paper focuses on the latter. Glass fibre reinforced polymer (GFRP) bars are non-corrosive and have emerged as an alternative to steel bars in reinforced concrete structures in harsh environment. They have other mechanical properties than steel and opens for alternative mix designs for concrete. However, the environmental impact of concrete structures reinforced with GFRP bars has not been fully investigated and most life-cycle assessment (LCA) studies have an exchange ratio of 1:1 between GFRP and steel bars despite differences in the mechanical properties. This paper studies the climate impact of concrete columns reinforced with GFRP bars through an LCA methodology, focusing on the functional unit.
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| 2. |
- Al-Ayish, Nadia
(författare)
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Environmental Impact of Concrete Structures - with Focus on Durability and Resource Efficiency
- 2017
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Concrete is essential for the construction industry with characteristic properties that make it irreplaceable in some aspects. However, due to the large volumes consumed and the energy intense cement clinker production it also has a notable climate impact. In order to reach the international and national sustainability goals it is therefore important to reduce the climate impact of concrete structures.There are many ways to influence the environmental impact of concrete and a detailed analysis is one of the actions that could push the industry and the society towards a sustainable development. The purpose of this research is to evaluate the environmental impact of concrete structures and the built environment and to highlight the possibilities to reduce that impact with choice of concrete mix and innovative design solutions.A life cycle assessment (LCA) was carried out to analyze the environmental impact of two thin façade solutions with innovative materials and to evaluate influences of different greenhouse gas reducing measures on concrete bridges. The influence of supplementary cementitious materials (SCM) in terms of climate impact and durability was also analyzed.The results indicate that SCMs have a twofold effect on the climate impact of reinforced concrete structures. Not only do they reduce the greenhouse gases through cement clinker replacement but also by an improvement of durability regarding chloride ingress. Currently, this is not considered in the regulations, which makes it difficult to foresee in LCA at early design stages. The results also show great possibilities to reduce the climate impact through different measures and design alternatives and the need for further development of products and solutions.
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| 3. |
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| 4. |
- Al-Ayish, Nadia, et al.
(författare)
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The influence of supplementary cementitious materials on climate impact of concrete bridges exposed to chlorides
- 2018
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Ingår i: Construction and Building Materials. - : Elsevier BV. - 0950-0618 .- 1879-0526. ; 188, s. 391-398
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Tidskriftsartikel (refereegranskat)abstract
- In order to reach a specific service life of reinforced concrete structures a certain cover thickness is needed. At present, this is regulated by national standards that also limit the amount and type of supplementary cementitious materials in different exposure environments. The regulations do not, however, consider the actual durability performance of concrete with supplementary cementitious materials. As a consequence, the LCA results might be misleading. This paper shows the environmental impact of concrete with supplementary cementitious materials in chloride environment considering their specific performances. Prescriptive and performance based service life prediction models for chloride ingress are applied and compared.
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| 5. |
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| 6. |
- Helsing, Elisabeth, et al.
(författare)
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A Nordic method for testing hydrophobic impregnations with regard to prevention of chloride ingress
- 2017
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Chloride induced corrosion of the reinforcement is the major cause of degradation of reinforced concrete structures. In particular in the Nordic countries, the use of de-icing salts during winter, leads to severe degradation of edge beams in road bridges. Thus, in order to extend the service life and decrease maintenance costs, hydrophobic impregnations are commonly used to prevent or slow down chloride ingress into concrete. There is a harmonised European standard for hydrophobic impregnations, EN 1504-2 [1], but the property “diffusion of chloride ions” is “subject to national standards and regulations”. The transport and road administrations of Sweden, Norway and Finland use different national methods to evaluate the performance of this type of products meaning that the same CEmarked product needs to meet different requirements. Therefore, the transport and road administrations of Sweden, Norway and Finland initiated a project with the aim to establish a common Nordic method for classification of hydrophobic impregnations with regard to their capability to protect concrete from chloride ingress. The project was divided into three phases consisting on the analysis of existing test standards (national and international), a pre-study to evaluate the influence of different tests parameters and a round robin test involving three laboratories (one in each country). A thorough comparison of the existing methods and review of relevant literature made it possible to define which test parameters could be used in the formulation of the new method and which ones required further studies. It was found that the type of surface to be treated, the length of the preconditioning period, the length of the curing period and whether the surface to be impregnated should be soaked with Ca(OH)2-solution or not should be further investigated. The results of the pre-study showed that the application of the impregnation to form surfaces led to somewhat better chloride blocking effect. Despite this, it was decided to use sawn surfaces in the method, since it is much easier to obtain reproducible surface characteristics that way. The characteristics of a form surface depend on e.g. the form material, use of release agents, curing conditions. Saturation of the surface with calcium hydroxide solution before impregnation was found slightly beneficial on the chloride blocking effect compared to when such a treatment was omitted. However, since this did not contribute to the robustness of the test results, it increased the number of experimental steps and it is not representative of practice in real structures, it was decided not to incorporate such a treatment in the new method. The chloride protection slightly increases with the impregnation curing time. It was not clear which factor was most dominant; if the continuous polymerization of the hydrophobic impregnation or the continuous cement hydration. Since enough curing time is necessary for the treatment to be efficient, it was decided that the curing period before exposure to chlorides should be 28 days. With the primary objective of determining the reliability and reproducibility of the new method, a round robin exercise was carried out. Three laboratories were involved in this phase; CBI-Borås in Sweden, SINTEF in Norway and VTT in Finland. The results show that despite some differences in both materials and methods, such as the type of cement or preconditioning and curing environments, highly reproducible results were obtained. In addition, a detailed discussion on the influence of the details of the method on the chloride profiles and on the filter effect is presented. Within the round robin test, the relative humidity before and after impregnation and the dry condition of the powder samples were found to be the major parameters leading to the discrepancy of the results. In addition, handling of the wet concrete surfaces after exposure to chlorides and the time period (and temperature) between the end of the chloride exposure and powder sampling for chloride analysis were found to have surprisingly large effects on the form of the chloride profiles in the samples. Therefore, these parts of the procedures were made much more precise in the final method, in order to increase its reproducibility. The method can be briefly described as follows: Concrete specimens are prepared by sawing 100 mm cubes into two halves, three cubes per test series. The sawn surfaces are defined as exposure faces. Three halves are treated with the hydrophobic impregnation to be tested and the other three halves are kept as untreated references. The specimens are exposed submerged in 15% NaCl-solution for 56 days. After exposure, the chloride ingress is determined by profile grinding and the total amount of penetrated chlorides is calculated. The chloride blocking effect of the hydrophobic impregnations, expressed as the Filter Effect, FE, which is determined as 1 minus the ratio between the amount of penetrated chlorides in treated and in non-treated concrete specimens. The results obtained in both the pre-study and round robin exercise were compared to those obtained with the existing national methods in order to establish proper requirement levels with the new method. Despite the many differences between the methods, it was found that a filter effect of approximately 0.65 correlates well with the existing requirement in the Swedish method and in the Norwegian method. However, given limited data available and also considering data from field investigations, a level of 0.60 is proposed as appropriate for a really well performing hydrophobic impregnation. The method was accepted as a Nordtest method in December 2015 with the denomination NT Build 515.
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| 7. |
- Mueller, Urs, et al.
(författare)
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Development of pore structure and hydrate phases of binder pastes blended with slag, fly ash and metakaolin – A comparison
- 2015
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Ingår i: ICCC 2015 Beijing.
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Konferensbidrag (refereegranskat)abstract
- Blended binder systems in concrete have been in use for many years. However, over the recent discussions on the sustainability of cement and concrete the topic became of paramount importance for the construction industry. In Sweden blended binder systems in concrete were applied fairly recently and supplementary cementitious materials (SCM) were not used largely before. In Sweden over the last 30 years engineering structures were built, with exceptions, with a low alkali, sulfate resistant Portland cement due to domestic requirements. Therefore, in context to blended binder systems durability is a major point being discussed. Most interest lays in the resistance towards frost, carbonation and chloride penetration and the experience with blended systems was limited. It is therefore the goal of this study to investigate blended binder systems over a longer hydration period of up to two years in context to durability. The results presented here will focus on the porosity and hydrate phase development within the first 90 days of hydration. In this study in total 9 different binder blends were studied. The blends included different replacement levels with granulated blast furnace slag from a Swedish producer, fly ash from a Danish power plant and commercially available metakaolin. The matrix included also one set of factory-blended cements (with interground fly ash and slag). The pore structure was investigated by mercury intrusion porosimetry (MIP), phase development by powder x-ray diffraction (XRD). The results are based on the evaluation of binder paste samples. Compared to a reference series consisting of a CEM I the slag containing series showed a continuous decrease of the total pore volume with increasing slag content over 90 days of hydration. The phase development showed a constant increase in monosulfate and hydrotalcite. The amount of these phases increased with increasing slag content. Notable was consumption of C4AF, which increased with the amount of slag and a decrease of C2S reaction. Compared to the reference Portland cement paste the fly ash containing pastes showed increased total pore volumes when the fly ash was just added. For the cement paste with interground fly ash the porosity development was the same as for the reference paste. The phase development for these series showed up to 28 days of hydration formation of ettringite, hemicarbonate and monocarbonate. After 91 days monosulfate was dominating and the amount of hemicarbonate was decreasing. The paste series with 15 % metakaolin showed a strong decrease in total pore volume compared to the reference series within 2 days. Afterwards the pore volume almost leveled to a constant value. The hydration phases included in the beginning large amounts of monosulfate, ettringite and hemicarbonate but changed after 91 days in favor to ettringite and monocarbonate. The metakaolin blend showed the lowest amounts of portlandite in all series, indicating a strong pozzolanic reactivity. The different hydrate phases, in particular AFm phases can help to explain a different behavior towards, e.g. chloride binding. The pore structure development has a large impact not only on strength development but also for ion and moisture transport as well as for carbonation in all series.
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| 8. |
- Mueller, Urs, et al.
(författare)
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Reactive powder concrete for facade elements : A sustainable approach
- 2016
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Ingår i: Journal of Facade Design and Engineering. - 2213-302X .- 2213-3038. ; 4:1-2, s. 53-66
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Tidskriftsartikel (refereegranskat)abstract
- Reactive powder concrete (RPC) is a fairly novel material with extraordinary strength and durability properties. Due to these properties, it is increasingly being utilized for external fa¸cade cladding thus enabling a considerable reduction in the thickness of concrete elements. Commercial RPC formulations on the market are usually expensive and less sustainable due to high cement clinker contents. In this study, improved RPC formulations with higher amounts of supplementary cementitious materials (SCMs) were developed. The formulations were combined with different types of reinforcements ranging from steel fibres to fibre textile grids primarily to enhance the ductility and tensile strength of the composite material. The results showed that even with clinker replacement levels of up to ca. 40% of the total binder amount, a satisfactory mechanical performance of the RPC mixes could still be achieved. A fairly steep strength gain rendered heat treatment unnecessary. The materials displayed good flow properties and a reasonably short initial setting time. The incorporation of carbon textile fibre grids proved to be highly effective in improving the post cracking behaviour of the RPC. The results validated a more sustainable approach for RPC applied to thin fa¸cade elements.
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| 9. |
- Mueller, Urs, et al.
(författare)
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Textile Reinforced Reactive Powder Concrete and its Application for Facades
- 2017
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Konferensbidrag (refereegranskat)abstract
- Reactive powder concrete (RPC) is a fairly novel material with extraordinary strength and durability properties. Due to these properties, it is increasingly being utilized also for external facade cladding thus enabling a considerable reduction in the thickness of concrete elements. Commercial RPC formulations on the market have drawbacks in terms of sustainability due to their high clinker content and heat curing which is often applied to increase final strength and material density. The presented study focusses on improved formulations with higher replacement levels of cement clinker by supplementary cementitious materials (SCMs). One different mix formulation was designed and tested in terms of mechanical properties. The formulation was combined with carbon textile reinforcements primarily to enhance the flexural and tensile behavior of the material. The results showed that even with clinker replacement levels of up to 33 % of the total binder amount, a satisfactory mechanical performance of the RPC mix could still be achieved. Fairly steep strength gains rendered heat treatment unnecessary. The incorporation of carbon textile fiber grids proved to be effective in improving the post peak performance of the RPC. However, their performance depended strongly on the bond between the carbon grid and the RPC. Higher moister contents in the concrete proved to reduce the bond strength between the carbon textile and the cement paste. This is maybe less relevant for facades but structural elements with textile reinforcement and RPC might perform less well in completely submerged environment.
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| 10. |
- Sadagopan, Madumita, 1987-, et al.
(författare)
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A modified pycnometer method to determine the water absorption of combined crushed concrete aggregate fractions
- 2019
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Ingår i: International Conference on Sustainable Materials, Systems and Structures (SMSS2019). - 9782351582176 ; , s. 286-292
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Konferensbidrag (refereegranskat)abstract
- Crushed Concrete Aggregates (CCA) as fine and coarse aggregates in new concrete helps achieve closed-loop recycling. Assessment of workability, mechanical properties and durability of concrete demands knowledge of the water absorbed by the CCA. The EN 1097-6standard method is difficult to execute due to the presence of entrapped air and CCAsedimentation while performing water absorption experiment for fine CCA. Additionally, the assessment of Saturated Surface Dry (SSD) state seems operator specific and nonreproducible;moreover, giving water absorption measurement only at 24 hours. However, findings from this paper show measurements at 15 minutes is influential for concrete workability. The modified pycnometer method analyses the water absorption of a combined fraction consisting of coarse and fine CCA as proportioned in a given concrete recipe. Furthermore, sedimentation and entrapped air are prevented by pre-soaking the CCA in a solution of distilled water and poly-carboxylate based superplasticizer before commencing the experiment. Ultimately, the combined fraction is drained to SSD condition by vacuum filtration, which is easy to handle by professional operators. In this way, the water absorption development is measured from starting point to 24 hours for the combined fraction to determine the appropriate water amount to saturate CCA during concrete mixing.
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