Browsing by Subject "Alkali-silica reaction"
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Item ASR/DEF-damaged bent caps: shear tests and field implications(2009-12) Deschenes, Dean Joseph; Bayrak, Oguzhan, 1969-; Folliard, Kevin J.Over the last decade, a number of reinforced concrete bent caps within Houston, Texas have exhibited premature concrete damage (cracking, spalling and a loss of material strength) due to alkali-silica reaction (ASR) and/or delayed ettringite formation (DEF). The alarming nature of the severe surface cracking prompted the Houston District of the Texas Department of Transportation to initiate an investigation into the structural implications of the premature concrete damage. Specifically, an interagency contract with the University of Texas at Austin charged engineers at Ferguson Structural Engineering Laboratory to: 1. Establish the time-dependent relationship between ASR/DEF deterioration and the shear capacity of affected bridge bent caps. 2. Develop practical recommendations for structural evaluation of in-service bridge bent caps affected by ASR and/or DEF. To accomplish these objectives, six large-scale bent cap specimens were fabricated within the laboratory. Four of the specimens (containing reactive concrete exposed to high curing temperatures) represented the most severe circumstances of deterioration found in the field. The remaining two specimens (non-reactive) provided a basis for the comparison of long-term structural performance. All of the specimens were subjected to a conditioning regimen meant to foster the development of realistic ASR/DEF-related damage. Resulting expansions were characterized over the course of the study through a carefully-planned monitoring program. Following a prolonged exposure period, three of the six bent cap specimens (representing undamaged, mild, and moderate levels of deterioration) were tested in shear. Observations made over the course of each test captured the service and ultimate load effects of ASR/DEF-induced deterioration. Six shear-critical spans were tested prior to this publication: three deep beam and three sectional shear tests. The remaining six shear spans (contained within the remaining three specimens) were retained to establish the effects of severe deterioration through future shear testing. Subsequent analysis of the expansion monitoring and shear testing data provided much needed insight into the performance and evaluation of ASR/DEF damaged bent structures. The results ultimately formed a strong technical basis for the preliminary assessment of a damaged bent structure within Houston, Texas.Item Durability of calcium-aluminate based binders for rapid repair applications(2016-05) Lute, Racheal Dawn; Folliard, Kevin J.; Thomas, Michael D.A.; Fowler, David W; Juenger, Maria C.G.; Wheat, Harovel G.Within the last few decades, the amount of vehicle miles traveled within the US has increased approximately 40% with the construction of new roads only increasing 4% during this same time period. This dramatic increase in traffic on existing infrastructure has led to the rapid decline of the condition our nation’s roads resulting in the increased need for maintenance and repair. Rapid hardening repair materials are in high demand for these applications as they allow for minimal traffic delays and road closures. Calcium aluminate cement (CAC) is a rapid hardening binder that is used for specialty applications where high early strength and increased durability are desired. In recent years, blended cement systems incorporating both CAC and calcium sulfate (C$) with portland cement (PC) have been developed to utilize the rapid hardening characteristics of CAC but at a reduced cost. While the durability of CAC is well researched and documented, the durability of these new blended systems is not yet fully understood. The focus of this research was to evaluate the performance and long term durability of various blended systems which utilize CAC or calcium sulfoaluminate cement (CSA) to attain rapid hardening. More specifically, these systems were evaluated to determine their resistance to common modes of concrete deterioration such as alkali-silica reaction, external sulfate attack, delayed ettringite formation, carbonation, and corrosion in marine environments through in-situ lab methods and large scale outdoor exposure. The results of the testing conducted related to alkali-silica reaction, external sulfate attack, and delayed ettringite formation identified the potential for large levels of expansion in blended systems of PC:CAC:C$ and PC:CSA. Details regarding each mode of deterioration and mechanisms of expansion are discussed.Item Evaluation of concrete structures affected by alkali-silica reaction and delayed ettringite formation(2012-08) Giannini, Eric Richard; Zhu, Jinying; Folliard, Kevin J.; Bayrak, Oguzhan; Fowler, David W.; Fournier, Benoit; Rivard, PatriceAlkali-silica reaction (ASR) and delayed ettringite formation (DEF) are expansive reactions that can lead to the premature deterioration of concrete structures. Both have been implicated in the deterioration of numerous structures around the world, including many transportation structures in Texas. As a result of considerable research advances, ASR and DEF are now avoidable in new construction, but evaluating and managing the existing stock of structures damaged by these mechanisms remains a challenge. While the published guidance for evaluating structures is very effective at diagnosing the presence of ASR and DEF, there remain significant weaknesses with respect to the evaluation of structural safety and serviceability and nondestructive testing (NDT) is a minor component of the evaluation process. The research described in this dissertation involved a wide range of tests on plain and reinforced concrete at multiple scales. This included small cylinders and prisms, larger plain and reinforced concrete specimens in outdoor exposure, full-scale reinforced concrete beams, and core samples from the outdoor exposure specimens and full-scale reinforced concrete beams. Nondestructive test methods were applied at all scales, and the full-scale beams were also tested in four-point flexure to determine the effects of ASR and DEF on flexural strength and serviceability. Severe expansions from ASR and DEF did not reduce the strength of the full-scale beams or result in excessive deflections under live loads, despite significant decreases in the compressive strength and elastic modulus measured from core samples. Most NDT methods were found to be effective at low expansions but had difficulty correlating to larger expansions. Two promising NDT methods have been identified for future research and development, and guidance regarding existing test methods is offered.Item Expansion behavior of reinforced concrete elements due to alkali-silica reaction(2016-08) Allford, Morgan Therese; Bayrak, Oguzhan, 1969-; Hrynyk, TrevorThe influence of reinforcement on the development and distribution of multiaxial expansions in reinforced concrete elements due to alkali-silica reaction (ASR) requires further research. Understanding how passive restraint provided by reinforcement in a given direction may simultaneously affect expansions in that direction as well as in other reinforced or unreinforced directions is important for assessment of ASR-affected structures. Few experimental studies to date have endeavored to monitor expansions in more than one direction for field-scale reinforced concrete specimens. A parametric study at The University of Texas at Austin was conducted in which thirty-three 19 in. reinforced concrete cubes were fabricated and monitored for ongoing ASR expansions. The cubes had variable uniaxial, biaxial, and triaxial reinforcement layouts and ratios. Three concrete mixtures of varying reactivity, controlled by altering the types of coarse and fine aggregate, were used. The cubes were conditioned in an outdoor, climate-monitored environmental facility and were regularly measured in three orthogonal directions to track expansions. The expansions monitored physically corresponded to micro- and macro-cracks that form due to ASR. The specimens exhibited typical surface cracking due to ASR. Random “map cracking” occurred on the surfaces of the triaxially restrained and unreinforced specimens. Large, discrete surface cracks formed between layers of reinforcement for the uniaxially and biaxially restrained specimens as the specimens expanded in the unreinforced directions. Cylinder tests were performed over the course of the program to gauge material property degradation due to ASR-induced expansions; however, due to the small size and fluctuating conditioning of the cylinders the results from these tests were not considered representative of the material property degradation associated with the cube specimens. Prism expansion monitoring was used to predict the free expansion potential of the cube specimens under idealized ASR conditioning. However, much like with mechanical property degradation, the small size and differential conditioning of the prisms limited effective correlation of prism expansions to cube specimen expansions. This study primarily focused on the development of ASR-induced reinforced concrete expansions over time. Cubes fabricated from the three mixes exhibited variable expansions due to the different reactivities of the coarse and fine aggregates; however, the use of different mixes did not change the overall axial expansion distribution trends documented across all specimens. Expansions in unreinforced directions exceeded those of the reinforced directions in all specimens. The rate of expansion of the reinforced directions of the uniaxially and biaxially restrained specimens was reduced once the expansion of the restrained axes reached and exceeded the steel yield strain. The unreinforced and triaxially reinforced specimens exhibited similar proportional axial expansions in all directions; however, the reinforcement did reduce expansions. Analysis of the axial distribution of volumetric expansions, i.e. the summation of the axial expansions, made it possible to remove the influence of concrete mixture reactivity and variable moisture and temperature conditioning during the timeline of specimen production and placement within the storage facility. The axial expansion distribution trends depicted the axial expansions influenced by the reinforcement and not the conditioning of the specimens. This permitted the development of expansion trends that were solely impacted by axial reinforcement conditions, and were independent of other extraneous factors.Item Experimental investigation of ASR/DEF-induced reinforcing bar fracture(2011-12) Webb, Zachary David; Bayrak, Oguzhan, 1969-; Zhu, Jinying; Jirsa, James O.Numerous cases of premature concrete deterioration due to alkali-silica reaction and/or delayed ettringite formation have developed within highway infrastructure in the state of Texas over the past two decades. Although experimental research and in-situ load testing on an international scale has indicated that moderate levels of deterioration are unlikely to pose a threat to structural safety, the discovery of reinforcing bar fracture in Japan due to ASR-related expansion has called into question the integrity of heavily damaged structures. A two-part experimental program was conducted at The University of Texas at Austin relating to ASR/DEF-induced reinforcing bar fracture. Work conducted under TxDOT Project 0-6491 included the fabrication and monitoring of four concrete specimens. Methods were employed to simulate a fracture of the transverse reinforcement within the time frame of the study and the applicability of various NDT monitoring techniques to detect bar fracture was evaluated. Furthermore, a number of reinforcing bar samples were tested and analyzed to investigate (1) the development of reinforcing bar cracking due to the bending operation and (2) the progression of cracks after application of an expansive opening force on bars with 90° bends. Research findings and conclusions form a preliminary assessment on the potential for reinforcing bar fracture within affected infrastructure in Texas.Item Experimental studies of the behavior of 'pessimum' aggregates in different test procedures used to evaluate the alkali reactivity of aggregates in concrete(2012-05) Arrieta Martinez, Gloriana; Folliard, Kevin J.; Drimalas, ThanoAlkali-silica reaction (ASR) is a common deterioration mechanism responsible for numerous concrete durability issues. Since ASR was first discovered in the 1940's, a significant number of investigations have been carried out in order to understand its mechanisms. However, due to the complexity of the reaction and to the numerous factors that affect its development, many aspects still remain unexplained. The research described in this document was funded by the Texas Department of Transportation (TxDOT), and it focused on a specific type of reactive aggregates, known as 'pessimum'; they present an unexpected behavior with respect to the relation between the amount of material present in the mixture and the extent of ASR related damage. The main objective of this investigation was to determine a method for identifying aggregates that exhibit the 'pessimum' behavior by means of a short-term testing regime. Modified versions of the Accelerated Mortar Bar Test (AMBT) and the Concrete Microbar Test (CMBT) were considered for this purpose. In addition, the behavior of a selected group of 'pessimum' aggregates in the Concrete Prism Test (CPT) and the Chemical Method was evaluated. The petrographic characteristics for a reduced number of the aggregates studied were linked to their performance in the ASR tests. The results obtained from the experimental program conducted were combined with results from previous investigations performed at UT Austin to draw conclusions about the overall behavior of ‘pessimum’ aggregates. ‘Pessimum’ aggregates were successfully identified with a modification proposed to the AMBT. As for their behavior, it was found that depending on the amount of reactive constituents present in each test, these aggregates are classified as reactive (for low chert contents) or as non-reactive (for chert contents above the 'pessimum' proportion). Whether these aggregates will generate durability problems depends on the amount of reactive silica in the concrete mixture.Item An investigation of means of mitigating alkali-silica reaction in hardened concrete(2013-05) Markus, Reid Patrick; Folliard, Kevin J.This research project, funded by the Federal Highway Administration (FHWA Project DTFH61-02-C-0097), focuses mainly on alkali-silica reaction (ASR) and techniques to mitigate the effects of alkali-silica reaction in hardened concrete. A large portion of this report discusses the construction and design of an outdoor exposure site built at the University of Texas at Austin where the goal was to cast field representative concrete elements with laboratory precision and expose them to real environmental conditions. The elements were monitored for expansion and deterioration. At discrete expansion levels a range of mitigation methods were implemented on the structures. After the concrete elements were treated, long-term monitoring was conducted to determine the best approach to provide effective suppression of alkali-silica reaction in the various element types.Item An investigative study on physical sulfate attack and alkali-silica reaction test methods(2011-05) Lowe, Travis Evans; Folliard, Kevin J.This thesis is unique in that it investigated two completely different forms of concrete deterioration: physical sulfate attack and the alkali-silica reaction (ASR). Research was undertaken to better understand physical sulfate attack in order to provide much needed guidance on how to prevent durable this form of deterioration. A testing regime was designed to evaluate and analyze different concrete mixtures with varying water to cementitious material ratios (w/cm), cement types (Type I and V), and use of supplementary cementing materials (SCMs) in accelerated laboratory exposure and outdoor exposure testing. The accelerated laboratory testing evaluated the performance of concrete cylinder segments fully submerged in 30% (by mass of solution) sodium sulfate solution exposed to a temperature and humidity cycle that would promote cycles of alternative conversion between anhydrous sodium sulfate (thenardite) and decahydrate sodium sulfate (mirabilite). In the outdoor exposure site, two different sized concrete cylinders per mixture proportion were partially submerged in 5% (33,000 ppm) sodium sulfate solution and exposed to alternative wetting and drying conditions, along with, temperature fluctuations that would promote conversion between thenardite (Na2SO4) and mirabilite (Na2SO4∙10H2O). With regard to ASR test methods, it has been shown with past research that it is not possible to evaluate “job mixtures” or determine alkali thresholds using ASTM C 1293 (Concrete Prism Test) with evaluating aggregates and concrete mixture proportions for the susceptibility of ASR when testing job mixtures. The most commonly cited issue with the concrete prism test is excessive leaching of alkalis during the course of the test, which may not be a major issue when using the standard, high-alkali concrete mixtures as per ASTM C 1293 but is clearly an issue when testing lower-alkali concrete mixtures. For low-alkali mixtures, alkali leaching can reduce the internal alkali content below the threshold that triggers expansion for a given aggregate. A comprehensive study was initiated that evaluated various modifications to ASTM C 1293, with the intention of developing a testing regime better suited to testing “job mixes” and/or low-alkali concrete mixtures.Item Nondestructive evaluation of reinforced concrete structures affected by alkali-silica reaction and delayed ettringite formation(2011-08) Kreitman, Kerry Lynn; Zhu, Jinying; Folliard, Kevin J.Alkali-silica reaction (ASR) and delayed ettringite formation (DEF) deterioration have been a problem for the concrete infrastructure in the state of Texas and around the world in recent decades. A great deal of research into the causes and mechanisms of the deterioration has helped to prevent the formation of ASR and DEF in new construction, but the evaluation and maintenance of existing structures remains a problem. The goal of this research is to investigate the use of several nondestructive testing (NDT) methods to evaluate the level of ASR and DEF deterioration in a structural element. Based on the results, recommendations are made as to which NDT methods have the most potential to be incorporated into the evaluation process.Item Shear performance of ASR/DEF damaged prestressed concrete trapezoidal box bridge girders(2010-08) Wang, Tz-Wei; Jirsa, J. O. (James Otis); Bayrak, Oguzhan; Ghannoum, Wassim M.; Wheat, Harovel G.; Zhu, JinyingConcrete bridges in Texas have developed large cracks in bent caps and pretensioned trapezoidal bridge girders. The bridges show premature concrete deterioration due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF). There is concern that deterioration due to ASR/DEF may lead to a loss of structural capacity. However, there are no quantitative guidelines to relate the level of concrete deterioration due to ASR/DEF to structural performance. Using such guidelines, the need for rehabilitation of beams with ASR/DEF cracking can be assessed. The goal of this research was to determine the shear capacity of pretensioned trapezoidal box girder specimens exhibiting varying degrees of ASR and/or DEF cracking and to use the shear testing results to evaluate the severity of the problem that may exist in Texas bridge structures. To achieve this goal, beams that were severely deteriorated due to ASR/DEF over a period of more than ten years were transported to the University of Texas for testing to failure. Both severely deteriorated and uncracked beams were tested in shear. The test results were used to evaluate the shear performance of trapezoidal box beams affected by ASR/DEF. In addition, three different types of forensic analyses were conducted on the beams to understand the nature of the ASR/DEF cracks and severity of the deterioration. After testing, it is found that the shear capacity of the test specimens was not significantly reduced even with heavy ASR/DEF cracking. Assessment using current US design provisions for bridges or buildings (ACI 318-08 and AASHTO LRFD 2008) and the proposed provision from an earlier project (TxDOT Project 5253) yielded conservative estimates of strength. Results from forensic analyses provided a qualitative indication of ASR/DEF damage but did not correlate with the observed levels of ASR/DEF deterioration.Item Structural performance of ASR/DEF damaged prestressed concrete trapezoidal box beams with dapped ends(2010-08) Larson, Nancy Anne, 1986-; Bayrak, Oguzhan, 1969-; Jirsa, James O.Across the State of Texas and many other areas of the world, relatively young concrete structures have developed signs of premature concrete deterioration. Large cracks form on the surface of the concrete due to expansive forces from alkali-silica reaction (ASR) and delayed-ettringite formation (DEF). The goal of this project is to assess the effect of ASR/DEF on the trapezoidal box beam bridges in the US 59 corridor and Katy Central Business District (CBD) HOV lanes in Houston, TX. Five dapped-end beams were rejected during the casting process and have been in storage at a local precast yard for nearly fifteen years. These beams have been subject to accelerated deterioration and represent the potential severity of the ongoing ASR/DEF distress within the dapped end regions of the in-service trapezoidal box beams. The results from five load tests, corresponding strut-and-tie models, and forensic investigation are used to provide insights into the relationship between the severity of the deterioration and the capacity margin.Item Tensile behavior of expansion and undercut anchors in concrete affected by alkali-silica reaction(2014-08) Neuhausen, Alissa; Bayrak, Oguzhan, 1969-; Eaton, David J.This thesis addresses the tensile capacity and load-deflection behavior of wedge-type expansion and undercut anchors in concrete affected by alkali-silica reaction (ASR). ASR is a chemical reaction that occurs between alkalis in the cement and silica in the aggregates. The reaction occurs with the presence of moisture, forming a gel which expands and causes micro-cracking in the concrete. Researchers conducted 85 static unconfined tensile tests on control and ASR-affected specimens. The results indicate that anchors in concrete cracked due to ASR perform like anchors in concrete cracked due to other mechanisms. Up to a threshold value of the Comprehensive Crack Index (CCI) of at least 1.5 mm/m, all cracking, regardless of cause, has the same effect on the tensile breakout capacity of mechanical and undercut anchors.