Polypropylene fiber reinforced concrete in railway crossties

Cracking of concrete crossties is a performance problem that reduces service life and increases maintenance costs. While strong in compression, plain concrete is relatively weak and brittle under tensile stresses. Inclusion of synthetic polypropylene macro fibers in concrete is known to improve crack resistance and is a feasible solution for prolonging the life of crossties. The present study investigated the performance of synthetic polypropylene macro fiber reinforced concrete and their application in railway crossties. The study involved a thorough review of the properties and testing of synthetic polypropylene fiber reinforced concrete (FRC). A standard test method for obtaining average residual strength of FRC was used to evaluate the performance of various concrete mixtures reinforced with synthetic polypropylene macro fibers. It was found out that the concrete with higher fiber proportions showed significantly higher residual load carrying capacity (post-cracking response). Moreover, the concrete mixtures had acceptable workability and showed only slight loss in compressive strength due to inclusion of fibers. Self-consolidating concrete (SCC) is an emerging class of concrete which flows and consolidates on its own without vibration. Fiber reinforcement can be used in SCC to enhance the mechanical properties of concrete. The present study investigated the rheological and mechanical properties of SCC reinforced with different proportions of fibers. Fresh property tests included slump flow test and rheological tests using a concrete rheometer. The study underscored the potential for fibers to be accommodated by adjusting the mixture proportions of concrete. It was shown that inclusion of fibers in SCC is feasible for the purpose of manufacturing structural elements like railway crossties. The present study also considered the current state of prestressed concrete crosstie design and the impact of FRC on mechanical performance of concrete crossties. The applicability of FRC in railway crossties was investigated by developing and testing prototype crossties. A comparative study was performed between a conventional crosstie and a fiber reinforced crosstie through tests at rail seat and center of crosstie. It was found out that the synthetic polypropylene fibers provided sustained capacity for deformation in the concrete crossties along with an improved crack resistance. Lastly, this study developed a tensile stress-strain model for FRC behavior. Four point bending test results of FRC beams were used to determine tensile behavior of FRC using an inverse analysis approach and a back calculator tool. Preliminary tensile stress-strain models were established which can be used to define constitutive properties for concrete when using finite element analysis (FEA) to analyze experimental results. FEA has not been performed as a part of this thesis work, but will be pursued in subsequent research activities at the University of Illinois

Determinación de la resistencia residual promedio (análisis postfisuración) del concreto reforzado con fibra sintética de pet+pp

Trabajo de investigaciónEl concreto siempre tendra la tendencia a generar por naturaleza el fenómeno de la fisuración a causa de los efectos en la etapa antes y despues del endurecimiento, esta fisuración a revelado que la matriz de concreto pierde totalmente la capacidad a la cual fue diseñado, por eso y mucho mas, se hace necesario la incusión de las macrofibras desde la etapa de diseño en una acción predictiva, poder garantizar que los efectos de fisuración afecten en menor proporcion la disminución de carga y permita devolverle al concreto una capacidad de esforzarse en condiciones fisuradas y a la vez poder reducir las posibilidades de falla, la norma ASTM C 1399-10 propone el metodo de medir cuales son los efectos resistentes en condiciones post-fisuración, y calcular la resistencia residual del concreto reforzado con fibra.1. INTRODUCCIÓN 2. ANTECEDENTES 3. PLANTEAMIENTO DEL PROBLEMA 4. OBJETIVOS 5. JUSTIFICACIÓN 6. ALCANCE 7. MARCO TEÓRICO Y CONCEPTUAL. 8. METODOLOGÍA 9. CONCLUSIONES. 10.RECOMENDACIONES 11.BIBLIOGRAFÍAEspecializaciónEspecialista en Ingeniería de Pavimento

Overview of Fiber-Reinforced Concrete Bridge Decks TPF-5(313)

This report summarizes the experience from existing bridge deck and bridge deck overlay construction projects that have employed fiber-reinforced concrete (FRC) materials. Included within this report is a summary of the laboratory and field performance of various FRC bridge decks along with key test methods and specification language developed by state departments of transportation. This document is a companion report to Fiber-Reinforced Concrete for Pavement Overlays: Technical Overview, which summarizes the state of the art regarding different fiber types, test methods, structural design, and the construction modifications required to accommodate FRC materials in concrete overlay

Increasing residual structural capacity of cracked concrete railroad crossties with polypropylene fibers

The purpose of this research was to employ polypropylene fibers into concrete railroad crossties to increase its residual structural capacity once the concrete has cracked. The center negative flexural cracking is considered as a serious failure mode in concrete railroad crossties, which decreases structural capacity and results in safety issues. It also leads to deterioration of prestressed concrete crossties and shortens the service life. The post-cracking flexural performance of fiber reinforced concrete (FRC) crossties is changed by the inclusion of polypropylene fibers. Fracture toughness, cracking resistance, and energy absorption capacity of the concrete are improved by incorporating fibers. Furthermore, restriction of crack size extends the service life of concrete railroad crossties and thus the maintenance cost decreases. Several tests were conducted to select the most suitable fibers in the following study. Six types of polyethylene fiber samples with different elastic modulus, surface texture, length, stiffness, and shape were evaluated. The performance of fibers was mainly evaluated by the workability of fresh FRC mixture, the compressive strength and the average residual strength (ARS) of hardened FRC specimens. The concrete mixture reinforced by Strux 90/40 macro polyethylene fibers had the best workability because no balling or clumping issue was found in the mixing process. It had the least effect on the reduction of compressive strength of hardened FRC specimens. The ARS value also indicates Strux 90/40 fibers can improve post-cracking performance of concrete. Therefore, Strux 90/40 macro polyethylene fibers were selected as the reinforcement material in this research. Flexural performance of full-scaled prestressed plain cement concrete (PCC) crossties and FRC crossties was evaluated by center negative bending test and rail seat positive bending test. Load-displacement curves of crossties in flexural tests were recorded. Fracture patterns of crossties in the flexural tests were also captured. Based on the experimental results, it was confirmed that the prestressed FRC crosstie had a higher fracture toughness. The FRC crosstie completely failed at a greater deflection in the flexural test. A numerical method was introduced to predict flexural performance of full-scaled prestressed FRC crossties in center negative bending test. The materials element modeling can be built based on experimental results from simple four-point bending tests on small FRC beams. The materials element modeling was input into an established structural member modeling of prototype prestressed crossties in Abaqus. For a given fiber volume fraction, the flexural performance of full-scaled prestressed FRC crossties can be simulated by inputting corresponding materials element modeling

Fiber reinforced concrete for bridge deck overlays

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Relevantne statičke i dinamičke metode za ocenu žilavosti mikroarmiranih betona

The paper deals with contemporary methods and relevant technical regulation in the field of toughness testing and evaluation of fiber-reinforced cement composites subjected to specific static loads (flexural and wedge-splitting tests), as well as to dynamic loads (impact and cyclic fatigue tests). Fibers are usually added to concrete in order to improve some of the composite's physical, mechanical, deformation, rheological and/or technological properties, such as: tensile and flexural strength, impact resistance, shrinkage, fatigue resistance, durability in different environment conditions, etc. To obtain these goals, it is essential to achieve the best possible interaction between the fibers and the cement-based matrix. The improved performance of fiber reinforced concrete is most significant when the enhancement of fracture energy absorption capacity (i.e. improvement of toughness) is concerned. The results obtained during static and dynamic testing of toughness (ductility) parameters can be very important, especially in order to compare the properties of different types of fiber reinforced composites, but also to solve specific practical engineering problems.U radu su prikazane savremene metode i relevantna tehnička regulativa u oblasti ispitivanja i ocene žilavosti mikroarmiranih kompozita izloženih specifičnim statičkim (savijanje i cepanje pomoću klina), kao i dinamičkim opterećenjima (udar i ciklični zamor materijala). Vlakna se obično dodaju betonu u cilju poboljšanja nekih fizičkih, mehaničkih, deformacionih, reoloških i/ili tehnoloških svojstava ovog kompozita, kao što su na primer: čvrstoća pri zatezanju, čvrstoća pri savijanju, udarna otpornost, deformacije skupljanja, otpornost na ciklični zamor, trajnost u različitim uslovima sredine, itd. Da bi se postigli navedeni ciljevi, suštinski je važno ostvariti najbolju moguću interakciju između vlakana i cementne matrice. Poboljšane performanse mikroarmiranih betona su najizraženije u domenu povećanja kapaciteta apsorbovanja energije loma - tj. povećanja žilavosti predmetnih kompozita. Eksperimentalni rezultati dobijeni tokom statičkih i dinamičkih ispitivanja parametara žilavosti (odnosno duktilnosti) mogu da budu veoma značajni, naročito u cilju poređenja svojstava različitih tipova mikroarmiranih kompozita, ali takođe i u slučaju rešavanja specifičnih inženjerskih problema u praksi

Propuesta Metodológica para el Estudio Experimental de la Fluencia en Flexión de Prismas Fisurados de SFRC

En la actualidad no existe una metodología de ensayo estandarizada para evaluar el fenómeno de la fluencia a flexión de SFRC en estado fisurado. Partiendo de las escasas investigaciones en el tema se han diseñado y puesto en marcha los equipos necesarios para estudiar este fenómeno, además se ha definido una terminología y parámetros de análisis.Arango Campo, SE. (2010). Propuesta Metodológica para el Estudio Experimental de la Fluencia en Flexión de Prismas Fisurados de SFRC. http://hdl.handle.net/10251/11605Archivo delegad

Fiber-Reinforced Concrete for Pavement Overlays: Technical Overview TPF-5(313)

This report summarizes the state of the art regarding different fiber types, test methods, structural design, and the construction modifications required to accommodate fiber-reinforced concrete (FRC) materials in concrete overlays. This document is a companion report to Overview of Fiber-Reinforced Concrete Bridge Decks, which summarizes the experience from existing bridge deck and bridge deck overlay construction projects that have employed FRC materials

Testing Methodologies and Effects Associated with Ceramic Materials

Ceramics are being used in numerous industrial and scientific applications. Advanced ceramics, in particular, have great future possibilities for use in a wide variety of applications as these are typically wear and corrosion resistant, lightweight, and thermodynamically stable. In addition, many advanced ceramics have electrical properties that make them advantageous for use in electronic applications such as electronic packaging. With the steadily increasing use of ceramics in industry, there exists an increasing demand to characterize and quantify the properties of ceramics. This leads to higher demand for improved testing techniques to yield more exact data used for activities such as design, safety analysis, quality control, and scientific understanding. This present study gives a brief overview of the major test methods currently being used, relative advantages and disadvantages to each other, and some common sources of error. In addition, a listing of standards that are both relevant and directly applicable to ceramics are given for various testing methods. This chapter considers the most common mechanical testing methods which are usually expected to be performed by students entering the first time into a lab. Tensile test-related parameters are evaluated. Very popular tests of ceramics are the various hardness tests (for example Vickers hardness test), which is not only a cost saving test, but also requires shorter times, since no specific specimen preparation, except of a smooth (often polished) surface is required. On small size specimens, Knoop hardness test is the general approach to obtain hardness data. Another accepted method of evaluating the mechanical properties of a ceramic is by a bending (flexural) test. The tests can be performed by three or four point bending tests. Compression tests are more popular than tension tests, since they tend to close pores, cracks and other flaws resulting in higher test results than by those obtained by tension, which tends to open rather than close cracks and microcracks. Toughness is an important criterion in ceramic properties (mechanical) evaluation. Because of the brittle nature of ceramics, special instrumented Charpy Impact Test machines were developed, primarily to evaluate the dynamic toughness of such materials. Creep and Fatigue tests are not included in this chapter and they will be evaluated in separate chapters. Because of the large scatter in the experimental results, Weibull statistical distribution is applied to obtain a mean value of the experimental results. In this manuscript, the descriptions of assorted testing methodologies associated with ceramics are presented