Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and t... more Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and thermal shrinkage), can have several detrimental effects on long-term behavior and durability. Cracking can also provide ingress of water that can drive chemical reactions, such as alkali-silica reaction (ASR) and sulfate attack. Because of the problems associated with cracking observed in bridge decks, and the impact of early-age cracking on long-term performance and durability, it is imperative that bridge decks be constructed with minimal early-age cracking and that exhibit satisfactory long-term performance and durability. To achieve these goals for bridges in the state of Texas, a research team has been assembled that possesses significant expertise and background in cement chemistry, concrete materials and durability, structural performance, computational mechanics (finite difference/element), bridge deck construction and maintenance, monitoring of in-site behavior of field structures, and the development of test methods and specifications aimed at practical implementation by state highway departments. This proposal describes a laboratory-and field-based research program aimed at developing a bridge deck cracking model that will ultimately be integrated into ConcreteWorks, a suite of software programs developed for TxDOT by this same research team. 17. Key Words Early-age cracking, drying shrinkage, bridge decks 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and t... more Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and thermal shrinkage), can have several detrimental effects on long-term behavior and durability. Cracking can also provide ingress of water that can drive chemical reactions, such as alkali-silica reaction (ASR) and sulfate attack. Because of the problems associated with cracking observed in bridge decks, and the impact of early-age cracking on long-term performance and durability, it is imperative that bridge decks be constructed with minimal early-age cracking and that exhibit satisfactory long-term performance and durability. To achieve these goals for bridges in the state of Texas, a research team has been assembled that possesses significant expertise and background in cement chemistry, concrete materials and durability, structural performance, computational mechanics (finite difference/element), bridge deck construction and maintenance, monitoring of in-site behavior of field structures, and the development of test methods and specifications aimed at practical implementation by state highway departments. This proposal describes a laboratory-and field-based research program aimed at developing a bridge deck cracking model that will ultimately be integrated into ConcreteWorks, a suite of software programs developed for TxDOT by this same research team. 17. Key Words Early-age cracking, drying shrinkage, bridge decks 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Early-age bridge deck cracking has been found to be a prevalent problem worldwide. While early-ag... more Early-age bridge deck cracking has been found to be a prevalent problem worldwide. While early-age cracking will not cause failure of a bridge deck system independently, the penetration of deleterious substances through the early-age cracks into the bridge deck concrete and the bridge superstructure can lead to costly serviceability issues, and possibly the loss of some structural integrity. This report describes research undertaken to evaluate the various factors affecting bridge deck cracking, and the results of this project have been implemented in a new bridge deck cracking module for ConcreteWorks, a software program that addresses a range of concrete properties and performance issues. 17. Key Words ConcreteWorks, bridge, deck cracking, strengthening 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Alkali-silica reaction (ASR) is a significant durability problem that has resulted in premature d... more Alkali-silica reaction (ASR) is a significant durability problem that has resulted in premature deterioration of various types of concrete structures in the United States and throughout the world. Although several viable methods exist to prevent AST-induced damage in new concrete structures, very few methods mitigate further damage in structures already affected by ASR-induced expansion and cracking. Lithium compounds have been recognized for more than 50 years as effectively preventing expansion due to ASR, and there has been renewed interest in recent years in using lithium compounds as either an admixture in new concrete or as a treatment of existing structures. This report is intended to provide practitioners with the necessary information and guidance to test, specify, and use lithium compounds in new concrete construction, as well as in repair and and service life extension applications. This report first provides a basic overview of ASR, including information on mechanisms, symptoms of ASR damage in field structures, mitigation approaches, test methods, and specifications. A comprehensive summary of lithium compounds is provided next, including information on their production, availability, and use in laboratory concrete studies and field applications (including a range of case studies). Guidelines for using lithium compounds as an admixture in new concrete and for treating existing structures suffering from ASR-induced damage then are presented, including information on how to assess the efficacy of lithium compounds in laboratory tests. Some basic information also is provided on the economics of using lithium both in new concrete and as a treatment for existing structures. Finally, the report provides a summary of conclusions and identifies several technical and practical issues that should be considered for future laboratory studies and field applications.
In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limeston... more In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limestone cements and their combinations with 30-50 % slag were examined at both 5 and 23°C according to CSA A3004-C8 (similar to ASTM C1012). Also, XRD was used to identify the phases formed after sulfate attack. It was found that in 23°C exposure, while 100 % cement mixes deteriorated due to conventional ettringite-based sulfate attack, partially replacing the cements with 30 or 50 % slag was effective in making the mixes highly sulfate-resistant. At 5°C, all of the 100 % cement mortar bars expanded more than the test limits and eventually completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30 % slag was only effective in controlling the deterioration for Portland cements but not Portland-limestone cements. However, all the Portland-limestone cements with 50 % slag were resistant to the thaumasite form of sulfate attack after 2 years.
In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limeston... more In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limestone cements and their combinations with 30-50 % slag were examined at both 5 and 23°C according to CSA A3004-C8 (similar to ASTM C1012). Also, XRD was used to identify the phases formed after sulfate attack. It was found that in 23°C exposure, while 100 % cement mixes deteriorated due to conventional ettringite-based sulfate attack, partially replacing the cements with 30 or 50 % slag was effective in making the mixes highly sulfate-resistant. At 5°C, all of the 100 % cement mortar bars expanded more than the test limits and eventually completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30 % slag was only effective in controlling the deterioration for Portland cements but not Portland-limestone cements. However, all the Portland-limestone cements with 50 % slag were resistant to the thaumasite form of sulfate attack after 2 years.
This report describes the evaluation of Class C fly ash in sulfate environments. The practical re... more This report describes the evaluation of Class C fly ash in sulfate environments. The practical relevance of this is especially critical in regions where high-calcium ash is the only type of fly ash available. Research is needed to identify what specific characteristics of high-calcium fly ash impact sulfate resistance, from a chemical and mineralogical perspective, and guidance is needed on how to incorporate high-calcium fly ash in concrete in sulfate-rich environments.
American Concrete Institute, Journal of, Oct 1, 2016
The B3 Model is a compliance model that was designed and calibrated to estimate instantaneous and... more The B3 Model is a compliance model that was designed and calibrated to estimate instantaneous and time-dependent strain behavior of concrete with a loading age of 1 day or more. Modifications were developed to correct the B3 model for rapidly changing viscoelastic and elastic properties of early-age concrete between setting and 1 day. Early-age stress and mechanical property development of 72 concrete mixtures with different materials, mixture proportions, and temperature histories were measured and compared to early-age stresses calculated using the Modified B3 Model. The unbiased estimate of standard deviation decreased from 0.78 to 0.42 MPa (113 to 60 psi), and the coefficient of determination increased from 0.59 to 0.80 when predictions with the Modified B3 Model are compared to the unmodified B3 Model. This magnitude of improvement is similar to that obtained when the Modified B3 Model was originally developed, which thus validates the Modified B3 Model.
Sulfate attack is a complex form of deterioration that has damaged concrete structures throughout... more Sulfate attack is a complex form of deterioration that has damaged concrete structures throughout the world. Sulfate attack is particularly complex because the source of sulfates can be external or internal (delayed ettringite formation), and the distress can be chemical in nature, due to alteration of hydration of products, or physical in nature, due to phase changes in the penetrating sulfate solution. Although sulfate attack has been recognized as a cause of concrete distress for many years, it remains a controversial, confusing, and complex topic. There are many unresolved issues, far too many to be tackled in a single investigation. The research described in this report aims to address several of these lingering issues, especially those that are particularly relevant to the state of Texas.
An accurate and practical method of determining the heat development of concrete mixtures under r... more An accurate and practical method of determining the heat development of concrete mixtures under real mixing, cooling, hauling, placement, and curing conditions would greatly benefit contractors and engineers in helping predict in-place concrete member temperatures. Semi-adiabatic calorimetry was performed at several construction sites in temperature controlled rooms using concrete sampled from concrete placements. Semi-adiabatic calorimetry was also performed for comparison with concrete made under laboratory conditions from materials sampled at the respective batch plants. An energy balance-based finite difference method is presented for calculating the concrete non-linear heat generation using the measured heat of hydration determined from semi-adiabatic calorimetry. This method was used in a program which allows the direct input of values from semi-adiabatic calorimetry testing and estimates the development of in-place temperatures in mass concrete members of various geometries. Estimated concrete member temperatures are compared to the values measured on-site. Best practice suggestions are also given for performing semi-adiabatic calorimetry using concrete sampled on-site.
Although fly ash can and typically does impart benefits to concrete, several technical and practi... more Although fly ash can and typically does impart benefits to concrete, several technical and practical issues must still be addressed. First, all fly ashes are not created equally. The chemical/mineralogical/ physical properties can vary significantly from one source to another, based on differences in fuel sources (coal), combustion conditions, and cooling regimes. Furthermore, the fly ash industry is quite dynamic and is rapidly changing due to recently imposed environmental regulations. As such, fly ash produced from a given power plant may be considerably different than fly ash produced from the same plant just a few years ago. Therefore, it is becoming increasingly important to be able to characterize fly ash in a way that best predicts how it will perform in concrete. This is the primary focus of this project.
Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and t... more Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and thermal shrinkage), can have several detrimental effects on long-term behavior and durability. Cracking can also provide ingress of water that can drive chemical reactions, such as alkali-silica reaction (ASR) and sulfate attack. Because of the problems associated with cracking observed in bridge decks, and the impact of early-age cracking on long-term performance and durability, it is imperative that bridge decks be constructed with minimal early-age cracking and that exhibit satisfactory long-term performance and durability. To achieve these goals for bridges in the state of Texas, a research team has been assembled that possesses significant expertise and background in cement chemistry, concrete materials and durability, structural performance, computational mechanics (finite difference/element), bridge deck construction and maintenance, monitoring of in-site behavior of field structures, and the development of test methods and specifications aimed at practical implementation by state highway departments. This proposal describes a laboratory-and field-based research program aimed at developing a bridge deck cracking model that will ultimately be integrated into ConcreteWorks, a suite of software programs developed for TxDOT by this same research team. 17. Key Words Early-age cracking, drying shrinkage, bridge decks 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and t... more Early-age cracking, typically caused by drying shrinkage (and often coupled with autogenous and thermal shrinkage), can have several detrimental effects on long-term behavior and durability. Cracking can also provide ingress of water that can drive chemical reactions, such as alkali-silica reaction (ASR) and sulfate attack. Because of the problems associated with cracking observed in bridge decks, and the impact of early-age cracking on long-term performance and durability, it is imperative that bridge decks be constructed with minimal early-age cracking and that exhibit satisfactory long-term performance and durability. To achieve these goals for bridges in the state of Texas, a research team has been assembled that possesses significant expertise and background in cement chemistry, concrete materials and durability, structural performance, computational mechanics (finite difference/element), bridge deck construction and maintenance, monitoring of in-site behavior of field structures, and the development of test methods and specifications aimed at practical implementation by state highway departments. This proposal describes a laboratory-and field-based research program aimed at developing a bridge deck cracking model that will ultimately be integrated into ConcreteWorks, a suite of software programs developed for TxDOT by this same research team. 17. Key Words Early-age cracking, drying shrinkage, bridge decks 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Early-age bridge deck cracking has been found to be a prevalent problem worldwide. While early-ag... more Early-age bridge deck cracking has been found to be a prevalent problem worldwide. While early-age cracking will not cause failure of a bridge deck system independently, the penetration of deleterious substances through the early-age cracks into the bridge deck concrete and the bridge superstructure can lead to costly serviceability issues, and possibly the loss of some structural integrity. This report describes research undertaken to evaluate the various factors affecting bridge deck cracking, and the results of this project have been implemented in a new bridge deck cracking module for ConcreteWorks, a software program that addresses a range of concrete properties and performance issues. 17. Key Words ConcreteWorks, bridge, deck cracking, strengthening 18. Distribution Statement No restrictions. This document is available to the public through the National Technical Information Service, Springfield, Virginia 22161; www.ntis.gov. 19. Security Classif. (of report) Unclassified 20. Security Classif.
Alkali-silica reaction (ASR) is a significant durability problem that has resulted in premature d... more Alkali-silica reaction (ASR) is a significant durability problem that has resulted in premature deterioration of various types of concrete structures in the United States and throughout the world. Although several viable methods exist to prevent AST-induced damage in new concrete structures, very few methods mitigate further damage in structures already affected by ASR-induced expansion and cracking. Lithium compounds have been recognized for more than 50 years as effectively preventing expansion due to ASR, and there has been renewed interest in recent years in using lithium compounds as either an admixture in new concrete or as a treatment of existing structures. This report is intended to provide practitioners with the necessary information and guidance to test, specify, and use lithium compounds in new concrete construction, as well as in repair and and service life extension applications. This report first provides a basic overview of ASR, including information on mechanisms, symptoms of ASR damage in field structures, mitigation approaches, test methods, and specifications. A comprehensive summary of lithium compounds is provided next, including information on their production, availability, and use in laboratory concrete studies and field applications (including a range of case studies). Guidelines for using lithium compounds as an admixture in new concrete and for treating existing structures suffering from ASR-induced damage then are presented, including information on how to assess the efficacy of lithium compounds in laboratory tests. Some basic information also is provided on the economics of using lithium both in new concrete and as a treatment for existing structures. Finally, the report provides a summary of conclusions and identifies several technical and practical issues that should be considered for future laboratory studies and field applications.
In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limeston... more In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limestone cements and their combinations with 30-50 % slag were examined at both 5 and 23°C according to CSA A3004-C8 (similar to ASTM C1012). Also, XRD was used to identify the phases formed after sulfate attack. It was found that in 23°C exposure, while 100 % cement mixes deteriorated due to conventional ettringite-based sulfate attack, partially replacing the cements with 30 or 50 % slag was effective in making the mixes highly sulfate-resistant. At 5°C, all of the 100 % cement mortar bars expanded more than the test limits and eventually completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30 % slag was only effective in controlling the deterioration for Portland cements but not Portland-limestone cements. However, all the Portland-limestone cements with 50 % slag were resistant to the thaumasite form of sulfate attack after 2 years.
In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limeston... more In this study, the sulfate resistance of five different high-C 3 A Portland and Portland-limestone cements and their combinations with 30-50 % slag were examined at both 5 and 23°C according to CSA A3004-C8 (similar to ASTM C1012). Also, XRD was used to identify the phases formed after sulfate attack. It was found that in 23°C exposure, while 100 % cement mixes deteriorated due to conventional ettringite-based sulfate attack, partially replacing the cements with 30 or 50 % slag was effective in making the mixes highly sulfate-resistant. At 5°C, all of the 100 % cement mortar bars expanded more than the test limits and eventually completely disintegrated due to the formation of thaumasite. Partially replacing cement with 30 % slag was only effective in controlling the deterioration for Portland cements but not Portland-limestone cements. However, all the Portland-limestone cements with 50 % slag were resistant to the thaumasite form of sulfate attack after 2 years.
This report describes the evaluation of Class C fly ash in sulfate environments. The practical re... more This report describes the evaluation of Class C fly ash in sulfate environments. The practical relevance of this is especially critical in regions where high-calcium ash is the only type of fly ash available. Research is needed to identify what specific characteristics of high-calcium fly ash impact sulfate resistance, from a chemical and mineralogical perspective, and guidance is needed on how to incorporate high-calcium fly ash in concrete in sulfate-rich environments.
American Concrete Institute, Journal of, Oct 1, 2016
The B3 Model is a compliance model that was designed and calibrated to estimate instantaneous and... more The B3 Model is a compliance model that was designed and calibrated to estimate instantaneous and time-dependent strain behavior of concrete with a loading age of 1 day or more. Modifications were developed to correct the B3 model for rapidly changing viscoelastic and elastic properties of early-age concrete between setting and 1 day. Early-age stress and mechanical property development of 72 concrete mixtures with different materials, mixture proportions, and temperature histories were measured and compared to early-age stresses calculated using the Modified B3 Model. The unbiased estimate of standard deviation decreased from 0.78 to 0.42 MPa (113 to 60 psi), and the coefficient of determination increased from 0.59 to 0.80 when predictions with the Modified B3 Model are compared to the unmodified B3 Model. This magnitude of improvement is similar to that obtained when the Modified B3 Model was originally developed, which thus validates the Modified B3 Model.
Sulfate attack is a complex form of deterioration that has damaged concrete structures throughout... more Sulfate attack is a complex form of deterioration that has damaged concrete structures throughout the world. Sulfate attack is particularly complex because the source of sulfates can be external or internal (delayed ettringite formation), and the distress can be chemical in nature, due to alteration of hydration of products, or physical in nature, due to phase changes in the penetrating sulfate solution. Although sulfate attack has been recognized as a cause of concrete distress for many years, it remains a controversial, confusing, and complex topic. There are many unresolved issues, far too many to be tackled in a single investigation. The research described in this report aims to address several of these lingering issues, especially those that are particularly relevant to the state of Texas.
An accurate and practical method of determining the heat development of concrete mixtures under r... more An accurate and practical method of determining the heat development of concrete mixtures under real mixing, cooling, hauling, placement, and curing conditions would greatly benefit contractors and engineers in helping predict in-place concrete member temperatures. Semi-adiabatic calorimetry was performed at several construction sites in temperature controlled rooms using concrete sampled from concrete placements. Semi-adiabatic calorimetry was also performed for comparison with concrete made under laboratory conditions from materials sampled at the respective batch plants. An energy balance-based finite difference method is presented for calculating the concrete non-linear heat generation using the measured heat of hydration determined from semi-adiabatic calorimetry. This method was used in a program which allows the direct input of values from semi-adiabatic calorimetry testing and estimates the development of in-place temperatures in mass concrete members of various geometries. Estimated concrete member temperatures are compared to the values measured on-site. Best practice suggestions are also given for performing semi-adiabatic calorimetry using concrete sampled on-site.
Although fly ash can and typically does impart benefits to concrete, several technical and practi... more Although fly ash can and typically does impart benefits to concrete, several technical and practical issues must still be addressed. First, all fly ashes are not created equally. The chemical/mineralogical/ physical properties can vary significantly from one source to another, based on differences in fuel sources (coal), combustion conditions, and cooling regimes. Furthermore, the fly ash industry is quite dynamic and is rapidly changing due to recently imposed environmental regulations. As such, fly ash produced from a given power plant may be considerably different than fly ash produced from the same plant just a few years ago. Therefore, it is becoming increasingly important to be able to characterize fly ash in a way that best predicts how it will perform in concrete. This is the primary focus of this project.
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