| 1. |
- Al-Gburi, Majid, et al.
(författare)
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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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Ingår i: Nordic Concrete Research. - : Walter de Gruyter. - 0800-6377 .- 2545-2819. ; 66:1, s. 41-54
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Tidskriftsartikel (refereegranskat)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.
(författare)
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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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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 67:2, s. 35-50
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Tidskriftsartikel (refereegranskat)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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| 3. |
- Baba Ahmadi, Arezou, 1985, et al.
(författare)
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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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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 63:2, s. 63-78
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Tidskriftsartikel (refereegranskat)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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| 4. |
- Gram, Annika, et al.
(författare)
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Evaluation of Crushed Fine Materials
- 2022
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 67:2, s. 65-77
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Hasholt, Marianne Tange, et al.
(författare)
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Nordic Concrete Research workshop : "Accelerated freeze-thaw testing of concrete", Lyngby, 20th April 2022
- 2022
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Ingår i: Nordic Concrete Research. - : SCIENDO. - 0800-6377 .- 2545-2819. ; 66:1, s. 113-133
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Hernández Vargas, Jose, et al.
(författare)
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Grading Material Properties in 3D Printed Concrete Structures
- 2022
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 66:1, s. 73-89
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 7. |
- Lindh, Per, et al.
(författare)
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Resonant Frequency Ultrasonic P-Waves for Evaluating Uniaxial Compressive Strength of the Stabilized Slag–Cement Sediments
- 2021
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 65:2/2021, s. 39-62
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Tidskriftsartikel (refereegranskat)abstract
- Marina sediment kan stabiliseras med ultrahöghållfasta bindemedel: cement, Cement Kiln Dust (CKD) och slagg. Egenskaperna hos den stabiliserade jorden indikerar potential för återanvändning. Den här studien undersökte prestandan för den enaxiella tryckhållfastheten (UCS) i smarina sediment stabiliserade med bindemedel (cement, CKD, slagg), testade med ultraljuds P-vågor. Material omfattar 194 prover insamlade från Göteborgs hamn. Experimentet utfördes av Sveriges Geotekniska Institutet (SGI). Tryckhållfastheten hos prover stabiliseras med olika förhållande av bindemedel (cement, CKD, slagg) testades med resonansfrekvenser (P-vågor). Korrelationsprofilerna för lågt vatten/hög bindemedel (LW/HB) cement/slagg (40/60 %) kontrollerades genom härdningstid. Simplextesten för slagg-cement-CKD visade UCS av prover med låg/hög vattenhalt och olika bindemedelsförhållande av cement (kg/m3). Förhållandet mellan cementbindemedel och härdningstid spelar en avgörande roll för ökningen av UCS följt av mekaniska egenskaper hos prover och spänningsintensitet. De högsta värdena 1000 m/s i P-vågor. Resultaten visade hög förklaringsgrad (97 %) och beröringsfritt tillvägagångssätt för att testa tryckhållfasthet hos stabiliserade sediment. Seismiska metoder fungerar bra och kan användas för att testa det stabiliserades sediment i labb och fält via seismisk CPT, ytvågsseismik eller cross hole seismik.
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| 8. |
- Oliva Rivera, Alexander, et al.
(författare)
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Accelerated Carbonation of Binders Containing SCM at High CO2 Concentration
- 2023
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Ingår i: Nordic Concrete Research. - : Nordic Concrete Federation. - 0800-6377 .- 2545-2819. ; 69:2, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Accelerated carbonation of recycled concrete aggregates (RCA) could be an efficient way to reduce the carbon footprint. High CO2-concentration under optimal relative humidity could accelerate the CO2 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 CO2 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 CO2 concentration of 10 % under controlled temperature at 20 C-degrees and 65 % RH. All tested binders presented a high CO2 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.
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| 9. |
- Peterson, Viktor, et al.
(författare)
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Static and Dynamic Four-Point Flexural Tests of Concrete Beams with Variation in Concrete Quality, Reinforcement Properties and Impact Velocity
- 2021
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter GmbH. - 0800-6377 .- 2545-2819. ; 65:2, s. 19-38
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Rajczakowska, Magdalena, et al.
(författare)
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Is Cement Paste Modified with Carbon Nanomaterials Capable of Self-Repair after a Fire?
- 2022
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Ingår i: Nordic Concrete Research. - : Walter de Gruyter. - 0800-6377 .- 2545-2819. ; 67:2, s. 79-97
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Tidskriftsartikel (refereegranskat)abstract
- 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 & DEG;C and 400 & DEG;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.
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