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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Propuesta de concretos de alto desempeño con cementos puzolanicos para la construccion de pavimentos CRCP en ambientes agresivos / High performance concrete proposal with pozzolanic cements for the construction of CRCP in aggressive environments

Párraga Requena, Cristhian Arturo, Torres Trigoso, Jose Luis 18 February 2020 (has links)
El objetivo principal de este estudio es desarrollar una gama de diseños de concretos de alto desempeño con cementos adicionados basados en resultados experimentales, para poder mejorar la durabilidad de los pavimentos rígidos continuamente reforzados expuesto a ambientes agresivos. En este documento se realizó el diseño de ocho mezclas de concreto con cementos puzolánicas en conformidad con las especificaciones técnicas descritas en la guía ACI 325.14R-7. Los cementos utilizados fueron tipo HS e IP (M) con relaciones agua-cemento 0.36, 0.38, 0.40 y 0.42. Dichos diseños aseguran una resistencia a la compresión superior a 310 kg/cm2, un módulo de rotura mayor de 35 kg/cm2 y con un asentamiento de 2 ½” en obra. Para validar estas tres características principales del concreto se realizaron ensayos en estado fresco y endurecido en laboratorio. Los resultados demuestran que las dosificaciones presentadas cumplen con los parámetros de trabajabilidad y resistencia, lo cual demuestra que su uso es apropiado con pavimentadora de encofrado deslizante. / The durability of concrete and long-term performance on rigid pavements affected by aggressive environments such as sulfate attack or resistance to freezing and thawing are the main causes of roadway concrete damage. In this document, eight concrete mixtures with pozzolanic cements were designed in accordance with the technical specifications described in the ACI 325.14R-7 committee. to be applications as an alternative solution to improve the durability of rigid road pavements. This design ensures a compressive strength of more than 310 kg / cm2 and a modulus of rupture greater than 35 kg / cm2 and with a 2½ ”drop on site, which is ideal for use with pavers. To validate these three main characteristics of concrete, concrete tests are carried out in a fresh and resistant state in the laboratory. Allowing the concrete with pozzolanic cements to perform without any inconvenience as a rigid pavement continuously reinforced on a road with high traffic. / Trabajo de investigación
2

Effects of support system on behavior and performance of continuously reinforced concrete pavement

Cho, Byoung Hooi 07 February 2011 (has links)
Support systems including base and subgrade layers play a pivotal role in manifesting and maintaining acceptable behavior and performance of continuously reinforced concrete pavement (CRCP). In Texas, especially, use of non-erodible stabilized base layers have been recommended to prevent failures of the CRCP related with pumping and erosion of the support materials. The non-erodible base materials, however, have given high initial construction cost of the rigid pavements. For this reason, it has been desired to decrease the construction cost with acceptable long-term performance of the pavement system. The primary objective of this study is to determine acceptable combination of support properties and concrete slab thickness satisfying not only adequate structural ability but also construction expense. For this purpose, field support conditions were investigated using Falling Weight Deflectometer (FWD), Dynamic Cone Penetrometer (DCP), and static plate load test in phase one. Previously developed support analysis models for rigid pavement design were examined using finite element analysis method, which model could more accurately express field support behavior. Also, effects of each support properties including base thickness, elastic modulus of base material, and subgrade k-value were mechanistically identified on composite k-value, and a method selecting optimum combinations of the support properties completing desired composite k-value was developed in phase two. Also, CRCP behavior were examined under not only diverse structural and material conditions of the support system but also the CRCP slab thickness and transverse crack spacing due to temperature and vehicle wheel loading conditions in phase three. In phase four, maximum critical stress induced in the CRCP slab was evaluated under various combinations of support conditions and slab thickness. Effects of the support properties and the slab thickness on the critical stress in the CRCP slab were mechanistically identified, and the factor with the greatest effect was verified. Moreover, regression equations were developed to estimate the maximum critical stresses for various support properties and the CRCP slab thickness under temperature and wheel loadings. In phase five, a guideline determining optimum combination of support properties and slab thickness were proposed as aspect of initial construction cost of the CRCP. / text
3

Effect of Portland cement concrete characteristics and constituents on thermal expansion

Siddiqui, Md Sarwar 15 September 2015 (has links)
The coefficient of thermal expansion (CTE) is one of the major factors responsible for distresses in concrete pavements and structures. Continuously reinforced concrete pavements (CRCPs) in particular are highly susceptible to distresses caused by high CTE in concrete. CRCP is a popular choice across the U.S. and around the world for its long service life and minimal maintenance requirements. CRCP has been built in more than 35 states in the U.S., including Texas. In order to prevent CRCP distresses, the Texas Department of Transportation (TxDOT) has limited the CTE of CRCP concrete to a maximum of 5.5 x10-6 strain/oF (9.9 x10-6 strain/oC). Coarse aggregate sources that produce concrete with CTE higher than the allowable limit are no longer accepted in the TxDOT CRCP projects. Moreover, CTE is an important input in the Mechanistic-Empirical Pavement Design Guide (MEPDG). Small deviations in input CTE can affect the pavement thickness significantly in MEPDG designs. Therefore, accurate determination of concrete CTE is important, as it allows for enhanced concrete structure and pavement design as well as accurate screening of CRCP coarse aggregates. Moreover, optimizing the CTE of concrete according to a structure’s needs can reduce that structure’s cracking potential. This will result in significant savings in repair and rehabilitation costs and will improve the durability and longevity of concrete structures. This study found that the CTEs determined from saturated concrete samples were affected by the internal water pressure. As a result, the TxDOT method yielded higher values than did the American Association of State Highway and Transportation Officials (AASHTO) method. To further investigate the effect of internal water pressure, an analytical model was developed based on the poroelastic phenomenon of concrete. According to the model, porosity, permeability, and the rate of temperature change are the major factors that influence the internal water pressure development. Increasing the permeability of concrete can reduce the internal water pressure development and can thus improve the consistency of measured CTE values. Preconditioning concrete samples by subjecting them to several heating and cooling cycles prior to CTE testing and reducing the rate of temperature change improved the consistency of the CTE test results. Concrete CTE can be reduced by blending low-CTE aggregates with high-CTE aggregates and reducing the cement paste volume. Based on these findings, a concrete CTE optimization technique was developed that provides guidelines for the selection of concrete constituents to achieve target concrete CTE. A concrete proportioning technique was also developed to meet the need for CTE optimization. This concrete proportioning technique can use aggregate from any sources, irrespective of gradation, shape, and texture. The proposed technique has the potential to reduce the cement requirement without sacrificing performance and provides guidelines for multiple coarse and fine aggregate blends. / text
4

Response of concrete pavements under moving vehicular loads and environmental effects

Darestani, Mostafa Yousefi January 2007 (has links)
The need for modern transportation systems together with the high demand for sustainable pavements under applied loads have led to a great deal of research on concrete pavements worldwide. Development of finite element techniques enabled researchers to analyse the concrete pavement under a combination of axle group loadings and environmental effects. Consequently, mechanistic approaches for designing of concrete pavements were developed based on results of finite element analyses. However, unpredictable failure modes of concrete pavements associated with expensive maintenance and rehabilitation costs have led to the use of empiricalmechanistic approach in concrete pavement design. Despite progressive knowledge of concrete pavement behaviour under applied loads, concrete pavements still suffer from deterioration due to crack initiation and propagation, indicating the need for further research. Cracks can be related to fatigue of the concrete and/or erosion of materials in sub-layers. Although longitudinal, midedge and corner cracks are the most common damage modes in concrete pavements, Austroads method for concrete pavement design was developed based on traditional mid-edge bottom-up transverse cracking introduced by Packard and Tayabji (1985). Research presented in this thesis aims to address the most common fatigue related distresses in concrete pavements. It uses comprehensive finite element models and analyses to determine the structural behaviour of concrete pavements under vehicular loads and environmental effects. Results of this research are supported by laboratory tests and an experimental field test. Results of this research indicate that the induced tensile stresses within the concrete pavement are significantly affected by vehicle speed, differential temperature gradient and loss of moisture content. Subsequently, the interaction between the above mentioned factors and concrete damage modes are discussed. Typical dynamic amplifications of different axle groups are presented. A new fatigue test setup is also developed to take into consideration effects of pavement curvature on fatigue life of the concrete. Ultimately, results of the research presented in this thesis are employed to develop a new guide for designing concrete pavements with zero maintenance of fatigue damage.

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