Shrinkage of self-compacting concrete. A comparative analysis

Self-compacting concrete (SCC) is a concrete type that does not require vibration for placing and compacting. SCC possesses special technical features and properties that recommend its application in many jobs. Nevertheless, in some situations, it has been observed an inadequate behaviour of the material at early ages due to shrinkage. The existing shrinkage prediction models were developed for standard concrete. In this paper three SCC mixtures, with different compressive strength, are studied in terms of autogenous and total shrinkage. The results are compared with the Eurocode 2 model. For the studied mixtures it was found that this model underestimates the autogenous shrinkage, while the total shrinkage is generally overestimated.Fundacao para a Ciencia e a Tecnologia (FCT), Portugal [UID/MULTI/00308/2013]info:eu-repo/semantics/publishedVersio

Strengthening of Corroded Reinforced SCC-RAP Members with CFRP

Corrosion is one of the major problems affecting the durability of reinforced concrete (RC) structures. This paper investigates the effect of rebar corrosion on the performance of reinforced self-consolidating concrete (SCC) members and the effectiveness of repair. A control RC member, which has no corrosion problem, was prepared to compare against corroded and repaired members. A number of reinforced concrete members having up to 50% corrosion level were constructed and tested to study the effect of corrosion on the structural performance of RC members. The beams with corrosion problem were repaired using carbon fiber reinforced polymer (CFRP) sheets and U-wraps. All of the beams constructed, which are either not repaired or repaired, in this study were tested under two static line loads until failure. The effect of corrosion and effectiveness of repairing technique were assessed by evaluating the performance in terms of load carrying capacity, deflection, and ductility. Test results revealed that as the corrosion level increases, the loss in load carrying capacity increases. Repairing using CFRP improved the performance of corroded members. For example, when 50% corrosion level was achieved, the beam lost approximately 57% of its load carrying capacity, but when it was repaired, it recovered about 42% of its load carrying capacity

SEISMIC RESPONSE ASSESSMENT AND RECOMMENDATIONS FOR THE DESIGN OF SKEWED HIGHWAY BRIDGES

Seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies examined the performance of skewed bridges under service and seismic loads. It is noted that results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters with the skew. The present study investigates the seismic response characteristics of two-span skewed post-tensioned box-girder bridges with skew angles varying from 0 to 60 degree. To facilitate a comprehensive analytical investigation simplified modeling techniques are introduced. The accuracy of simplified beam-stick models are verified against counterpart finite element models. Effect of various parameters on the overall seismic performance was examined and implications were presented. Finally, nonlinear time history analysis was used to generate system fragility functions for a range of three-span highway bridges (straight, moderate skew, and significant skew). It is shown that simplified beam-stick models have the capability to capture the nonlinear time history response of skewed bridges. Using incremental dynamic analysis (IDA) method, fragility functions were developed and the effect of the skew on the vulnerability of highway bridges is investigated. Furthermore, analytical fragility functions of skewed bridges were compared to HAZUS fragility functions. The soil type, presence of shear keys, and aspect ratio are determined to have a significant effect on the seismic performance of skewed bridges. Also, it was concluded that highway bridges with large skew angles (> 30°) are more vulnerable to seismically induced damages compared to those with moderate skew angles (< 30°)

Effect of Layer and Film Thickness and Temperature on the Mechanical Property of Micro- and Nano-Layered PC/PMMA Films Subjected to Thermal Aging

Multilayered polymer films with biomimicking, layered structures have unique microstructures and many potential applications. However, a major limitation of polymer films is the deterioration of mechanical properties in working environments. To facilitate the design and development of multilayered polymer films, the impact of thermal aging on the mechanical behavior of micro- and nano-layered polymer films has been investigated experimentally. The composition of the polymer films that have been studied is 50 vol% polycarbonate (PC) and 50 vol% poly(methyl methacrylate) (PMMA). The current study focuses on the effect of film and layer thickness and temperature on the mechanical properties of the materials subjected to thermal aging. To study the effect of film and layer thickness, films with the same thickness, but various layer thicknesses, and films with the same layer thickness, but various film thicknesses, were thermally aged at 100 °C in a constant temperature oven for up to six weeks. The results show that as the layer thickness decreases to 31 nm, the film has a higher stiffness and strength, and the trend of the mechanical properties is relatively stable over aging. The ductility of all of the films decreases with aging time. To study the effect of temperature, the films with 4,096 layers (31 nm thick for each layer) were aged at 100 °C, 115 °C and 125 °C for up to four weeks. While the 100 °C aging results in a slight increase of the stiffness and strength of the films, the higher aging temperature caused a decrease of the stiffness and strength of the films. The ductility decreases with the aging time for all of the temperatures. The films become more brittle for higher aging temperatures

Seismic Response Assessment and Recommendations for the Design of Skewed Post-Tensioned Concrete Box-Girder Highway Bridges

Report No. CCEER-08-03Seismic vulnerability of highway bridges remains an important problem and has received increased attention as a consequence of unprecedented damage observed during several major earthquakes. A significant number of research studies have examined the performance of skewed bridges under service and seismic loads. It is noted that results of these studies are particularly sensitive to modeling assumptions in view of the interacting parameters which may include: 1. Skew angle 2. Superstructure flexibility 3. Boundary conditions 4. In-span hinges (if any 5. Width-to-span ratios 6. Mass and stiffness eccentricity In this study, three dimensional improved beam stick models of two-span highway bridges with skew angles varying from 0 to 60 degree are developed to investigate seismic response characteristics of skewed reinforced concrete box-girder bridges. Relative accuracy of simplified beam-stick models are verified against counterpart finite element models. Both SAP2000 and DRAIN3DX programs were evaluated and the latter was used for the nonlinear time history analyses of the bridges. A total of six ground motions were selected such that the average acceleration response spectra (ARS) for the different intensities matched the corresponding CALTRANS target design ARS. Effect of various parameters on the overall seismic response was examined such as: effect of skew angle, support (foundation) conditions, end conditions with and without abutment-soil interaction and with and without transverse shear-keys, soil conditions, various ground motion intensities, and various aspect ratios

Investigation of Likelihood of Cracking in Reinforced Concrete Bridge Decks

One of the biggest problems affecting bridges is the transverse cracking and deterioration of concrete bridge decks. The causes of early age cracking are primarily attributed to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. The cracks can be influenced by material characteristics, casting sequence, formwork, climate conditions, geometry, and time dependent factors. The cracking of bridge decks not only creates unsightly aesthetic condition but also greatly reduces durability. It leads to a loss of functionality, loss of stiffness, and ultimately loss of structural safety. This investigation consists of field, laboratory, and analytical phases. The experimental and field testing investigate the early age transverse cracking of bridge decks and evaluate the use of sealant materials. The research identifies suitable materials, for crack sealing, with an ability to span cracks of various widths and to achieve performance criteria such as penetration depth, bond strength, and elongation. This paper also analytically examines the effect of a wide range of parameters on the development of cracking such as the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits live-load deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. The deflection is found to be an important parameter to affect cracking. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented. © 2013 The Author(s)

Performance of Strengthened Non-Uniformly Corroded Reinforced SCC-RAP Members

This research examines the performance of strengthened non-uniformly corroded reinforced self-consolidating concrete (SCC) members. This paper focuses on three aspects of concrete including corrosion, concrete cover loss, and repair technique. Up to a 50% corrosion level is considered in this study. Corrosion was experimentally induced and was simulated in other cases. Twenty-six reinforced concrete (RC) members with various corrosion levels or simulated corrosion levels were constructed and investigated. The beams with corrosion problems including those that had experimentally induced corrosion or simulated corrosion, with or without concrete cover, were repaired using carbon fiber reinforced polymer (CFRP) sheets and U-wraps. Two line loads were applied to all of the non-repaired and repaired beams constructed in this study until failure. It was found that it is conservative to model the actual corrosion by simulating the equivalent area of steel reinforcing for up to a 20% level of corrosion. For corrosion levels over 20%, the simulated corrosion over predicts the load capacity of the actual corrosion cases. When the concrete cover was lost and for a corrosion level larger than 10%, the repaired beam did not reach similar performance to that of a repaired beam with a concrete cover that was still intact. It appears that using two layers of CFRP sheet did not improve the load capacity further, but rather improved the ductility of the deteriorated RC member

Strengthening of Corroded Reinforced SCC-RAP Members with CFRP

Corrosion is one of the major problems affecting the durability of reinforced concrete (RC) structures. This paper investigates the effect of rebar corrosion on the performance of reinforced self-consolidating concrete (SCC) members and the effectiveness of repair. A control RC member, which has no corrosion problem, was prepared to compare against corroded and repaired members. A number of reinforced concrete members having up to 50% corrosion level were constructed and tested to study the effect of corrosion on the structural performance of RC members. The beams with corrosion problem were repaired using carbon fiber reinforced polymer (CFRP) sheets and U-wraps. All of the beams constructed, which are either not repaired or repaired, in this study were tested under two static line loads until failure. The effect of corrosion and effectiveness of repairing technique were assessed by evaluating the performance in terms of load carrying capacity, deflection, and ductility. Test results revealed that as the corrosion level increases, the loss in load carrying capacity increases. Repairing using CFRP improved the performance of corroded members. For example, when 50% corrosion level was achieved, the beam lost approximately 57% of its load carrying capacity, but when it was repaired, it recovered about 42% of its load carrying capacity

A parametric study of the development of transverse deck cracking

Bridges and especially bridge decks experience problems of transverse cracking and deterioration. The causes of early age cracking are mainly due to plastic shrinkage, temperature effects, autogenous shrinkage, and drying shrinkage. Many parameters can affect the development of such cracks. The cracks can be influenced by material characteristics, formwork, climate conditions, geometry, load patterns, amount of deflection, and time dependent factors. It is important to resolve the issue of transverse deck cracking otherwise several bridge decks may experience loss of stiffness and the possibility loss of function which may affect the safety of bridges. This paper examines the effect of a wide range of parameters on the development of cracking. The parameters include, the number of spans, the span length, girder spacing, deck thickness, concrete compressive strength, dead load, hydration, temperature, shrinkage, and creep. The importance of each parameter is identified and then evaluated. Also, the AASHTO Standard Specification limits live-load deflections to L/800 for ordinary bridges and L/1000 for bridges in urban areas that are subject to pedestrian use. One of the main objectives of the study is also to ensure that the current deflection limit is adequate. It is determined that the deflection limit is an important parameter to affect cracking. The current deflection limit needs to be revisited and modified. A set of recommendations to limit the transverse deck cracks in bridge decks is also presented. © Civil-Comp Press, 2012