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Author: Daniel Stephen Lane
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 18
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Book Description
Petrographic examinations of specimens from two recently constructed concrete pavements suggested that complete consolidation of the concrete may not have been achieved. Consequently, a quantitative evaluation of the degree of consolidation in these specimens was undertaken. The pavements were of plain, jointed design with dowels for load transfer. Both projects were constructed using slip-form paving machines with spud vibrators. It was found that the entrapped void content was excessive. In both cases, the entrapped void content of the lower half of the pavement was higher than the upper half. This situation apparently occurred because the vibrators were set to ride above the preplaced dowel assemblages. In one pavement the consolidation of the upper half was adequate, but the entrapped void content of the upper half of the other pavement was also found to be excessive. The following recommendations are made: (1) During preplacement conferences and actual construction, emphasize the importance of adequate consolidation of concrete throughout the pavement, especially in the vicinity of dowel assemblages. (2) Consider alternative methods of dowel placement. Pavers with dowel bar inserters are available. (3) Investigate methods to evaluate and monitor consolidation during construction. Nuclear gauges are used for this purpose in some states although not all applications have been successful. Ultrasonic techniques show promise for this application.
Author: Daniel Stephen Lane
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 18
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Book Description
Petrographic examinations of specimens from two recently constructed concrete pavements suggested that complete consolidation of the concrete may not have been achieved. Consequently, a quantitative evaluation of the degree of consolidation in these specimens was undertaken. The pavements were of plain, jointed design with dowels for load transfer. Both projects were constructed using slip-form paving machines with spud vibrators. It was found that the entrapped void content was excessive. In both cases, the entrapped void content of the lower half of the pavement was higher than the upper half. This situation apparently occurred because the vibrators were set to ride above the preplaced dowel assemblages. In one pavement the consolidation of the upper half was adequate, but the entrapped void content of the upper half of the other pavement was also found to be excessive. The following recommendations are made: (1) During preplacement conferences and actual construction, emphasize the importance of adequate consolidation of concrete throughout the pavement, especially in the vicinity of dowel assemblages. (2) Consider alternative methods of dowel placement. Pavers with dowel bar inserters are available. (3) Investigate methods to evaluate and monitor consolidation during construction. Nuclear gauges are used for this purpose in some states although not all applications have been successful. Ultrasonic techniques show promise for this application.
Author: Shiraz D. Tayabji
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 112
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Book Description
Author: Ernest J. Barenberg
Publisher:
ISBN:
Category : Nondestructive testing
Languages : en
Pages : 88
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Author: Jennifer A. Distlehorst
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 53
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Book Description
The purpose of this study was to investigate methods of reducing the size and total volume of the entrapped air voids in concrete slabs that are over 9 in. thick. Laboratory and field tests were designed to investigate the effect of variations in vibration frequency and aggregate gradation on entrapped air content, strength and performance factors such as smoothness, faulting, adhesion failures, and spalling. In 1993, a test section was constructed to compare the effects of increasing the proportion of coarse aggregate to fine aggregate and increasing vibration frequency. Annual surveys of joint sealant failures, spalling and joint faulting were performed from 1994 to 2001 on this test section. Samples from this project were cut, polished and analyzed to determine entrained and entrapped air content. In 1994, another test section was constructed to assess the effect of controlling the total gradation of concrete aggregate and increasing vibration frequency. A profilograph test was performed in 1996 to measure pavement smoothness on this project. Core samples were taken from both the wheel path and the wheel gap and nuclear density meters were used on both projects to measure the in-situ density of the pavements.
Author:
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 204
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Author: Shane Tymkowicz
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 108
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Book Description
The Iowa Department of Transportation has discovered an increase in the occurrence of excessively vibrated portland cement concrete (PCC) pavements. The overconsolidation of PCC pavements has been observed in several projects across the state. Overconsolidation is also believed to be a factor in acceleration of premature deterioration of at least two pavement projects in Iowa. To address the problem, a research project in 1995 documented the vibratory practices of PCC slipform paving in Iowa in order to determine the effect of vibration on consolidation and air content of pavement. Paver speed, vibrator frequency, and air content relative to the location of the vibrator were studied. The study concluded that the Iowa Department of Transportation specification of 5,000 to 8,000 vibrations per minute (vpm) for slipform pavers is effective for normal paver speeds on the three projects that were examined. Excessive vibration was clearly identified on one project where a vibrator frequency of 12,000 vpm was discovered. When the paver speed was reduced to half the normal speed, hard air contents indicate that excessive vibration was beginning to occur in the localized area immediately surrounding the vibrator at a frequency of 8,000 vpm. The study also indicates that the radius of influence of the vibrators is smaller than has been claimed.
Author: James K. Cable
Publisher:
ISBN:
Category : Vibrated concrete
Languages : en
Pages : 72
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Author: Kejin Wang
Publisher:
ISBN:
Category : Concrete
Languages : en
Pages : 68
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Book Description
Over-consolidation is often visible as longitudinal vibrator trails in the surface of concrete pavements constructed using slip-form paving. Concrete research and practice have shown that concrete material selection and mix design can be tailored to provide a good compaction without the need for vibration. However, a challenge in developing self-consolidating concrete for slip-form paving (SF SCC) is that the new SF SCC needs to possess not only excellent self-compactibility and stability before extrusion, but also sufficient "green" strength after extrusion, while the concrete is still in a plastic state. The SF SCC to be developed will not be as fluid as the conventional SCC, but it will (1) be workable enough for machine placement, (2) be self-compacting with minimum segregation, (3) hold shape after extrusion from a paver, and (4) have performance properties (strength and durability) compatible to current pavement concrete. The overall objective of this project is to develop a new type of SCC for slip-form paving to produce more workable concrete and smoother pavements, better consolidation of the plastic concrete, and higher rates of production. Phase I demonstrated the feasibility of designing a new type of SF SCC that can not only self-consolidate, but also have sufficient green strength. In this phase, a good balance between flowability and shape stability was achieved by adopting and modifying the mix design of self-consolidating concrete to provide a high content of fine materials in the fresh concrete. It was shown that both the addition of fine particles and the modification of the type of plasticizer significantly improve fresh concrete flowability. The mixes used in this phase were also found to have very good shape stability in the fresh state. Phase II will focus on developing a SF SCC mix design in the lab and a trial of the SF SCC in the field. Phase III will include field study, performance monitoring, and technology transfer.
Author: David Whiting
Publisher: Strategic Highway Research Program (Shrp)
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 304
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Book Description
This synthesis reviews the literature in the field of concrete materials, construction practices, and major application areas as applied to highway construction technology. It covers current and projected developments in materials including cements, aggregates, admixtures, fibers, and sealers. Topic areas covered include mix proportioning, batching and transport, placement, finishing, and curing. The applications included here focus on repair and reconstruction including full depth repairs, slab replacement, partial depth repairs, overlays, and recycling. Quality control of concrete including traditional approaches as well as new test methods and quality assurance schemes are discussed. The appendix describes the history of developments in concrete pavement construction in Europe.
Author: Bert E. Colley
Publisher:
ISBN:
Category : Pavements, Concrete
Languages : en
Pages : 71
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Book Description
