Дисертації з теми "High strength concrete Effect of temperature on"
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1
Acquaye, Lucy. "Effect of high curing temperatures on the strength, durability and potential of delayed ettringite formation in mass concrete structures." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013837.
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2
TSIMBROVSKA, MARIANA. "Dégradation des bétons à hautes performances soumis à des températures élevées : évolution de la perméabilité en liaison avec la microstructure." Université Joseph Fourier (Grenoble), 1998. http://www.theses.fr/1998GRE10030.
Повний текст джерелаАнотація:
Les betons a hautes performances (bhp), grace a leur durabilite et resistance mecanique elevees, sont de plus en plus utilises dans la construction. Cependant, sous certaines sollicitations thermiques (incendie, accident nucleaire) ces betons manifestent parfois un comportement fragile appele eclatement. Un des principaux parametres regissant l'eclatement est la permeabilite qui controle les transferts des fluides. Cette propriete est fonction de la microstructure du materiau, caracterisee par la porosite, la distribution des tailles de pores, la connectivite et la tortuosite du reseau poreux, la densite et l'ouverture des fissures. Ce travail a pour but d'etudier l'evolution de la permeabilite intrinseque des bhp degrades suite a un echauffement (jusqu'a 400c) et de correler cette evolution aux caracteristiques de microstructure. Une etude comparative avec les betons ordinaires est effectuee. La permeabilite intrinseque des betons est estimee a partir des mesures de la permeabilite aux gaz. Avant traitement thermique la permeabilite intrinseque des bhp est inferieure d'environ un ordre de grandeur a celle des betons ordinaires. Cependant sous l'effet de la temperature cette propriete augmente plus rapidement dans les bhp (2 ordres de grandeur) et apres traitement thermique a 400c les bhp sont plus permeables que les betons ordinaires. Le sous-espace poreux efficace vis-a-vis de la permeabilite est identifie comme celui constitue de pores de diametre superieur a 0,1m. L'evolution de ce sous-espace poreux avec la temperature et la microfissuration expliquent les variations de la permeabilite dans chaque type de materiau. Trois modeles reliant la permeabilite a la microstructure sont appliques et leurs previsions sont comparees aux resultats experimentaux. Cette comparaison est satisfaisante mais montre les limites des representations topographique et geometrique des reseaux poreux utilisees dans la modelisation des transferts de masse.
3
Marquis, Glenn M. "Effect of high-strength concrete on the seismic response of concrete frames." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ37270.pdf.
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4
Sheikh, Vassiem. "Fresh properties, temperature rise and strength development of high strength concrete with binary and tertiary blended cements." Thesis, University College London (University of London), 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395651.
Повний текст джерелаАнотація:
The use of high strength concrete in the construction industry has become more frequent as both the knowledge of the behaviour of the material and the confidence in its production have increased. An appropriate formulation of materials and mix proportions can result in significantly enhanced performance such as high early strength, reduced heat of hydration and increased durability. As a step towards obtaining optimum performance, an investigation has been carried out on the fresh properties (workability), temperature rise during hydration and strength development. This research was aimed at understanding the role of supplementary cementing materials in binary (OPC+PFA, GGBS, CSF) and ternary (OPC+ CSF/PFA, CSF/GGBS) combinations in these three areas. With respect to workability the use of binary mixes of PFA or CSF reduce the superplasticiser dosage required to obtain a target slump, whereas GGBS increases it. Optimum replacement levels of 10% CSF, 40%PFA+l0%CSF and 60%GGBS+l0% CSF were found at a water/binder ratio of 0.26. Binary mixes of 40% PFA or 60% GGBS reduce the peak semi-adiabatic temperature rise compared to their equivalent OPC mix at 0.26 water/binder ratio. Ternary combinations of 10% CSF with PFA or GGBS have shown significant reductions in peak temperature rise compared to their equivalent binary mixes. Measurement of the in-situ strength by temperature matched curing (TMC) has shown higher early age strengths but lower long term strengths for both binary and ternary mixes compared to cubes cured under standard conditions (20°C). Microstructural evaluation of hardened cement paste indicates that these differences in strength are likely to be associated with stresses generated at the paste/aggregate interface. A novel non-destructive technique to assess the in-situ strength has shown good correlation between conductivity and strength development of high strength concrete.
5
Ghannoum, Carla M. "Effect of high-strength concrete on the performance of slab-column specimens." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0027/MQ50609.pdf.
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6
Ghannoum, Carla M. "Effect of high-strength concrete on the performance of slab-column specimens." Thesis, McGill University, 1998. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=21294.
Повний текст джерелаАнотація:
The behaviour of interior slab-column connections in flat plates is investigated. The first part of this thesis discusses six two-way slab-column specimens which were designed such that they would fail in punching shear. The parameters investigated were the use of high-strength concrete and the concentration of the slab flexural reinforcement in the immediate column region. The effects of these parameters on the punching shear capacity, negative moment cracking, and stiffness of the two-way slab specimens are investigated.The second part of this thesis is a comparison of the test results obtained from this experimental program with the punching shear predictions of the Canadian CSA A23 3-94 Standard and the American ACI 318-95 Code. Some comparisons of the punching shear strength provisions of the British BS 8110-85 Standard and the European CEB-FIP 1990 Model Code are also carried out. Furthermore, the CSA Standard and the ACI Code predictions are compared to the experimental results obtained from some slab-column connections tested in this experimental program and tested by various investigators.
The beneficial effects of the use of high-strength concrete and of the concentration of flexural reinforcement in the immediate column vicinity are demonstrated. It is also concluded that the punching shear strength of slab-column connections is a function of the flexural reinforcement ratio and that the shear design of slabs according to the current Canadian and American codes can be unconservative under certain conditions. It is recommended that the punching shear expressions of the CSA Standard and the ACI Code be modified to include the effect that the flexural reinforcement ratio has on the shear capacity of slab structures.
7
Trende, Uwe. "Interface fracture mechanics of high strength concrete : size effect and aggregate roughness." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/11812.
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8
Griškevičius, Mečislavas. "High Temperature Effect On Resistance Of Timber Structures." Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2010. http://vddb.laba.lt/obj/LT-eLABa-0001:E.02~2010~D_20101119_134602-29128.
Повний текст джерелаАнотація:
The present dissertation and its main subjects inquires into the pine and oak timber strength property changes-temperature relations. It also explores the behaviour of slender timber elements in axial compression at higher temperatures; and the comparative analysis of obtained results.
The work seeks to accomplish the following major tasks: to obtain test data about the influence of high temperature on the properties of different natural – pine and oak – timber; to investigate the behaviour of slender timber elements under axial compression exposed to fire. Taking into account the investigated real fire effect to correct accordingly the existing in LST EN 1995-1-2 procedure for the fire resistance calculation of timber slender elements in compression.
The dissertation consists of an introduction, five chapters, general conclusions, a list of references, a list of author’s publications on the dissertation subject, and 2 Annexes.
Chapter 1 provides a literature review. It focuses on the publications inquiring into the loss of strength properties by timber at higher temperatures, the fire resistance of timber structures in compression. The chapter ends with the formulation of conclusions and the adjustment of research tasks.
Chapter 2 offers the methodology of the research on strength properties of timber at higher temperatures, and the schemes of the developed testing equipment.
Chapter 3 presents the procedure of the research on the behaviour of slender timber elements... [to full text]Disertacijoje nagrinėjami pušinės ir ąžuolinės medienos stipruminių savybių pokyčių temperatūriniai sąryšiai bei medinių centriškai gniuždomų liaunų elementų elgsena veikiant aukštesnėms temperatūroms. Pagrindiniai tyrimo objektai yra Lietuvos spygliuočių ir lapuočių medienos savybių pokyčiai didėjant temperatūrai ir centriškai gniuždomų liaunų medinių elementų elgsenos veikiant kaitrai eksperimentiniai tyrimai bei rezultatų lyginamoji analizė. Darbe spręsti tokie pagrindiniai uždaviniai: gauti eksperimentinius duomenis apie aukštos temperatūros poveikį skirtingos natūralios – pušinės ir ąžuolinės – medienos savybėms, atlikti centriškai gniuždomų liaunų medinių elementų elgsenos ugnyje tyrimus. Atsižvelgiant į tyrinėtą tikrovišką gaisro poveikį patikslinti esamą EN 1995-1-2 medinių liaunų gniuždomų elementų atsparumo ugniai skaičiavimo metodiką. Disertaciją sudaro įvadas, penki skyriai, bendrosios išvados, naudotos literatūros ir autoriaus publikacijų disertacijos tema sąrašai ir du priedai. Pirmasis skyrius skirtas literatūros apžvalgai. Jame pateikta darbų, kuriuose nagrinėjamas aukštesnės temperatūros veikiamos medienos, stipruminių savybių mažėjimas ir kuriuose pateikiami gaisro sąlygomis gniuždomų medinių elementų laikomosios galios tyrimų rezultatai. Pabaigoje formuluotos išvados ir disertacijos tikslai ir uždaviniai. Antrajame skyriuje pateikta medienos stipruminių savybių aukštesnėse temperatūrose tyrimo metodika ir sukurtų nestandartinių bandymo įrenginių schemos... [toliau žr. visą tekstą]
9
De, Carufel Sarah. "Effect of High-Performance Steel Materials on the Blast Behaviour of Ultra-High Performance Concrete Columns." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/35380.
Повний текст джерелаАнотація:
Previous events have demonstrated the vulnerability of reinforced concrete infrastructure to blast loading. In buildings, ground-story columns are key structural components, and their failure can lead to extensive damages which can cause progressive collapse. To prevent such disasters, the steel reinforcement in such columns must be properly detailed to ensure sufficient strength and ductility. The use of modern concrete materials such ultra-high performance concrete (UHPC) is one potential solution to improve the blast performance of columns. UHPC shows high compressive strength, high tensile resistance and superior toughness, properties which make it ideal for use in the blast-resistant design of columns. The combined use of UHPC and high-performance steels can potentially be used to further enhance the blast resistance of columns. This thesis presents an experimental and analytical study which investigated the use of high-performance materials to increase the blast capacity and ductility of reinforced concrete columns. As part of the experimental study, a total of seventeen columns were tested under simulated blast loading using the University of Ottawa Shock-Tube. Parameters investigated included the effect of concrete type (NSC and UHPC), steel reinforcement type (normal-strength, high-strength or highly ductile), longitudinal reinforcement ratio, seismic detailing and fiber properties. The test program included two control specimens built with normal-strength concrete, five specimens built with UHPC in combination with high-strength steel, and ten columns built with highly ductile stainless steel reinforcement. Each column was subjected to a series of increasing blast pressures until failure. The performance of the columns is investigated by comparing the displacements, impulse capacity and secondary fragmentation resistance of the columns. The results show that using high-performance steels increases the blast performance of UHPC columns. The use of sufficient amounts of high-strength steel in combination with UHPC led to important increases in column blast capacity. The use of ductile stainless steel reinforcement allowed for important enhancements in column ductility, with an ability to prevent rupture of tension steel reinforcement. The study also shows that increasing the longitudinal reinforcement ratio is an effective means of increasing the blast resistance of UHPC columns
The thesis also presents an extensive analytical study which aimed at predicting the response of the test columns using dynamic inelastic, single-degree-of-freedom (SDOF) analysis. A sensitivity analysis was also performed to examine the effect of various modelling parameters on the analytical predictions. Overall, it was shown that SDOF analysis could be used to predict the blast response of UHPC columns with reasonable accuracy. To further corroborate the results from the experimental study, the thesis also presents an analytical parametric study examining the blast performance of larger-scale columns. The results further demonstrate the benefits of using UHPC and high-performance steel reinforcement in columns subjected to blast loading.
10
Kim, Byoungil. "Effect of fiber types on the mechanical properties and permeability of high strength concrete." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0015827.
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11
Melançon, Christian. "Effect of High-Performance Concrete and Steel Materials on the Blast Performance of Reinforced Concrete One-Way Slabs." Thesis, Université d'Ottawa / University of Ottawa, 2016. http://hdl.handle.net/10393/34102.
Повний текст джерелаАнотація:
The mitigation of blast hazards on critical reinforced concrete structures has become a major concern in regards to the safety of people and the integrity of buildings. Recent terrorist incidents and accidental explosions have demonstrated the need to study the effects of such threats on structures in order to develop effective methods of reducing the overall impact of blast loads. With the arrival of innovative materials such as steel fibre reinforced concrete (SFRC), ultra-high performance fibre reinforced concrete (UHPFRC) and high strength steel reinforcement, research is required in order to successfully adapt these new materials in blast-resistant structures. Hence, the objective of this thesis to conduct an experimental parametric study with the purpose of investigating the implementation of these innovative materials in reinforced concrete slabs and panels.
As part of the study, a total of fourteen one-way slab specimens with different combinations of concrete, steel fibres and steel reinforcement are tested under simulated blast loads using the University of Ottawa Shock-Tube Facility. The test program includes three slabs constructed with normal-strength concrete, five slabs constructed with SFRC and six slabs constructed with UHPFRC. Among these specimens, four are reinforced with high-performance steel reinforcement. The specimens are subjected to repeated blast loading with gradually increasing reflected pressure and reflected impulse until failure. The performance of the slabs is studied using various criteria such as failure load and mode, maximum and residual deflections, as well as tensile cracking, spalling and secondary fragmentation control.
The behaviour of all specimens is compared in different categories to determine the effects of concrete type, steel reinforcement type, steel fibre content and steel fibre type on blast performance.
As part of the analytical study the response of the slab specimens is predicted using dynamic inelastic single-degree-of-freedom (SDOF) analysis. The dynamic analysis is conducted by generating load-deformation resistance functions for the slabs incorporating dynamic material properties.
12
Azizipesteh, Baglo Hamid Reza. "Effect of various mix parameters on the true tensile strength of concrete." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12560.
Повний текст джерелаАнотація:
The primary aim of this research was to develop a method for determining the true uniaxial tensile strength of concrete by conducting a series of cylinder splitting, modulus of rupture (MOR) and cylinder/cube compression tests. The main objectives were: • Critically reviewing previous published research in order to identify gaps in current knowledge and understanding, including theoretical and methodological contributions to the true uniaxial tensile strength of concrete. In order to maintain consistency and increase the reliability of the proposed methods, it is essential to review the literature to provide additional data points in order to add additional depth, breathe and rigor to Senussi's investigation (2004). • The design of self compacting concrete (SCC), normal strength concrete (NSC) and high strength concrete (HSC) mixes and undertaking lab-based experimental works for mixing, casting, curing and testing of specimens in order to establish new empirical evidence and data. • Analysing the data, presenting the results, and investigating the application of validity methods as stated by Lin and Raoof (1999) and Senussi (2004). • To draw conclusions including comparison with previous research and literature, including the proposal of new correction factors and recommendations for future research. 29 batches of NSC, 137 batches of HSC, 44 batches of fly ash SCC and 47 batches of GGBS SCC were cast and their hardened and fresh properties were measured. Hardened properties measured included: cylinder splitting strength, MOR, cylinder compressive strength and cube compressive strength. A variety of rheological tests were also applied to characterise the fresh properties of the SCC mixes, including: slump flow, T50, L-box, V-funnel, J-ring and sieve stability. Cylinders were also visually checked after splitting for segregation. The tensile strength of concrete has traditionally been expressed in terms of its compressive strength (e.g. ft = c x c f ). Based on this premise, extensive laboratory testing was conducted to evaluate the tensile strength of the concretes, including the direct tension test and the indirect cylinder splitting and MOR tests. These tests however, do not provide sufficiently accurate results for the true uniaxial tensile strength, due to the results being based upon different test methods. This shortcoming has been overcome by recently developed methods reported by Lin and Raoof (1999) and Senussi (2004) who proposed simple correction factors for the application to the cylinder splitting and MOR test results, with the final outcome providing practically reasonable estimates of the true uniaxial tensile strength of concrete, covering a wide range of concrete compressive strengths 12.57 ≤ fc ≤ 93.82 MPa, as well as a wide range of aggregate types. The current investigation has covered a wide range of ages at testing, from 3 to 91 days. Test data from other sources has also been applied for ages up to 365 days, with the test results reported relating to a variety of mix designs. NSC, SCC and HSC data from the current investigation has shown an encouraging correlation with the previously reported results, hence providing additional wider and deeper empirical evidence for the validity of the recommended correction factors. The results have also demonstrated that the type (size, texture and strength) of aggregate has a negligible effect on the recommended correction factors. The concrete age at testing was demonstrated to have a potentially significant effect on the recommended correction factors. Altering the cement type can also have a significant effect on the hardened properties measured and demonstrated practically noticeable variations on the recommended correction factors. The correction factors proved to be valid regarding the effects of incorporating various blended cements in the HSC and SCC. The NSC, HSC and SCC showed an encouraging correlation with previously reported results, providing additional support, depth, breadth and rigor for the validity of the correction factors recommended.
13
Mansour, Marwan. "Experimental tests on the effect of temperature on the short term behavior of FRC beams." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
Знайти повний текст джерелаАнотація:
The effect of temperature under short term behavior on macro-synthetic polypropylene fibers reinforced concrete (MSFRC) was evaluated, to understand how this condition may affect the performance of this material. An experimental campaign of three-point bending, compressive tests and elastic modulus tests have been performed on prisms, cubes and cylinders cured at 6 temperatures, ranging from -30°C to +60°C. The results highlighted that, for the material tested, the increment of temperature causes a decrement of the peak and post-peak flexural strength. Further analysis have been done on the fibers number and failure type.
14
Ranjbar, Sahar. "Effect of pre-wetted perlite and fibers on autogenous and plastic shrinkage of high strength concrete." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44023.
Повний текст джерелаАнотація:
This thesis deals with the mitigation of plastic shrinkage in high strength concrete through internal curing and fiber reinforcement. In addition, the effects of mixture proportioning, internal curing and fiber reinforcement on elimination of autogenous shrinkage in mortar were studied. Internal curing can prevent cement paste from self-desiccation by providing small water reservoirs within the mortar or concrete. Fiber reinforcement can potentially increase the early age tensile strength.
Plastic shrinkage cracks were observed only on the control concrete specimens. That is, the addition of fibers and partial replacement of fines with pre-wetted perlite both provided viable mechanisms to mitigate or reduce plastic shrinkage in high strength concrete. The fibers had a negligible effect on compressive strength. However, there was a significant decrease in compressive strength for mixes containing 25% perlite by volume of fine aggregate. Based on these results, 0.15% fibers by volume appears to be more useful than 25% perlite by volume for mitigating plastic shrinkage in high strength concrete.
The mixes without pre-wetted perlite underwent autogenous shrinkage; while the internally cured mixes underwent some swelling. That is, partial replacement of fines with pre-wetted perlite provided viable mechanism to completely eliminate autogenous shrinkage in high strength mortar. The mortar mix with fly ash exhibited the least amount of autogenous shrinkage. Therefore, in cases where addition of pre-wetted perlite is not desirable due to the loss in mechanical properties, sacrifices, fly ash can be considered as a good replacement for internal curing agent.
15
Evans, Christopher Michael. "The influence of fly ash and early-age curing temperature on the durability and strength of high-performance concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ28830.pdf.
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16
Mahmoud, Karam Abdou Awad. "Shear behaviour of continuous concrete beams reinforced with GFRP bars." ASCE, 2015. http://hdl.handle.net/1993/30951.
Повний текст джерелаАнотація:
Continuous beams represent main structural elements in most reinforced concrete (RC) structures such as parking garages and overpass bridges. Deterioration of such structures due to corrosion of steel reinforcement is common in North America. To overcome the corrosion problems, the use of fiber-reinforced polymer (FRP) bars and stirrups becomes a viable alternative to steel reinforcement. However, to date, the shear behaviour of FRP-RC continuous beams has not been explored yet. As such, the objective of this study is to investigate the shear behaviour of such beams.
In this study, twenty four full-scale continuous concrete beams were constructed and tested. The test beams had rectangular cross section with 200-mm width and a height of 300, 550 or 850 mm and were continuous over two equal spans. The main investigated parameters were concrete strength, type and ratio of longitudinal reinforcement, type and ratio of transverse reinforcement and beam effective depth. Moreover, a 3-D nonlinear finite element model (FEM) was constructed to simulate the behaviour of FRP-RC continuous beams. The model was verified against the experimental results and validated against test results from previous studies. Then, the verified/validated model was used to conduct a parametric study to investigate the effect of a wide range of the parameters on the shear behaviour of GFRP-RC beams.
The experimental and FEM results showed that shear-critical GFRP-RC continuous beams exhibited moment redistribution. Also, it was observed that increasing the concrete strength and the longitudinal reinforcement ratio increased the shear strength significantly. Moreover, the presence of GFRP stirrups significantly enhanced the shear strength of the tested beams. Regarding the size effect, test results showed that there was adverse or no size effect on the shear strength of GFRP-RC continuous beams when they failed in the interior shear span while beams failed in the exterior shear span exhibited clear size effect. Furthermore, a comparison between the test results and the provisions of the available models and FRP standards and design guidelines in North America revealed that these design provisions can be safely applied to continuous beams.February 2016
17
Li, Jieren. "The combined effect of silica fume and fly ash on microstructure and properties of high-strength concrete." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0035/NQ38485.pdf.
Повний текст джерела
18
Yahya, Mohmed Alkilani. "The effect of polymer materials on the fracture characteristics of high performance concrete (HPC)." Thesis, Edinburgh Napier University, 2015. http://researchrepository.napier.ac.uk/Output/464157.
Повний текст джерелаАнотація:
Compared with most construction materials, concrete is considered as a brittle material, and its brittleness increases with the compressive strength. For super-high-strength concrete, failure can be sudden, explosive and disastrous. Also the tensile strength is not proportionally increased. Therefore, it is necessary to carry out research on the brittleness of concrete in order to establish parameters for assessing the brittleness, find ways to improve the brittleness and tensile strength, and eventually design and manufacture concrete materials with high strength and low brittleness. In this study, strengthening and toughening effects of polymer materials on the high performance concrete (HPC) were investigated. The HPC was manufactured using ordinary Class 52.5 N Portland cement, silica fume and superplasticizer. The adopted polymers included the styrene-butadiene-rubber (SBR) latex, polyvinylidene chloride (PVDC), linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) with contents of 1.5%, 3% and 5% in weight of cement content. The measured material and fracture properties included compressive and tensile strengths, modulus of rupture, Young's modulus, fracture energy, fracture toughness and brittleness. The test results at 28 days indicate that the addition of 1.5% and 3% SBR, PVDC, LLDPE and HDPE into the HPC could largely improve the compressive strength by up to 15.7%, while the addition of 5% SBR, LLDPE and HDPE did not show any enhancement except for 5% PVDC which increased the compressive strength by 10.9%. The tensile strength was considerably increased for all dosages of polymers, with the maximum increases of 72.7% and 83.2% for 3% SBR and 1.5% LLDPE, respectively. The fracture energy were also enhanced by adding 1.5% SBR and all dosages of LLDPE, with a maximum increase of 24.3%, while there were no indications of enhancement for other dosages of polymers. The modulus of rupture, fracture toughness and Young's modulus were not improved for lower dosages of polymers but slightly decreased for higher dosages. The brittleness decreased monotonically with increasing amount of LLDPE, but it increased with increasing amounts of SBR, PVDC and HDPE.
19
Khokhar, Muhammad Irfan. "Optimisation of concrete mix design with high content of mineral additions: effect on microstructure, hydration and shrinkage." Doctoral thesis, Universite Libre de Bruxelles, 2010. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209985.
Повний текст джерелаАнотація:
The cement being used in the construction industry is the result of a chemical processlinked to the decarbonation of limestone conducted at high temperature and results in a
significant release of CO2. This thesis is part of the project EcoBéton (Green concrete) funded
by the French National Research Agency (ANR), with a purpose to show the feasibility of
high substitution of cement by mineral additions such as blast furnaces slag, fly ash and
limestone fillers. Generally for high percentages of replacements, the early age strength is
lower than Portland cement concrete. To cope with this problem, an optimisation method for
mix design of concrete using Bolomey’s law has been proposed. Following the encouraging
results obtained from mortar, a series of tests on concretes with different substitution
percentages were carried out to validate the optimisation method. To meet the requirements of
the construction industry related to performance of concrete at early age, which determine
their durability, a complete experimental study was carried out. Standard tests for the
characterization of the mechanical properties (compressive strength, tensile strength, and
setting) allowed to validate the choice of mix design on the basis of equivalent performance.
We focused on the hydration process to understand the evolution of the mechanical
properties. Setting time measurement by ultrasound device at different temperatures (10°C,
20°C and 30°C) showed that ground granulated blast furnace slag (GGBFS) and fly ash
delayed the setting process, while use of limestone filler may accelerate this process.
Calorimetric studies over mortars and concretes made possible to calculate the activation
energy of the different mixtures and a decrease in heat of hydration of concretes with mineral
additions was observed which is beneficial for use in mega projects of concrete. Scanning
Electron Microscopy observations and thermal analysis have given enough information about
the hydration process. It was observed that the hydration products are similar for different
concrete mixtures, but the time of their appearance and quantity in the cement matrix varies
for each concrete mix.
Last part of the thesis was dedicated to the study of main types of shrinkage. First of all,
deformations measured were correlated to hydration, capillary depression and porosity
evolution. Results allowed concluding that the use of mineral additions has an actual effect on
the plastic shrinkage behaviour, but its impact is not proportional to the percentage of
additions. Substitution of cement by the additions seems to have a marked influence on the
kinetics of the shrinkage without any effect on its long term amplitude. The study of
restrained shrinkage under drying conditions by means of ring tests showed that concretes
with high percentage of slag addition seem more prone to cracking than the Portland cement
concretes.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
20
Nince, Andréia Azeredo. "Lascamento do concreto exposto a altas temperaturas." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/3/3146/tde-27072007-143816/.
Повний текст джерелаАнотація:
Esta pesquisa foi motivada pela existência de controvérsia na literatura sobre concreto exposto a altas temperaturas, das dúvidas ainda por solucionar acerca da matéria e da lacuna na norma brasileira para a matéria. Este tema reapareceu após os vários acidentes em túneis ao redor do mundo ocorridos nos últimos dez anos, nos quais se verificou a ocorrência de lascamento explosivo de forma intensa, afetando a estabilidade estrutural. O objetivo principal da tese é correlacionar os parâmetros tecnológicos de dosagem (relação água/cimento, teor de argamassa e consumo total de água) às condições de risco de lascamento, associados à umidade ambiente, que indiretamente, influencia no grau de saturação do concreto. O segundo objetivo é otimizar o uso de fibras de polipropileno para minimizar o efeito do lascamento. Adotou-se empregar a curva-padrão H durante 55 minutos em corpos-de-prova cúbicos aquecidos apenas em uma das fases com sua dilatação térmica lateral restringida. O nível de lascamento foi avaliado usando o volume lascado, obtido pela espessura medida diretamente nos corpos-de-prova, multiplicada pela área lascada, calculada pelo AUTOCAD 2000. Os resultados mostraram que o parâmetro tecnológico mais relevante na ocorrência de lascamento foi a relação água/cimento e a umidade ambiente apresentou capacidade de alterar as condições de risco de lascamento. No estudo com as fibras percebeu-se diferentes teores de fibras e diferentes características das fibras para cada grupo de a/c. Conclui-se que a relação água/cimento mais baixa associada a umidade a ambiente mais elevada é a condição mais propícia a ocorrência de lascamento. Conclui-se também que o teor de fibras de 600g/m³ é o teor mínimo para se reduzir o lascamento no grupo a/c=0,50 e 1750g/m³ no grupo a/c=0,25. A fibra L=12mm F=36µm PF=140°C mostrou-se a mais eficaz no grupo a/c=0,50 apenas o comprimento L=6 mm mostrou-se eficiente na redução do lascamento.The present research was motivated by the going controversy in the literature about concrete exposed to high temperatures, the yet unanswered doubts existent on this subject and in the absence of regulation on the matter in Brazil. The theme gained significance after the occurrence of several accidents in tunnels all over the world in the last ten years, in which were observed a very intense form of explosive spalling that affected structural stability of the sites. The main purpose of this work is set up a correlation between technological parameters of dosage in concrete (water cement rate -w/c, mortar content - a, and total water consumption - H) and risk conditions of spalling, which are related to environment humidity that indirectly effects concrete saturation level. The second goal is to optimize the use of polypropylene fiber in order to minimize spalling. The standard H curve was applied during 55 minutes in cubic samples with only a single surface exposed to heat and with restrained lateral thermo dilatation. The response variable was the observed volume of spalling (with multiplied by area of spalling in the sample). The results showed the rate water/cement as the most relevant technology parameter related to spalling risk conditions. Whereas the use of fiber is concerned, efficiency required different fiber content and characteristic for each water/cement rate combined with higher environment humidity provides proper conditions for the occurrence of spalling were 600g/m³ and 1750g/m³ for water/cement ratios of 0,5 and 0,25 respectively. It was also found that the fiber with L=12mm, F=36µm PF=140°C was the most effective in reducing spalling for a water/cement ratio of 0,50 whilst for a effective in reducing spalling for a water/cement ratio of 0,50 whilst for a water/cement ratio of 0,50 whilst for a water/cement ratio 0,25 only the length (L=6 mm) appeared as a significant factor.
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Nilforoush, Rasoul. "Anchorage in Concrete Structures : Numerical and Experimental Evaluations of Load-Carrying Capacity of Cast-in-Place Headed Anchors and Post-Installed Adhesive Anchors." Doctoral thesis, Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-66333.
Повний текст джерелаАнотація:
Various anchorage systems including both cast-in-place and post-installed anchors have been developed for fastening both non-structural and structural components to concrete structures. The need for increased flexibility in the design of new structures and strengthening of existing concrete structures has led to increased use of various metallic anchors in practice. Although millions of fasteners are used each year in the construction industry around the world, knowledge of the fastening technology remains poor. In a sustainable society, buildings and structures must, from time to time, be adjusted to meet new demands. Loads on structures must, in general, be increased to comply with new demands, and the structural components and the structural connections must also be upgraded. From the structural connection point of view, the adequacy of the current fastenings for the intended increased load must be determined, and inadequate fastenings must either be replaced or upgraded. The current design models are generally believed to be conservative, although the extent of this behavior is not very clear. To address these issues, the current models must be refined to allow the design of new fastenings and also the assessment of current anchorage systems in practice. The research presented in this thesis consists of numerical and experimental studies of the load-carrying capacity of anchors in concrete structures. Two different types of anchors were studied: (I) cast-in-place headed anchors, and (II) post-installed adhesive anchors. This research focused particularly on the tensile load-carrying capacity of cast-in-place headed anchors and also on the sustained tension loading performance of post-installed adhesive anchors. The overall objective of this research was to provide knowledge for the development of improved methods of designing new fastening systems and assessing the current anchorage systems in practice. For the cast-in-place headed anchors (I), the influence of various parameters including the size of anchor head, thickness of concrete member, amount of orthogonal surface reinforcement, presence of concrete cracks, concrete compressive strength, and addition of steel fibers to concrete were studied. Among these parameters, the influence of the anchor head size, member thickness, surface reinforcement, and cracked concrete was initially evaluated via numerical analysis of headed anchors at various embedment depths. Although these parameters have considerable influence on the anchorage capacity and performance, this influence is not explicitly considered by the current design models. The numerical results showed that the tensile breakout capacity of headed anchors increases with increasing member thickness and/or increasing size of the anchor head or the use of orthogonal surface reinforcement. However, their capacity decreased considerably in cracked concrete. Based on the numerical results, the current theoretical model for the tensile breakout capacity of headed anchors was extended by incorporating several modification factors that take the influence of the investigated parameters into account. In addition, a supplementary experimental study was performed to verify the numerically obtained findings and the proposed refined model. The experimental results corresponded closely to the numerical results, both in terms of failure load and failure pattern, thereby confirming the validity of the proposed model. The validity of the model was further confirmed through experimental results reported in the literature. Additional experiments were performed to determine the influence of the concrete compressive strength and the addition of steel fiber to concrete on the anchorage capacity and performance. These experiments showed that the anchorage capacity and stiffness increase considerably with increasing concrete compressive strength, but the ductility of the anchor decreases. However, the anchorage capacity and ductility increased significantly with the addition of steel fibers to the concrete mixture. The test results also revealed that the tensile breakout capacity of headed anchors in steel fiber-reinforced concrete is significantly underestimated by the current design model. The long-term performance and creep behavior of the post-installed headed anchors (II) was evaluated from the results of long-time tests on adhesive anchors under sustained loads. In this experimental study, adhesive anchors of various sizes were subjected to various sustained load levels for up to 28 years. The anchors were also exposed to several in-service conditions including indoor temperature, variations in the outdoor temperature and humidity, wetness (i.e., water on the surface of concrete), and the presence of salt (setting accelerant) additives in the concrete. Among the tested in-service conditions, variations in the outdoor temperature and humidity had the most adverse effect on the long-term sustained loading performance of the anchors. Based on the test results, recommendations were proposed for maximum sustained load levels under various conditions. The anchors tested under indoor conditions could carry sustained loads of up to 47% of their mean ultimate short-term capacities. However, compared with these anchors, the anchors tested under outdoor conditions exhibited larger creep deformation and failure occurred at sustained loads higher than 23% of their mean ultimate short-term capacities. Salt additives in concrete and wet conditions had negligible influence on the long-term performance of the anchors, although the wet condition resulted in progressive corrosion of the steel. Based on the experimental results, the suitability of the current testing and approval provisions for qualifying adhesive anchors subjected to long-term sustained tensile loads was evaluated. The evaluations revealed that the current approval provisions are not necessarily reliable for qualifying adhesive anchors for long-term sustained loading applications. Recommendations were given for modifying the current provisions to ensure safe long-term performance of adhesive anchors under sustained loads.
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Eppers, Sören. "Assessing the autogenous shrinkage cracking propensity of concrete by means of the restrained ring test." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2011. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-65454.
Повний текст джерелаАнотація:
The autogenous shrinkage due to self-desiccation of high- and ultra-high performance concretes with very low water-cement ratio in case of restraint leads to considerable stresses starting from very early age. The resultant risk of cracking presently cannot be adequately investigated. Parameters that are particularly difficult to capture experimentally are the concrete temperature and the viscoelasticity. The primary objective of this work was to assess as precise as possible the autogenous shrinkage cracking propensity of representative concretes at strong restraint and constant room temperature. Test methods needed to be chosen and enhanced in a way that preferably allowed for the efficient and precise investigation of all relevant factors in the future. Ideally, a method suitable for a complete empirical modeling was provided. First the methodological requirements and the advantages and disadvantages of existing test methods were discussed. Based on this, optimized test methods were proposed. Their suitability was verified using the example of ultra-high strength concrete. The choice of concrete compositions considered the essential measures for reducing shrinkage (internal curing, shrinkage-reducing admixtures, reduction of the fraction of Portland cement in the binder). The autogenous shrinkage was measured with the shrinkage cone method. This new test method was validated by investigations of the repeatability and reproducibility and proved efficient and precise. It allows for measurements under non-isothermal conditions; no established test method exists for that purpose to date. The autogenous shrinkage of the ultra-high strength concretes at the age of 24 h, investigated under quasi-isothermal conditions (20 °C), was between 0,25 mm/m and 0,70 mm/m. It was particularly low when a shrinkage-reducing admixture was added and when superabsorbent polymers were used. The stresses due to restraint were determined with the restrained ring test. A large part of the stresses to be expected according to Hooke’s Law were eliminated by creep and relaxation. The relaxation capacity being very pronounced at very early age was the main reason that no visible cracking occurred, not even with the concretes with high autogenous shrinkage. The development of the autogenous shrinkage cracking propensity was described as ratio of restraint stress and splitting tensile strength. By means of modified ring tests, used to determine the maximum tensile stress, it could be shown that the ratio of stress to strength is an appropriate failure criterion. However, the cracking propensity can be calculated correctly only if the strongly age-dependent ratio of uniaxial to splitting tensile strength is accounted for. Besides, it needs to be considered that at very early age a plastic stress redistribution may occur in restrained ring tests. The reference concrete showed a high cracking propensity of up to 0.68. The fact that shrinkage-reducing measures led to significantly lower values reveals their relevance for the safe application of ultra-high strength concrete. However, the investigations carried out here at 20 °C do not allow for a final assessment of the cracking propensity under typical on-site conditions. To empirically model the autogenous shrinkage cracking propensity as a function of temperature and stress level in the future, an analytical stress solution for non-isothermal restrained ring tests and a new approach for investigating the residual stress and relaxation capacity by means of non-passive restrained ring tests was suggestedDas durch Selbstaustrocknung verursachte autogene Schwinden von besonders leistungsfähigen Betonen mit sehr niedrigem Wasserzementwert führt bei Dehnungsbehinderung bereits in sehr frühem Alter zu erheblichen Zwangsspannungen. Die Gefahr der Rissbildung, die sich daraus ergibt, lässt sich bislang nur unzureichend untersuchen. Experimentell besonders schwer zu erfassende Faktoren sind die Betontemperatur und die Viskoelastizität. Das vorrangige Ziel der Arbeit war die möglichst genaue Ermittlung der autogenen Schwindrissneigung repräsentativer Betone bei starker Dehnungsbehinderung und konstanter Raumtemperatur. Dabei waren die Prüfverfahren möglichst so zu wählen und weiterzuentwickeln, dass sich zukünftig alle relevanten Faktoren effizient und genau untersuchen lassen. Im Idealfall sollte eine Methode entstehen, die eine vollständige empirische Modellierung erlaubt. Zunächst wurden die methodischen Anforderungen und die Vor- und Nachteile existierender Prüfverfahren diskutiert. Darauf aufbauend wurden optimierte Verfahren vorgeschlagen. Ihre Eignung wurde an ultrahochfestem Beton überprüft. Bei der Auswahl der Betone wurden die wesentlichen Maßnahmen zur Schwindreduzierung berücksichtigt (innere Nachbehandlung, schwindreduzierende Zusatzmittel, Verringerung des Portlandzementanteils am Bindemittel). Das autogene Schwinden wurde mit dem Schwindkegelverfahren gemessen. Das neue Verfahren wurde durch Untersuchungen zur Wiederhol- und Vergleichsgenauigkeit validiert und erwies sich als effizient und genau. Es ermöglicht Messungen unter nicht-isothermen Bedingungen; hierfür existiert bisher kein etabliertes Verfahren. Das autogene Schwinden der untersuchten ultrahochfesten Betone unter quasi-isothermen Bedingungen (20 °C) betrug im Alter von 24 h zwischen 0,25 mm/m und 0,70 mm/m. Besonders gering war es bei Zugabe eines schwindreduzierenden Zusatzmittels bzw. Verwendung superabsorbierender Polymere. Mit dem Ring-Test wurden die bei Dehnungsbehinderung entstehenden Spannungen ermittelt. Ein großer Teil der gemäß Hooke’schem Gesetz zu erwartenden Spannungen wurde durch Kriechen und Relaxation abgebaut. Die im sehr frühen Alter stark ausgeprägte Relaxationsfähigkeit war der wesentliche Grund dafür, dass es selbst bei Betonen mit hohem autogenen Schwinden zu keiner erkennbaren Rissbildung kam. Die Entwicklung der autogenen Schwindrissneigung wurde als Verhältnis von Zwangsspannung und Spaltzugfestigkeit beschrieben. Durch modifizierte Ring-Tests, mit deren Hilfe die maximale Zugspannung ermittelt wurde, konnte gezeigt werden, dass das Verhältnis von Spannung und Festigkeit als Versagenskriterium geeignet ist. Die Rissneigung lässt sich aber nur dann korrekt berechnen, wenn das stark altersabhängige Verhältnis von einaxialer Zugfestigkeit und Spaltzugfestigkeit berücksichtigt wird. Außerdem ist zu beachten, dass es im sehr frühen Alter zu einer plastischen Spannungsumlagerung in Ring-Tests kommen kann. Der Referenzbeton wies eine hohe Rissneigung von bis zu 0,68 auf. Dass die schwindreduzierenden Maßnahmen zu deutlich geringeren Werten führten, zeigt deren Bedeutung für den sicheren Einsatz von ultrahochfestem Beton. Die hier bei 20 °C durchgeführten Untersuchungen erlauben allerdings keine abschließende Bewertung der Rissneigung unter baustellentypischen Bedingungen. Um die autogene Schwindrissneigung zukünftig als Funktion der Temperatur und des Lastniveaus empirisch modellieren zu können, wurden eine analytische Spannungslösung für nicht-isotherme Ring-Tests und ein neuer Ansatz zur Untersuchung der Resttrag- und Relaxationsfähigkeit mit Hilfe nicht-passiver Ring-Tests vorgeschlagen
23
Miah, Md Jihad. "The effect of compressive loading and cement type on the fire spalling behaviour of concrete." Thesis, Pau, 2017. http://www.theses.fr/2017PAUU3015/document.
Повний текст джерелаАнотація:
La recherche présentée dans cette thèse vise à examiner le mécanisme d’écaillage des bétons exposés au feu et comprendre l’influence du chargement mécanique appliqué en compression durant le chauffage. Des cubes (200 x 200 x 200 mm3) et des dalles (800 x 800 x 100 mm3) de béton fabriqués avec des ciments CEM II et CEM III (B40-II et B40-III: fc28days ≈ 40 MPa) ont été exposés à un feu ISO 834-1 sous différents niveaux de chargement uniaxial (cubes) et biaxial (dalles). En outre, l'effet du chargement mécanique (pression de confinement et charge uniaxiale) sur la perméabilité résiduelle au gaz a été étudié. Afin de mieux analyser les résultats expérimentaux et comprendre les mécanismes à l’origine de l'écaillage, des calculs numériques ont été réalisés en utilisant un modèle thermo-mécanique du code aux éléments finis CAST3M. Les résultats expérimentaux ont clairement montré que les éprouvettes chargées (uniaxial et biaxial) présentent un risque d’écaillage plus important que les éprouvettes non chargées. L’écaillage augmente avec le niveau de contrainte appliquée. Une partie des essais mais pas tous, ont montré que le B40-II (3% de laitier) présente un écaillage plus important que celui du béton B40-III (43% de laitiers).À partir de cette étude sur deux bétons ordinaires, il peut être mis en évidence qu'un certain niveau de contrainte de compression externe (uniaxiale ou biaxiale) est nécessaire pour induire l'écaillage du béton ordinaire. Les pressions des pores se combine avec les contraintes thermiques dûes aux gradients thermiques. Les contraintes de compression appliquées empêchent la création de certaines fissures générées par l'incompatibilité des déformations thermiques de la pâte de ciment et des granulats et des gradients thermiques. Pour l'échantillon non chargé, la création de fissures augmente la perméabilité et empêche naturellement le développement des pressions de pores.Pendant un feu réel, les membres structurels en béton sont toujours chargés ou retenus. La présence d'un chargement compressif pendant le chauffage augmente considérablement le stress de compression (diminue le stress de traction) et la grandeur de la pression des pores, ce qui augmente le risque d'écaillage. Ensuite, le stress compressif appliqué est un facteur clé très important que la conception de la résistance au feu des structures en béton devrait prendre en compte lors de l'écaillage. Par conséquent, il est recommandé que les essais d'écaillage ne soient pas effectués uniquement sur des échantillons non chargésThe research presented in this thesis seeks to examine and understand the mechanism of fire spalling role played by the external compressive loading during heating. Concrete cube (200 x 200 x 200 mm3) and slab (800 x 800 x 100 mm3) specimens made with CEM II and CEM III cements (B40-II and B40-III: fc28days ≈ 40 MPa) were exposed to ISO 834-1 fire curve under different levels of external uniaxial (for cube) and biaxial (for slab) compressive stress. Additionally, the effect of external compressive loading (confining pressure and uniaxial load) on the residual gas permeability of concretes have been investigated. In order to better analyse the experimental results and to provide more insight into the mechanism behind the fire spalling behaviour of concrete, numerical computations were carried out by using the existing thermo-mechanical model implemented in a finite element code CAST3M. The experimental results have clearly shown that the loaded specimens (uniaxial and biaxial) are more prone to spalling than unloaded specimens, with increasing amounts of spalling for higher values of applied compressive stress. Part of the tests, but not all have shown that B40-II (3% of slag) exhibited higher spalling than the B40-III (43% of slag).From this study on two ordinary concretes, it highlights that a certain level of external compressive stress (uniaxial or biaxial) was necessary to induce spalling. A possibility is that the applied compressive stress prevents the creation of cracks naturally due to thermal mismatch between cement paste and aggregates and thermal gradients. For unloaded specimen, the creation of cracks increases the permeability and naturally prevents the pore pressure to exceed a value that favours spalling.During a real fire, concrete structural members are always loaded or restrained. The presence of compressive loading during heating significantly increases the compressive stress (decreases the tensile stress) and the magnitude of pore pressure, which increase the risk of fire spalling. Then, the applied compressive stress is a very important key factor that the fire resistance design of concrete structures should take into account when considering spalling. Hence, it is recommended that the fire spalling test should not be carried out only on unloaded specimens, especially for the ordinary concrete
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Pereira, Tobias Azevedo da Costa. "Concreto auto-adensável, de alta resistência, com baixo consumo de cimento Portland e com adições de fibras de lã de rocha ou poliamida." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-14012011-104648/.
Повний текст джерелаАнотація:
O objetivo deste trabalho é apresentar uma metodologia que possibilita a obtenção de uma linha de concretos auto-adensáveis de alta resistência, econômicos e com reduzido impacto ambiental quando comparados com os concretos correntes. Para atingir estes resultados foram estabelecidos critérios de dosagem e de produção visando à sinergia entre os materiais constituintes do concreto. Foram pesquisados métodos de empacotamento dos agregados e adições minerais, estudada a interação entre o aditivo superplastificante e os materiais cimentícios e a incorporação de fibras de lã-de-rocha ou poliamida. Os concretos com matriz densa sob efeito de temperaturas elevadas tendem a sofrer lascamentos explosivos. Diante disso foi verificado o comportamento de corpos de prova e os resultados indicaram a importância da adição da fibra de poliamida nessa condição, onde o concreto resistiu a uma temperatura de 400ºC. Ensaios de resistência à abrasão indicaram que a fibra de lã-de-rocha melhora essa propriedade do concreto e, como esperado, essa adição não inibe o lascamento explosivo do concreto. Também foram determinadas as propriedades mecânicas dos concretos e concluiu-se que é possível o emprego de um concreto estrutural auto-adensável com consumo de cimento Portland da ordem de 325 kg/\'M POT.3\', fc7 = 53 MPa, fc28 = 71 MPa e Ec28 = 43 GPa. Devido à ação das adições minerais, estes concretos atingiram uma grande reserva de resistência à compressão após a idade de referência de 28 dias, obtendo-se 89 MPa aos 131 dias de idade. A densificação da pasta hidratada, a melhoria da zona de interface desta com os agregados, além da fissuração reduzida decorrente do baixo consumo de cimento e da adição de fibras indicam que este material tem desempenho superior ao prescrito pela NBR 6118 para as diversas classes de agressividade ambiental e de resistência.The aim of this work is to show a methodology that allows to realize a set of high strength self-consolidating concrete, economic and with lower environmental impact when compared with current concretes. To get these results, criteria for production and mix design had been established aiming at to synergy between constituent materials of the concrete. Methods of particles packing (aggregates and mineral additions), the interaction between the superplasticizer and cementitious materials and the fiber incorporation were researched. The concretes with dense matrix under effect of high temperatures are susceptible to explosive spalling. In this situation, concretes were evaluated by testing cylindrical specimens and results evidenced the importance of the polyamide fiber when the concrete supported 400ºC. Tests of abrasion resistance indicated a good application for the wool-of-rock fiber, but this material not avoids explosive spalling. The mechanical properties of the concretes were determined and show that is possible to product a self consolidate concrete with low cement content (325 kg/\'M POT.3\'), fc7 = 53 MPa, fc28 = 71 MPa and Ec28 = 43 GPa. Due to action of the mineral additions, these concretes had a great reserve of compressive strength after the age of reference of 28 days and achieved 89 MPa at 131 days of age. The high density cement paste, the improvement of the matrix-aggregate interfacial zone and the reduced cracking due to the low cement content and the fibre addition indicate that these materials has superior performance to those prescribed for the NBR 6118 for diverse strength classes and aggressive environmental exposure.
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OBADIA, BAROGHEL SYLVIA. "Frittage de melanges al::(2)o::(3) + sio::(2) gel pour moules de fonderie : developpement des microstructures et deformation a chaud." Paris, ENMP, 1987. http://www.theses.fr/1987ENMP0079.
Повний текст джерелаАнотація:
Etude du frittage reactif de melanges prepares a partir de la silice colloidale et l'alumine alpha entrant dans la composition des moules. Influence du temps, de la temperature et de la composition initiale sur l'affaissement des moules carapaces de fonderies pour la coulee/solidification dirigee des aubes de turbine des reacteurs d'avions
26
Castillo, Carlos. "Effect of transient high temperature on high-strength concrete." Thesis, 1987. http://hdl.handle.net/1911/13275.
Повний текст джерелаАнотація:
The effect of transient high temperature in the uniaxial compressive strength of high strength concrete was investigated. The temperatures studied varied from 100$\sp\circ$ to 800$\sp\circ$C. The presence of loads in a structure was simulated by preloading the test specimens during the heating period.
Results showed that exposure to temperatures between 100$\sp\circ$ and 300$\sp\circ$C decreased the compressive strength of high strength concrete by 15 to 20 percent. For temperatures between 400$\sp\circ$ and 800$\sp\circ$C,the compressive strength of concrete decreased to thirty percent of that at room temperature. One third of the preloaded specimens failed explosively during the heating period. In the remaining specimens the presence of a preload had a beneficial effect and a smaller loss of strength was observed compared to unstressed specimens. Exposure to high temperature caused the modulus of elasticity to decrease in all specimens regardlessly of the preload condition and the strength of concrete.
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Chang, Yen-Shiang, and 張晏祥. "EFFECT OF HIGH TEMPERATURE ON THE MACRO- AND MICRO-PROPERTIES OF HIGH STRENGTH CONCRETE." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/68233472311136753617.
Повний текст джерела
28
Yeh, Ming-Jia, and 葉明家. "The Effects of Fire-Retardant Coating on Strength of Concrete under High Temperature." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/56898374716502358124.
Повний текст джерелаАнотація:
碩士國立屏東科技大學
土木工程系所
98
Student ID: N9633018 Title: The Effects of Fire-Retardant Coating on Strength of Concrete under High Temperature Pages: 49 Name of Institute: National Pingtung University of Science and Technology Name of Department: Department of Civil Engineering Date of Graduation: January 2010 Degree Conferred: Master Name of student: Ming-Jia Yeh Adviser: Dr. Jun-Kai Lu Abstract content: Fire-Retardant Coatings are used wildly in wooden building, steel structures and interior partitions. It is hardly used in concrete structure. The concrete are very popular material for structure in Taiwan. The mechanical behaviors of concrete are changing with respected to the changing of temperature. Present paper investigates the effects of the Fire-Retardant Coating on strength of concrete under high temperature. Three different Fire-Retardant Coatings are investigated. Five different temperatures are discussed in present paper. There are room temperature, 400℃,500℃,600℃,700℃. It is shown that the strength of concrete specimen with Fire-Retardant Coating are high than the strength of concrete specimen without fire-retardant coating. Also, the strength of concrete specimen with different fire-retardant coating is different from each other.
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EN, LEE CHEN, and 李承恩. "The Effects of Fire Resistance Materials on Strength of Concrete and Bonding Strength of Rebar under High Temperature." Thesis, 2019. http://ndltd.ncl.edu.tw/handle/69vhk8.
Повний текст джерелаАнотація:
碩士逢甲大學
土木工程學系
107
This study is to investigate the difference in compressive strength and the bonding strength between concrete specimens and specimens coated with fire resistance material under various fire temperatures. There are a total of 84 concrete cylindrical specimens with dimensions of ∅12cm×24cm, in which 21 specimens are embedded with 22 cm length of #4 rebar and 24 specimens with different embedment length of #3 rebar, all with design strength of 245 kgf/〖"cm" 〗^"2" . The experimental parameters include the thickness of fire resistance material coating, fire temperature, and fire exposure duration. The concrete compression test and pullout test of concrete specimens and reinforced concrete specimens are made after the specimens are exposed to fire. From the test results, the compressive strength of concrete cylindrical specimen decreases less as the thickness of fire resistance material increases, with a better fire protection effect. The pullout strength of reinforced concrete specimen drops less as the thickness of fire resistance material increases, with a better bonding strength protection effect. The results also show that the pullout strength of the specimen coated by the fire resistance material increases as the embedment length of rebar increases after being heated, with a better bonding force protection effect.
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Hlabangana, Mthulisi. "Effect of high-volume fly ash, curing temperature and water to cement ratio on strength development and durability of concrete." Thesis, 2020. https://hdl.handle.net/10539/31341.
Повний текст джерелаАнотація:
A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2020High volume fly ash concrete presents a sustainable and environmentally friendly alternative to production of construction materials. However, it has not been fully embraced in high strength concrete applications due to the challenge of reduced early age compressive strength. This study investigated the influence of high volume fly ash replacement, curing temperature, water to cement ratio and Ca(OH)2 activation on compressive strength and durability of concrete. High strength concrete incorporating ordinary Portland cement and ultra-fine fly ash contents of 25%, 35% and 50% was used to prepare samples for compressive strength and durability testing. Ultra-fine fly ash was used in order to attain high strength concrete. A total of 16 concrete mixes were prepared. Eight concrete mixes had a w/c ratio of 0.45 and the other eight mixes had aw/c ratio of 0.35. Ca(OH)2 was added to eight concrete mixes in order to activate the fly ash and improve early age compressive strength and durability. Concrete cubes of 100mm dimensions were cast and cured in water at either 23⁰C or 40⁰C. The concrete properties measured included compressive strength, chloride conductivity, oxygen permeability and water absorption. Compressive strength tests were done at 1 day, 3 days, 7 days, 28 days, 90 days and 180 days. The results showed that some fly ash concrete mixes yielded higher compressive strength compared to the ordinary portland cement concrete mixes. Adding Ca(OH)2 and curing at 40⁰C significantly improved the rate of compressive strength development of fly ash concrete. Durability index tests were conducted at the age of 28 days in accordance with the South African durability index testing methods. Concrete with water to cement ratio of 0.35 yielded higher compressive strength and durability results compared to concrete with water to cement ratio of 0.45. Curing at 40⁰C reduced the late age strength of ordinary Portland cement concrete whereas curing at 40⁰C and adding Ca(OH)2 improved the strength of fly ash concrete. 50% fly ash concrete was the most responsive to Ca(OH)2 activation and high temperature curing. The chloride conductivity index for ordinary Portland cement concrete was significantly higher than that of fly ash concrete. Fly ash concrete cured at 40⁰C was more resistant to chloride penetration compared to fly ash concrete cured at 23⁰C. All the durability index test results signified concrete of high quality. An economic analysis for the binder material indicates that high volume fly ash replacement yielded significant economic benefits
CK2021
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Wang, Tien-Chih, and 王天志. "Strength recovery of high performance concrete with polypropylene fiber after high temperature." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/00103855991742997785.
Повний текст джерелаАнотація:
碩士國立交通大學
土木工程學系研究所
85
Abstract: The application of high performance concrete (HPC) has become in- creasingly popular. However, many researchers have concerned and question its propertiesafter high temperature. This study is aimed at the investigation of the residual compressive strength and the nondestructive testing behavior of H PC after high temperature. Although research studies showed that HPC will easily be explosive under high temperature, but Mobil Oil Company found that the addition of polypropylene fiber in HPC will reduce this problem. However, many researchers have still concerned about the recovery strength of high per- formance polypropylene fiber concrete (HPPC)after high temperature. This study is devoted to investigate the effects of high temperature ( Celsius degree:200 ,400,600,800 ) on the recovery strength of HPPC. The major experimental param- eters include cooling method (natural cooling,force cooling), re-curing method ( air curing,water curing ), and curing time ( 1,7,28,91 days). In addition, the impact-echo testing machine is used to study the nondestructive testing be havior of HPPC after high temperature. Furthermore, a correlation between the velocity of stress waveand compressive strength is estiblished.
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Wang, Chun Wen, and 王俊文. "An Analyse on Concrete which Under High Temperature with Strength Change." Thesis, 2000. http://ndltd.ncl.edu.tw/handle/10820847277773015638.
Повний текст джерелаАнотація:
碩士國立雲林科技大學
營建工程研究所
88
An Analyse on Concrete which Under High Temperature with Strength Change Student：Wang, Chun Wen Advisors：Dr. Tsai, Cho Liang Institute of Construction Engineering National Yunlin University of Science & Technology ABSTRACT Under normal conditions of environment exposure, concrete is subjected to temperatures below about 50C. For many problems of concrete engineering, however, higher temperatures ranging from 50C to several hundred degrees Celsius can become of great importance. The first attempt at the study of concrete under high temperatures came from problems with the fire resistance of buildings. Concrete has excellent properties in this regard compared with most of traditional constructional materials and can be used effectively to shield other structural materials such as steel. The response of concrete to different temperature and exposure time needs to be studied if the fire resistant capability of the RC structure is to be estimated. The response of concrete to high temperature is complicated. Chemical and micromechanic behaviors of the concrete are not in the scope of this study. Experiments are conducted to characterize the macromechanic response. The residual strength of concrete after heat treatment is related to the temperature and exposure time mathematically from the analysis of the experimental data. The result can be used to predict the residual strength of concrete after any kind of heat treatment with variable temperature time history.
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Lu, Chien-Chung, and 呂建忠. "Research on the Temperature Development of High-Strength Concrete at Early Age." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/50886806493483792880.
Повний текст джерелаАнотація:
碩士國立中興大學
土木工程學系所
94
The High-Strength Concrete (HSC) generally containing high amount of cement and silica fume may generate large hydration heat at early age . The interior temperature of HSC will be increased dramatically and may result in a temperature crack. This research aims to investigate the interior temperature developments of HSC adding pozzolanic materials, such as silica fume and fly ash at early age. The research variables includes：three water-to-binder ratios (W/B) (0.25, 0.35, 0.40) , three silica fume contents (5%, 10%, 15%) , three fly ash contents (10%, 20%, 30%) and three sand contents (30%, 35%, 40%). Test results show that the initial and the maximum central temperature of the HSC decrease with the increase of W/B. However, W/B does not show a clear influence on the time to second hydration heat peak. Increasing the silica fume content level will enhance the initial temperature and shorten the time to reach the second hydration heat peak. In addition, by increasing the fly ash content level, it can have effects of delaying the time to the second hydration heat peak and also reducing the maximum temperature observed.
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Xiao, Wan-Xuan, and 蕭宛瑄. "The Effect of Carbon Dioxide Curing on High Strength Pervious Concrete." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/6fa29n.
Повний текст джерелаАнотація:
碩士國立中央大學
土木工程學系
106
In recent years, the global environmental protection has risen in the development of industry and changes of environment. Promoting the technology of carbon capture and storage in the world, and the way how to consume the carbon dioxide could become a part of the research. Using pervious concrete is one of the recommended methods to reduce the urban heat island effect. However, the pervious concrete is not so wide at all and the strength of pervious concrete is much lower than general concrete because of the permeability requirement. The research tried to produce a high strength pervious concrete and use carbon dioxide for curing to find out whether it could enhance the compressive strength. Two dimensions of cylinders are Φ10×20 cm and Φ15×30 cm samples for testing compressive strength, elastic modulus, abrasion resistance, X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results show that the compressive strength of the control group increases rapidly and its 90-day compressive strength closed to 60 MPa. Although the porosity is less than 15%, the permeability coefficient complies with the regulations of ACI 522. The compressive strength has a major impact after 1 hour of CO2 curing and their strength decreased by about 0% to 23% as compared to the control group. This result is similar to the value of literature-based recommendation, 12000, and the aggregate with small particle size has a higher modulus of elasticity. The test results showed that abrasion resistance of high strength pervious concrete is about 0.06% weight loss less than the normal concrete and has excellent abrasion resistance properties. XRD analysis showed that the surface product of the test piece decreased with the increase of age, for example calcite, aragonite, vaterite, portlandite, quartz and ettringite, but the peak value has no obvious relationship with both the pressure and time of CO2 curing. SEM analysis revealed that the surface product of the test piece, such as ettringite, was increased after CO2 curing.
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Tessema, Eden. "The effect of high strength concrete on the bondability of prestressing strands /." 2006. http://digital.library.okstate.edu/etd/umi-okstate-1858.pdf.
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TANG, ZHAO-WEI, and 湯兆緯. "Effect of confinement on the ductility of reinforced high-strength concrete beam." Thesis, 1988. http://ndltd.ncl.edu.tw/handle/88625296641524057927.
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Jheng, Guan-wei, and 鄭冠威. "Effect of Fire on Compressive Strength of Early Cured High Performance Concrete." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/80688395868400507545.
Повний текст джерелаАнотація:
碩士國立高雄第一科技大學
環境與安全衛生工程研究所
100
This study investigated the effect of high temperature on early cured concrete with and without fly ash (w/c=0.5). Parameters studied included the ratio of fine/coarse aggregates (1:1 and 1.5:1), curing duration (3, 7, 14, 28 and 56 days), exposure temperature (300℃, 450℃, 600℃ and 850℃). After specimens were exposed to the high temperatures, residual compressive strength test (RCS) and ultrasonic pulse velocity test (UPV) were carried out on the next day, 35th day after casting and 21-day recurring. The data shows that the UPV decreased for all specimens after exposed to high temperature, and the reduction was more significant for specimens with higher temperature. Internal structural damage caused by the high temperature lowered their densities. In addition, the RCS of normal concrete significantly rose after the concrete exposed to 450℃. The rise was attributed to the evaporation of free water and crystallization water, and then transportation of moisture in concrete. The high temperatures accelerated hydration at the early stage of concrete. Furthermore, the compressive strength at 450℃ decreased for the fly ash concrete. Because fly ash concrete has low permeability and high density, water vapor did not easily dissipate, increasing the pore pressure and eventually leading the production of microcracks. Additionally, insignificant recovery of the UPV and RCS after post-fire-curing existed. Moisture supply with air-curing to continue and expedite the rehydration reactions was not effective.
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Ling, Fan, and 范櫺. "Effect of Coarse Aggregate Content on Cracking Shear Strength Of High-Strength Concrete Beams without Shear Reinforcement." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/76407693396442458589.
Повний текст джерелаАнотація:
碩士國立中興大學
土木工程學系所
105
The intention of this study was to investigate the shear behavior of concrete beams without shear reinforcement with different amount of coarse aggregate. A total of 16 beam specimens were made in this study. The compressive strength of concrete were 42 and 50 MPa. The coarse aggregate contents are 750 kg/m3, 850 kg/m3, 950 kg/m3 and 1050 kg/m3 . Two no. 5 bars and three no. 5 bars were used on the longitudinal reinforcement. The compressive strength, coarse aggregate content and axial reinforcement are the main experimental variables. The result shows that : 1. The cracking shear strength of rest beams increases with an increases of coarse aggregate content . 2. The coarse aggregate content dose not have a significant effect on the ultimate shear strength. 3. Beams with coarse aggregate content between 850 kg/m3 and 950 kg/m3 have better crack control ability when the concrete strength is 50 MPa. 4. The stiffness of beam decreases with an increase of coarse aggregate content. The stiffness reaches the largest when the content of coarse aggregate is 750 kg / m3. Increase of longitudinal reinforcement also increases the stiffness
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Smit, Martha S. "The effect of mixture proportions on the properties of high strength concrete pavements." Diss., 2015. http://hdl.handle.net/2263/50787.
Повний текст джерелаАнотація:
Ultra-Thin Continuously Reinforced Concrete Pavement (UTCRCP) is an innovative pavement type that has the potential to fulfil South Africa’s pavement repair strategy requirements. It consists of a thin high strength concrete layer reinforced with steel mesh. Premature pavement failure occurs in UTCRCP and has been linked to the formation of cracks wide enough to allow water ingress into the supporting layers. Crack formation is influenced by environmental conditions and concrete mixture proportions of which the mixture proportions is the only factor that can be controlled by the manufacturers. To ensure that UTCRCP reaches its potential the effect of mixture proportions on the properties of High Strength Concrete (HSC) must be investigated with the aim of preventing excessive crack formation.
A literature study had revealed that fly ash, silica fume, superplasticizers and high paste contents are commonly used in HSC. The influence of these mixture constituents was investigated in three sets of experiments. In the first set the effect of fly ash and silica fume was tested using mortars. A ternary cement blend was also selected to be used in the second set of experiments where the effect of paste content and superplasticizers on HSC was determined using multivariable analysis. The effect of a wider range of paste content on the properties of HSC was investigated in the third set of experiments. Results confirm that fly ash and silica fume are complimentary when used in ternary blends and these two supplementary cementitious materials may increase the total early-age deformation in mortars. The multivariable analysis revealed that within the parameter range tested paste content and superplasticizer dosage influenced the early-age properties but not the long-term properties of HSC. Through variation of the paste content over a wider range, from 25% to 60%, it was found that paste content does influence both the early-age and long-term properties of HSC. Overall it could be recognised that high paste contents have a detrimental effect on the properties of HSC with regards to early-age and long-term crack formation, and that caution should be exercised when selecting paste content during mix design.Dissertation (MEng)--University of Pretoria, 2015.
tm2015
Civil Engineering
MEng
Unrestricted
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Chang, Feng-Chan, and 張豐展. "Study on the Confining Effect of Reinforced Concrete Columns Using High Strength Materials." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/66940303956414373975.
Повний текст джерелаАнотація:
碩士臺灣大學
土木工程學研究所
98
In common building structures, columns play important roles as vertical and lateral load carrying members. For some columns of high rise buildings, especially those located at the lower parts, the effect of axial load becomes more dominant, causing a huge size in dimension if designed using normal strength materials. However, due to the development of high strength materials, such as high strength concrete and high strength steel, engineers can now yield a more efficient and economical design of columns. Based on the current available research on high strength columns, most of the experimental work was related to the testing of reduced-scale specimens due to the limited testing capacity of the laboratory. This thesis focuses on the experimental study of 5 full-scale specimens (600×600 mm) of high strength columns subjected to quasi-static cyclic loading under constant high axial load, which is made executable because of the availability of MATS (Multi Axial Testing System) in National Center Research on Earthquake Engineering (NCREE), Taiwan. The main purpose of this research is to clarify the size effect, as well as to study the confinement effect and lateral load carrying capacity of reinforced concrete columns with high strength concrete (70, 100 MPa) and reinforced with high yielding strength reinforcement bars, 685 MPa and 785 MPa for column longitudinal and transverse reinforcement bars, respectively. Finally, a verification of the applicability of existing ACI 318-08 code design equation is also evaluated.
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Lin, Hua-Xi, and 林華璽. "Effect of Coarse Aggregate Content on Shear Friction Behavior of High Strength Concrete." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/23500644847562091059.
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Tsai, Yan-Ming, and 蔡彥鳴. "Effect of Coarse Aggregate Size on Shear Friction Behavior of High-Strength Concrete." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/98689092625384424762.
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Tsai, Wei-Tsung, and 翟慰宗. "Effect of Elevated Temperature on Strength and Ultrasonic Pulse Velocity of Recycled Concrete using Brick Aggregates." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/56896544854499088172.
Повний текст джерелаАнотація:
博士中原大學
土木工程研究所
99
The purpose of this paper is to investigate the effect on the properties of recycled concrete and mortar with various percentages of natural coarse, fine aggregates and cement replaced by crushed construction brick and tile aggregates. To find the relative compressive strength ratio, the increase in compressive strength between 28-91 days The percentage of decrease in residual strength and the change on compressive strength and ultrasonic pulse velocity (UPV) after subjected to elevated temperatures of recycled concrete and mortar are performed. A simple regression method used to establish the regression equation of compressive strength and temperature of recycled concrete. Experiment results revealed that the development of long-term strength of recycled concrete and mortar is better than that of the natural concrete and mortar. The use of brick coarse and fine aggregate affects the compressive strength slightly. Experiment results revealed that the reduction of UPV of recycled concrete with coarse and fine brick aggregate is higher than that of natural concrete. The UPV of recycled concrete with coarse tile aggregate is higher than that of natural concrete. The use of tile fine aggregate affects the UPV slightly. Regression analysis results revealed that the compressive strength and UPV of recycled concrete with the same coarse brick aggregate replacement had a high relevance. The recycled concrete with various water to cement ratio had a low relevance due to the content of aggregate. The analysis results revealed that the residual strength and residual UPV of recycled concrete with the coarse or fine brick aggregate had a high relevance after elevated temperatures exposure. Experimental results revealed that the compressive strength and UPV of recycled concrete with the same coarse tile aggregate replacement had a high relevance. The replacement of tile affects the regression slightly. The residual strength and residual UPV of recycled concrete with the coarse or fine tile aggregate had a high relevance after elevated temperatures exposure.
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fen, Fang sheng, and 方聖棻. "The effect of the lightweight aggregate concrete properties from Sediment at high temperature." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/89063378381137052225.
Повний текст джерелаАнотація:
碩士國立高雄應用科技大學
土木工程與防災科技研究所
94
The merits of lightweight aggregate concrete are having the low rate of thermal conductivity and good condition of fire resistant. Therefore, it is a good aseismatic material. In this research, which used the lightweight aggregate concrete in local reservoir mud and adopted the closle-packed theory from desified mixture design algorithm. In the meanwhile, it discussed the effect of concrete under high temperature between the lightweight aggregate with a grain which density 800 and 1600 kg/m3 and the normal-weight aggregate.The change of water-to-binder ratio respectively in 0.28,0.32 and 0.40 and the amount of mixing water in 170Kg/m3 .Adding the admixtures of fly ash, slg powder and superplasticizer（SP）etc. All these led to the design of the lightweight aggregate concrete to meet the requirement of high proficiency in working. Also, the reduction of cement amount and mixing water met the socioeconomic and durability too.High temperature stove in Germany was used in this investigation. Fixed the rate of heating in 4℃/min and accorded to the three types of temperature respectively at 250℃, 500℃and 750℃.Furthermore, two types of time delay respectively in 1 and 2 hours used to test the high temperature delay.It was Compared with the room temperature（25℃） and confer the change of contracture nature assisting the SEM testing, and the observation of the change of mico-structure after high temperature. After high temperature, the lightweight aggregate concrete still remained high resistance of strength remanent rate between 56％and 99％. The electrical resistanty remanent rate was between 40% and 93% and the ultrasonic pulse velocity remanent rate was between 45% and 86%. The crack width was between 86μm and 398μm, but it was corroded by the sodium sulfate. After heating, the temperature of lightweight aggregate concrete was low and its heat insulation was fine. It showed that the lightweight aggregate concrete is the superiority quality after high temperature. As a result, it is favorable to the fire resistance of buildings. But need to pay attention to the durability problem was made by micro-cracks.
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Horng, Gwo-Shyang, and 洪國祥. "Study on the Effect of High-Temperature Steam Curing on Taiwan Concrete(TAICON)." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/05119369277207166374.
Повний текст джерелаАнотація:
碩士國立交通大學
土木工程系
87
The objective of this study is to substitute a portion of cement with fly ash, add appropriate amounts of superplasticizer, and then to study how the resultant concrete reacts under high-temperature steam curing to determine the best high-temperature steam curing model in hopes of using the results of the experiment to produce medium strength, high performance Taiwan concrete (Taicon) suitable for use by the local construction industry. The results of this study show that high-temperature steam curing produces a slowing down of growth or no growth at all in later-age strengths, especially after undergoing 16 hours of catalytic time at temperatures of 180°C. High-temperature steam curing also reduces dry shrinkage and weight change. Early age strength and 91st day strength are virtually the same. High-temperature steam curing has lower Ec than that of standard curing. Curing temperatures of 180°C are best, while 150°C is second best, and 120°C is least ideal. Curing for 16 hours has the best effect-16 hours of catalytic time is superior to 8 hours, which is superior to 4 hours, which is superior to 2. The best curing model is as follows: Curing temperatures of 180°C、8 hours of presetting time and 16 hours of catalytic time. Early-age strength is about 180% of that of the first 28 days of standard curing methods. Early-age strength is virtually identical to 91st day strength.
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Sheu, Shiou Haur, and 許修豪. "Effect of different cooling method and re-curing method on strength recovery of concrete suffering elevated temperature." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/61525513751783620614.
Повний текст джерелаАнотація:
碩士國立交通大學
土木工程系
87
The compressive strength of concrete was lost significantly at high temperature, and might affect the safety of the structure. But partial recovery in strength may occur by appropriate re-curing. This study is aimed at the investigation of the strength recovery of Normal Strength Concrete and High Performance Concrete after suffering elevated temperature with different cooling method and re-curing method. This study is devoted to investigate the effects of re-curing method. The major experimental parameters include cooling method (natural cooling, forced cooling), re-curing method (air curing, intermittent water curing, sustained water curing), and curing time (1, 7, 28, 91 days). Result shows that intermittent water curing can get the best recovery strength.
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Chen, Yen-Jui, and 陳彥睿. "Study of Mechanical Behavior of High Strength Fiber Reinforced Concrete Filled with Steel Tube at Elevated Temperature." Thesis, 1999. http://ndltd.ncl.edu.tw/handle/15002564513978334532.
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Kuo, Yao-Jen, and 郭耀仁. "Study of the Mechanical Properties and Confinement Effect of High Strength Steel Fiber Reinforced Concrete." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/20414469715840489155.
Повний текст джерелаАнотація:
碩士國立臺灣大學
土木工程學研究所
100
From 1988 to 1992, the Japanese government carried on a five-year national project, New RC Project, to substantially increase the strength of the construction materials of the reinforced concrete for high rise buildings. The concrete strength rises from 40 MPa to 120 MPa, and the yielding strength of steel bar rises from 420 MPa to 685 MPa. Up to 2007, Janpan already has more than 500 New RC buildings. Due to brittleness of high strength concrete, much more confinement is needed to improve the ductility and satisfy seismic requirements for high strength reinforced column, particularly under high axial loading demands. Furthermore, early cover spalling trigs substantial compressive strength loss and thus sudden failure occurs. Many studies show that addition of steel fibers can not only effectively prevent the early cover spalling, but also increase the toughness and ductility of high-strength concrete. This study investigates the mechanical properties and confinement effect of high-strength steel fiber reinforced concrete. The objective is to understand the relationship between the toughness and the volume fraction of steel fibers of high-strength steel fiber reinforced concrete, and proposed the regressive formulation of the toughness of high strength steel fiber reinforced concrete. The confinement efficiency provided by steel fibers or stirrups is also proposed by the regressive formulation of the toughness. In addition, the shrinkage experiments, including measurement of autogenous shrinkage and total drying shrinkage, are conducted to verify the volume stability of high-strength steel fiber reinforced concrete.
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Vidya, Sagar R. "Concrete Fracture And Size Effect - Experimental And Numerical Studies." Thesis, 2008. http://hdl.handle.net/2005/912.
Повний текст джерелаАнотація:
Most materials including concrete have pre-existing flaws or defects. The fracture energy of concrete is a basic material property needed to understand fracture initiation and propagation in concrete. Whether fracture energy is size dependent or not is being discussed world over. Strictly the fracture energy if taken as a material property should be constant, and should be independent of the method of measurement, test methods, specimen shapes and sizes. A computational study on simulation of fracture in concrete using two dimensional lattice models is presented. A comparison is made with acoustic emission (AE) events with the number of fractured elements. A three-point bend specimen (TPB) is modeled using regular triangular lattice network. It was observed that the number of fractured elements increases near the peak load and beyond the peak load. AE events also increase rapidly beyond the peak load. Singular Fractal Functions (S.F.F) has been employed to interpret the size effect of quasi-brittle materials like concrete. The usual size dependent fracture energy of High Strength Concrete (HSC) beam is reported. The results are presented which are obtained directly from the experiments related to size effect in concrete carried out in the Structural engineering laboratory, Department of Civil engineering, IISc. Various fracture parameters studied in this experimental program are (a) Nominal strength N (b) Fracture energy, Gf (c)Fracture toughness, KIc, (c) Crack mouth opening displacement, CMOD (d) Size effect on the strength of concrete. Three-point-bend (TPB) specimen was chosen for the experimental study. Six different concrete mixes viz. A-mix, B-Mix, C-mix, D-Mix, E-mix, F-Mix were used. Acoustic Emission (AE) experiments are conducted to relate acoustic emission energy to fracture energy. It is interesting to note that both acoustic emission energy and fracture energy have similar characteristics. The advantage of the above relationship is that now it is possible to evaluate fracture energy by non-destructive testing methods. The b-value analysis of AE was carried out to study the damage in concrete structures. The Guttengberg-Richter relation for frequency versus magnitude can be applied to the AE method to study the scaling of the amplitude distribution of the acoustic emission waves generated during the cracking process in the test specimen at laboratory or in engineering structures. In the next part of this chapter b-value at various stages of damage of a reinforced concrete beam are obtained experimentally under typical cyclic loadings. The b-values at different levels of damage are tabulated. As fracture is size dependent, it may not be very useful unless its size dependency is eliminated. An effort is made to obtain size independent fracture energy by a hybrid technique.
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Chung-Chin, Cheng, and 陳忠慶. "Effect of Silica Fume on the Bond Strength of Tensile Deformed Bars of High-Performance Concrete." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/39373072748494893357.
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