| 1. |
- Cwirzen, A., et al.
(författare)
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Properties of high yield synthesised carbon nano fibres/portland cement composite
- 2009
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 21:4, s. 141-146
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Tidskriftsartikel (refereegranskat)abstract
- The compressive strength and electrical resistivity of hardened pastes produced either from nanomodified Portland sulfate-resistant cement (CHH) or a mixture of nanomodified and pristine sulfate-resistant cements were determined. The nanomodification included grow carbon nanotubes (CNTs) and carbon nanofibres (CNFs) on the cement particles. Pastes having a water-to-binder ratio of 0-5 were produced. The test results revealed that partial replacement of sulfate-resistant cement by CHH cement decreased the electrical resistivity of the 28 day old specimens but worsened the mechanical properties. The lower compressive strength was attributed to a lower degree of hydration of the CHH cement. The addition of a mixture of surfactants enabled the production of specimens consisting entirely of CHH cement. The hardened material obtained was characterised by a nearly doubled compressive strength in comparison with the reference specimens made from pristine sulfate-resistant cement. This was attributed to a high degree of hydration as well as reinforcing action of the CNTs and CNFs. The electrical resistivity was lowered by one order of magnitude classifying this material as a semiconductor.
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| 2. |
- Cwirzen, A., et al.
(författare)
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SEM/AFM studies of cementitious binder modified by MWCNT and nano-sized Fe needles
- 2009
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Ingår i: Materials Characterization. - : Elsevier BV. - 1044-5803 .- 1873-4189. ; 60:7, s. 735-740
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Tidskriftsartikel (refereegranskat)abstract
- Several compositions of cement paste samples containing multiwalled carbon nanotubes were produced using a small-size vacuum mixer. The mixes had water-to-binder ratios of 0.25 and 0.3. Sulfate resistant cement has been used. The multiwalled carbon nanotubes were introduced as a water suspension with added surfactant admixtures. The used surfactant acted as plasticizing agents for the cement paste and as dispersant for the multiwalled carbon nanotubes. A set of beams was produced to determine the compressive and flexural strengths. The scanning electron microscope and atomic force microscope studies of fractured and polished samples showed a good dispersion of multiwalled carbon nanotubes in the cement matrix. The studies revealed also sliding of multiwalled carbon nanotubes from the matrix in tension which indicates their weak bond with cement matrix. In addition to multiwalled carbon nanotubes also steel wires covered with ferrite needles were investigated to determine the bond strength between the matrix and the steel wire. These later samples consisted of 15-mm-high cylinders of cement paste with vertically cast-in steel wires. As reference, plain steel wires were cast, too. The bond strength between steel wires covered with nano-sized Fe needles appeared to be lower in comparison with the reference wires. The scanning electron microscope studies of fractured samples indicated on brittle nature of Fe needles resulting in shear-caused breakage of the bond to the matrix. © 2008 Elsevier Inc. All rights reserved.
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| 3. |
- Cwirzen, A., et al.
(författare)
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Surface decoration of carbon nanotubes and mechanical properties of cement/carbon nanotube composites
- 2008
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 20:2, s. 65-73
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Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the effects of the method of surface decoration on the wetability of multi-walled carbon nanotubes (MWCNTs) and the mechanical properties of the cement paste incorporating these dispersions. The results showed that stable and homogenous dispersions of MWCNTs in water can be obtained by using surface functionalisation combined with decoration using polyacrylic acid polymers. The cement paste specimens incorporating these dispersions revealed good workability and an increase in the compressive strength of nearly 50% even with only a small addition of the MWCNTs, namely 0-045-0-15% of the cement weight. These results indicate the existence of chemical bonds between the OH groups of the functionalised MWCNTs and probably the C-S-H phase of the cement matrix, which enhanced the transfer of stresses. A second method that was studied included decoration of MWCNTs with polyacrylic acid polymers and gum Arabic. These dispersions appeared to be homogeneous only for approximately 2 h after which a progressive sedimentation occurred. Good workability was found for the cement pastes produced with all of the dispersions; the only significant difference being the slower hydration of the cement incorporating gum Arabic. The mechanical properties of the cement pastes incorporating MWCNTs treated with polyacrylic polymers were unchanged.
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| 4. |
- Nasibulin, Albert G., et al.
(författare)
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A novel cement-based hybrid material
- 2009
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Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 11
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nanotubes (CNTs) and carbon nanofibers (CNFs) are known to possess exceptional tensile strength, elastic modulus and electrical and thermal conductivity. They are promising candidates for the next-generation high-performance structural and multi-functional composite materials. However, one of the largest obstacles to creating strong, electrically or thermally conductive CNT/CNF composites is the difficulty of getting a good dispersion of the carbon nanomaterials in a matrix. Typically, time-consuming steps of purification and fimctionalization of the carbon nanomaterial are required. We propose a new approach to grow CNTs/CNFs directly on the surface of matrix particles. As the matrix we selected cement, the most important construction material. We synthesized in a simple one-step process a novel cement hybrid material (CHM), wherein CNTs and CNFs are attached to the cement particles. The CHM has been proven to increase 2 times the compressive strength and 40 times the electrical conductivity of the hardened paste, i.e. concrete without sand. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.
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| 5. |
- Cnudde, V., et al.
(författare)
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Porosity and microstructure characterization of building stones and concretes
- 2009
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Ingår i: Engineering Geology. - : Elsevier BV. - 0013-7952 .- 1872-6917. ; 103:3-4, s. 76-83
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure of building materials greatly influences engineering properties like permeability, strength and durability. To determine this microstructure, different techniques were developed, each with its own limitations. The purpose of this study on concrete and natural building stones was to compare and to combine data obtained by X-ray computed micro-tomography (micro-CT), water absorption under vacuum and mercury intrusion porosimetry (MIP). Pore-size distribution curves ranging from 10 nm to 1 mm and total porosity results were obtained. Furthermore, micro-CT revealed the presence of an interfacial transition zone (ITZ) and of micro-cracks inside the aggregates of the concrete samples after mercury intrusion. Micro-CT visualized mercury inside large air bubbles within the concrete samples. Both micro-CT and MIP were compared and their respective advantages and disadvantages discussed. © 2008 Elsevier B.V. All rights reserved.
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| 6. |
- Cwirzen, A., et al.
(författare)
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Reactive powder based concretes : Mechanical properties, durability and hybrid use with OPC
- 2008
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Ingår i: Cement and Concrete Research. - : Elsevier BV. - 0008-8846 .- 1873-3948. ; 38:10, s. 1217-1226
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Tidskriftsartikel (refereegranskat)abstract
- The basic mechanical properties, frost durability and the bond strength with normal strength concretes of the ultra high strength (UHS) mortars and concretes were studied. The produced mixes had plastic or fluid-like consistency. The 28-day compressive strength varied between 170 and 202 MPa for the heat-treated specimens and between 130 and 150 MPa for the non-heat-treated specimens. The shrinkage values were two times higher for the UHS mortars in comparison with the UHS concretes. After the initial shrinkage, swelling was noticed in the UHS mortars. The lowest creep values were measured for the non-heat-treated UHS concretes. The frost-deicing salts durability of the UHS mortars and concretes appeared to be very good even despite the increased water uptake of the UHS concretes. The study of the hybrid concrete beams indicated the formation of low strength transition zone between the UHS mortar and normal strength concrete. © 2008 Elsevier Ltd. All rights reserved.
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| 7. |
- Cwirzen, A.
(författare)
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The effect of the heat-treatment regime on the properties of reactive powder concrete
- 2007
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Ingår i: Advances in Cement Research. - : Thomas Telford Ltd.. - 0951-7197 .- 1751-7605. ; 19:1, s. 25-33
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the curing regime on the mechanical properties and microstructure of ultra-high-strength mortar was studied. Nine different curing procedures were applied in which the start and duration of the heat treatment were varied. The studied mortars had a water-to-binder ratio of 0·17 and additions of amorphous silica fume and fine quartz filler. The microstructure and microchemistry were investigated by electron scanning microscopy and mercury intrusion porosimetry. The results revealed that longer heating times increased the degree of hydration, refined the microstructure and resulted in higher ultimate compressive strength, Very late and very early application of the heat treatment caused a lower degree of hydration and a smaller long-term increase of compressive strength. The scanning electron microscopy investigation revealed the formation of one hydration rim around anhydrous cement particles and the presence of a hollow shell in all investigated specimens. © 2007 Thomas Telford Ltd.
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| 8. |
- Horoshenkov, K. V., et al.
(författare)
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The sound speed and attenuation in loose and consolidated granular formulations of high alumina cements
- 2003
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Ingår i: Applied Acoustics. - 0003-682X .- 1872-910X. ; 64:2, s. 197-212
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Tidskriftsartikel (refereegranskat)abstract
- Clinkers of high alumina cements are separated into three granular formulations with particle sizes in the range 0.6-0.71 mm, 0.71-1.18 mm and greater than 1.18 mm. These are used to manufacture consolidated samples of porous concrete in an autoclave. The acoustic and microscopic properties of loose and consolidated porous samples of concrete are investigated using both experimental methods and mathematical modelling. Values of porosity, flow resistivity, tortuosity and parameters of the pore size distribution are determined and used to predict closely the sound speed, acoustic attenuation and normal incidence absorption coefficient of these materials. It is shown that high alumina cements do not require additional binders for consolidation and that the structural bonds in these cements are developed quickly between individual clinkers in the presence of water. The hydration product build-up during the consolidation process is insignificant which ensures good acoustic performance of the consolidated samples resulting from a sufficient proportion of the open pores. The value of porosity in the consolidated samples was found to be around 40%, which is close to that measured in some commercial acoustic absorbers. This work provides a foundation for the development of acoustically efficient and structurally robust materials, which can be integrated in environmentally sustainable concrete and masonry structures. © 2002 Elsevier Science Ltd. All rights reserved.
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| 9. |
- Lahtinen, J., et al.
(författare)
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LEED and DFT investigation on the (2 × 2)-S overlayer on Co(0 0 0 1)
- 2005
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 599:1-3, s. 113-121
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Tidskriftsartikel (refereegranskat)abstract
- The geometric surface structure of a (2 × 2)-S layer formed by adsorption of hydrogen sulfide at 185 K on the Co(0 0 0 1) surface has been determined by low energy electron diffraction (LEED) experiments and density-functional theory (DFT) calculations. The favored atomic configuration consists of sulfur atoms residing at the fcc-hollow sites with S-Co distance of 2.2 ± 0.1 Å. Buckling in the first layer is negligible and the three nearest-neighbor Co atoms below the S atom are symmetrically moved by 0.05 ± 0.09 Å along the surface away from the S atom. The DFT calculations confirm the hollow-site adsorption and give further information on the electronic structure of the system. © 2005 Elsevier B.V. All rights reserved.
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| 10. |
- Patil, Aniket
(författare)
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Nonlinear Numerical Simulations of Interactions Between Ice Rubble and Structure
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This research is focused on three distinct but interconnecting topics:1) investigation of physical and mechanical properties of ice rubble, 2) material modelling of ice rubble, 3) numerical simulation of the interaction between ice rubble structure interaction. large scatter in the values of physical and mechanical properties of ice rubble can be seen in the literature due to non-standardised methods. Therefore, important tests are identified, and their major findings are presented. The shear box and punch through tests are important methods for deriving ice rubble properties, yet the interpretation of the results of the test is not straightforward. Numerical simulation of these tests offers a unique way to gain insight into rubble behaviour and to calibrate a material model for ice rubble. The accurate modelling of the ice rubble is needed when designing marine structures in ice-covered waters.The friction coefficient between ice-ice, ice-rubber and ice-steel was investigated by measuring contact forces in controlled laboratory experiments. The experiments revealed that surface topology, speed and temperature play important roles in determining the friction coefficient on ice surfaces. Given the similarities between cohesionless ice rubble and brash ice, like discrete nature, these two ice features can be explored together. A large-scale simple shear test and a pull-up test were conducted at Luleå harbour. The data collected over two test campaigns for large scale simple shear was analysed. An attempt was made to estimate, elastic properties (bulk and shear modulus), yield strength, kinematic and volumetric hardening parameters for continuous surface cap model (CSCM) based on large-scale test data.The calibration of material model CECM was done by curve fitting of simulation data to tests. Three tests were simulated using the finite element method (shear-box test and punch through the test) and smoothed particle hydrodynamics (punch through and pull-up test). The automated optimization algorithms were used to find the admissible combination input parameters. The assumptions of isotropy and continuity of surfaces reduced the number of input parameters. Despite the mesh distortion issue, the simulation of punch through test post-peak behaviour was simulated correctly. In the simulation shear box, expansion due to shear stress in the rubble was observed. In the simulation, the results clearly demonstrated that the evolution of the deformation patterns was related to the load records in the experiments.A seemingly promising numerical method i.e. smoothed particle hydrodynamics (SPH) was explored in this research. The limitation posed by mesh size in finite element formulation is removed in SPH formulation, yet this formulation takes advantage of the numerically robust underlying Lagrangian formulation. The plug formation in the simulation of punch through test and pull-up test was similar to that of test observations. Good agreement in the initial, peak and post-peak part of the load-displacement relationship was achieved by calibrating the material model parameter. It can be seen clearly while by comparing simulation results, that Mohr-Coulomb criteria are not fit to simulate the post-peak behaviour of ice rubble in the tests.The Cohesive Element Method (CEM) was used to simulate two full-scale load events recorded at Lighthouse Norströmsgrund in the Gulf of Bothnia. Two load events were identified out of full-scale measurement campaigns, “Measurements of Structure in Ice” (STRICE), to simulate ice rubble stricture interaction process with CEM. a scaling formula, based on ice rubble porosity, is explored to estimate material properties such as elastic modulus, fracture toughness and fracture energy. The hydrodynamic effects of water were added to the numerical model by the spring dash-pot system which was developed during this work for the research on ice mechanics. The frictional forces were also part of the numerical model. A relative velocity based dynamic friction coefficient was introduced. The mass damping and stiffness damping were part of the numerical model for interaction between ice rubble structure interaction but were not fully investigated.
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| 11. |
- Sistonen, E., et al.
(författare)
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Corrosion mechanism of hot-dip galvanised reinforcement bar in cracked concrete
- 2008
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Ingår i: Corrosion Science. - : Elsevier BV. - 0010-938X .- 1879-0496. ; 50:12, s. 3416-3428
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, probable corrosion mechanisms of hot-dip galvanised reinforcement bar in cracked concrete based on long-term durability tests and other studies are determined. The fist mechanism consists of a local dissolution of eta (η) and zeta (ζ) phase. In the second mechanism due to non-uniform zinc coating local dissolution of eta (η) and zeta (ζ) phase together with longitudinal and perpendicular cracking in zinc layer may lead to separation of zinc layer. In the third mechanism due to non-uniform zinc coating full dissolution of eta (η) and partial dissolution of zeta (ζ) phase together with longitudinal and perpendicular cracking in ferrite may lead to separation of zinc layer and ferrite. Corrosion rate with used cement type was decreasing. That is not dependent on concrete quality. However, concrete type has an effect on corrosion rate and moisture conditions. © 2008 Elsevier Ltd. All rights reserved.
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