This research was undertaken to study the effects of high performance concrete (HPC) mix design modifications on the propensity of early-age cracking. Seven mixtures were tested: one 35 MPa conventional concrete (CC) mixture made with ordinary Portland cement with blended slag; one typical 50 MPa HPC mixture containing slag and silica fume; and five modified HPC mixtures using extra set-retarder, increased slag replacement, shrinkage-reducing admixture (SRA), pre-saturated lightweight aggregate (LWA), and decreased cement paste content to improve thermal and/or shrinkage properties. The mixtures were tested for durability, mechanical, thermal, and shrinkage properties. All modified HPC mixtures showed reduced shrinkage relative to the HPC control mixture, and the most shrinkage mitigation was observed in the mixture containing LWA. While SRA reduced restrained shrinkage in HPC to the magnitude of CC, it provided very low rapid chloride penetrability, and using LWA in HPC resulted in significant restrained shrinkage reduction compared to CC.

This research was undertaken to study the effects of high performance concrete (HPC) mix design modifications on the propensity of early-age cracking. Seven mixtures were tested: one 35 MPa conventional concrete (CC) mixture made with ordinary Portland cement with blended slag; one typical 50 MPa HPC mixture containing slag and silica fume; and five modified HPC mixtures using extra set-retarder, increased slag replacement, shrinkage-reducing admixture (SRA), pre-saturated lightweight aggregate (LWA), and decreased cement paste content to improve thermal and/or shrinkage properties. The mixtures were tested for durability, mechanical, thermal, and shrinkage properties. All modified HPC mixtures showed reduced shrinkage relative to the HPC control mixture, and the most shrinkage mitigation was observed in the mixture containing LWA. While SRA reduced restrained shrinkage in HPC to the magnitude of CC, it provided very low rapid chloride penetrability, and using LWA in HPC resulted in significant restrained shrinkage reduction compared to CC.

During its service life, concrete experiences volume changes. One of the types of deformation experienced by concrete is shrinkage. The four main types of shrinkage associated with concrete are plastic, autogeneous, carbonation and drying shrinkage. The volume changes in concrete due to shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, the cracking may produce a direct path for chloride ions to reach the reinforcing steel. Once chloride ions reach the steel surface, the steel will corrode, which itself can cause cracking, spalling, and delamination of the concrete. The development of concrete shrinkage performance specifications that limit the amount of drying shrinkage for concrete mixtures typically used by the Virginia Department of Transportation (VDOT) were assessed. Five existing shrinkage prediction models were also assessed to determine the accuracy and precision of each model as it pertains to the VDOT mixtures used in this study. The five models assessed were the ACI 209 Code Model, Bazant B3 Model, CEB90 Code Model, Gardner/Lockman Model, and the Sakata Model. The percentage length change limits for the portland cement concrete mixtures were 0.0300 at 28 days, and 0.0400 at 90 days. For the supplemental cementitious material mixtures, the percentage length change limits were 0.0400 at 28 days, and 0.0500 at 90 days. The CEB90 Code model performed best for the portland cement concrete mixtures, while the Gardner/Lockman Model performed best for the supplemental cementitious material mixtures. / Ph. D.

Yes / The shrinkage force exerted by restrained shape memory polymers can potentially be used to close cracks in structural concrete. This paper describes the physical processing and experimental work undertaken to develop high shrinkage die-drawn Polyethylene Terephthalate (PET) shape memory polymer tendons for use within a crack closure system. The extrusion and die-drawing procedure used to manufacture a series of PET tendon samples is described. The results from a set of restrained shrinkage tests, undertaken at differing activation temperatures, are also presented along with the mechanical properties of the most promising samples. The stress developed within the tendons is found to be related to the activation temperature, the cross-sectional area and to the draw rate used during manufacture. Comparisons with commercially-available PET strip samples used in previous research are made, demonstrating an increase in restrained shrinkage stress by a factor of two for manufactured PET filament samples. / Thanks must go to the EPSRC for their funding of the Materials for Life (M4L) project (EP/K026631/1) and to Costain Group PLC. for their industrial sponsorship of the project and author.

The industrial concrete floor is a very important part of an industrial building, distribution center, storage or shopping mall, and it must have high quality surfaces for operation. To achieve the high quality we must know the problems and how to treat them. The most important problems on the concrete floors are: (i) cracks which are caused by shrinkage and creep, (ii) curling resulting in a loss of contact between concrete slab and sub-base, and (iii) unevenness In this thesis, it is aimed to investigate the effect of optimizing the concrete mix with and without additional shrinkage reducing agents (SRA) to reduce the crack risk in industrial concrete floors. Four types of concrete recipes are used (A-D) which include a recipe with optimized mix design for minimum shrinkage, a reference recipe (standard mix), an optimized mix with SRA and a fourth recipe with the reference plus SRA. The testing program extended to 224 days of age and comprised e.g. free-shrinkage, restrained shrinkage, weight change, modulus of elasticity, compressive strength, splitting tensile strength and creep of concrete. At early ages, a 28 days, there are large differences in shrinkage-time relations for different mixes. Later than 28 days, the relations are closer. A comparison among shrinkage and creep test results of four recipes shows that recipes A and C have greater crack risk than recipes B and D. The recipe D has also the best result in restrained shrinkage test. These results are because of the aggrega-te graduation, type of cement and shrinkage reducing agents which all have a direct influence on the concrete properties. These tests were done by CBI (The Swedish Cement and Concrete Research Institute) during 2009.

No description available.

Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation. The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program. Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future. / Master of Science

Abstract: The use of self-consolidating concrete (SCC) in the concrete industry in cast-in-place applications, including repair applications, is growing given the various advantages offered in both fresh and hardened states. The present study deals with the design and performance of fiber-reinforced self-consolidating concrete (FR-SCC) as a repair material of concrete infrastructure. The study also considers the use of various steel and synthetic fibers (five fibers in total) that were used to produce FR-SCC and fiber-reinforced self-consolidating mortar (FR-SCM) that can be employed for structural and non-structural repair applications. The study evaluates the effect of material properties and mixture composition of the fibrous concrete and mortar on workability, mechanical, visco-elastic, durability, and structural behavior. The investigation that is presented in this thesis included the testing of 28 full-scale beams under four-point flexural loading. The majority of these beams were repaired by casting concrete to fill a relatively thin section along the tension zone of the beams. The repair technique was based on the FR-SCC characteristics including the maximum fiber volume and length. This technique required mixtures of high range of fluidity. The optimized FR-SCC and FR-SCM mixtures exhibited excellent flow characteristics along the 3.2-m long beams without blockage, segregation, nor debonding at the interface of repair-substrate concrete. Based on the structural characteristics of the composite beams, the overall performance of the beams repaired using the FR-SCC and FR-SCM was similar or higher (up to 2.6 times) than that of monolithic beams made with conventional vibrated concrete (CVC). The use of optimized FRSCC mixtures enabled the replacement of 50% of the tension steel reinforcement in repair sections; i.e., the number of bars in the tension zone decreased from three bars to two bars with the addition of fibers in the SCC without mitigating structural performance. The degree of prediction of crack width, cracking load/moment, ultimate loads, and deflection of various FR-SCC and FR-SCM mixture was evaluated using several design and code models. The results indicate that these code models can provide safe predictions for crack and ultimate loads, as well as crack width of FR-SCC. The deflection of FR-SCC is unsafe but predictable by these code models. In total, 18 large-scale beams were tested in four-point for flexural creep. FR-SCC incorporating steel fibers combined with expansive agent provided overall performance up to 10 times of that obtained with CVC with the same fiber type and volume. The cracking under constant load was reduced by 60% to 80% using self-consolidating fibrous mixtures made with or without expansion agents, compared to SCC without fibers. The best combination to reduce the cracking potential when the restrained shrinkage ring test was employed was obtained with SCC mixtures made with steel fibers and expansive agent. Models were elaborated to predict the time-to-cracking for FR-SCC and FR-SCM mixtures based on mixture modulus of elasticity and drying and autogenous shrinkages. The project involved extensive testing of highly flowable fibrous materials to determine drying shrinkage (nearly 260 prisms), modulus of rupture (nearly 180 prisms), as well as compressive and splitting tensile strengths and elastic modulus (nearly 2100 cylinders). Based on the results, models were proposed to predict these key material properties that affect the performance of FR-SCC and FR-SCM used in repair applications. In addition to FR-SCC, the investigation also was set to evaluate the feasibility of using fiber-reinforced superworkable concrete (FR-SWC) in construction and repair applications. Such highly flowable concrete that requires limited vibration consolidation can represent some advantages over FR-SCC (lower admixtures demand, lower risk of segregation, greater robustness, lower formwork pressure, etc.). The energy needed to ensure proper consolidation, using either vibration or rodding, applied on samples made with FR-SWC was determined. The energy requirement took into consideration the development of mechanical properties, the resistance to segregation, and the development of proper surface quality. The study also demonstrated the higher overall structural performance of optimized FR-SWC compared to the corresponding FR-SCC mixtures. The findings of the thesis on the design and performance of highly workable fiber-reinforced cementitious materials should facilitate the acceptance of such novel high-performance material in infrastructure construction and repair applications. // Résumé: L'utilisation du béton autoplaçant (BAP) dans l'industrie du béton dans les applications du coulage sur place incluant les applications de la réparation, est en croissance vu les divers avantages offerts à l'état frais et à l'état durci. La présente étude traite de la conception et la performance des bétons autoplaçants fibrés (BAPF) en tant que matériau de réparation des infrastructures en béton. L'étude considère également l'usage de différentes fibres métalliques et synthétiques (cinq fibres au total) qui ont été utilisées pour produire des BAPF et des mortiers autoplaçants fibrés (MAPF) pour des applications de réparations structurales et non structurales. L'étude évalue l'effet des propriétés du matériau et la composition des bétons et mortiers fibrés sur l'ouvrabilité, les propriétés mécaniques, viscoélastiques, de durabilité et le comportement structural. L'étude présentée dans cette thèse a inclus 28 poutres à grande échelle testées sous un chargement flexionnel à quatre points. La majorité de ces poutres a été réparée par le coulage du béton pour remplir une section relativement mince tout au long de la zone tendue des poutres. La technique de réparation a été basée sur les caractéristiques des BAPF incluant le volume maximal et la longueur maximale de fibres. Cette technique a requis des mélanges de haut niveau de fluidité. Les BAPF et MAPF ont exhibé d'excellentes caractéristiques d'écoulement le long de 3,2 m, la longueur de la poutre, sans blocage, ségrégation, ni décollement à l'interface entre le béton de base et le béton de réparation. En se basant sur les caractéristiques structurales des poutres composites, la performance globale des poutres réparées en utilisant les BAPF et les MAPF était similaire ou supérieure (jusqu'à 2,6 fois) que celle des poutres monolithiques fabriquées d'un béton conventionnel vibré (BCV). L'utilisation des mélanges de BAPF optimisés a permis de remplacer 50% du ferraillage tendu dans les sections de réparation; c'est-à-dire que le nombre des barres d'armatures dans la zone tendue a réduit de trois barres à deux barres avec l'addition de fibres dans le BAP sans mitiger la performance structurale. Le degré de prédiction de la largeur de fissures, charge de fissuration, charge ultime et déflexion de différents mélanges de BAPF et MAPF a été évalué en utilisant quelques designs et modèles de codes. Les résultats ont montré que ces modèles ont pu fournir de prédictions sécuritaires pour les charges de fissuration et ultime, ainsi que la fissuration des BAPF. La déflexion des BAPF est non sécuritaire mais reste prédictible par ces modèles de codes. En total, 18 poutres à grande échelle ont été testées en fluage flexionnel de quatre points. Des BAPF contenant des fibres métalliques combinées avec un agent expansif ont fourni une performance globale jusqu'à 10 fois celle obtenue avec un BCV contenant le même type et volume de fibres. La fissuration sous une charge constante a été réduite de 60% à 80% en utilisant des mélanges autoplaçants fibrés fabriqués avec ou sans agents expansifs, par rapport au BAP sans fibres. La meilleure combinaison pour réduire le potentiel de fissuration avec l'essai du retrait restreint a été obtenue avec des mélanges de BAP contenant de fibres d'acier et un agent expansif. Des modèles ont été élaborés pour prédire le temps de fissuration des mélanges de BAPF et MAPF basés sur le module d'élasticité du mélange et les retraits de séchage et endogène. Le projet comportait de nombreux essais sur les mélanges fibrés de haute fluidité à savoir la détermination du retrait de séchage (près de 260 prismes), le module de rupture (près de 180 prismes), ainsi que la résistance en compression, la résistance en traction et le module d'élasticité (plus de 2100 cylindres). En se basant sur les résultats, des modèles ont été proposés pour prédire ces propriétés clés qui affectent la performance des BAPF et MAPF destinés aux applications de réparation. En plus des BAPF, l'étude a aussi été faite pour évaluer la faisabilité de l'utilisation des bétons semi-fluides fibrés (BSFF) dans les applications de construction et de réparation. Tels bétons de haute fluidité requérant une consolidation limitée peuvent présenter certains avantages par rapport aux BAPF (plus faible demande en adjuvants, plus faible risque de ségrégation, robustesse supérieure, plus faible pression sur les coffrages, etc.). L'énergie nécessaire pour assurer une propre consolidation, en utilisant soit la vibration ou le piquage, appliquée sur des échantillons de BSFF a été déterminée. Les exigences de cette énergie considèrent le développement des propriétés mécaniques, la résistance à la ségrégation et la propre qualité de surface. L'étude a aussi démontré une performance structurale globale supérieure des BSFF optimisés par rapport aux mélanges de BAPF correspondant. Les conclusions de la thèse sur le design et la performance des matériaux cimentaires renforcés de fibres et de haute fluidité devraient faciliter l'acceptation de tels nouveaux matériaux de haute performance dans les applications de la construction et la réparation des infrastructures.

abstract: There has been a renewed interest to understand the degradation mechanism of concrete under radiation as many nuclear reactors are reaching their expiration date. Much of the information on the degradation mechanism of concrete under radiation comes from the experiments, which are carried out on very small specimens. With the advent of finite element analysis, a numerical predictive tool is desired that can predict the extent of damage in the nuclear concrete structure. A mesoscale micro-structural framework is proposed in Multiphysics Object-Oriented Simulation Environment (MOOSE) finite element framework which represents the first step in this direction. As part of the framework, a coupled creep damage algorithm was developed and implemented in MOOSE. The algorithm considers creep through rheological models, while damage evolves exponentially as a function of elastic strain and creep strain. A characteristic length is introduced in the formulation such that the energy release rate associated with each element remains the same to avoid vanishing energy dissipation with mesh refinement. A creep damage parameter quantifies the effect of creep strain on the damage that was calibrated using three-point bending experiments with varying rates of loading. The creep damage model was also validated with restrained ring shrinkage tests on cementitious materials containing compliant/stiff inclusions subjected to variable drying conditions. The simulation approach explicitly considers: (i) moisture diffusion driven differential shrinkage along the depth of the specimen (ii) viscoelastic response of aging cementitious materials (iii) isotropic damage model with Rankine′s failure initiation criterion, and (iv) random distribution of tensile strengths of individual finite elements. The model was finally validated with experimental results on neutron-irradiated concrete. The simulation approach considers: (i) coupled hygro-thermal model to predict the temperature and humidity profile inside the specimen (ii) radiation-induced volumetric expansion of aggregates (RIVE) (iii) thermal, shrinkage and creep effects based on the temperature and humidity profile and (iv) isotropic damage model with Rankine’s criterion to determine failure initiation. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2020