| 1. |
- Folkeson, Nicklas, 1981, et al.
(författare)
-
Fireside corrosion of stainless and low alloyed steels in a waste-fired CFB boiler; The effect of adding sulphur to the fuel
- 2008
-
Ingår i: Materials Science Forum. ; 595-598, s. 289-297
-
Tidskriftsartikel (refereegranskat)abstract
- Corrosion field tests have been carried out in the superheater region of a commercial waste-fired 75MW CFBC boiler using air cooled probes. Exposure time was 24 and 1000 hours. The effect of adding sulphur to the fuel on the corrosion of two high alloyed steels and a low alloyed steel was studied. The fuel consisted of 50% household waste and 50% industrial waste. The exposed samples were analyzed by ESEM/EDX and XRD. Metal loss was determined after 1000 hours. Both materials suffered significant corrosion in the absence of sulphur addition and the addition of sulphur to the fuel reduced corrosion significantly. The rapid corrosion of the high alloyed steel in the absence of sulphur addition is caused by the destruction of the chromium-containing protective oxide by formation of calcium chromate. Adding sulphur to the fuel inhibited chromate formation and increased the sulphate/chloride ratio in the deposit. Iron(II) chloride formed on the low alloyed steel regardless of whether sulphur was added or not.
|
|
| 2. |
|
|
| 3. |
- Al-Gburi, Majid, et al.
(författare)
-
Effect of casting sequences on the restraint in slab-on-ground
- 2014
-
Konferensbidrag (refereegranskat)abstract
- One of the widespread issues in concrete structures is cracks occurring at early age. Cracks that appear in the young concrete may cause early start of corrosion of rebars or early penetration of harmful liquids or gases into the concrete body. These situations could result in reduced service life and in significantly increased maintenance cost of structures. Therefore it is important for construction companies to avoid these cracks. Restraint represents one of the main sources of thermal and shrinkage stresses at early age concrete. The casting sequence is affected by the restraint from adjacent structures. The present study discusses the influence of five casting sequences for the typical structure slab-on-ground. The aim is to map restraints for a number of possible casting sequences, and to identify the sequence with the lowest restraint. The study covers both continuous and jumped casting sequences, which include one, two and three contact edges. The result shows that the best casting sequence is the continuous technique with one contact edge.
|
|
| 4. |
- Al-Gburi, Majid, et al.
(författare)
-
Effect of the boundary conditions on the crack distribution in early age concrete
- 2014
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 50, s. 347-351
-
Tidskriftsartikel (refereegranskat)abstract
- Restrained movement in early age concrete may cause cracking. The boundary conditions – restraint – influence the possible crack distribution. This study aims at highlighting the effect of such restraint on the crack distribution. This is done by using the “Cracking Model for Concrete” in ABAQUS/Explicit simulating the non-linear behaviour under and after cracking. In the study the typical case wall-on-slab was in focus using a structure previously been tested in laboratory with both fixed and free bottom slab. The result of the modelling shows fairly good agreement with the cracks observed in the tests.
|
|
| 5. |
- Al-Gburi, Majid, et al.
(författare)
-
Prediction of Restraint in Second Cast Sections of Concrete Culverts using Artificial Neural Networks
- 2018
-
Ingår i: European Journal of Environmental and Civil Engineering. - : Taylor & Francis. - 1964-8189 .- 2116-7214. ; 22:2, s. 226-245
-
Tidskriftsartikel (refereegranskat)abstract
- Estimation of restraint is very important for accurately predicting the risk of early thermal and shrinkage cracking in concrete structures. The stress in young concrete is affected by changes in its dimensions during hydration and the restraint imposed by adjoining structures. In concrete culverts, the restraints from existing structures acting upon the first and second casting sections to be cast are different, causing them to exhibit different early cracking behaviour. This work presents a new method for predicting restraint in complex concrete structures using artificial neural networks (ANNs). Finite element calculations were performed to predict restraint in 108 slabs, 324 walls and 972 roofs from second sections of concrete culverts, and the results obtained were used to train and validate ANN models. The ANN models were then used to study the effects of varying selected parameters (the thickness and width of the roof and slab, the thickness and height of the walls, and the length of the culvert section) on the predicted restraint. Mathematical expressions for predicting restraint values in slabs, walls and roofs were derived based on the ANN models’ output and implemented in an Excel spreadsheet that provides a simple way of predicting restraint in practical applications. Restraint values predicted in this way agree well with the results of finite-element calculations
|
|
| 6. |
- Al-Gburi, Majid, et al.
(författare)
-
Reducing Thermal Crack Risks Caused by Restraint in Young Concrete - A Case Study on Walls of Water Tanks
- 2022
-
Ingår i: Nordic Concrete Research. - : Walter de Gruyter. - 0800-6377 .- 2545-2819. ; 66:1, s. 41-54
-
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.
|
|
| 7. |
- Al-Gburi, Majid, et al.
(författare)
-
Reduction of Early Age Crack Risks in Concrete Walls by Using a New Casting Technique
- 2016
-
Ingår i: Structural Engineering International. - : International Association for Bridge and Structural Engineering. - 1016-8664 .- 1683-0350. ; 26:3, s. 216-224
-
Tidskriftsartikel (refereegranskat)abstract
- Volumetric changes in early age concrete that are restrained might lead to cracks. The degree of restraint is influenced by the casting sequence and the dimensions of the castings. In the current study a new casting technique is proposed to reduce restraint in the newly cast concrete with a new arrangement of the structural joint to the existing old concrete. The proposed technique is valid for the typical structure wall-on-slab using one structural joint. This casting method means that lower part of the wall is cast together with the slab, and that part is called a kicker. Hereby, the behavior of the structure changes from a typical case wall-on-slab to a typical case wall-on-wall. It has been proven by the beam theory and demonstrated by numerical calculations that there is a clear reduction in the restraint from the slab to the wall using kickers. In the paper different kicker heights are studied with the aim of determining the minimum restraint in the upper part of the wall cast in contact with the kicker. The technique using kickers is compared with common measures used in the field to avoid cracking, such as cooling pipes in the new casting and/or heating cables in the adjoining old concrete. The presented method is both cost and time effective, as it opens the possibility to use larger structural length of each casting sequence.
|
|
| 8. |
- Al-Gburi, Majid, et al.
(författare)
-
Simplified methods for crack risk analyses of early age concrete : Part 2: Restraint factors for typical case wall-on-slab
- 2012
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 46:2, s. 39-56
-
Tidskriftsartikel (refereegranskat)abstract
- Existing restraint curves have been applied to the method of artificial neural networks (ANN) to model restraint in the wall for the typical structure wall-on-slab. It has been proven that ANN is capable of modeling the restraint with good accuracy. The usage of the neural network has been demonstrated to give a clear picture of the relative importance of the input parameters. Further, it is shown that the results from the neural network can be represented by a series of basic weight and response functions. Thus, the results can easily be made available to any engineer without use of complicated software.
|
|
| 9. |
- Al-Gburi, Majid, et al.
(författare)
-
Simplified methods for crack risk analyses of early age concrete : Part 1: Development of Equivalent Restraint Method
- 2012
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 46:2, s. 17-38
-
Tidskriftsartikel (refereegranskat)abstract
- The present study deals with both the compensation plane method, CPM, and local restraint method, LRM, as alternative methods studying crack risks for early age concrete. It is shown that CPM can be used both for cooling and heating, but basic LRM cannot be applied to heating. This paper presents an improved equivalent restraint method, ERM, which easily can be applied both for usage of heating and cooling for general structures. Restraint curves are given for two different infrastructures, one founded on frictional materials and another on rock. Such curves might be directly applied in design using LRM and ERM.
|
|
| 10. |
- Al-Gburi, Majid, et al.
(författare)
-
Using Artificial Neural Network to Predict the Restraint in Concrete Culvert at Early Age
- 2015
-
Ingår i: Structural Engineering International. - 1016-8664 .- 1683-0350. ; 25:3, s. 258-265
-
Tidskriftsartikel (refereegranskat)abstract
- Estimation of restraint is very important for accurate prediction of the risk of concrete cracking at early age. The present study predicts the restraint in 324 walls and 972 roofs for a concrete culvert. A parametric study included the thickness and width of the roofs, thickness and height of the walls, thickness and width of the slab, and length of the structures. Each parameter increased or decreased the restraint in the walls and the roofs. The calculation of the restraint was done elastically by the finite-element method (FE). The results were used by an artificial neural network (ANN) tool, where firstly an influential percentage was investigated as input parameters on the restraint prediction. Equations have been derived by the ANN model to calculate the restraint in the walls and the roofs. It was then used in an Excel sheet to calculate the restraint and compare the result with the result from the finite-element calculations giving high accuracy between the ANN model and the FE calculations
|
|
| 11. |
|
|
| 12. |
- Edrees Saeed, Tarek, et al.
(författare)
-
Investigation of changes in modal characteristics before and after damage of a railway bridge: a case study
- 2015
-
Ingår i: The IES Journal Part A. - : Informa UK Limited. - 1937-3260 .- 1937-3279. ; 8:2, s. 131-144
-
Tidskriftsartikel (refereegranskat)abstract
- The linear, time-invariant transfer function Txy has been utilized for the construction of FRF, based on the ambient vibration measurements. The results presented here indicated the possibility to identify and localize damages in steel railway bridges from the variations in the modal characteristics of the structure. The comparison between the modal characteristics for the healthy and collapsed bridge confirmed that damage had been existed. The abnormal percentage of change in modal damping, between the healthy and any other condition for a structure, can be regarded as a serious indicator for early stages of damage, while the high percentage of change in modal damping can clearly indicate the existence of damage in that structure. The average ratio of change in the damping ratio from the healthy to the collapsed bridge was about 206 % and this ration could be regarded as an index for the existence of a serious damage in steel bridges, which needs further evaluation in other test cases.
|
|
| 13. |
- Edrees, Tarek, et al.
(författare)
-
A comparative study on the identification of building natural frequencies based on parametric models
- 2014
-
Ingår i: Proceedings of the 33rd IASTED International Conference on Modelling, Identification and Control.
-
Konferensbidrag (refereegranskat)abstract
- The analysis and design of civil engineering structures is a complex problem, which is based on many assumptions to simplify these operations. This in turn, leads to a difference in the structural behaviour between calculations based models and real structures. Structural identification was proposed by many researchers as a tool to reduce this difference between models and actual structures. Moreover, Parametric models and non-parametric models were used intensively for system identification by many researchers. In this research effort, the system identification concept is utilized to identify the natural frequencies for a steel building’s frames. Different black box linear parametric models such as Transfer Function model (TF), Auto-Regressive model with eXternal input model (ARX), Auto-Regressive Moving Average with eXternal input (ARMAX) model, Output Error model structure (OE), and Box-Jenkins model (BJ) were examined for identifying the first 10th natural frequencies for the building’s frames, based on simulation results. Abaqus 6.12 finite-element software was utilized to perform the time history analysis for the examples and the obtained responses at one point of the roofs (assumed as a sensor) were further processed by the parametric models to obtain the building’s natural frequencies based on the Abaqus time history analysis results (assumed as a measurements). After that, Abaqus 6.12 was utlized again to perform another analysis, which is called frequency analysis to obtain the building’s natural frequencies and mode shapes based on the stiffness and mass (not the measurements) of the buildings. The results showed that the linear parametric models TF, ARX, ARMAX, OE, and BJ are robust to identify the natural frequencies of building and they are recommend for future work.
|
|
| 14. |
- Edrees, Tarek, et al.
(författare)
-
A state-of-the-art review of Structural Control Systems
- 2015
-
Ingår i: Journal of Vibration and Control. - : SAGE Publications. - 1077-5463 .- 1741-2986. ; 21:5, s. 919-937
-
Tidskriftsartikel (refereegranskat)abstract
- Nowadays the utilization of structural control systems for alleviating the responses of civil engineering structures, under the effects of different kinds of dynamics loadings, has become a standard technology, while still there are numerous of current research approaches for advancing the effectiveness of these methodologies. The aim of this article is to review the state of the art technologies in structural control systems by introducing a general literature review for all the types of vibrations control systems that have been appeared till now. These systems can be classified into four main groups: a) passive, b) semi active, c) active, and d) hybrid based on their operational mechanism. A brief description of each of these main groups and their subgroups, with their corresponding advantages and disadvantages will be also extendedly reported in this review. This article will conclude by providing an overview of some innovative practical implementations of devices, which are able to demonstrate their potentials and future directions of structural control systems in civil engineering.
|
|
| 15. |
- Edrees, Tarek, et al.
(författare)
-
Comfort level identification for irregular multi-storey building
- 2015
-
Ingår i: Automation in Construction. - : Elsevier BV. - 0926-5805 .- 1872-7891. ; 50, s. 40-49
-
Tidskriftsartikel (refereegranskat)abstract
- In this article, the System Identification approach is being used to identify the vertical frequencies of the top storey in a multi-storey building prefabricated from reinforced concrete in Stockholm. Before building construction, detailed investigation indicated that the building will not be affected by train vibrations from the nearby railway yard. After building completion, disturbing vibrations were observed in the building. Three measurement types namely: ambient vibration test, forced vibration test on the rails, and forced vibration test have been performed in order to specify the probable reasons for these vibrations.Five methods of structural identification approach, specifically: ARX, ARMAX, BJ, OEand State Space Models have been implemented for the identification process in this study usingthe tests' results. All the test types and model structures utilized have identified a concentration inthe floor only, which is close to the frequencies of human body parts. Furthermore, the article concludes that the ARMAX model and the Output Error model have indicated an excellent performance to predict the mathematical models of vibration's propagation in the building, when compared with other models used from the three types of tests.In addition, the results of the aforementioned system identification methods, implemented for this study, have indicated that there are no other reasons for the disturbing vibrations still observed in the building. Furthermore, the results confirmed the correctness of the previous theoretical and experimental results obtained by different specialists, who stated that the values of floor acceleration are within the acceptable limits, and the probable reason for any disturbance is the resonance between the generated low frequencies and the human body parts’ frequencies.
|
|
| 16. |
- Edrees, Tarek, et al.
(författare)
-
Semi-active structural control strategies
- 2014
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 50, s. 31-34
-
Tidskriftsartikel (refereegranskat)abstract
- The utilization of structural control systems to alleviate the responses of civil engineering structures, under the effects of dynamics loadings, has become a standard technology, while still there are numerous of current research approaches for advancing the effectiveness of these methodologies. It is important for successful application of smart structure to provide an effective control algorithm to compute the control forces to be applied on the building in order to reduce the external disturbances. The aim of this article is to provide a review of the control strategies to control the performance of semi-active systems utilized in civil engineering structures.
|
|
| 17. |
- Ekerfors, Katarina, et al.
(författare)
-
Behaviour of young high-strength concrete
- 1993
-
Ingår i: Utilization of High Strength Concrete : Proceedings. - Oslo : Norsk Betongforening. - 8291341001 ; , s. 691-697
-
Konferensbidrag (refereegranskat)
|
|
| 18. |
|
|
| 19. |
|
|
| 20. |
|
|
| 21. |
|
|
| 22. |
- Elfgren, Lennart, et al.
(författare)
-
High performance concrete with energetically modified cement (EMC)
- 2004
-
Ingår i: Proceedings International Symposium on Ultra-High Performance Concrete. - Kassel : Kassel University Press GmbH. - 3899580869 ; , s. 93-102
-
Konferensbidrag (refereegranskat)abstract
- The demands of the modern building industry require development of new types of binder materials with improved properties for high and ultra high strength concretes and with significantly improved durability. They will provide new potential possibilities for the controlling of high performance concrete technology. In the Department of Civil Engineering at Luleå University of Technology a study of energetically modified cement (EMC) indicates that it is possible to obtain much more rapid hardening cement than the original cement used. As an example the strength of EMC-concrete increases about 100 per cent at the age of one day compared with a conventional high strength concrete.A new type of the cement gives possibilities to obtain required workability of the concrete mixtures with low water to binder ratios (w/B < 0.24) and achieve the strength levels up to 200 MPa with binder content not exceeding 550 kg/m3. The modification process used in this study means a special mechanochemical treatment in vibrating milling equipment of the blend containing Ordinary Portland Cement (OPC) and silica fume (SF), which increases the surface energy and the chemical reactivity of the newly obtained binder. This results in an accelerating effect, which maintains at least for nine months. According to ongoing investigations the energetically modified cement appears to give a considerable acceleration effect in the whole range of studied temperature. Concretes produced with EMC cement demonstrated very high durability at very severe testing conditions, including drying, saturation in sodium chloride solution and freezing-thawing. These results are very promising and it might be used in a lot of applications as winter concreting, precast element production, special structural elements, repair of buildings, rehabilitation, topping of concrete, floors, roads, etc.
|
|
| 23. |
|
|
| 24. |
- Emborg, Mats, et al.
(författare)
-
Designing robust SCC for industrial construction with cast in place concrete
- 2005
-
Ingår i: Second North American Conference on the Design and Use of Self-Consolidating Concrete [and] Fourth International RILEM Symposium on Self-Compacting Concrete; [October 30 - November 2, 2005];Second North American Conference on the Design and Use of Self-Consolidating Concrete [and] Fourth International RILEM Symposium on Self-Compacting Concrete; [October 30 - November 2, 2005. - Hanley Wood. ; , s. 1251-1257
-
Konferensbidrag (refereegranskat)
|
|
| 25. |
|
|
| 26. |
|
|
| 27. |
- Fernlund, Eva, et al.
(författare)
-
Hereditary hypertrophic cardiomyopathy in children and young adults—The value of reevaluating and expanding gene panel analyses
- 2020
-
Ingår i: Genes. - : MDPI AG. - 2073-4425. ; 11:12
-
Tidskriftsartikel (refereegranskat)abstract
- Introduction: Sudden cardiac death (SCD) and early onset cardiomyopathy (CM) in the young will always lead to suspicion of an underlying genetic disorder. Incited by the rapid advances in genetic testing for disease we have revisited families, which previously tested “gene-negative” for familial predominantly pediatric CM, in hopes of finding a causative gene variant. Methods: 10 different families with non-syndromic pediatric CM or hypertrophic cardiomyopathy (HCM) with severe disease progression and/or heredity for HCM/CM related SCD with “gene-negative” results were included. The index patient underwent genetic testing with a recently updated gene panel for CM and SCD. In case of failure to detect a pathogenic variant in a relevant gene, the index patient and both parents underwent clinical (i.e., partial) exome sequencing (trio-exome) in order to catch pathogenic variants linked to the disease in genes that were not included in the CM panel. Results: The mean age at clinical presentation of the 10 index cases was 12.5 years (boys 13.4 years, n = 8; girls 9 years, n = 2) and the family history burden was 33 HCM/CM cases including 9 HCM-related SCD and one heart transplantation. In 5 (50%) families we identified a genetic variant classified as pathogenic or likely pathogenic, in accordance with the American College of Medical Genetics and Genomics (ACMG) criteria, in MYH7 (n = 2), RBM20, ALPK3, and PGM1, respectively, and genetic variants of unknown significance (VUS) segregating with the disease in an additional 3 (30%) families, in MYBPC3, ABCC9, and FLNC, respectively. Conclusion: Our results show the importance of renewed thorough clinical assessment and the necessity to challenge previous genetic test results with more comprehensive updated gene panels or exome sequencing if the initial test failed to identify a causative gene for early onset CM or SCD in children. In pediatric cardiomyopathy cases when the gene panel still fails to detect a causative variant, a trio exome sequencing strategy might resolve some unexplained cases, especially if a multisystemic condition is clinically missed.
|
|
| 28. |
- Fjellström, Peter, et al.
(författare)
-
Crack-free concrete : an understanding of creep
- 2011
-
Ingår i: Nordic Concrete Research. - Oslo : The Nordic Concrete Federation. - 9788282080255 ; , s. 477-480
-
Konferensbidrag (refereegranskat)abstract
- A durable structure of concrete is achieved when no cracking occurs during the young ages of the hardening process. Therefore, it’s of importance to address shrinkage and creep correctly. Drying is the primary source of shrinkage, and the time development in shrinkage is an effect of the balance between drying and creep. Therefore, creep is to be measured on sealed and non-sealed specimens in order to investigate the nature of drying creep. Measurements will be performed for loading ages up to 1 year. These experimental data will be used to create accurate models, including both short and long term effects.
|
|
| 29. |
- Fjellström, Peter, et al.
(författare)
-
Heat loss compensation for semi-adiabatic calorimetric tests
- 2013
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 47:1, s. 39-60
-
Tidskriftsartikel (refereegranskat)abstract
- Heat of hydration has long been of importance since it affects the temperature levels within a concrete structure, and thus, potentially affects its durability. The only source of energy is the reaction between cement and water. This energy warms up the concrete sample and all the ambient materials. Therefore, in order to model these energies, the TSA (traditional semi-adiabat) setup is transformed into an associated sphere. By this, the temperature distribution and the energies within each layer of the TSA can be calculated. The sum of all energies gives the total heat of hydration. A refined model using a correction factor is introduced, which accounts for energies lost to the TSA setup materials. Results show that the effect of this factor cannot be disregarded, especially not for TSAs with low cooling factors.
|
|
| 30. |
- Fjellström, Peter, et al.
(författare)
-
Model for concrete strength development including strength reduction at elevated temperatures
- 2012
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 45:1, s. 25-44
-
Tidskriftsartikel (refereegranskat)abstract
- When casting concrete structures, one of the most important properties is the concrete strength development. The need of actions on site is different at various stages of hardening, from the fresh concrete to the hardened concrete. The paper defines a model analysing maturity and associated strength growth within three important time periods. The model can be applied separately within each of these periods depending on test data available.It is shown in the paper that the temperature plays an important role on the strength development of concrete structures. The hydration rate increases with increased temperatures, which can be described by maturity functions. If the concrete temperature remains high, strength reduction at later ages usually occurs compared to hardening at lower temperature, which may be denoted strength reduction at elevated temperatures or cross over effects. Both these phenomena have been implemented in the model for strength growth presented in the paper. The functionality of the model is demonstrated by evaluation of laboratory tests for five concrete mixes and two types of cement.
|
|
| 31. |
|
|
| 32. |
- Hatem, Mohammed, et al.
(författare)
-
Design of concrete mixes by systematic steps and ANN
- 2012
-
Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 2:4, s. 232-251
-
Tidskriftsartikel (refereegranskat)abstract
- The current research caters for the possibility of arriving at a system for designing concrete mixeseasily using available materials locally by specified wide ranges of pre-requisites of three mainprescribed properties to cover a good variety of practical mixes, which are water, water-cement ratioand total aggregate-cement ratio. Using these three properties, a tri-linear form was constructed bygraphical technique manner based on absolute volume approach. This approach defines as asummation of absolute volume for each of these three materials individually water, cement andaggregate should be equal to the absolute volume of whole concrete mixture based on thesealtogether. A quad-form area which includes a wide range of mixes can be formed from thisrepresentation. This area should achieve all the prescribed properties aforementioned. Artificial neuralnetwork concept used in this study also to build easily and quickly system which can be translatedinto Excel sheet. This system predict proportions of concrete mixture and the compressive strengthusing the results designed by the quad-form area method in addition to the data from literature around500 mixes based on local materials used in Iraq. Six input parameters (water to cement ratio, theslump, % of fine to total aggregate content, maximum aggregate size, fineness modulus of fineaggregate and the compressive strength) were used in this system to get the outputs. In addition, nineinput parameters ((water, cement, sand and gravel contents) and the properties of the mix (Finenessmodulus, W/C ratio, the slump, % of fine to total aggregate and the M.A.S)) were used as basis ofcompressive strength model. The algorithm of this system aimed to reduce the high number of trailmixes error as well as saving the labors, cost and time. Results indicated that the concrete mix designand the compressive strength model can be predicted accurately by using graphical perspective andthe ANN approach.
|
|
| 33. |
- Hatem, Mohammed, et al.
(författare)
-
Performance of Cement-poor Concrete with Different Superplasticizers
- 2014
-
Ingår i: International Journal of Research and Reviews in Applied Sciences. - 2076-734X .- 2076-7366. ; 18:2, s. 163-172
-
Tidskriftsartikel (refereegranskat)abstract
- Concrete can be used for casting plugs in deep boreholes where fracture zones are intersected. They will be exposed to flowing groundwater and be in contact with very tight seals of smectite clay installed where the surrounding rock is tight. The cast concrete must be able to carry the clay segments placed over it after a few days. Its bearing capacity does not have to be very high after that since the clay soon adheres to the rock and carries itself. The concrete must be poor in cement for minimizing the risk of creation of voids caused by dissolution of the cement and it should have “inert” aggregate of quartz-rich material. Inorganic superplasticizers instead of conventional organic ones should be used for eliminating the risk of degradation and loss by formation of colloids that can carry radionuclides to the biosphere from holes bored in repository rock. The two concrete types discussed in the present study had Portland and Merit 5000 low pH cement as binders and crushed quartzite as aggregate. Talc mineral powder and ordinary organic Glenium 51 were used as superplasticizers for comparing their impact on the physical properties. The matrix of the cement-poor talc concrete gave ductile behaviour during initial hardening. The very dense matrix of either of the concretes would not lead to compression of the system even after complete loss of cement, which will happen over a longer period of time. The overall conclusion was that talc as superplasticizer and conditioner of the concrete can make the concrete sufficiently fluid for constructing seals at depth in boreholes, and react with cement to provide high strength with some delay. pH is much lower in Merit than in Portland concrete, which causes less impact on the clay seals. Portland concrete has five times higher strength than Merit concrete after a week but three times lower strength after 28 days.
|
|
| 34. |
- Hatem, Mohammed, et al.
(författare)
-
Proportioning of cement-based grout for sealing fractured rock-use of packing models
- 2013
-
Ingår i: Engineering. - : Scientific Research Publishing, Inc.. - 1947-3931 .- 1947-394X. ; 5:10, s. 765-774
-
Tidskriftsartikel (refereegranskat)abstract
- Fractured, very permeable rock hosting repositories for radioactive waste will require grouting. New grout types of possible use where long-term performance is needed should have a small amount of cement for minimizing the increase in porosity that will follow from the ultimate dissolution and erosion of this component. They have to be low-viscous and gain strength early after injection and packing theory can assist designers in selecting suitable proportions of various grout components. Optimum particle packing means that the porosity is at minimum and that the amount of cement paste needed to fill the voids between aggregate particles is very small. Low porosity and microstructural stability must be guaranteed for long periods of time. Organic additives for reaching high fluidity cannot be used since they can give off colloids that carry released radionuclides and talc can be an alternative superplasticizer. Low-pH cement reacts with talc to give high strength with time while Portland cement gives early but limited strengthening. The clay mineral palygorskite can be used for early gelation because of its thixotropic properties. Once forced into the rock fractures or channels in soil it stiffens and serves as a filter that prevents fine particles to migrate through it be lost. However, its hydrophilic potential is too high to give the grout a high density and high strength. According to the experiments carried out most of the investigated grouts are injectable in fractures with apertures down to 100 μm.
|
|
| 35. |
- Hatem, Mohammed, et al.
(författare)
-
Rheological properties of low pH cement-palygorskite injection grout
- 2013
-
Ingår i: Journal of Advanced Science and Engineering Research. - 2231-8844. ; 3:3, s. 167-192
-
Tidskriftsartikel (refereegranskat)abstract
- The rheological properties of cementitious materials containing fine particles, such as mineral admixture were investigated using a Viso Star-L rheometer with cylindrical spindles. Selected features of the behavior of these materials are evaluated from a rheological perspective through literatures results for the past 30 years. One of the important factors that governs the ability of grout to penetrate fractures, channels and porous material is the rheology. The mineral admixture was clay palygorskite which can be used for early gelation because of its thixotropic properties as well as the powder quartz used as aggregate. The cementitious materials were designed and three recipes (MPG1, MPG2 and MPG3) were examined in this research by changing the mix proportions of the mineral admixture palygorskite and water content. For ensuring the accuracy of rheological measurement for the candidate’s grouts, necessary verification was been evaluated such as, influence of mixing time, stability and “time effect” to the accuracy of viscosity measurement, and yield stress as well as the physical properties at 3, 7 and 28 days. The results showed that grouts recipes with quartzite aggregate of different granulometry, are chemically compatible and fulfill the requirement of containing no organic matter. Candidate’s grouts found to satisfy the stable sedimentation criteria with sedimentation rates less than 5% after 2 hours. Furthermore, it was found that the grout recipe 3 followed by 1 showed lower yield stress and plastic viscosity which are (0.1 Pa and 0.269 Pas) and (0.288 Pa and 0.531 Pas) respectively.
|
|
| 36. |
- Hedlund, Hans, et al.
(författare)
-
Analysis of early age cracking in HPC structures
- 1999
-
Ingår i: Utilization of high strength/high performance concrete : proceedings. - Oslo : Norsk Betongforening. - 8291341257 ; , s. 1134-1143
-
Konferensbidrag (refereegranskat)
|
|
| 37. |
|
|
| 38. |
- Hedlund, Hans, et al.
(författare)
-
Grönare betong
- 1999
-
Ingår i: Bygg och Teknik. - 0281-658X .- 2002-8350. ; 91:7, s. 12-13
-
Tidskriftsartikel (populärvet., debatt m.m.)
|
|
| 39. |
- Hedlund, Hans, et al.
(författare)
-
Hardening technology for concrete structures
- 1997
-
Ingår i: Advanced design of concrete structures. - Barcelona : International Center for Numerical Methods in Engineering (CIMNE). - 8487867944 ; , s. 313-318
-
Konferensbidrag (refereegranskat)
|
|
| 40. |
|
|
| 41. |
- Hedlund, Hans, et al.
(författare)
-
Härdningsstyrning av betongkonstruktioner
- 1996
-
Ingår i: Byggforskning : Byggforskningsrådets tidning för en bättre byggd miljö. - 1102-3686. ; :3, s. 38-39
-
Tidskriftsartikel (populärvet., debatt m.m.)
|
|
| 42. |
- Hedlund, Hans, et al.
(författare)
-
Measurements of self-desiccation and shrinkage of hardening concrete
- 1997
-
Ingår i: Moisture Measurement in Concrete Constructions Exposed to Temperature and Moisture Variations. - Espoo : Valtion teknillinen tutkimuskeskus. Tie- ja liikennelaboratorio. - 9513845656 ; , s. 73-101
-
Konferensbidrag (refereegranskat)
|
|
| 43. |
|
|
| 44. |
|
|
| 45. |
- Hösthagen, Anders, et al.
(författare)
-
Equivalent Restraint Method Correlated to Empirical Measurements
- 2014
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 50, s. 505-508
-
Tidskriftsartikel (refereegranskat)abstract
- The present study deals with the correlation between numerical models and empirical observations in newly cast concrete specimens. The model used is the equivalent restraint method, ERM, which is established from several local restraint method calculations, LRM. The csating of walls in a tunnel construction is investigated. Correlation between models and empirical measurements is established in three steps.
|
|
| 46. |
- Hösthagen, Anders, 1979-, et al.
(författare)
-
Evaluation of Material Properties for Young Concrete
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Restrained volumetric changes in early age concrete may cause tensile strength failure, i.e. crack initiation and propagation. The volumetric changes are primarily induced by a change in thermal and moisture states, and it is of great importance to quantify the resulting stresses and strains that arise when the volumetric changes are restrained. Large economical and technical benefits are gained if measures to avoid cracking can be determined by calculations prior to casting. To perform such calculations, the following property areas of the concrete needs to be known; strength development, heat of hydration, basic shrinkage, thermal dilation, basic creep and stress at full restraint. This work demonstrates how the concrete can be tested in a laboratory environment and how to evaluate the numerical data, thus yielding a parameter set that may be used during stress and strain development calculations. Furthermore, a brief investigation is performed on how sensitive the evaluation for each test is, with respect to crack risk estimation. It is showed that the measured stress development from the stress development at full restraint test can be considered as a checkpoint for the total parameter set. The reason is that the calculated stress development, which is compared to the measured counterpart, is influenced by all evaluated parameters. It is discussed that out of the performed tests, three are of significant importance when it comes to provide an operational parameter set for the calculations. These tests are the ones achieving strength development, heat of hydration and stress at full restraint.
|
|
| 47. |
- Hösthagen, Anders, 1979-
(författare)
-
Thermal Crack Risk Estimation and Material Properties of Young Concrete
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents how to establish a theoretical model to predict risk of thermal cracking in young concrete when cast on ground or an arbitrary construction. The crack risk in young concrete is determined in two steps: 1) calculation of temperature distribution within newly cast concrete and adjacent structure; 2) calculation of stresses caused by thermal and moisture (due to self-desiccation, if drying shrinkage not included) changes in the analyzed structure. If the stress reaches the tensile strength of the young concrete, one or several cracks will occur.The main focus of this work is how to establish a theoretical model denoted Equivalent Restraint Method model, ERM, and the correlation between ERM models and empirical experiences. A key factor in these kind of calculations is how to model the restraint from any adjacent construction part or adjoining restraining block of any type.The building of a road tunnel and a railway tunnel has been studied to collect temperature measurements and crack patterns from the first object, and temperature and thermal dilation measurements from the second object, respectively. These measurements and observed cracks were compared to the theoretical calculations to determine the level of agreement between empirical and theoretical results.Furthermore, this work describes how to obtain a set of fully tested material parameters at CompLAB (test laboratory at Luleå University of Technology, LTU) suitable to be incorporated into the calculation software used. It is of great importance that the obtained material parameters describe the thermal and mechanical properties of the young concrete accurately, in order to perform reliable crack risk calculations. Therefore, analysis was performed that show how a variation in the evaluated laboratory tests will affect the obtained parameters and what effects it has on calculated thermal stresses.
|
|
| 48. |
- Hösthagen, Anders, et al.
(författare)
-
Thermal crack risk estimations for tunnel : equivalent restraint method correlated to empirical observations
- 2014
-
Ingår i: Nordic Concrete Research. - 0800-6377. ; 49, s. 127-143
-
Tidskriftsartikel (refereegranskat)abstract
- The present study deals with the correlation between numerical models and empirical observations in newly cast concrete structures. The model used is the equivalent restraint method, ERM, which is established from several local restraint method calculations, LRM. The casting of walls and roof in a tunnel construction is investigated. Correlation between models and empirical measurements is established in three steps: 1) the restraint situation is analyzed; 2) the calculated temperature developments are compared to empirical temperature measurements to calibrate the models; and 3) calculated strain ratios are compared with observed crack patterns, and in general a good correlation is achieved
|
|
| 49. |
- Hösthagen, Anders, et al.
(författare)
-
Thermal Crack Risk Estimations of Concrete Walls : Temperature and Strain Measurements Correlated to the Equivalent Restraint Method
- 2017
-
Ingår i: Proceedings of the 23rd Nordic Concrete Research Symposium. - Oslo, Norway : Nordic Concrete Federation. - 9788282080569
-
Konferensbidrag (refereegranskat)abstract
- Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. The method has previously been analyzed but needs to be further examined and validated. Recordings of tunnel sections were performed and compared to calculated values by ERM. Satisfying correlation between theoretically estimated and observed temperatures, strains and time of through cracking was achieve which is promising for future implementation and testing of the method.
|
|
| 50. |
- Hösthagen, Anders, 1979-, et al.
(författare)
-
Thermal Crack Risk Estimations of Concrete Walls – Temperature and Strain Measurements Correlated to the Equivalent Restraint Method
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Self-induced non-elastic deformations in hardening concrete, caused by restrained volume changes due to thermal dilatation and moisture deformations, often leads to cracking. In thermal crack risk analyses, determination of the degree of restraint is vital. One model to estimate the restraint and calculate the thermal crack risk is the Equivalent Restraint Method, ERM. This method has previously been analysed but needs to be examined and validated further. Measurements of wall castings were performed and compared to calculations with ERM in order to establish a correlation to empirical observations. A satisfying correlation between theoretically estimated and measured time of through cracking was achieved. Based on this study and other, ERM is thus considered to work satisfyingly.
|
|
