Reducing Cracks in Concrete Bridge Decks Using Shrinkage Reducing

Reducing Cracks in Concrete Bridge Decks Using Shrinkage Reducing
Author: Harikrishnan Nair
Publisher:
Total Pages: 44
Release: 2016
Genre: Concrete
ISBN:

Restrained shrinkage cracking of concrete bridge decks creates a significant durability problem. Major admixture suppliers in the United States have introduced a new category of chemical admixtures called shrinkage reducing admixtures (SRAs). SRAs work by reducing the surface tension of pore water and thereby decreasing the capillary stress and shrinkage induced by drying. Several studies have reported that using SRAs in concrete mixtures is one of the most effective ways of reducing shrinkage cracking. The purpose of this study was to investigate the effectiveness of SRAs in reducing drying shrinkage in Virginia Department of Transportation (VDOT) concrete mixtures and thus reducing cracks in bridge decks. Nine bridges located in VDOT Northern Virginia, Staunton, and Fredericksburg districts were selected for study. Three different SRA products were used. With the exception of one mixture, the maximum cementitious content was limited to 600 lb/yd3. Fresh and hardened concrete properties were determined for each mixture, and field placement details were documented. The results showed that low cementitious concrete with SRA was effective in minimizing bridge deck cracking. The study showed that bridges with fewer and narrower cracks or no cracks can be constructed and that proper construction practices are needed to reduce bridge deck cracking. The study recommends the use of SRA with a lower cementitious content in VDOT bridge deck concrete mixtures. A VDOT special provision was developed for the future use of SRA in concrete mixtures.

Reducing Cracks in Concrete Bridge Decks Using Shrinkage Reducing Admixture

Reducing Cracks in Concrete Bridge Decks Using Shrinkage Reducing Admixture
Author:
Publisher:
Total Pages: 44
Release: 2016
Genre: Concrete
ISBN:

Restrained shrinkage cracking of concrete bridge decks creates a significant durability problem. Major admixture suppliers in the United States have introduced a new category of chemical admixtures called shrinkage reducing admixtures (SRAs). SRAs work by reducing the surface tension of pore water and thereby decreasing the capillary stress and shrinkage induced by drying. Several studies have reported that using SRAs in concrete mixtures is one of the most effective ways of reducing shrinkage cracking. The purpose of this study was to investigate the effectiveness of SRAs in reducing drying shrinkage in Virginia Department of Transportation (VDOT) concrete mixtures and thus reducing cracks in bridge decks. Nine bridges located in VDOT’s Northern Virginia, Staunton, and Fredericksburg districts were selected for study. Three different SRA products were used. With the exception of one mixture, the maximum cementitious content was limited to 600 lb/yd3. Fresh and hardened concrete properties were determined for each mixture, and field placement details were documented. The results showed that low cementitious concrete with SRA was effective in minimizing bridge deck cracking. The study showed that bridges with fewer and narrower cracks or no cracks can be constructed and that proper construction practices are needed to reduce bridge deck cracking. The study recommends the use of SRA with a lower cementitious content in VDOT bridge deck concrete mixtures. A VDOT special provision was developed for the future use of SRA in concrete mixtures.

Field Monitoring of Shrinkage Cracking Potential in a High-performance Bridge Deck

Field Monitoring of Shrinkage Cracking Potential in a High-performance Bridge Deck
Author: Timothy Walkowich
Publisher:
Total Pages: 107
Release: 2011
Genre: Bridges
ISBN:

Over the past decade many state engineers throughout New Jersey have reported cracking on High Performance Concrete (HPC) bridge decks at early ages. The presence of cracking early in the life of a high performance deck offsets the benefits gained in using the material as the potential for corrosion begins at the onset of cracking. While many factors apply to bridge deck cracking, the shrinkage of the concrete's mass is a primary concern. Because of shear studs and boundary conditions, among other causes that act in restraining the deck itself, it is important to understand the mechanics of concrete under restraint. The AASHTO Passive Ring Test (PP 34-06) is seeing an increase in use in studies analyzing restrained shrinkage. The test simulates a concrete member of infinite length and allows researchers to study the effects of various parameters on restrained shrinkage. This thesis presents the results of a study that analyzed the ring test's ability to simulate restrained shrinkage on HPC bridge decks. The investigation incorporated an instrumented, simply supported composite bridge deck with laboratory samples taken on the day of the pour as well as a finite element analysis. The results suggest the AASHTO Passive Ring Test simulates the restrained shrinkage of simply supported HPC decks reasonably well. Fewer than 1% of all cracking present on the ring specimens saw complete penetration through the sample with 80-90% of all cracking considered to be micro cracking. While the presence of several cracks along the bridge deck itself showed no correlation with the shrinkage ring specimens, finite element analysis suggests these cracks are a result of adjacent live load. Also, the findings of this study highlight the importance of following design in the field as well as the effect of live load on staged construction of HPC bridge decks.

Review and Specification for Shrinkage Cracks of Bridge Decks

Review and Specification for Shrinkage Cracks of Bridge Decks
Author: Jafar Allahham
Publisher:
Total Pages: 40
Release: 2016
Genre: Bridges
ISBN:

An existing standard method ASTM C157 is used to determine the length change or free shrinkage of an unrestrained concrete specimen. However, in bridge decks, the concrete is actually under restrained conditions, and thus free shrinkage test methods do not represent the same condition of bridge decks and are not correlated to in field bridge deck shrinkage. An alternative for restrained shrinkage is to use one of the two existing standards AASHTO T334-08 or ASTM C1581. In these two restrained test methods, the concrete is cast in the circumference around an inner steel ring. The purpose of this study was to construct the apparatus for the AASHTO T334-08 method to estimate the cracking age of concrete mixtures that may be used in bridge decks. In the processes of the apparatus setup, several limitations to the method were discovered, such as the influence of the surrounding environment and the repeatability of the method. Thus, an additional study was done to evaluate the sensitivity of shrinkage measurements (ASTM C157 and AASHTO T334-08) in different surrounding environments, with different mix designs (e.g., varying w/cm, binder content and aggregate size), and different concrete specimen thicknesses. Overall, it was confirmed that most mixtures did not even indicate any cracking unless a high cement volume content of 24% with no coarse aggregates was tested using the existing AASHTO T334-08 restrained ring method. A thinner ring (2” of concrete instead of 3”) had a decreased age of cracking. The free shrinkage ASTM C157 is still the easiest, and a relatively fast method to use and can provide relative comparisons between different mixtures or between different environments.