The steel–concrete interface

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made

Use of fine ground dune sand as a supplementary cementing material

The process of Portland cement production is associated with high consumption of energy and resources. Therefore, there is a need to replace the Portland cement with environmental friendly materials. This study was conducted to determine the feasibility of using ground dune sand as cement replacement materials under different curing conditions. Portland cement was replaced by ground dune sand at five levels of replacement (0–40% by weight). The compressive strength of mortar under standard and autoclave curing conditions and the influence of different autoclave temperatures and durations were investigated. The microstructure of selected mixtures was analyzed by XRD and SEM. Results showed that the compressive strength under the standard curing decreased as the level of replacement increased. However, under autoclave curing compressive strength increased as the content of ground dune sand increased. XRD and SEM revealed the absence of calcium hydroxide and the formation of secondary calcium silicate hydrate. The improvement of compressive strength and the absence of calcium hydroxide under autoclave curing indicated that the pozzolanic reaction between silica of dune sand and calcium hydroxide occurred

Statistical variations in impact resistance of polypropylene fibre-reinforced concrete.

yesImpact resistance of polypropylene fibre-reinforced concrete was investigated using the repeated drop weight impact test recommended by ACI Committee 544. The results were analysed based on a statistical approach. The variation in results was examined within the same batch and between different batches. Statistical parameters were compared with reported variations in impact resistance of concrete composites reinforced with other types of fibres such as carbon and steel fibres. Statistical analysis indicated that the results obtained from this test had large variations and it is necessary to increase the number of replications to at least 40 specimens per concrete mix to assure an error below 10%. It is concluded that this test with its current procedures and recommendations should not be considered a reliable impact test. This study has highlighted the need for modifying this test in such a way as that increases its accuracy and reduces the large variation in results

Influencia de las fibras PET en la velocidad de corrosión del acero en concreto reforzado

Auxiliar de investigaciónSe presenta un estudio sobre la influencia de las fibras PET en la velocidad de corrosión del acero en concreto reforzado. Se adicionan tres tipos de contenidos de fibras PET a la mezcla de concreto (0 kg, 0.029 kg, 0.057kg) y se funden en dos tipos de probetas una de sección 4” y una de 5 cm de diámetro por 10 cm de altura (tiene una varilla incrustada en la centro de la base del molde) para un total de 27 especímenes. Las probetas de concretos se sumergieron en el agua por un periodo de 28 días. Por último se les realizaron ensayos de compresión y módulo de elasticidad a las probetas de 4” y a las probetas más pequeñas se les aplico la técnica de resistencia a la polarización lineal (LPR).RESUMEN INTRODUCCIÓN 1. GENERALIDADES 2. MARCO REFERENCIAL 3. MATERIALES Y MÉTODOS 4. DISEÑO DE MEZCLA Y ELABORACIÓN DE MUESTRAS 5. CARACTERIZACIÓN DE MUESTRAS 6. ANÁLISIS DE RESULTADOS 7. CONCLUSIONES Y RECOMENDACIONES BIBLIOGRAFÍA ANEXOSPregradoIngeniero Civi

Self-Protection Through Dynamic Reconfigurations

Modern computer systems have become more complex over time and traditional resilience mechanisms built around static configurations may no longer adequately protect them against cyberattacks and failures. To address these limitations, systems have to become more dynamic to increase their resilience and adaptability to environmental changes. Adaptation through dynamic reconfiguration can improve quality of service, increase fault-tolerance, help recover from failures, prevent and recover from cyberattacks. A major challenge of dynamic reconfiguration is the performance and availability degradation that may occur during system reconfiguration. Dynamic reconfiguration is primarily a mechanism that reconfigures one or more of a system's resources. Although multiple dynamic reconfiguration techniques have been described in the literature, there is no comprehensive method to quantify their tradeoffs due to reconfiguration overhead. Therefore, a quantification framework for dynamic reconfiguration is needed to formally analyze and optimize performance tradeoffs. This dissertation formalizes the problem of dynamic reconfiguration and demonstrates several theorems regarding the use of dynamic reconfiguration to reduce the incidence of cyberattacks and protect from failures.This work defines functions that capture the effect of dynamic reconfigurations on a system's resilience to cyberattacks and failures. Metrics are also developed that capture the impact of reconfigurations on a system's execution time and on the probability of cyberattacks and failure. This work also derives analytic models for predicting the effect of dynamic reconfigurations on execution time and resilience to cyberattacks and failures. Several theorems regarding the tradeoff between resilience and performance and availability are presented. An optimization problem is defined, formalized with the help of these theorems, to determine the optimal reconfiguration frequency to meet performance-resilience tradeoffs. This dissertation also applied an approach inspired by Moving Target Defense (MTDs) to increase workflow-based applications robustness to cyberattacks. This approach is based on dynamic reconfigurations of workflow tasks to reduce an attacker's probability of succeeding in completing the reconnaissance phase of a workflow before launching an attack. To determine the impact of task reconfigurations on a workflow's execution time and resilience against cyberattacks, this work designed recursive algorithms for computing the execution time of a workflow and the reconnaissance function of a workflow, and derived an analytic model that captures the tradeoff between security and execution time of workflow-based applications. To validate the result the experiments used a trace-driven simulation analysis of 6,000 workflows from the Workflow Trace Archive consisting of real-life workflow traces from three different domains: scientific computing, engineering, and industrial