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Tensile behavior of expansion and undercut anchors in concrete affected by alkali-silica reactionNeuhausen, Alissa 30 September 2014 (has links)
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. / text
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Development of a Reaction Signature for Combined Concrete MaterialsGhanem, Hassan A. 2009 May 1900 (has links)
Although concrete is widely considered a very durable material, if conditions are such, it
can be vulnerable to deterioration and early distress development. Alkali-Silica Reaction
(ASR) is a major durability problem in concrete structures. It is a chemical reaction
between the reactive silica existent in some types of rocks and alkali hydroxides in the
concrete pore water. The product of this reaction is a gel that is hygroscopic in nature.
When the gel absorbs moisture, it swells leading to tensile stresses in concrete. When
those stresses exceed the tensile strength of concrete, cracks occur. The main objective of
this study was to address a method of testing concrete materials as a combination to assist
engineers to effectively mitigate ASR in concrete. The research approach involved
capturing the combined effects of concrete materials (water cement ratio, porosity,
supplementary cementitious materials, etc.) through a method of testing to allow the
formulation of mixture combinations resistant to ASR leading to an increase in the life
span of concrete structures.
To achieve this objective, a comprehensive study on different types of aggregates
of different reactivity was conducted to formulate a robust approach that takes into
account the factors affecting ASR; such as, temperature, moisture, calcium concentration
and alkalinity. A kinetic model was proposed to determine aggregate ASR characteristics
which were calculated using the System Identification Method. Analysis of the results
validates that ASR is a thermally activated process and therefore, the reactivity of an
aggregate can be characterized in terms of its activation energy (Ea) using the Arrhenius
equation. Statistical analysis was conducted to determine that the test protocol is highly
repeatable and reliable.
To relate the effect of material combinations to field performance, concrete
samples with different w/cm?s and fly ash contents using selective aggregates were tested
at different alkalinities. To combine aggregate and concrete characteristics, two models were proposed and combined. The first model predicts the Ea of the aggregate at levels of
alkalinity similar to field conditions. The second model, generated using the Juarez-
Badillo transform, connects the ultimate expansion of the concrete and aggregate, the
water cement ratio, and the fly ash content to the Ea of the rock. The proposed models
were validated through laboratory tests. To develop concrete mixtures highly resistant to
ASR, a sequence of steps to determine threshold total alkali in concrete were presented
with examples. It is expected that the knowledge gained through this work will assist
government agencies, contractors, and material engineers, to select the optimum mixture
combinations that fits best their needs or type of applications, and predict their effects on
the concrete performance in the field.
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Performance-based approach to evaluate alkali-silica reaction potential of aggregate and concrete using dilatometer methodShon, Chang Seon 15 May 2009 (has links)
The undesirable expansion of concrete because of a reaction between alkalis and certain type of reactive siliceous aggregates, known as alkali-silica reactivity (ASR), continues to be a major problem across the entire world. The renewed interest to minimize distress resulting from ASR has emphasized the need to develop predictable modeling of concrete ASR behavior under field conditions. Current test methods are either incapable or need long testing periods in which to only offer rather limited predictive estimates of ASR behavior in a narrow and impractical band of field conditions. Therefore, an attempt has been made to formulate a robust performance approach based upon basic properties of aggregate and concrete ASR materials derived from dilatometry and a kinetic-based mathematical expressions for ASR behavior. Because ASR is largely an alkali as well as a thermally activated process, the use of rate theory (an Arrhenius relationship between temperature and the alkali solution concentration) on the dilatometer time-expansion relationship, provides a fundamental aggregate ASR material property known as “activation energy.” Activation energy is an indicator of aggregate reactivity which is a function of alkalinity, particle size, crystallinity, calcium concentration, and others. The studied concrete ASR material properties represent a combined effects of mixture related properties (e.g., water-cementitious ratio, porosity, presence of supplementary cementitious materials, etc.) and maturity. Therefore, the proposed performance-based approach provides a direct accountability for a variety of factors that affect ASR, such as aggregate reactivity (activation energy), temperature, moisture, calcium concentration, solution alkalinity, and water-cementitious material ratio. Based on the experimental results, the following conclusion can be drawn concerning the performance-based approach to evaluate ASR potential of aggregate and concrete using dilatometer method; (i) the concept of activation energy can be used to represent the reactivity of aggregate subjected to ASR, (ii) the activation energy depends on the reactivity of aggregate and phenomenological alkalinity of test solution, and (iii) The proposed performance-based model provides a means to predict ASR expansion development in concrete.
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Effects of Lithium Nitrate Admixture on Early Age Concrete BehaviorMillard, Marcus J. 11 July 2006 (has links)
Alkali silica reaction (ASR), a reaction which occurs between reactive siliceous mineral components in the aggregate and the alkaline pore solution in concrete, is responsible for substantial damage to concrete structures in the U. S. and across the world. Lithium admixtures, including lithium nitrate (LiNO3), have been demonstrated to mitigate ASR damage, and are of particular interest for use in concrete airfield pavement construction, where ASR damage has been recently linked to the use of certain de-icing chemicals. Although the effectiveness of lithium admixtures at ASR-mitigation is well-researched, relatively less is known regarding the potential effects, including negative effects, on overall concrete behavior. The goal of this research is to better understand the influence of LiNO3 admixture on early age concrete behavior, and to determine if a maximum dosage rate for its use exists.
Isothermal calorimetry, rheology and bleed water testing, time of setting, chemical shrinkage, autogenous shrinkage, free and restrained concrete shrinkage, and compressive and flexural strength were measured for pastes and concretes prepared with a range of LiNO3 dosages (i.e., 0, 50, 100, 200, and 400% of the recommended dosage). In addition, the interaction of LiNO3 with cement was evaluated by comparing results obtained with six cements of varying alkali and tricalcium aluminate (C3A) contents. Additionally, one of these cements, was examined alone and with 20% by weight Class F fly ash replacement.
Results indicate that the hydration of the tricalcium silicate and tricalcium aluminate components of cement are accelerated by the use of LiNO3, and that low alkali cements (typically specified to avoid damage by ASR) may be particularly susceptible to this acceleration. However, inclusion of Class F fly ash at 20% by weight replacement of cement (also common in applications where ASR is a concern) appears to diminish these possibly negative effects of LiNO3 on early age hydration acceleration and heat generation. Dosages higher than the current standard dosage of LiNO3 may have minor effects on fresh concrete workability, causing slight decreases in Bingham yield stress, corresponding to slightly higher slump. Fresh concrete viscosity may also be affected, though more research is necessary to confirm this effect. LiNO3 had no effect on quantity of bleed water in the mixes tested. Generally, LiNO3 had no effect on initial and final setting times, although increasing dosages caused faster set times in the lowest alkali (Na2Oeq = 0.295%) cement examined. In shrinkage testing, higher LiNO3 dosages appeared to cause initial expansion in some sealed paste specimens, but in all cases the highest dosage led to greater autogenous shrinkage after 40 days. In concrete specimens, however, the restraining effect of aggregates diminished shrinkage, and no effect of the LiNO3 was apparent. In no cases, with any dosage of lithium tested, with or without fly ash replacement, did restrained shrinkage specimens show any cracking. Strength testing produced mixed results, with laboratory specimens increasing in 28-day compressive strength, but companion specimens cast in the field and tested by an outside laboratory, exhibited lower 28-day compressive strength, with increasing lithium dosages. Flexural specimens, also cast in the field and tested by an outside laboratory, appeared to show an increase in 28-day flexural strength with increasing lithium dosages. However, because of the conflicting results when comparing the various strength data, further research is necessary for conclusive evidence of LiNO3 effects on concrete strength.
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Performance-based approach to evaluate alkali-silica reaction potential of aggregate and concrete using dilatometer methodShon, Chang Seon 15 May 2009 (has links)
The undesirable expansion of concrete because of a reaction between alkalis and certain type of reactive siliceous aggregates, known as alkali-silica reactivity (ASR), continues to be a major problem across the entire world. The renewed interest to minimize distress resulting from ASR has emphasized the need to develop predictable modeling of concrete ASR behavior under field conditions. Current test methods are either incapable or need long testing periods in which to only offer rather limited predictive estimates of ASR behavior in a narrow and impractical band of field conditions. Therefore, an attempt has been made to formulate a robust performance approach based upon basic properties of aggregate and concrete ASR materials derived from dilatometry and a kinetic-based mathematical expressions for ASR behavior. Because ASR is largely an alkali as well as a thermally activated process, the use of rate theory (an Arrhenius relationship between temperature and the alkali solution concentration) on the dilatometer time-expansion relationship, provides a fundamental aggregate ASR material property known as “activation energy.” Activation energy is an indicator of aggregate reactivity which is a function of alkalinity, particle size, crystallinity, calcium concentration, and others. The studied concrete ASR material properties represent a combined effects of mixture related properties (e.g., water-cementitious ratio, porosity, presence of supplementary cementitious materials, etc.) and maturity. Therefore, the proposed performance-based approach provides a direct accountability for a variety of factors that affect ASR, such as aggregate reactivity (activation energy), temperature, moisture, calcium concentration, solution alkalinity, and water-cementitious material ratio. Based on the experimental results, the following conclusion can be drawn concerning the performance-based approach to evaluate ASR potential of aggregate and concrete using dilatometer method; (i) the concept of activation energy can be used to represent the reactivity of aggregate subjected to ASR, (ii) the activation energy depends on the reactivity of aggregate and phenomenological alkalinity of test solution, and (iii) The proposed performance-based model provides a means to predict ASR expansion development in concrete.
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The Effects of Using Alkali-Silica Reaction Affected Recycled Concrete Aggregate in Hot Mix AsphaltGeiger, Brian James 2010 August 1900 (has links)
The effects of using alkali-silica reaction (ASR) affected recycled concrete
aggregate (ASR-RCA) in hot mix asphalt (HMA) were investigated in this study.
Dilatometer and modified beam tests were performed to determine the possibility of new
ASR occurring in reactive aggregates within the HMA or re-expansion of existing gel.
The Lottman test and micro-calorimeter were used to determine the moisture
susceptibility of HMA made with ASR-RCA. A differential scanning calorimeter
(DSC) with thermogravimetric analysis (TGA) was used to evaluate the drying of an
artificial gel and x-ray diffraction (XRD) was used to check for the potential presence of
gel in the filler fraction of the ASR-RCAs. Micro-deval and freeze-thaw tests were
evaluated for their potential to indicate the presence of excess micro-cracks or ASR gel.
Expansion testing indicated that both ASR-RCAs were still reactive with 0.5 N
NaOH solution saturated with calcium hydroxide (CH) at 60 degrees C. Dilatometer testing of
HMA specimens in NaOH CH solution at 60 degrees C indicated a reaction between the asphalt
binder and the solution, but little, if any, ASR. The lack of expansion in the modified
beam test supports the binder-solution interaction. However, dilatometer testing in
deicer solution at the same temperature indicated that some ASR may have occurred
along with the primary binder-solution interaction. The volume change characteristics
associated with the binder-solution interaction with and without ASR was supported by
the change in pH and alkali concentration of the test solution.
DSC/TGA testing indicated that the artificial gel dehydrated at approximately
100 degrees C. XRD analysis of the filler indicated that some gel may have accumulated in this
fraction. Moisture damage testing indicated good resistance to moisture damage by
HMA mixtures made with ASR-RCA especially compared to a virgin siliceous
aggregate. Micro-deval and freeze-thaw tests can detect the presence of micro-cracks
due to ASR in ASR-RCAs as higher mass loss than the virgin aggregate.
The potential distress mechanisms that may occur when using ASR-RCA in an
HMA pavement were identified. Results obtained using accelerated laboratory
conditions were extrapolated based on anticipated field conditions. Guidelines for the
mitigation of potential distresses in HMA made with ASR-RCA are presented.
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Nondestructive evaluation of reinforced concrete structures affected by alkali-silica reaction and delayed ettringite formationKreitman, Kerry Lynn 29 September 2011 (has links)
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. / text
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Alternative Test Methods for Evaluating Fly Ash for use in Concretede Groot, Andre Pieter 23 August 2011 (has links)
Fly Ash was tested in relation to its ability to mitigate alkali-silica reaction, its contribution to strength, electrical resistance and heat release with the aim of recommending improvements to fly ash specifications. ASTM C 1567 accelerated mortar bar test results were in agreement with an expansion limit of 0.10 % at 14 days. A non-standard alkali leaching test showed that with high alkali fly ashes as replacement level increases the amount of alkalis leached increases while prism expansions decrease. Measures of pozzolanic activity can be improved by measuring against non-pozzolanic fillers, This requires high replacement levels to reduce statistical variability. Isothermal calorimetry tests showed that high calcium fly ashes can lead to delays in hydration, these delays can be reduced by calcium hydroxide additions. Calcium sulphate additions can also improve hydration.
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Potassium Acetate Deicer and Concrete DurabilityGhajar-Khosravi, Sonia 07 December 2011 (has links)
An investigation on the damaging effects of potassium acetate deicer (KAc) on concrete durability was conducted. Different SCM replacement levels were used. ASTM C 1293 and ASTM C 1260 test methods results indicated that KAc is capable of inducing alkali-silica reaction (ASR) expansion in specimens containing reactive aggregate. Class C fly ash was ineffective even at a replacement level of 45%. Class F fly ash and slag were effective in mitigating ASR expansion for specimens exposed to diluted (25% by weight) KAc. KAc showed an increase in pH value upon exposure to concrete specimens. Concrete specimen without SCM and exposed to deicers had higher [K]/[Na] molar ratio near the surface but ions penetrated less compared to specimens containing SCM. ASTM C 666 and MTO LS-412 test methods results showed that air-entrained concrete slabs and prisms without SCM and exposed to KAc are resistant to scaling and freezing and thawing damage.
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Alternative Test Methods for Evaluating Fly Ash for use in Concretede Groot, Andre Pieter 23 August 2011 (has links)
Fly Ash was tested in relation to its ability to mitigate alkali-silica reaction, its contribution to strength, electrical resistance and heat release with the aim of recommending improvements to fly ash specifications. ASTM C 1567 accelerated mortar bar test results were in agreement with an expansion limit of 0.10 % at 14 days. A non-standard alkali leaching test showed that with high alkali fly ashes as replacement level increases the amount of alkalis leached increases while prism expansions decrease. Measures of pozzolanic activity can be improved by measuring against non-pozzolanic fillers, This requires high replacement levels to reduce statistical variability. Isothermal calorimetry tests showed that high calcium fly ashes can lead to delays in hydration, these delays can be reduced by calcium hydroxide additions. Calcium sulphate additions can also improve hydration.
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