| 1. |
- Abrahamsson, Camilla, et al.
(författare)
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Characterization of airborne dust emissions from three types of crushed multi-walled carbon nanotube-enhanced concretes
- 2024
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Ingår i: NanoImpact. - : Elsevier B.V.. - 2452-0748. ; 34
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Tidskriftsartikel (refereegranskat)abstract
- Dispersing Multi-Walled Carbon Nanotubes (MWCNTs) into concrete at low (<1 wt% in cement) concentrations may improve concrete performance and properties and provide enhanced functionalities. When MWCNT-enhanced concrete is fragmented during remodelling or demolition, the stiff, fibrous and carcinogenic MWCNTs will, however, also be part of the respirable particulate matter released in the process. Consequently, systematic aerosolizing of crushed MWCNT-enhanced concretes in a controlled environment and measuring the properties of this aerosol can give valuable insights into the characteristics of the emissions such as concentrations, size range and morphology. These properties impact to which extent the emissions can be inhaled as well as where they are expected to deposit in the lung, which is critical to assess whether these materials might constitute a future health risk for construction and demolition workers. In this work, the impact from MWCNTs on aerosol characteristics was assessed for samples of three concrete types with various amounts of MWCNT, using a novel methodology based on the continuous drop method. MWCNT-enhanced concretes were crushed, aerosolized and the emitted particles were characterized with online and offline techniques. For light-weight porous concrete, the addition of MWCNT significantly reduced the respirable mass fraction (RESP) and particle number concentrations (PNC) across all size ranges (7 nm – 20 μm), indicating that MWCNTs dampened the fragmentation process by possibly reinforcing the microstructure of brittle concrete. For normal concrete, the opposite could be seen, where MWCNTs resulted in drastic increases in RESP and PNC, suggesting that the MWCNTs may be acting as defects in the concrete matrix, thus enhancing the fragmentation process. For the high strength concrete, the fragmentation decreased at the lowest MWCNT concentration, but increased again for the highest MWCNT concentration. All tested concrete types emitted <100 nm particles, regardless of CNT content. SEM imaging displayed CNTs protruding from concrete fragments, but no free fibres were detected.
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| 2. |
- Alonso, Maria Cruz, et al.
(författare)
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Self-protection concrete measures as prevention measure from chloride transport and corrosion of reinforcement
- 2023
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Ingår i: MATEC Web of Conferences. - 2261-236X. ; 378
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Tidskriftsartikel (refereegranskat)abstract
- Incorporation of additives into a reinforced concrete matrix to delay or even completely avoid the initiation of corrosion during the service-life of the construction is a widely pursued topic. One of the new promising technologies achieving increased interest is to incorporate corrosion inhibitors encapsulated in layered double hydroxide (LDH). LDH structures follow a controlled release of the inhibitor while chloride is efficiently trapped at the same time. Another type of nanostructure additive offering self-protection ability in concrete is polyhedral oligomeric silsesquioxanes (POSS) developed to exhibit water-repellent functionalities protecting the reinforcement from corrosive attack. In the present laboratory work, the enhanced performance of concrete infrastructures in a marine environment was studied using a SCC design. The addition of LDH (0.5, 1 and 2 % by mass of binder (bmb)) and POSS (2 and 4 % additive level) was explored. Migration and diffusion Cl transport tests have been performed towards corrosion protection of reinforcing bars. The results showed that Cl transport decreases with the concrete maturity, and this is even more effective for concretes with LDH and POSS. This delay effect is more pronounced in the unidirectional diffusional Cl transport. LDH is significantly retarding the initiation of rebar corrosion.
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| 3. |
- Hesselgren, Lars, et al.
(författare)
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NuMo – New Urban Mobility : New urban infrastructure support for autonomous vehicles
- 2019
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Foreword All transport systems have a certain capacity determined by its configurations. For cars the most efficient current form is constant speed driving, e.g. the motorway. Its capacity is limited by the time separation between vehicles. Any transport system that stops because of congestion or other causes by definition sees its capacity reduced to zero. Hence traffic jams are hugely disruptive. Public transport operates on a model inherited from the 19 th Century. Vehicles (buses, trams, railways, metros) run on a regular (timetabled) basis and stops at every station (bus stop). Since there is no pre-booking and the need of transport is hard to foresee, the vehicles are often almost empty, at other times hugely congested. The NuMo technology emerges from decades of work across the whole transportation industry. Autonomous electric vehicles (AEVs) equipped with vehicle-to-vehicle (V2V) communication can safely keep shorter distances. In practical terms this means that a platooned car system has the same capacity in one lane as a double-lane motorway. Automated intelligent controls ensure that the NuMo systems never stops, thus achieving the highest capacity. Instead of waiting for the mass deployment of fully automated vehicles, NuMo starts with dedicated networks that integrate tightly with existing infrastructure for step-wise smooth transition to fully automated transport system. NuMo includes an on-demand public transport system which only runs when it is needed. The system will take advantage of close-spacing possible with robot controls – vehicles can run close together and also use less road width by less wiggling. Equally importantly stations and access to the normal road network is arranged such that the traffic flow never stops. The urban impact can be imagined by understanding the impact of modern public transport systems currently under construction. Some of them are underground to avoid disrupting the street patterns. Some are elevated, some rely on physical separation at grade. One interesting option is to use tunnels underground or in water to further reduce disruption. Many cities are abandoning the traditional port infrastructure giving huge opportunities to again regard water as a connector rather than something to cross. The NuMo system uses all of those techniques and detailed design studies are under way for each of those options. NuMo will make an important contribution to environmental sustainability in many respects. Firstly, it will accelerate adoption of electric propulsion; secondly it will encourage vehicle sharing; and thirdly by only running when needed will save on unnecessary movements and finally its construction costs will be less than conventional systems. Sketches of NuMo networks are presented on places as diverse as Stockholm, Gothenburg and New York. Naturally the system will also be crucial in the development of new cities. This report is a summary of the studies performed within the project “New urban infrastructure support for autonomous vehicles” financed by Vinnova through the Strategic Innovation Program InfraSweden2030. The aim is to explore the infrastructure support to accelerate the introduction of autonomous electric vehicles for future mobility.
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| 4. |
- Hingorani, Ramon, et al.
(författare)
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Consequence classes and associated models for predicting loss of life in collapse of building structures
- 2020
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Ingår i: Structural Safety. - : Elsevier B.V.. - 0167-4730 .- 1879-3355. ; 85
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Tidskriftsartikel (refereegranskat)abstract
- Most building design codes distinguish structural reliability levels in terms of failure consequences, for which they normally define consequence classes based on building type and use. Although readily applicable in everyday practice, that approach may entail adopting inconsistent safety requirements. Such a significant drawback could be minimised by establishing separate reliability levels for key members on the grounds of the potential consequences of their collapse. Further to those concerns, this paper proposes a series of consequence classes determined in keeping with the number of persons at risk in a given collapse scenario and the extent of the respective damage. Consequence class-related models for predicting loss of life are derived from statistical assessments of data on over 150 collapsed buildings. The models developed estimate the number of fatalities and conditional probability of death of building users under given collapse circumstances. In addition to their utility in establishing target reliability values, these models can be applied in risk analysis of specific building structures, especially where the potential consequences of failure are high.
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| 5. |
- Mir, Zahid Mohammad, et al.
(författare)
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Numerical and Experimental Analysis of Self-Protection in Reinforced Concrete due to Application of Mg–Al–NO2 Layered Double Hydroxides
- 2020
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Ingår i: Advanced Engineering Materials. - : Wiley-VCH Verlag. - 1438-1656 .- 1527-2648.
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Tidskriftsartikel (refereegranskat)abstract
- Concrete possesses an intrinsic chloride binding capacity. Chloride ions from the environment bind with the hydrated cementitious phases in the form of bound chlorides. The contribution of chemically bound chlorides toward increasing the service life of concrete structures is vital as they help in slowing down the chloride diffusion in the concrete thereby delaying reinforcement depassivation. The authors attempt to increase the chloride binding capacity of concrete by adding a small amount of Mg–Al–NO2 layered double hydroxides (LDHs) with the objective to delay reinforcement corrosion and by this to considerably extend the service life of concrete structures situated in harsh environments. This study presents numerical and experimental analysis of the action of LDH in concrete. Formation factor is used to determine the effective chloride diffusion coefficient. In addition, the chloride binding isotherms together with Poisson–Nernst–Planck equations are used to model the chloride ingress. A comparable chloride binding is observed for concrete with and without Mg–Al–NO2, depicting only a slight chloride uptake by Mg–Al–NO2. Further investigations are conducted to understand this behavior by studying the stability and chloride entrapping capacity Mg–Al–NO2 in concrete. © 2020 The Authors.
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| 6. |
- Prieto Rábade, Miguel, et al.
(författare)
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CRACKSTP – Analysis and mitigation of cracking in prefab concrete façade elements–Report of WP2 to Strängbetong
- 2022
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Cracking of prefab sandwich panels impact s not only the appearance of buildings aesthetically but has also consequences for the material durability, as well as the thermal and acoustic performance of the building envelope as a whole. The project investigates the possible causes of cracks from the design to the production stage, transport and final application and exposure. The study w ill focus on material related causes due to the different types of restrained shrinkage, considering also mitigation measures by shrinkage reducing/compensating admixt ures, to design related factors and to environmental factors during transport and the service life of the elements. The actual study will focus o n the drying shrinkage as well as shrinkage mitigating possibilities. Restraining and environmental factors will be investigated experimentally and by FEA. The results of the project will be evaluated and concluded in a list of recommendations for mitigating cracking in sandwich elements.
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| 7. |
- Prieto Rábade, Miguel, et al.
(författare)
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Model for the assessment of bond in corroded steel ribbed bars
- 2022
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Konferensbidrag (refereegranskat)abstract
- The aim of the present paper is to further validate a model proposed for assessing bond strength in corroded and non-corroded steel bars. The model was obtained by applying multiple linear regression analysis to an initial database obtained from literature containing over 650 bond tests: 372 with corroded steel bars. In this paper, a second stage for further validating the model has been conducted with new database consisting of 131 new tests of bond with corroded steel bars resulting in a final database of 500 tests of bond with corroded reinforcing steel bars. In this model, bond strength is considered as an average stress on the nominal surface of a straight length of a bar over the bond length. The corrosion effect is considered using the cross-section loss (% Cor) considered as uniform corrosion along the bonded length of the bar. In addition to the cross-section loss, corrosion effect in bond is additionally considered with an additional variable that implicitly includes the effect of cracking depending on the range of cross section loss, bond condition and presence of transverse reinforcement. In the paper, the former formulation proposed in is compared with the formulation adapted with rounded coefficients for the former database, the new database and the combined database with different statistical criteria to compare the accuracy of the bond strength predictions obtained with the model. Finally, the predictions of the model show a good fitting with the experimental results with the new database and also have a low scatter. This is showing its utility in the safety assessment of bond strength in reinforced concrete members.
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| 8. |
- Prieto Rábade, Miguel, et al.
(författare)
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Tillstånd- och konsekvensbaserad livslängdsbedömning av betongkonstruktioner för dricksvatten
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden, there are many assets for drinking water such as water towers, water treatment plants and pipes. Many of these structures are made of reinforced concrete and were built between 1950 – 1970. The normal design life of these structures is 50 years meaning that they are reaching their intended design lifespan. In addition, these structures face harsh environments that can lead to degradation. All these leads to the need of repair and renovation of these specifics assets. For that purpose, methodologies and tools for performing inspections, assessing the condition and the time to intervention are needed. Nowadays, in general the procedures for condition assessment are based on the judgement and expertise of engineers performing the inspection. In this project a compilation of best practices for performing the condition assessment for drinking water structures has been performed. This assessment should include an ocular inspection of the object, documentation, tests to ensure certain parameters and an overall analysis of the assessment of the object and finally provide a proposal for measures. The measures must be designed so that both the method and the time aspect are specified. In addition, in this project a methodology and a simplified tool has been developed to accommodate the condition assessment of reinforced concrete drinking water infrastructures and the time to intervention after the assessment. The tool also includes the uncertainty analysis of the condition assessment performed.
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| 9. |
- Suchorzewski, Jan, et al.
(författare)
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An experimental study of self-sensing concrete enhanced with multi-wall carbon nanotubes in wedge splitting test and DIC
- 2020
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Ingår i: Construction and Building Materials. - : Elsevier Ltd. - 0950-0618 .- 1879-0526. ; 262
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Tidskriftsartikel (refereegranskat)abstract
- Concrete is the worldwide most utilized construction material because of its very good performance, forming ability, long-term durability, and low costs. Concrete is a brittle material prone to cracking. Extensive cracking may impact durability and performance over time considerably. The addition of a small amount of carbon nanotubes (CNT) increases the concrete's overall electrical conductivity, enabling internal structure condition monitoring (self-sensing). This article presents the mechanical and self-sensing properties of regular and high-performance concrete (HPC) with multi-wall carbon nanotubes (MWCNT). The stress detection was investigated in cyclic compression, while damage detection was assessed by means of wedge splitting tests combined with the digital image correlation (DIC) method. The results proved that a small addition of MWCNT (0.05% and 0.10%) enhances the stress detection capabilities and enables the monitoring of microcracking.
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| 10. |
- Suchorzewski, Jan, et al.
(författare)
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Concrete mix design for tidal turbine foundation
- 2021
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The Sabella D10 tidal turbine was immersed in the Fromveur Strait in June 2015 and became the first, and at the time only, grid-connected full scale marine current turbine (MCT) in France. However, the future of MCT industrial projects lies in lowering the levelized cost of electricity (LCOE). Evaluating new possibilities to design a competitive foundation will be a key issue for the future commercial development of SABELLA’s technology. The purpose of CF2T project is to develop a competitive foundation, immerse it as part of a precommercial project and validate the concept in real sea environment. The innovative foundation was designed to decrease construction costs, with modular interfaces to allow an installation in several packages (foundation parts, ballasts, turbine) in order to limit the installation vessel’s crane capacity requirement, which will also reduce installation costs. A concrete foundation with steel footings and turbine bed were considered to lower the manufacturing costs and increase the foundation durability comparing to currently used steel foundations. RISE Infrastructure and Concrete Technology supported the process of concrete material selection and casting technology. The material design was preceded with numerical analysis of early cracking due to hydration heat development, which indicated that there exists a substantial risk of thermal cracking. Three different variants of concrete mixes complying the design strength and stiffness criteria with low hydration heat were developed concerning various available casting technologies. The mixes were tested for standard concrete properties: compressive and flexural strength, modulus of elasticity, consistency, and shrinkage. The selected materials were submitted to accelerated durability testing including shrinkage and chloride migration. A basic life cycle analysis (LCA) of the concrete material, manufacturing was performed and compared to steel foundation solution to assess the sustainability of the designed structural and material solutions. The innovative concrete foundation and traditional steel foundation with D14 turbines are meant to be monitored with a specially developed sensors and data acquisition system in real sea environment.
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