Electrical resistivity as microstructural parameter for the calculation of reinforcement service life

There is an increasing interest in developing models for prediction of the service life regarding reinforcement corrosion. In present communication a proposal is made based on the electrical resistivity to calculate both the initiation and propagation periods as well as for predicting concrete aging related to durability and for measuring the efficiency of curing. The model is fundamented in that the Resistivity is a property depending on the concrete porous system and its degree of moisture, and then from its values in saturated conditions, it is possible to find relations between diffusivity and resistivity, then linking concrete microstructure and transport resistance. The relation of resistivity and time is quantified through the square root law, either for chloride penetration as for carbonation. However some additional information is needed due to the reaction of chlorides and carbon dioxide with cement phases: the resistivity has to be factorised by a "reaction factor" accounting for it. Concerning the corrosion propagation period the relation between corrosion and resistivity is provided by an expression previously developed by one of the authors. Aging is introduced by measuring the evolution of the resistivity with time. The paper presents an example of application of the model. Finally it is mentioned that the concrete mix can be designed for a target resistivity and that this parameter can also be used as a performance parameter (Corrosion indicator). Being the measurement of resistivity a non destructive method, it can be as well used for on-site quality control

Concrete Mixture Design Based on Electrical Resistivity.

Current codes have requirements for the durability design of concrete based on compressive strength and provisions related to cement content and water - cement ratio. However, such requirements do not take into account important parameters related to the behaviour of concrete against to aggressive attack. The electrical resistivity of the hardened concrete is related to connectivity of pores network under saturated condition.. This paper proposes a methodology of design based on the Archie law, which is originated from the concept of diffusion and provides properties such as electrical resistivity, porosity, and tortuosity, for estimating the ideal mix of concrete (maximum water cement, the minimum content of cement and cement type) for a specific environmental class and service life. It also considers the chemical reaction of chloride and carbonation with the phases of cement, so called factor of reaction (r) which depends on the type of cement and indicates the delay on the agressi vc penetratio

The use of electrical resistivity as a NDT for the specification of concrete durability

The calculation of the time to reinforcement corrosion and service life duration is a subject of increasing interest. In present communication is explained how to use the electrical resistivity to calculate both the initiation and propagation periods in the case of carbonation and chloride penetration, although only the case of chlorides is illustrated here. The main advantage is that resistivity is an inexpensive non destructive measurement that can be used for routine quality control. The resistivity is an indication of the porosity and pore connectivity. It increases with time as hydration proceeds which is an indication of aging or pore refinement. In addition to the measurement of the resistivity it is necessary to calculate a "reaction factor" for accounting of the binding with cement phases. Conceming the propagation period, the electrical resistivity is an indication of the moisture content of concrete and therefore, it has a relationship with the corrosion cement. A model is proposed in which the resistivity is introduced in the square root of time la

Embedded Sensors For The Monitoring Of Durability

Embedded Sensors For The Monitoring Of Durabilit

Recubrimientos recomendables por razones de durabilidad, a disponer en estructuras de hormigón sometidas a la clase específica de exposición Qb (ataque químico de intensidad media)

Es una realidad cada vez más aceptada que la durabilidad del hormigón es una propiedad igual de importante que la resistencia mecánica o la estabilidad de volumen. No es el objeto del presente trabajo ahondar en las causas de esta evidencia sino en contribuir a hacer del diseño de la durabilidad una materia incorporada al quehacer diario de los técnicos y especialistas. Solo si la durabilidad de una estructura se puede proyectar y verificar, será posible conseguir vidas útiles con una cierta garantía o seguridad en que se alcanzarán los periodos de servicio que se especifiquen. En el diseño de la durabilidad se ha dedicado mucho tiempo en el pasado a aclarar los mecanismos de ataque (por ejemplo: por sulfatos o por reacción árido-álcali) o como realizar ensayos acelerados en estos casos y también en el caso concreto de la corrosión de la armadura. En el caso de la corrosión, la envergadura de los costes de reparaciones ha estimulado la publicación de modelos y ensayos que, si bien necesitan todavía calibración, al menos suponen una cierta ayuda para el proyectista

Infecção urinária em recém-nascido de termo: análise de fatores de risco

OBJETIVOS: Analisar a contribuição dos fatores de risco para a ocorrência de infecção urinária em recém-nascidos de termo. CASUÍSTICA E METODOLOGIA: Estudo retrospectivo (1997), incluindo recém-nascidos de termo com urocultura positiva por saco coletor. A indicação desta coleta foi baseada em: hipertermia (T>;37,8ºC), perda de peso>;10% do peso de nascimento, alterações do estado geral (recusa alimentar, ganho insuficiente de peso e hipoatividade) ou presença de malformações nefro-urológicas. Nesses recém-nascidos foi realizada punção suprapúbica para confirmação diagnóstica. Os recém-nascidos foram divididos em dois grupos, segundo o resultado das uroculturas: Grupo I (diagnóstico presuntivo de infecção urinária) e Grupo II (diagnóstico confirmado de infecção urinária), para avaliação dos fatores de risco pela análise do risco relativo. RESULTADOS: Foram estudadas 61 crianças (5,1% dos recém-nascidos de termo) - Grupo I n=42 (68,9%) e Grupo II n=19 (31,1%). Os fatores de risco avaliados (patologias infecciosas associadas, uso prévio de antibióticos, malformações nefro-urológicas, ventilação mecânica, nutrição parenteral e o uso de cateteres) foram mais freqüentes no Grupo II (pOBJECTIVE: To analyze the correlation of risk factors to the occurrence of urinary tract infection in full-term newborn infants. PATIENTS AND METHODS: Retrospective study (1997) including full-term infants having a positive urine culture by bag specimen. Urine collection was based on: fever, weight loss >; 10% of birth weight, nonspecific symptoms (feeding intolerance, failure to thrive, hypoactivity, debilitate suction, irritability), or renal and urinary tract malformations. In these cases, another urine culture by suprapubic bladder aspiration was collected to confirm the diagnosis. To compare and validate the risk factors in each group, the selected cases were divided into two groups: Group I - positive urine culture by bag specimen collection and negative urine culture by suprapubic aspiration, and Group II - positive urine culture by bag specimen collection and positive urine culture by suprapubic aspiration . RESULTS: Sixty one infants were studied, Group I, n = 42 (68.9%) and Group II, n = 19 (31.1%). The selected risk factors (associated infectious diseases, use of broad-spectrum antibiotics, renal and urinary tract malformations, mechanical ventilation, parenteral nutrition and intravascular catheter) were more frequent in Group II (

Bone density and genomic analysis unfold cold adaptation mechanisms of ancient inhabitants of Tierra del Fuego

The Fuegians, ancient inhabitants of Tierra del Fuego, are an exemplary case of a cold-adapted population, since they were capable of living in extreme climatic conditions without any adequate clothing. However, the mechanisms of their extraordinary resistance to cold remain enigmatic. Brown adipose tissue (BAT) plays a crucial role in this kind of adaptation, besides having a protective role on the detrimental effect of low temperatures on bone structure. Skeletal remains of 12 adult Fuegians, collected in the second half of XIX century, were analyzed for bone mineral density and structure. We show that, despite the unfavorable climate, bone mineral density of Fuegians was close to that seen in modern humans living in temperate zones. Furthermore, we report significant differences between Fuegians and other cold-adapted populations in the frequency of the Homeobox protein Hox-C4 (HOXC4) rs190771160 variant, a gene involved in BAT differentiation, whose identified variant is predicted to upregulate HOXC4 expression. Greater BAT accumulation might therefore explain the Fuegians extreme cold-resistance and the protection against major cold-related damage. These results increase our understanding of how ecological challenges have been important drivers of human–environment interactions during Humankind history

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries