Dissertations / Theses on the topic 'Concrete – Cracking'
To see the other types of publications on this topic, follow the link: Concrete – Cracking.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Concrete – Cracking.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Whigham, Jared Anthony. "Evaluation of restraint stresses and cracking in early-age concrete with the rigid cracking frame." Auburn, Ala., 2005. http://repo.lib.auburn.edu/2005%20Summer/master's/WHIGHAM_JARED_54.pdf.
Full text
2
Sayahi, Faez. "Plastic Shrinkage Cracking in Concrete." Licentiate thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-133.
Full textAbstract:
Early-age (up to 24 hours after casting) cracking may become problematic in any concrete structure. It can damage the aesthetics of the concrete member and decrease the durability and serviceability by facilitating the ingress of harmful material. Moreover, these cracks may expand gradually during the member’s service-life due to long-term shrinkage and/or loading. Early-age cracking is caused by two driving forces: 1) plastic shrinkage cracking which is a physical phenomenon and occurs due to rapid and excessive loss of moisture, mainly in form of evaporation, 2) chemical reactions between cement and water which causes autogenous shrinkage. In this PhD project only the former is investigated. Rapid evaporation from the surface of fresh concrete causes negative pressure in the pore system. This pressure, known as capillary pressure, pulls the solid particles together and decreases the inter-particle distances, causing the whole concrete element to shrink. If this shrinkage is hindered in any way, cracking may commence. The phenomenon occurs shortly after casting the concrete, while it is still in the plastic stage (up to around 8 hours after placement), and is mainly observed in concrete elements with high surface to volume ratio such as slabs and pavements. Many parameters may affect the probability of plastic shrinkage cracking. Among others, effect of water/cement ratio, fines, admixtures, geometry of the element, ambient conditions (i.e. temperature, relative humidity, wind velocity and solar radiation), etc. has been investigated in previous studies. In this PhD project at Luleå University of Technology (LTU), in addition to studying the influence of various parameters, effort is made to reach a better and more comprehensive understanding about the cracking governing mechanism. Evaporation, capillary pressure development and hydration rate are particularly investigated in order to define their relationship. This project started with intensive literature study which is summarized in Papers I and II. Then, the main objective was set upon which series of experiments were defined. The utilized methods, material, investigated parameters and results are presented in Papers III and IV. It has been so far observed that evaporation is not the only driving force behind the plastic shrinkage cracking. Instead a correlation between evaporation, rate of capillary pressure development and the duration of dormant period governs the phenomenon. According to the results, if rapid evaporation is accompanied by faster capillary pressure development in the pore system and slower hydration, risk of plastic shrinkage cracking increases significantly.
3
Meadows, Jason Lee. "Early-age cracking of mass concrete structures." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Spring%20Theses/MEADOWS_JASON_53.pdf.
Full text
4
Meadows, Jason Lee Schindler Anton K. "Early-age cracking of mass concrete structures." Auburn, Ala., 2007. http://repo.lib.auburn.edu/2007%20Spring%20Theses/MEADOWS_JASON_53.pdf.
Full text
5
Chan, Simon Hang Chi. "Bond and cracking of reinforced concrete." Thesis, Cardiff University, 2012. http://orca.cf.ac.uk/36698/.
Full textAbstract:
Ribbed reinforcement is described as “high bond” in Eurocode 2 (EC2) and within the code serviceability checks make no allowance for variations in either the ductility or bond characteristics of these bars. In this work, this matter is explored, and the crack development and behaviour of concrete beams reinforced with various types of ribbed steel bar are investigated, using both numerical and experimental approaches. The objective of the experimental approach is to undertake a series of experiments to compare the performance of beams made with standard reinforcement with that of beams formed with a new high-ductility bar produced by CELSA UK. The relationship between the bond strength and the rib pattern of reinforcing steel was studied and the behaviour at SLS load levels of RC beams with reinforcement of different rib patterns in flexure is discussed. The cracking of beams was monitored both visually and using a non-destructive Digital Image Correlation system to trace in-plane deformations and strains on the surface of the specimens. The test results showed that specimens with bars which had the highest relative rib area (fR value) exhibited the smallest crack spacing and crack width. A numerical model was developed to explore the crack development of reinforced concrete beams under flexural loading. The model employed a non-linear material model for concrete and a smeared crack approach. In order to address the well known numerical stability problems, associated with softening models, a non-local gradient method was used. Crack widths cannot be obtained directly from such models, due to the diffuse nature of non- local simulations, therefore a post-processing procedure was developed to allow the crack characteristics to be calculated. Several numerical examples are presented to illustrate the satisfactory performance of the model. In addition, a series of numerical simulations of the BOND AND CRACKING OF REINFORCED CONCRETE Simon H.C. Chan Page vi experimental beams tested in the present study were used validate the numerical model and conversely, to provide confidence in the consistency of the experimental results.
6
luo, Cheng Hong. "Early age thermal cracking of concrete." Thesis, University of Leeds, 1998. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.589517.
Full text
7
Fejzo, R. "Dynamic behaviour of concrete structures with cracking." Thesis, Swansea University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636965.
Full textAbstract:
The subject of this thesis is the behaviour of concrete structures under dynamic loading conditions and its modelling. In particular, the modelling of material behaviour is treated and a new material model for the description of plain concrete behaviour is proposed. For the modelling of the uncracked concrete behaviour, a strain rate sensitive elasto - viscoplastic material model developed by Bicanic is used. For the modelling of cracked concete behaviour, a distributed - smeared crack representation has been adopted. Crack initiation and propagation are controlled by a crack monitoring algorithm employing a critical strain criterion, allowing multiple cracking and controlled strain softening during the first crack opening cycle, linking the shear transfer across the crack to the magnitude of crack opening and preserving the crack directionality. Implementation of the proposed material model in a finite element computer program DEGDYN is described and a computer program listing is given. An explicit time stepping scheme is used, so the computer memory requirement is small and the program may be run even on small personal computers. Material model and computer program performance are verified using simple examples. Application of the material model in the analysis of the Koyna dam is demonstrated and results of several parameter sensitivity analyses are presented.
8
Momeni, Amir Farid. "Y-cracking in continuously reinforced concrete pavements." Thesis, Kansas State University, 2013. http://hdl.handle.net/2097/15642.
Full textAbstract:
Master of ScienceDepartment of Civil Engineering
Kyle A. Riding
When transverse cracks meander there is a high possibility for transverse cracks to meet at a point and connect to another transverse crack, creating a Y-crack. Y-cracks have been blamed for being the origin of punchouts and spallings in CRCPs. When the direction of maximum principal stress changes, it could cause a change in the crack direction, potentially forming a Y-crack. Finite Element Models (FEMs) were run to model the change in principal stress direction based on design and construction conditions. The finite element model of CRCP using typical Oklahoma CRCP pavement conditions and design was assembled. The model included the concrete pavement, asphalt concrete subbase, and soil subgrade. The effect of areas of changed friction on the direction of principal stress was simulated by considering a patch at the pavement-subbase interaction. Investigated factors related to this patch were location of patch, friction between patch and subbase, and patch size. Patches were placed at two different locations in the pavement: a patch at the corner of the pavement and a patch at the longitudinal edge between pavement ends. A change in the friction at the corner had a large effect on the stress magnitude and direction of principal stress, while a patch in the middle did not significantly change the stress state. Also, patch size had a noticeable effect on stress magnitude when the patch was at the corner. Another model was developed to understand the effect of jointed shoulder on direction of maximum principal stress. Analysis of this model showed that the stresses were not symmetric and changed along the width of the pavement. This meandering pattern shows a high potential for Y-cracking. Also, several finite element models were run to understand the effects of different shrinkage between mainline and shoulder. In order to simulate the effects of the differential drying shrinkage between the hardened mainline concrete and the newly cast shoulder, different temperature changes were applied on the mainline and shoulder. For these models, the orientation of the maximum principal stress was not significantly changed from different amounts of temperature decreases between mainline and shoulder. Also, effect of different longitudinal steel percentages was investigated by comparing two finite element models with different steel percentage. The model with higher steel percentage (0.7%) indicated more variation in stress, potentially leading to more crack direction diverging.
9
Bazzo, Jeffrey D. "Analysis of Uncontrolled Concrete Bridge Parapet Cracking." Cleveland State University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=csu1351032089.
Full text
10
Gómez, Navarro Miguel. "Concrete cracking in the deck slabs of steel-concrete composite bridges /." Lausanne : EPFL, 2000. http://library.epfl.ch/theses/?nr=2268.
Full text
11
Chen, Gongfa. "Cracking, damage and strain localization in concrete structures /." [St. Lucia, Qld.], 2001. http://www.library.uq.edu.au/pdfserve.php?image=thesisabs/absthe16282.pdf.
Full text
12
Nejadi, Shamsaddin Civil & Environmental Engineering Faculty of Engineering UNSW. "Time-dependent cracking and crack control in reinforced concrete structures." Awarded by:University of New South Wales. School of Civil and Environmental Engineering, 2005. http://handle.unsw.edu.au/1959.4/22440.
Full textAbstract:
Due to the relatively low tensile strength of concrete, cracks are inevitable in reinforced concrete structures. Therefore, studying the cracking behaviour of reinforced concrete elements and controlling the width of cracks are necessary objectives both in research and in design. The introduction of higher strength reinforcing steel has exacerbated the problem of crack control. Using higher strength steel, means less steel is required for a given structure to satisfy the strength requirements. The stiffness after cracking is reduced and wider crack widths will occur under normal service loads. Unserviceable cracking may encourage corrosion in the reinforcement and surface deterioration, and may lead to long term problems with durability. Indeed excessive cracking results in a huge annual cost to the construction industry because it is the most common cause of damage in concrete structures. In this study cracking caused by both shrinkage and external loads in reinforced concrete members is examined experimentally and analytically. The mechanisms associated with cracking and the factors affecting the time-varying width and spacing of both direct tension cracks due to restrained shrinkage deformation and flexural cracks due to the combined effects of constant sustained service loads and shrinkage are examined. Laboratory tests on eight fully restrained slab specimens were conducted for up to 150 days to measure the effects of drying shrinkage on the time-dependent development of direct tension cracks due to restrained deformation. The effect of varying the quantity, diameter, and spacing of reinforcing steel bars was studied. In addition, an analytical model previously developed without experimental verification by Gilbert (1992) to study shrinkage cracking was modified and recalibrated. A second series of tests on twenty four prismatic, singly reinforced concrete beams and slabs subjected to monotonically increasing loads or to constant sustained service loads for up to 400 days, were also conducted. The effects of steel area, steel stress, bar diameter, bar spacing, concrete cover and shrinkage were measured and quantified. An analytical model is presented to simulate instantaneous and time-dependent flexural cracking. The tension chord model (Marti et al, 1998) is modified and used in the proposed model to simulate the tension zone of a flexural member and the time-dependent effects of creep and shrinkage are included. The analytical predictions of crack width and crack spacing are in reasonably good agreement with the experimental observations.
13
Peterson, J. Eric. "A time to cracking model for critically contaminated reinforced concrete structures." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-08042009-040446/.
Full text
14
Sullivan, William Garrett. "Calibrating triboluminescent light to cracking in concrete structures." Tallahassee, Fla. : Florida State University, 2010. http://purl.fcla.edu/fsu/lib/digcoll/undergraduate/honors-theses/2181949.
Full textAbstract:
Thesis (Honors paper)--Florida State University, 2010.Advisor: Dr. Okenwa Okoli, Florida State University, College of Engineering, Dept. of Industrial Engineering and Dept. of Civil and Environmental Engineering. Includes bibliographical references.
15
Bosnjak, Daniela. "Self-induced cracking problems in hardening concrete structures." Doctoral thesis, Norwegian University of Science and Technology, Department of Structural Engineering, 2000. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-1512.
Full textAbstract:
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.
16
Abrishami, Homayoun H. (Homayoun Hosseini). "Studies on bond and cracking of structural concrete." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28463.
Full textAbstract:
This thesis presents new testing methods to study the bond characteristics of reinforcing bars and pretensioned strands. For reinforcing bars, the new technique, which simulates a more uniform bond stress, enabled the study of both pullout failures and splitting failures. Variables studied included concrete cover, bar size and the effect of epoxy coatings on the bars. Analytical expressions for predicting the bond stress versus slip response and the bond stress distribution for different types of pullout tests are developed. For pretensioned strand, the testing technique enabled the study of the bond characteristics along both the transfer and the flexural bond lengths. Equations for predicting the transfer and development lengths are given.The tensile behaviour of concrete members reinforced with a single reinforcing bar are studied. Variables studied included concrete strength, presence of steel fibres, bar size and the effect of epoxy coatings on the bars. Both transverse cracks and splitting cracks were studied and a factor accounting for the influence of splitting cracks on tension stiffening is introduced. A procedure for predicting the response of tension members, accounting for the concrete cover and bar size and the presence of steel fibres is given. Equations are suggested to determine the transfer length and crack spacing.
Experimental investigations were carried out to study the post-cracking behaviour of beams without stirrups. The influence of concrete strength and the presence of epoxy-coated reinforcement on the crack development, type of cracking, ductility and failure mechanism are discussed. Typical slab-column connections found in parking structures were tested, simulating the construction stages. The effects on crack development of both concrete quality and the presence of epoxy coatings on the reinforcement were studied. Modification factors for predicting crack widths in beams and two-way slabs, accounting for the presence of epoxy coatings, are given in a form suitable for implementation in codes of practice.
17
Tajik, Nosratollah. "The early age thermal cracking in concrete structures." Thesis, University of Westminster, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502220.
Full textAbstract:
Investigations on the assumptions, the limitations and the factors influencing the development of early age thermal cracking in concrete have been carried out for many decades, but there is a better understanding of these phenomena in the recent years. Review of the literature on the early age thermal cracking (EATC) of concrete structures has shown that this phenomenon is very important and has significant influence on the durability, serviceability and aesthetically aspects of concrete structures, however despite this its mechanisms are still not well understood. Furthermore, most efforts to control this type of cracking have been by specifically designing distribution reinforcement, but this is proving uneconomic and is not a failsafe technique. The experimental technique carried out in this research investigation is an improvement on the past research on early age cracking. The experiments were carried out successfully and the effects of internal and external restraints were studied. Further methods of assessing the risk of early age thermal cracking in mass concrete under natural environmental conditions developed and the results were compared with those recorded under laboratory conditions. It has been shown that the early age· thermal cracking in concrete resulted from either internal restraint caused by differential expansion within concrete member during heating due to larger temperatures gradient between the core, and that the adjacent media or by external restraint to contract on cooling from a temperature peak of the concrete specimen are the critical factors in developing early age thermal cracking. It has been found that the temperature differential that causes early age thermal cracking . in concrete is greater than that figure found previous research. Other factors influencing the development of the thermal cracking were investigated and recommendations on controlling the early age thermal cracking were given.
18
Razzaghi, Langroudi Javad. "Comparative study of cracking models in concrete structures." Thesis, Heriot-Watt University, 2001. http://hdl.handle.net/10399/498.
Full text
19
GANESH, PRAKASH. "TRANSVERSE CRACKING OF HIGH PERFORMANCE CONCRETE BRIDGE DECKS." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1163737229.
Full text
20
Williams, Andrew Robert. "Cracking Potential and Temperature Sensitivity of Metakaolin Concrete." Scholar Commons, 2016. http://scholarcommons.usf.edu/etd/6603.
Full textAbstract:
Metakaolin is a pozzolanic material with the potential to reduce permeability and chloride ingress; however, quantification of the effects of metakaolin use on the cracking sensitivity of concrete mixtures is needed to ensure that these improvements in performance are not compromised. This study was conducted to investigate the early age cracking potential due to restraint stresses from incorporating metakaolin in concrete. Calorimetry testing showed that metakaolin was more sensitive to temperature than mixtures with only Portland cement. Results showed more shrinkage, less stress relaxation, and higher restraint stress from the inclusion of metakaolin, potentially increasing cracking sensitivity of mixtures.
1 This section was published in Construction and Building Materials[57]. Permission is included in Appendix A
21
Kaur, Nimratpal. "Cracking of Concrete, its Healing and Simultaneous Monitoring." Thesis, Curtin University, 2022. http://hdl.handle.net/20.500.11937/89253.
Full textAbstract:
This thesis addresses premature deterioration of concrete built infrastructure by introducing intrinsic healing. Emulating living organisms, a healing technique for concrete has been developed using live bacteria. The healing has been monitored using an advanced ultrasonic technology. An innovative method for testing long term durability of concrete is developed. The thesis demonstrates that the healing impedes deterioration of concrete, especially reinforcement corrosion.
22
Zhuang, Jianmin. "Evaluation of concrete mix designs to mitigate early-age shrinkage cracking in bridge decks." Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Summer2009/j_zhuang_072709.pdf.
Full textAbstract:
Thesis (M.S. in civil engineering)--Washington State University, August 2009.Title from PDF title page (viewed on Sept. 21, 2009). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 93-96).
23
William, Gergis W. "Effect of temperature variations on premature cracking of dowel jointed concrete pavements." Morgantown, W. Va. : [West Virginia University Libraries], 2003. http://etd.wvu.edu/templates/showETD.cfm?recnum=3015.
Full textAbstract:
Thesis (Ph. D.)--West Virginia University, 2003.Title from document title page. Document formatted into pages; contains viii, 139 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 123-139).
24
Rahman, Md Mahfuzur. "Influence of concrete cracking on service conditions of prefabricated and reinforced concrete members." Thesis, The University of Sydney, 2015. http://hdl.handle.net/2123/14286.
Full textAbstract:
This thesis investigates the instantaneous and time-dependent behaviour of reinforced concrete slabs and the response of lifting anchors used in prefabricated construction, particularly the development of cracks and how these influence the overall structural response. In this context, four sets of experiments were carried out on a total of ten simply-supported and three continuous lightly reinforced concrete slabs as well as thirty-six prefabricated concrete panels with different lifting anchors and reinforcement arrangements. In the first set of tests, the influence of concrete age of first loading and different drying conditions on the cracking patterns, time-dependent deformation and degradation in the stiffness of the reinforced concrete slabs were investigated. A second set of experiments was carried out to investigate the influence of different levels of cracking on the time-dependent behaviour and the degradation in the stiffness of simply-supported and continuous reinforced concrete slabs introducing a particular loading system devised to load/unload the samples. A well-defined setup for measuring the relative humidity in concrete was also proposed to gain better understanding of the development of non-linear shrinkage profile in concrete over time. The experimental results were modelled by finite element method accounting for the cracking and tension-stiffening of the concrete for the instantaneous response and for time effects, such as creep and shrinkage, during the long-term behaviour. The first set of experiments on prefabricated panels was focused on the behaviour and comparison of different edge lifting anchors and their ultimate capacities. A design procedure was proposed to account for the shape of the different lifting anchors by introducing a shape modification factor for individual lifting anchors. The behaviour of different lifting anchors influenced by the additional reinforcements was investigated in the last set of experiments.
25
Barbiero, Marialuisa. "Cover cracking of concrete slabs induced by rebar corrosion." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2019.
Find full textAbstract:
The phenomenon of concrete cracking due to corrosion of embedded reinforcement steel bars in concrete has been investigated for years. As a consequence of the steel corrosion that is accelerated by cold climates, sea water, spray and from chloride-based acceleration agents, internal cracks form. These agents originate a slow propagation of corrosion products around the embedded steel, forming a passive film, which can be elementary understood as a radial force present all around the steel, creating compressive stresses in concrete. This pressure causes the formation of microcracks that permit the passive film to infill in the structure and propagate. A finite element analysis will be carried out, in order to study the relationship of reinforced concrete features. These are the bar diameter, space between the rebars, concrete strength and the cover thickness. In order to simulate and describe the behaviour of the concrete, the Concrete Damaged Plasticity – CDP, is used. The elastic is easily described by the elastic modulus and the Poisson’s ratio, while the non-linear is more complex. The CDP method considers both compression and tension strengths, gaining as output the cracking pattern. The simulation proposed consists by the modelling of a two-dimensional model, in which the reinforced steel bars will be inserted as holes in the geometric features. The model features internal boundary conditions placed on each side of the rebars/holes. At the end, four groups of simulations are proposed, in which various combinations of the parameters considered, are provided. These corresponds of four different concrete strengths, three different diameters of the steel rebars, five different cover thicknesses and four different spacings between the rebars. The simulations show the probable cracking paths, based on the internal displacement given by the pressure formed by the corrosion products.
26
Kelly, Patrick James. "Bearing Zone Cracking of Precast Prestressed Concrete Bridge Girders." Thesis, Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14555.
Full textAbstract:
This thesis presents the results of a research project that tested five friction reducing techniques on the bearing ends of precast prestressed concrete bridge girders. The five techniques were the following: an oil coated surface, embedded steel plate with an oil coated surface, embedded steel angle with an oil coated surface, teflon pad, and a wax lubricant.
27
Qadir, Adnan. "Investigation Of Low Temperature Cracking In Asphalt Concrete Pavement." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612696/index.pdf.
Full textAbstract:
In this study, low temperature cracking of asphalt concrete is investigated based on a laboratory experimental program including the design variables of aggregate type, gradation, asphalt content, binder grading, binder modification, and the experimental variables of cooling rate, and specimen size. The design of experiment is proposed according to the fractional factorial design principles to reduce the required number of test specimens. Mix designs are performed according to the Superpave mix design guidelines using materials obtained from the Turkish General Directorate of High-ways. In the course of this study, a test setup for thermal stress restrained specimen test for asphalt concrete is developed and used successfully to test a number of as-phalt concrete beam specimens. The same setup is also used for measuring the glass transition temperatures to obtain various thermo-volumetric properties of mixtures. Statistical methods are used to identify the effect of experimental variables on frac-ture strength, fracture temperature and other dependent variables obtained from the testing program. Statistical models are also developed to predict the fracture strength, fracture temperature and other thermo-volumetric properties of mixtures. Results of analyses show that aggregate type, binder modification, and asphalt content significantly affect both the fracture strength and fracture temperature of asphalt concrete. While the glass transition temperature is affected by only aggregate type, coefficients of contraction before and after the glass transition temperature are not influenced by any of the experimental variables. The results of this study provide an important basis to prevent low temperature cracking in asphalt concrete pavements.
28
Cai, Qingbo. "Finite element modelling of cracking in concrete gravity dams." Thesis, Pretoria : [s.n.], 2007. http://upetd.up.ac.za/thesis/available/etd-01302008-160623.
Full text
29
Siswosukarto, Suprapto. "Early thermal cracking of concrete under various restraint conditions." Thesis, University of Leeds, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.410896.
Full text
30
McLeod, Christina Helen. "Investigation into cracking in reinforced concrete water-retaining structures." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/80207.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2013.Durability and impermeability in a water-retaining structure are of prime importance if the structure is to fulfill its function over its design life. In addition, serviceability cracking tends to govern the design of water retaining structures. This research concentrates on load-induced cracking specifically that due to pure bending and to direct tension in South African reinforced concrete water retaining structures (WRS). As a South African design code for WRS does not exist at present, South African designers tend to use the British codes in the design of reinforced concrete water-retaining structures. However, with the release of the Eurocodes, the British codes have been withdrawn, creating the need for a South African code of practice for water-retaining structures. In updating the South African structural design codes, there is a move towards adopting the Eurocodes so that the South African design codes are compatible with their Eurocode counterparts. The Eurocode crack model to EN1992 (2004) was examined and compared to the corresponding British standard, BS8007 (1989). A reliability study was undertaken as the performance of the EN1992 crack model applied to South African conditions is not known. The issues of the influence of the crack width limit and model uncertainty were identified as being of importance in the reliability crack model.
31
Dolphyn, Bradley P. "Laminar cracking in post-tensioned concrete nuclear containment buildings." Diss., Georgia Institute of Technology, 2016. http://hdl.handle.net/1853/55017.
Full textAbstract:
As a critical public safety-related structure, the long-term integrity of post-tensioned concrete containment buildings (PCCs) is necessary for continued operation of the reactors they house. In 2009, during preparations for a steam generator replacement, extensive subsurface laminar cracking was identified in a portion of the Crystal River 3 (CR3) PCC in Florida, and the plant was permanently shut down in 2013. This study investigates potential contributing factors to the identified cracking with particular focus on the effects of high early-age temperatures on the cracking risk of the concrete, on the development of the concrete properties, and on the late-age structural behavior of the concrete. Two planar, full-scale mock-ups of a portion of the CR3 PCC were constructed and instrumented with temperature and strain gauges to monitor the thermal and mechanical behavior during representative concrete curing and post-tensioning loading. Standard- and match-cured concrete specimens were tested for determination of the time- and temperature-dependent development of thermal and mechanical concrete properties, and hydration parameters were determined for the mock-up cement paste for modeling the heat generation in the concrete. These properties and parameters were utilized in 3D finite element analysis of the mock-ups in COMSOL Multiphysics and compared with experimental results. Non-destructive evaluation via shear wave tomography was conducted on the mock-ups to identify flaws and determine the effectiveness of the methods for identifying delaminations between post-tensioning ducts approximately 10 inches beneath the concrete surface. Though early-age thermal stresses were determined not to have caused cracking in the mock-ups, the high early-age concrete temperatures resulted in decreased late-age mechanical properties that were shown to contribute to greater concrete cracking risk when the mock-up was post-tensioned. Tensile stresses exceeding the tensile strength of the concrete were identified along the post-tensioning ducts when biaxial post-tensioning loads were applied in finite element analysis, but the stresses decreased rapidly with increased distance from the ducts. Through parametric modeling, increasing the tensile strength of the concrete was identified as an effective means of reducing the cracking risk in PCCs. Additionally, relationships between the mechanical properties for the standard- and match-cured specimens were identified that could enable prediction of in-place or match-cured concrete properties based only on the results of tests on fog-cured specimens.
32
Chilwesa, Masuzyo. "Assessing the age at cracking of concrete repair mortars." Master's thesis, University of Cape Town, 2012. http://hdl.handle.net/11427/5054.
Full textAbstract:
Includes abstract.Includes bibliographical references.
The amount of concrete infrastructure needing repair and rehabilitation is increasing worldwide. The bonded overlay technique, which involves removal- of a damaged concrete layer on an existing concrete base (substrate) and replacing it with a new layer is one of the most widely used techniques. Due to thermal and hygral differences in the two composites, differential shrinkage occurs. This leads to overlay shrinkage restraint by the relatively mature substrate. Restrained shrinkage in bonded overlays can cause stress build up and may result in cracking. Cracking due to restrained deformation is a major problem as it may lead to durability concerns. Overlay resistance to crack initiation, development and propagation depends on a number of time-dependent properties of the concrete. To be able to predict the onset of cracking requires knowledge of the different material properties and how they interact with each other. In this study, an investigation was carried out on whether the performance with respect to cracking of concrete overlays can be adequately predicted from tests such as ring test, free shrinkage strain, tensile strength test, tensile relaxation and elastic modulus. Five concrete mortar types i.e. three commercially available mortars and two laboratory mixed mortars with water-tocement ratio (w/c) = 0.45 and w/c = 0.6 were used in the ring test and material property tests. The influence of curing on the crack resistance of overlays was also investigated. An analytical madel for predicting age at cracking in bonded overlays based upon time-development of overlay material properties and the superposition principle was developed. Results from the model were compared with results from the ring test. Results indicate that crack resistance of repair mortars depends upon the combined influence of the different material properties. In particular tensile stress relaxation appears to have a large influence. Curing was observed to delay the onset of cracking. Results also indicate that although the ring test will give the correct order of cracking, it will not give the actual age at cracking when assessing materials for crack resistance.
33
Liu, Youping. "Modeling the Time-to Corrosion Cracking of the Cover Concrete in Chloride Contaminated Reinforced Concrete Structures." Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/30541.
Full textAbstract:
Significant factors on steel corrosion in chloride contaminated reinforced concrete and time-to-corrosion cracking were investigated in this study. Sixty specimens were designed with seven admixed chloride contents, three concrete cover depths, two reinforcing steel bar diameters, two exposure conditions, and a typical concrete with water to cement ratio of 0.45. Corrosion current density (corrosion rate), corrosion potential, ohmic resistance of concrete and temperature were measured monthly on these specimens using both the 3LP and Gecor devices. Metal loss measurements were performed in accordance with ASTM G1-90, method C3.5, after specimens cracked. The actual corrosion weight loss of the steel reinforcing bars was then compared to the result obtained from the corrosion rate measurement devices. An interaction model for characterizing the dynamic corrosion process was developed based on the five-year corrosion database. The model demonstrates that the corrosion rate is a function of chloride content, temperature at reinforcement depth, ohmic resistance of concrete, and corrosion time after initiation. A time-to-corrosion cracking model was suggested based on a corrosion-cracking conceptual model and critical mass of corrosion products. The model predicted times to corrosion cracking are in good agreement with the observed times to corrosion cracking of the cover concrete.Ph. D.
34
Rao, Akash Schindler Anton K. "Evaluation of early-age cracking sensitivity in bridge deck concrete." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/FALL/Civil_Engineering/Thesis/Rao_Akash_56.pdf.
Full text
35
Sudoi, Elias K. Nasrazadani Seifollah. "Factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP)." [Denton, Tex.] : University of North Texas, 2008. http://digital.library.unt.edu/permalink/meta-dc-9025.
Full text
36
Loria-Salazar, Luis Guillermo. "Reflective cracking of flexible pavements literature review, analysis models,and testing methods /." abstract and full text PDF (free order & download UNR users only), 2008. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1453593.
Full text
37
Farag, Hassan Mohamed. "The transient analysis and non linear behaviour of reinforced concrete elements." Thesis, University of Salford, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.308130.
Full text
38
Montazeri, Sara. "Assessing repeatability of four-point bending method for estimating fatigue cracking of hot mix asphalt." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Full text
39
Ulbinas, Darius. "Cracking and stiffness analysis of steel fiber reinforced concrete members." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2013~D_20130211_185704-20674.
Full textAbstract:
In last decades, fibre reinforcement is widely used in many countries as ad-ditive for concrete and cement mortar mixture for production of structures. Fibre reinforcement applications in Lithuania are often restricted to production of concrete floor for different purposes. Whereas, in other countries (USA, Japan, Germany and other) application area of fibre reinforcement is much wider, for example: bridge deck, thin-walled structures for special constructions (tunnels, reservoirs, etc), covering of roadway, airport landing strip, pipelines, pile foundation. Application of fibre reinforcement is considered as one of the most important development area of structural construction in the world.
Fibre reinforcement significantly improves service properties of concrete. Fibre reinforcement does not have considerable influence on concrete compressive strength, however it significantly changes fracture characteristics of tensile concrete. Fracture of non-reinforced tensile concrete is brittle, whereas with fibre reinforcement–plastic. This is due to restraining of tensile deformations by distributed fibres. Fibre reinforcement influence on concrete member is more effective than bar reinforcement, as tensile deformations are restrained in the whole volume of tensile zone. Whereas, tensile deformations in a RC member are restrained in the specific interaction area of reinforcement and concrete. Main advantages of fibre reinforcement are slow crack propagation, greater tensile and... [to full text]Jau kelis dešimtmečius plieno plaušas visame pasaulyje plačiai taikomas kaip priedas betono ir cementinio skiedinio mišiniams, naudojamiems statybinių konstrukcijų gamybai. Lietuvoje dispersinis armavimas dažniausiai naudojamas betonuojant įvairios paskirties pastatų grindis. Tuo tarpu, kitose pasaulio šalyse (JAV, Japonijoje, Vokietijoje ir kt.) dispersinė armatūra naudojama daug plačiau, pvz.: tiltų perdangoms, plonasienėms specialiųjų statinių (tunelių, rezervuarų ir t. t.) konstrukcijoms, kelių dangoms, oro uostų pakilimo takams, vamzdynams, poliniams pamatams ir t. t. Dispersinės armatūros taikymas visame pasaulyje laikoma viena iš prioritetinių statybinių konstrukcijų vystymosi sričių. Dispersinis armavimas neturi didesnės įtakos gniuždomajam betono stipriui, tačiau lemia visiškai skirtingą tempiamojo betono suirimo pobūdį. Nearmuoto tempiamojo betono suirimas yra trapus, tuo tarpu dispersiškai armuoto – plastinis. Tai lemia dispersiškai pasiskirsčiusio plaušo sukeliamas tempimo deformacijų suvaržymas. Dispersinio armavimo poveikis betoniniam elementui yra daug efektyvesnis nei strypinės armatūros, kadangi tempimo deformacijos varžomos visame tempiamosios zonos tūryje. Tuo tarpu klasikiniame gelžbetoniniame elemente tempimo deformacijos varžomos tik tam tikrame armatūros ir betono sąveikos plote. Lėtesnis plyšių vystymasis, didesnis atsparumas smūgiams ir nuovargiui bei plastiškumas yra pagrindiniai veiksniai, lemiantys dispersiškai armuotų gelžbetoninių konstrukcijų... [toliau žr. visą tekstą]
40
Kong, Kok Loon. "Cracking and tension zone behaviour in reinforced concrete flexural members." Thesis, University of Leeds, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427779.
Full text
41
Oladiran, Olayinka Gbolahan. "Assessment of restrained shrinkage cracking of concrete through elliptical rings." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/8224.
Full textAbstract:
An elliptical ring test method is presented to replace the circular ring test method for assessing cracking potential of concrete and other cement-based materials under restrained condition. The latter is recommended by both ASTM (American Society of Testing Materials (C1581/C 1581M-09a) and AASHTO (American Association of State Highway and Transportation Officials (PP34–39, 2004)) as a standard test method for such purpose. However, there is no research published so far on comparing circular and elliptical ring test for assessing the relative likelihood of cracking of concrete and other cement-based materials as proposed in this study. Besides, ASTM proposes to use thin concrete rings with the wall thickness of 1.5 inches while AASHTO to use thick concrete rings with the wall thickness of 3 inches. The implication of these two ring wall thicknesses has not been well studied. The elliptical ring geometry employed here was used to facilitate unique ways of analysing cracking sensitivity of concrete. In line with this, the test program and numerical model developed was focused on investigating the mechanism of the elliptical ring test, irrespective of the concrete materials used which is also novel in this research as efforts towards this assessment are still yet to be published. The new experimental method investigated the use of elliptical rings for assessing the potential of concrete cracking under restrained condition to enable a faster and more reliable assessment of cracking tendency of concrete and other cement-based materials. A series of thin and thick elliptical concrete rings were tested alongside circular ones until cracking. Cracking age, position and propagation in various rings were carefully examined. It was found that thin elliptical rings with appropriate geometry can initiate crack quicker than circular ones which is desirable for accelerating the ring test. There were multiple visible cracks that occurred in elliptical rings and some cracks initiated but did not propagate through the ring wall, an interesting finding reported as the first time by this study. The features of multiple cracks in restrained elliptical rings were examined and their impact on interpreting elliptical ring test results was discussed. In addition, in restrained thin concrete rings, cracks initiated at their inner circumference and propagated towards their outer one while cracks initiated at the outer circumference and propagated towards their inner one for thick rings. To explore the mechanism of this new test method, a numerical model was developed to simulate stress development and crack initiation in concrete ring specimens under restrained shrinkage in which the effect of concrete shrinkage was simulated by an artificial temperature field externally applied on concrete causing the same strain as shrinkage does. A uniform artificial temperature field across the concrete ring wall generated good results and works well for simulating shrinkage cracking of thin concrete rings while an artificial temperature field with linear gradient across the concrete ring wall should be employed in order to predict cracking behaviour of thick concrete rings under restrained shrinkage reasonably well. Stress developed in concrete rings in the restrained shrinkage test was thus obtained through a combined thermal and structural analysis. Based on the maximum tensile stress cracking criterion, cracking age and position of a series of circular and elliptical, thin and thick rings were obtained from numerical analyses. It was found that numerical results match the experimental results in terms of initial cracking ages and position for a number of circular and elliptical concrete rings subject to restrained shrinkage. The effects of ring geometry on cracking in concrete were equally investigated by comparing the behaviour of the elliptical and the circular rings under restrained shrinkage. Both experimental and numerical results indicated that the ratio between the major and the minor semi-axes of an elliptical ring emerges as the main factor which affects the maximum circumferential tensile stress in concrete when subjected to restrained shrinkage. Thin elliptical rings with appropriate geometry can enable crack initiating earlier than circular rings, which is able to accelerate the ring test for assessing the potential of cracking of concrete mixtures. On the other hand, thick elliptical concrete rings do not to possess a favourable geometry effect over circular ones in accelerating ring test due to a relatively weaker restraining effect provided by the central steel ring. The results on crack position and stress development in concrete rings based on numerical analysis were examined to further explore the mechanism of the proposed elliptical ring test for assessing cracking potential of concrete. It was also found that the drying direction of the concrete ring has a substantial influence on the cracking age when thin concrete rings are considered.
42
Quispe, C., D. Lino, J. Rodríguez, and A. Hinostroza. "Concrete cracking control in underwater marine structures using basalt fiber." IOP Publishing Ltd, 2021. http://hdl.handle.net/10757/655950.
Full textAbstract:
The construction of coastal ports requires the use of materials that meet the demands of the marine environment, to prevent underwater concrete structures from cracking and spalling easily; basalt fiber is used to delay the expansion of concrete and prevent the formation of cracks. This research studies the behavior of concrete for prefabricated piles with Portland Cement Type I and basalt fibers added in 0.1%, 0.3% and 0.6%; the results indicate that the fiber is suitable for concrete, the slump decreases, the compressive strength increases for specimens cured in tap water and sea water, the relationship between resistances does not vary, and the depth of carbonation decreases.
43
Sudoi, Elias K. "Factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP)." Thesis, University of North Texas, 2008. https://digital.library.unt.edu/ark:/67531/metadc9025/.
Full textAbstract:
This research presents the results on an experimental investigation to identify the significant factors influencing horizontal cracking in continuously reinforced concrete pavements (CRCP). An in-depth analysis of the microstructure, morphological characteristics of the interfacial transition zone (ITZ) and the observation of cracking using the environmental scanning electron microscope (ESEM) was done. Characterization of oxides using Fourier transform infrared spectroscopy (FTIR) and electron dispersive x-ray spectroscopy (EDS) was also performed. Water to cement ratio (w/c) and rebar temperature had a significant influence on the rebar-concrete bond strength. The 28-day shear strength measurements showed an increase in rebar-concrete bond strength as the water to cement ratio (w/c) was reduced from 0.50 to 0.40. There was a reduction in the peak pullout load as the temperature increased from 14oF to 252oF for the corroded and non-corroded rebar experiments. The corroded rebar pullout test results showed a 20-50 % reduction in bond strength compared to the non-corroded rebars. FTIR measurements indicated a presence of lepidocrocrite (γ -FeOOH) and maghemite (γ -Fe2O3) on the ITZ. ESEM images showed the existence of microcracks as early as three days after casting with the bridging of these cracks between coarse aggregate locations in the interfacial zone propagating through the mortar.
44
Mattsson, Johan, and Fredrik Åman. "Cracking in a slender concrete slab due to thermal variation." Thesis, KTH, Betongbyggnad, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-259932.
Full textAbstract:
Concrete slabs used in thepulp and paper industries are often situated outdoors, which means that theslabs are exposed to temperature variations due to different weatherconditions. These temperature variations together with operational temperaturesassociated with the manufacturing process, may introduce high temperaturegradients in the concrete. It is believed that the combination of these thermalloads have resulted in cracking in a slender concrete slab.The aim of this degree project has been to determine if the combination ofseasonal temperature and operational temperature is sufficient to introduce thetype of cracking seen in-situ in the concrete slab of a factory in Sundsvall,400 km north of Stockholm. This was achieved by simulating the development ofcracks in a slender concrete slab exposed to thermal loads using finite elementanalysis (FEA). In order to determine the accuracy of the model, the resultswere compared and evaluated against a crack mapping produced by Sweco. Furthersimulations were also carried out, in order to investigate if continuedcracking would occur beyond the time span of the Sweco investigation.The material model Concrete damage plasticity (CDP) in BRIGADE/Plus and Abaquswas used to predict the crack pattern and crack width in the concrete slab.Linear-elastic and non-linear material properties were used in the modelling ofthe concrete slab. The linear-elastic model indicated that thermal variationshowed significant risk of cracking. Thereafter, non-linear material propertieswere used in the modelling process. The cracking was simulated using ambienttemperature data and operational temperatures from the production plant.The results showed that cracking started when thermal loads were introduced tothe model. The ambient seasonal temperature alone was not enough to introducethe type of cracking seen in-situ on the slab. The combination of seasonalambient temperature and operational temperature was needed, in order for cracksto develop in the concrete slab. The results also indicated that the crackswill propagate further, but this can only be confirmed by performing additionalcrack mapping on site.Betonggrunder som används för utrustning inom massa- och pappersindustrin befinner sig ofta utomhus vilket betyder att dessa är utsatta för vädrets förändringar. Temperaturvariationer i omgivningen och temperaturer som kommer från tillverkningsprocesserna kan medföra att höga temperaturgradienter skapas i betongen. Det är troligt att kombinationen av dessa termiska belastningar har gett upphov till sprick-bildning i en betonggrund.Målet för detta examensarbete har varit att bestämma, om huruvida kombinationen av års- temperaturer och temperaturer från industriprocessen är tillräckligt för att skapa den typ av sprickbildning i betonggrunden som iaktagits på plats hos en fabrik i Sundsvall. Det gjordes genom simulering av sprickbildning på betonggrunden, där grunden utsattes för termiska belastningar genom att använda finita element analys (FEA). För att bestämma tillförlitligheten hos metoden jämfördes och utvärderades resultatet mot en sprickkartering utförd av Sweco baserad på observationer ute på fabriken. Vidare gjordes ytterligare simuleringar utöver det tidsspann som Swecoundersökningarna visade, detta för att undersöka om huruvida sprickningen skulle fortgå.Materialmodellen Concrete damage plasticity (CDP) som finns i programmen BRIGADE/Plus och Abaqus användes för att förutse sprickbildning och sprickbredd i betonggrunden. Linjärelastiska och icke-linjära materialparametrar användes i modelleringen av betonggrunden. Utetemperatursdata tillsammans med temperaturer från industriprocessen användes för att undersöka anledningen till sprickbildningen.Resultaten av analyserna visade att sprickbildning uppkom när betonggrunden ut-sattes för termiska laster. Temperaturer från omgivningen var inte tillräckligt för att initiera sprickbildning. Kombinationen av temperaturer från omgivningen och industriprocessen behövdes för att sprickbildning skulle ske. Resultaten visade även att sprickbildningen kan fortsätta, med fler och bredare sprickor som följd.För att förhindra att sprickor uppstår i framtiden är det väsentligt att betona vikten av att minska uppkomsten av stora temperaturgradienter i betonggrunden.
45
Van, der Westhuizen Daniel Erasmus. "Using synthetic fibres in concrete to control drying shrinkage cracking in concrete slabs-on-grade." Thesis, Stellenbosch : Stellenbosch University, 2013. http://hdl.handle.net/10019.1/85696.
Full textAbstract:
Thesis (MScEng)-- Stellenbosch University, 2013.ENGLISH ABSTRACT: Macro synthetic fibre reinforced concrete (SynFRC) is a relatively new concrete for the purpose of being used in structural elements which only require minimum reinforcement and are supported continuously by sub-layers. One structural element that is of particular interest is slabs-on-grade which is supported by a subgrade/sub-base and requires minimum reinforcement to control the shrinkage strains which may result in cracking. The aim of this project is to investigate the potential use of macro SynFRC in the application of controlling drying shrinkage cracking (DSC) in concrete slabs-on-grade. The focus is on the use of concrete slabs-on-grade that is intended for industrial floors. The SynFRC material parameters of interest were characterised first with the aid of various experimental tests. These are: flexural tests, compression tests, friction tests between the SynFRC and wooden surfaces used for full scale testing, and the shrinkage of the concrete. Next the post-cracking tensile behaviour of the SynFRC was determined by way of an inverse analysis. These tensile responses were subsequently used to perform a series of different finite element analyses. These analyses were performed on specific slabs-on-grade to determine the effects of the added tensile behaviour of the SynFRC on the DSC. The results obtained concerned: the spacing of cracks, the maximum and average crack width, and the difference in crack width between the normal concrete (NC) and the SynFRC. These changes take place in accordance to the concrete age. From the analyses it was determined that the addition of fibres gives the concrete a ductility that allows the concrete to crack more than NC, yet does not allow the cracks to propagate. This applies to low fibre contents of less than 0.4% by volume and a slab thickness of 200mm, as well as to fibre contents that have Re,3 values of 0.51 and higher. Moreover, it results in improvements seen when adding fibres if the friction is sticky, meaning when the maximum friction between the slab and the subgrade is reached with a very small amount of movement. With a stickier friction though smaller crack widths occur within both the NC and the SynFRC.
AFRIKAANSE OPSOMMING: Makro sintetiese vesel versterkte beton (SynFRC) is 'n relatiewe nuwe beton. Dit het ten doel om gebruik te word in strukturele elemente wat minimale versterking benodig en wat deurlopend deur sublae ondersteun word. Een spesifieke strukturele element van belang is grondvloere wat deur 'n sublaag ondersteun word en wat minimale ondersteuning benodig om die krimping vervorming te beheer wat moontlike krake kan veroorsaak. Die doel van die projek was om die potensiële gebruik van makro sintetiese vesels te ondersoek tydens die beheer van die uitdroog krimp kraking van 'n beton grondvloer. Die fokus was op die gebruik van betonvloere vir fabrieksdoeleindes. Die eienskappe van SynFRC materiale is vooraf vasgestel vir die doel van verskeie eksperimentele toetse. Hierdie toetse sluit in buigbaarheidstoetse, druktoetse, krimping van beton en toets van wrywing tussen die SynFRC en hout oppervlaktes wat gebruik is vir volskaalse toets. Die trek gedrag van SynFRC na kraking is vasgestel deur inverse analise. Hierdie trek gedrag is dan gebruik om 'n reeks eindige element analises uit te voer. Hierdie analises is uitgevoer op spesifieke grondvloere om die effek te bepaal van verhoogde trek gedrag van SynFRC op die uitdroog krimp kraking. Volgens die uitslae sodoende verkry was die kraakspasiëring, die maksimum en gemiddelde kraakwydte en die verskil in die kraakwydte tussen normale beton en die SynFRC as ‘n funksie van beton oudedom. Vanuit die analises het dit duidelik geblyk dat die byvoeging van vesels die beton se smeebaarheid verhoog het en dit het tot gevolg gehad dat die beton meer krake vorm, maar dat die krake nie vergroot nie. Dit is waargeneem by 'n lae vesel inhoud van minder as 0.4% per volume en 'n betonblad met 'n dikte van 200mm. Dit is ook waargeneem by 'n hoër vesel volume wat Re,3 waardes van 0.51 en hoër het. Kleiner kraakwydte is waargeneem waar vesel volume verhoog is indien die wrywing hoër is, bedoelende dat die maksimum wrywing tussen die betonblad en die sublaag bereik is met baie min beweging. Daar het wel kleiner kraakwydtes in beide die normale beton en die SynFRC voorgekom waar daar hoër wrywing was.
46
Busba, Ezeddin Rafaa. "Effect of Localized Corrosion of Steel on Chloride-Induced Concrete Cover Cracking in Reinforced Concrete Structures." Scholar Commons, 2013. http://scholarcommons.usf.edu/etd/4872.
Full textAbstract:
Abstract: Concrete cover cracking due to reinforcement corrosion is widely accepted as a limit-state indicator in defining the end of functional service life for existing reinforced concrete (RC) structures undergoing corrosion. Many of the currently available durability prediction models are incapable of providing realistic estimates of remaining service lives of RC structures beyond the corrosion initiation point. Therefore, the need to incorporate the length of the corrosion propagation stage in a comprehensive durability prediction approach has recently received much research attention. Previous research focus however was mostly limited to the case of uniformly corroding reinforcement with only few studies addressing the commonly encountered case of localized rebar corrosion. It was empirically shown in a previous study that localized corrosion can have a mitigating effect on time to concrete cover cracking due to the larger required depth of rebar corrosion penetration (Critical penetration or Xcrit). The present research was focused on developing a model for predicting Xcrit for various degrees of corrosion localization including new cases of highly localized corrosion. Accelerated corrosion testing of controlled anodic regions along axial rebars in sound concrete cylinders suggested that localized corrosion can increase Xcrit by up to about a factor of 10. The effect of corrosion localization on the orientation of corrosion-induced surface cracks was also addressed. Testing of freely corroding pre-cracked RC pipe specimens in a chloride-containing environment indicated that steel corrosion can be localized at intersection regions with the pre-existing cracks and uniformly distributed around the reinforcing steel perimeter. Numerical modeling was undertaken to substantiate the experimentally observed trends on a theoretical basis for various degrees of corrosion localization. A mechanical model was developed to improve understanding of the underlying mechanism responsible for corrosion-induced stresses. A thick-walled multiple-cylinder approach was employed to simulate crack initiation and propagation to account for the residual strength property of concrete after cracking by applying the principles of applied elasticity. For a given concrete cover depth, the amount of Xcrit was shown by modeling to be largely determined by the length of corroding region and the capacity of the induced cracks to accommodate produced rusts. The properties of both concrete-rebar interface and corrosion products were also found to have a significant impact on Xcrit. Based on the model and experimental trends and comparisons with literature data, an improved relationship for the estimation of Xcrit was proposed. An electrochemical model was also formulated to address the possible role of corrosion aggravation due to macrocell coupling in counteracting the mitigating effect of increased Xcrit on time to concrete cover cracking. Findings confirmed that corrosion localization can reasonably be considered a mitigating factor for extending the corrosion propagation stage, and provided more precise quantification to that effect.
47
Ellison, Travis S. "Preliminary Evaluation of Cool-crete." Ohio University / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1460388587.
Full text
48
Hearn, Nataliya. "Saturated permeability of concrete as influenced by cracking and self-sealing." Thesis, University of Cambridge, 1993. https://www.repository.cam.ac.uk/handle/1810/251545.
Full text
49
Combrinck, Riaan. "Plastic shrinkage cracking in conventional and low volume fibre reinforced concrete." Thesis, Stellenbosch : University of Stellenbosch, 2011. http://hdl.handle.net/10019.1/6572.
Full textAbstract:
Thesis (MScEng (Civil Engineering))--University of Stellenbosch, 2011.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.
50
Combrinck, Riaan. "Plastic shrinkage cracking in conventional and low volume fibre reinforced concrete." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71648.
Full textAbstract:
Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Plastic shrinkage cracking (PSC) is the cracking caused by the early age shrinkage of concrete within the first few hours after the concrete has been cast. It results in unsightly surface cracks that serve as pathways whereby corroding agents can penetrate the concrete which shortens the expected service life of a structure. PSC is primarily a problem at large exposed concrete surfaces for example bridge decks and slabs placed in environmental conditions with high evaporation rates. Most precautionary measures for PSC are externally applied and aimed to reduce the water loss through evaporation. The addition of a low dosage of polymeric fibres to conventional concrete is an internal preventative measure which has been shown to reduce PSC. The mechanisms involved with PSC in conventional and low volume fibre reinforced concrete (LV-FRC) are however not clearly understood. This lack of knowledge and guidance leads to neglect and ineffective use of preventative measures. The objective of this study is to provide the fundamental understanding of the phenomena of PSC. To achieve the objective, an in depth background study and experiments were conducted on fresh conventional concrete and LV-FRC. The three essential mechanisms required for PSC are: 1→ Capillary pressure build-up between the particles of the concrete is the source of shrinkage. 2→ Air entry into a concrete initiates cracking. 3→ Restraint of the concrete is required for crack forming. The experiments showed the following significant findings for conventional and LV-FRC: PSC is only possible once all the bleeding water at the surface has evaporated and once air entry has occurred. The critical period where the majority of the PSC occurs is between the initial and final set of concrete. Any preventative measure for PSC is most effective during this period. The bleeding characteristics of a mix have a significant influence on PSC. Adding a low volume of polymeric fibres to concrete reduces PSC due to the added resistance that fibres give to crack widening, which increases significantly from the start of the critical period. The fundamental knowledge gained from this study can be utilized to develop a practical model for the design and prevention of PSC in conventional concrete and LV-FRC.
AFRIKAANSE OPSOMMING: Plastiese krimp krake (PSK) is die krake wat gevorm word a.g.v. die vroeë krimping van beton binne die eerste paar ure nadat die beton gegiet is. Dit veroorsaak onooglike oppervlak krake wat dien as kanale waardeur korrosie agente die beton kan binnedring om so die dienstydperk van die struktuur te verkort. Dit is hoofsaaklik ʼn probleem by groot blootgestelde beton oppervlaktes soos brug dekke en blaaie wat gegiet is in klimaat kondisies met hoë verdamping tempo’s. Meeste voorsorgmaatreëls vir PSK word ekstern aangewend en beperk die water verlies as gevolg van verdamping. Die byvoeging van ʼn lae volume polimeriese vesels is ʼn interne voorsorgmaatreël wat bekend is om PSK te verminder. Die meganismes betrokke ten opsigte van PSK in gewone beton en lae volume vesel versterkte beton (LV-VVB) is vaag. Die vaagheid en tekort aan riglyne lei tot nalatigheid en oneffektiewe aanwending van voorsorgmaatreëls. Die doel van die studie is om die fundamentele kennis oor die fenomeen van PSK te gee. Om die doel te bereik is ʼn indiepte agtergrond studie en eksperimente uitgevoer op gewone beton en LV-VVB. Die drie meganismes benodig vir PSK is: 1→ Kapillêre druk tussen die deeltjies van die beton is die hoof bron van krimping. 2→ Lugindringing in die beton wat krake inisieer. 3→ Inklemming van die beton is noodsaaklik vir kraakvorming. Die eksperimente het die volgende noemenswaardige bevindinge opgelewer: PSK is slegs moontlik indien al die bloeiwater van die beton oppervlakte verdamp het en indien lug die beton ingedring het. Die kritiese periode waar die meerderheid van die PSK plaasvind is tussen die aanvanklike en finale set van die beton. Enige voorsorgmaatreël vir PSK is mees effektief gedurende die periode. Die bloei eienskappe van ʼn meng het ʼn noemenswaardige effek op die PSK. Die byvoeging van ʼn lae volume polimeriese vesels tot beton verminder die PSK deur die addisionele weerstand wat die vesels bied teen die toename in kraakwydte. Die weerstand vergroot noemenswaardig vanaf die begin van die kritiese periode. Die fundamentele kennis wat in die studie opgedoen is, kan gebruik word vir die ontwikkeling van ʼn praktiese model vir die ontwerp en verhoed van PSK in gewone beton en LV-VVB.