<p>This thesis deals with prediction of early age cracking caused by restrained temperature dilation and autogenous deformation. Traditonally, prediction of early-age cracking has been based on temperature criteria. The temperature criteria alone are, however, not sufficiently accurate for cracking prediction. Stress-strain criteria are more reliable because they consider all the crucial factors: thermal dilation, autogenous deformaion, mechanical properties and restraint condtions.</p><p>The purpose of this dr.ing. project is to extend the general appliicability of stress/srain based curing technology, and to contribute to better understanding and better prediction of stresses during hardeing of concrete structures. </p><p>In the first part of the thesis the major features of hardening concrete are described and mathematical descriptions of the phenomena are given. Different models are discussed, and on the basis of such discussion, new models have been implemented in the FE program DIANA. First, the equivalent time was introduced in parallel to the degree of hydration, so that all material properties may be considered equivalent-time dependent. it is shown that the simpler and more common equivelent-time based model for the heat of hydration development can describe temperature development with the same accurancy as the degree of hydration based model. Further, the activation energy is made temperature depentent instead of being constant. A modified CEB equation for E.modulus development is implemented. The temperature influence on creep is modified by introducing a thermal transitonal creep term.</p><p>A mathematical decription of stress-and strain development in hardening concrete structures is presented, and special attention given to the viscoelastic behavior of concrete. The influence of creep on Self-induced stresses is examined. The emphasis is put on creep importance in different periods of the hardening process. In externally restrained structures, prone to through cracking, creep in the early period (heating phase) reduces the compressive stresses, and consequently increases the tensile stresses in the subsequent cooling period, thus increasing the cracking risk. For internally restrained structures, prone to surface cracking in the early period, creep obviosly reduces the cracking risk. In the cooling phase creep reduces the tensile stresses. For externally restrained structures, the effects of creep in the cooling and heating phases are counteracting, and in some cases they annul each other. The present results do not diminish the importance of creep on thermal stresses, to the contrary, it emphasises the necessity of correct prediction of creep during the whole period of hardening.</p><p>Three creep models for young concrete are compared: Double Power Law, Maxwell chain model and Burgers model. The models are calibrated against the same experimental data and used in calculation of therimal stresses. The temperature dependency of the models is also investigated. A good agreement between the Double Power Law and the Maxwell Chain was obtained, wheras the Burgers model, which consists of one Kelvin unit and one viscous damper, gave different results. Although the major reason for the deviation is due to the simplicity of the Burgers model, the deviation is also coused by differnt descriptions of the temperature dependence, and the nature of the test data used in the calibration. Test methods are also discussed, with special weight on the Temperature Stress Testing Machine tests. Although this type of test is indispensible, and very useful to check the validity of the material models and the calculation methods, the shortcomings by using it to predict the creep model parameters are also shown. </p><p>Restraint conditions and their influlence on thermal stresses were also investigated. Different ways of modelling the structure and the interaction with the subgrade were analysed and compared. Influence of the stiffness of the ground and the structural geometry on thermal stresses and cracking risk was investigated by means of 3D analyses.</p><p>The last part of the work is numerical simulation of temperature and stress/strain development in real structure, the Maridal culvert in Olso. A comprehensive laboratory test program was performed at NTNU to identify material parameters. Both thermal and mechanical properaties were tested. Material models were checked in the TSTM for three different realistic temperature histories. Within the Brite-Euram project IPACS a large field instrumentation programme has been carried out to measure temperature and strain development in the culvert. 3D analysis of the foundations and walls in two of the instrumented sections of this structure were performed with DIANA and calculated results are compared to measurements. Deviation between calculated and measured temperature is within range of ±5⁰<i>C. </i>Deviation between calculated and measured strains is about ±50x10^-6.Possible reasons of disagreement between calculations and measurements are discussed. When all uncertainties in materail modelling and measuring methods are sonsidered it is concluded that results of the simulation are satisfying. </p>

This thesis deals with prediction of early age cracking caused by restrained temperature dilation and autogenous deformation. Traditonally, prediction of early-age cracking has been based on temperature criteria. The temperature criteria alone are, however, not sufficiently accurate for cracking prediction. Stress-strain criteria are more reliable because they consider all the crucial factors: thermal dilation, autogenous deformaion, mechanical properties and restraint condtions. The purpose of this dr.ing. project is to extend the general appliicability of stress/srain based curing technology, and to contribute to better understanding and better prediction of stresses during hardeing of concrete structures. In the first part of the thesis the major features of hardening concrete are described and mathematical descriptions of the phenomena are given. Different models are discussed, and on the basis of such discussion, new models have been implemented in the FE program DIANA. First, the equivalent time was introduced in parallel to the degree of hydration, so that all material properties may be considered equivalent-time dependent. it is shown that the simpler and more common equivelent-time based model for the heat of hydration development can describe temperature development with the same accurancy as the degree of hydration based model. Further, the activation energy is made temperature depentent instead of being constant. A modified CEB equation for E.modulus development is implemented. The temperature influence on creep is modified by introducing a thermal transitonal creep term. A mathematical decription of stress-and strain development in hardening concrete structures is presented, and special attention given to the viscoelastic behavior of concrete. The influence of creep on Self-induced stresses is examined. The emphasis is put on creep importance in different periods of the hardening process. In externally restrained structures, prone to through cracking, creep in the early period (heating phase) reduces the compressive stresses, and consequently increases the tensile stresses in the subsequent cooling period, thus increasing the cracking risk. For internally restrained structures, prone to surface cracking in the early period, creep obviosly reduces the cracking risk. In the cooling phase creep reduces the tensile stresses. For externally restrained structures, the effects of creep in the cooling and heating phases are counteracting, and in some cases they annul each other. The present results do not diminish the importance of creep on thermal stresses, to the contrary, it emphasises the necessity of correct prediction of creep during the whole period of hardening. Three creep models for young concrete are compared: Double Power Law, Maxwell chain model and Burgers model. The models are calibrated against the same experimental data and used in calculation of therimal stresses. The temperature dependency of the models is also investigated. A good agreement between the Double Power Law and the Maxwell Chain was obtained, wheras the Burgers model, which consists of one Kelvin unit and one viscous damper, gave different results. Although the major reason for the deviation is due to the simplicity of the Burgers model, the deviation is also coused by differnt descriptions of the temperature dependence, and the nature of the test data used in the calibration. Test methods are also discussed, with special weight on the Temperature Stress Testing Machine tests. Although this type of test is indispensible, and very useful to check the validity of the material models and the calculation methods, the shortcomings by using it to predict the creep model parameters are also shown. Restraint conditions and their influlence on thermal stresses were also investigated. Different ways of modelling the structure and the interaction with the subgrade were analysed and compared. Influence of the stiffness of the ground and the structural geometry on thermal stresses and cracking risk was investigated by means of 3D analyses. The last part of the work is numerical simulation of temperature and stress/strain development in real structure, the Maridal culvert in Olso. A comprehensive laboratory test program was performed at NTNU to identify material parameters. Both thermal and mechanical properaties were tested. Material models were checked in the TSTM for three different realistic temperature histories. Within the Brite-Euram project IPACS a large field instrumentation programme has been carried out to measure temperature and strain development in the culvert. 3D analysis of the foundations and walls in two of the instrumented sections of this structure were performed with DIANA and calculated results are compared to measurements. Deviation between calculated and measured temperature is within range of ±50C. Deviation between calculated and measured strains is about ±50x10-6. Possible reasons of disagreement between calculations and measurements are discussed. When all uncertainties in materail modelling and measuring methods are sonsidered it is concluded that results of the simulation are satisfying.

Diss. Luleå : Luleå tekniska univ., 2003.

No description available.

Lic.-avh. Luleå : Luleå tekniska univ., 2004.

Diss. Luleå : Luleå tekniska univ., 2003.

Lic.-avh. Luleå : Luleå tekniska univ., 2008. / Härtill 4 uppsatser.

<p>Concrete is a very common construction material. It´s characteristics are strength, durability and formablility. Superplasticizer is a common admixture, which changes the properties of concrete.</p><p>Today (spring 2007) there are no certian mathematical methods to calculate the required percentage of this admixture needed to give the necessary set slump flow in the overall concrete recipe.</p><p>Concrete batching companies must therefor experiment with different amount of superplasticizer in order to meet the specified slump and strength.</p><p>The purpose og this report is to investigate if any mathematical relation can be established between the amount of superplasticizer used and the slump flow achieved.</p><p>After carrying out some practical experiments using four different superplasticizers a direct relationship can be establish between the percentage of admixture used and the slump/flowability achieved. Unfortunatly at present due to the numerous variables, the calculation of mathematical formula can not be achieved.</p>

<p>På grund av maskinernas behov av att transportera bort restprodukter samt att nödvändiga vätskor ska kunna tillföras, har hål borrats ut ur betongbjälklaget i verkstad 77 vid Sandvik Toolings anläggning i Gimo under flera år. Detta utan att några större åtgärder har genomförts för att återställa bjälklaget till sin ursprungliga hållfasthet.</p><p>Examensarbetets syfte är att kontrollera möjligheterna att göra hål i betongbjälklaget. Detta görs teoretiskt. Det som även skall besvaras är om det finns någon metod som kan återge betongbjälklaget en del av sin hållfasthet.</p><p>Från Sandviks arkiv i Sandviken erhölls de ritningar som var aktuella. Dessa ritningar gav svar på byggnadens konstruktion. Från dessa bestämdes de områden som skulle undersökas.</p><p>Vid område 1 kunde det kapas stänger vid varje fält och stöd:</p><p>Vid upplag 1 kan 18 stänger kapas, upplag 2 kan 2 stänger kapas, upplag 3 kan 14 stänger kapas och vid upplag 4 kan 12 stänger kapas.</p><p>Vid fält 1 kan 11 stänger kapas, fält 2 kan 17 stänger kapas, fält 3 kan 15 stänger kapas och vid fält 4 kan 12 stänger kapas</p><p>Vid område 2 kan det kapas stänger i båda riktningarna över pelaren som studeras, totalt 12 i x-led och y-led tillsammans.</p><p>Detta resultat baseras på de antaganden som har gjorts vid de olika områdena. Det vill säga att de stänger som kan kapas i område 1 är de som kan kapas i den fem meter breda strimla som studeras, i område 2 är antalet stänger som kan kapas baserade på enbart den pelare som studeras.</p> / <p>The waste that is created by the machines due to the process needs to be transported away and necessary liquids must be transported to the machines. This requires that holes are drilled through the concrete slab in building 77 at Sandvik Toolings facilities in Gimo, this has been done for several years. For some holes insufficient attempts to restore the concrete slabs strength has been done.</p><p>The purpose of this degree thesis is to investigate the possibility to make holes in the concrete slab. This will be done theoretical. Another question that shall be answered is if there are any methods for the concrete slab to regain strength.</p><p>The blueprints that were needed where obtained from Sandviks archive in Sandviken. From the blueprints the areas which were to be investigated was selected.</p><p>In area 1 reinforcement bars could be cut of in both field and support areas:</p><p>At support 1, 18 reinforcement bars could be cut of. At support 2, 2 reinforcement bars could be cut of. At support 3, 14 reinforcement bars could be cut of and at support 4, 12 reinforcement bars could be cut of.</p><p>In field 1, 11 reinforcement bars could be cut of. At field 2, 17 reinforcement bars could be cut of. At field 3, 15 reinforcement bars could be cut of and at support 4, 12 reinforcement bars could be cut of.</p><p>In area 2, reinforcement bars could be cut of in both directions that were studied, in total 12 bars in x-direction and y-direction combined.</p><p>These results are based on the assumptions that have been made in each area. Videlicet that the number of bars that can be cut of in area 1 are the number of bars that can be cut of in five meters shred that is studied. In area 2 the number of bars that can be cut of is based only on the pillar that is studied.</p>

Abstract Today there is an opportunity to reinforce concrete with steel fiber reinforcement. In some cases, completely replace the conventional reinforcement. Replacing conventional mesh reinforcement with steel fiber reinforcement in slabs on ground has shown economic benefits, less crack width and less reinforcement amount. Today there are no Swedish standard for designing steel fiber reinforced concrete, what is there is different international recommendations. In this work, design methods for steel fiber concrete are used according to RILEM and Bekaer Swedish AB's software DRAPRO. For other design methods Eurokod 2 is followed. In this work, the design of slabs on ground that are not exposed by large tension strength been designed. Design of crack-reinforcement and restrictions of crack width have been conducted in three different slabs on ground. The calculations have been performed using only conventional reinforcement and only steel fiber reinforcement, and the results are then compared. The results of the theoretical analysis are summarized in tables that compare the amount of reinforcement, crack width and economic cost. This work showed that the slabs on the ground reinforced with steel fibers provide less crack width with a minor amount of reinforcement. The use of steel fiber concrete was also shown to reduce the reinforcement costs by about 70-75%. The absence of a Swedish standard may have caused some uncertainty among Swedish structural engineers using steel fiber reinforced concrete and there is a limited understanding of the material advantages. This may be a reason for the use of steel fiber concrete is relatively small in Sweden. Another reason why the use of steel fiber concrete is not expanding may be that the current mesh is so easy to reinforce with and is therefore used of traditional reasons. Hopefully, this work will make structural engineers to review the possibility of using steel fiber reinforcement instead of conventional mesh reinforcement in slabs on grade. Partly because of its economic advantage but also its ability to minimize crack width with a reminiscent reinforcement amount, which in turn can be beneficial from an environmental perspective.