Quantification of the service life extension and environmental benefit of chloride exposed self-healing concrete

Formation of cracks impairs the durability of concrete elements. Corrosion inducing substances, such as chlorides, can enter the matrix through these cracks and cause steel reinforcement corrosion and concrete degradation. Self-repair of concrete cracks is an innovative technique which has been studied extensively during the past decade and which may help to increase the sustainability of concrete. However, the experiments conducted until now did not allow for an assessment of the service life extension possible with self-healing concrete in comparison with traditional (cracked) concrete. In this research, a service life prediction of self-healing concrete was done based on input from chloride diffusion tests. Self-healing of cracks with encapsulated polyurethane precursor formed a partial barrier against immediate ingress of chlorides through the cracks. Application of self-healing concrete was able to reduce the chloride concentration in a cracked zone by 75% or more. As a result, service life of steel reinforced self-healing concrete slabs in marine environments could amount to 60-94 years as opposed to only seven years for ordinary (cracked) concrete. Subsequent life cycle assessment calculations indicated important environmental benefits (56%-75%) for the ten CML-IA (Center of Environmental Science of Leiden University-Impact Assessment) baseline impact indicators which are mainly induced by the achievable service life extension

How to better exploit the use of LCA analysis for Ultra High Performance Concrete (UHPC) through a constitutive law which integrates chloride and sulfate attack

Structural applications of advanced cementitious materials such as Ultra High Performance Concrete (UHPC) have been already assessed in harsh exposure conditions with presence of chlorides or sulfates. Nevertheless, the limited availability of design standards has not favoured so far a widespread use of these materials. Moreover, previous studies employed a constitutive model only partially representative of the real behavior of such materials when exposed to aggressive conditions. Therefore, this work, employing a “scenario dependent” constitutive law, estimates the serviceability limit state in correspondence of which it is needed to carry out the maintenance activities and investigates, through the Life Cycle Assessment (LCA) methodology, the ecological and economic profile of a UHPC water basin structure subjected to chloride and sulfate attack. The CML impact assessment method has been employed for the specific purpose to compare such structure to one made with ordinary reinforced concrete (ORC) using as system boundary the A1-B7 stages indicated in EN 15804

The Effect of Common-Mode Voltage Elimination on the Iron Loss in Machine Core Laminations of Multilevel Drives

This paper studies the effect of common-mode voltage elimination (CMVE) on the iron loss of electrical machine core laminations under multilevel converter supply. Three identical magnetic ring cores are excited by either a three-level converter or a five-level voltage source converter to study the behavior of CMVE on a three-phase system. Both multilevel converters are controlled by using a space vector pulse width modulation as it is one of the most often used techniques for CMVE. These experimental results are confirmed numerically with a dynamic iron loss model. In addition, the effect of CMVE, at different switching frequencies, on the core loss of a synchronous machine is numerically studied. The results presented in this paper show that the core loss is considerably increased when the CMVE is implemented. However this iron loss increase in five-level drive systems is lower compared to the three-level ones. Therefore, it is important that the designers of drive systems take such effects into consideration.Peer reviewe

LCA assessment related to the evolution of the earthquake performance of a strategic structure

Several buildings and infrastructures, located in urban areas, are identified as strategic in the case of an earthquake event. This is the case of a water treatment plant which is currently built in Genoa, Italy, and which has been assessed for the scope of this research. Since the structure has been designed following the seismic design prescriptions, this work aims to provide a preliminary assessment of how the degradation mechanisms do affect its earthquake response. To this purpose, both chloride attack and carbonation are taken into account as main degradation mechanisms. Moreover, due to the importance of the water treatment plant, to develop a realistic Life Cycle Assessment (LCA) analysis, the earthquake resistance of the structure and its evolution over time as a function of the aforesaid degradation mechanisms, have been accounted as Serviceability Limit State to estimate the frequency of the maintenance activities needed in a timeframe of 100 years

Complete re-utilization of waste concretes–Valorisation pathways and research needs

Global demand for buildings and infrastructure is extremely high as provision of shelter, sanitation and healthcare are paramount to safeguard the world's growing population. Concrete is a preferred construction material to meet this demand, but its production is leading to overexploitation of natural gravel and sand, causing an environmental crisis in regions where these materials are extracted unsustainably. Waste concrete is available globally, particularly in regions with fast growth of the built environment, and those struck by coordinated attacks, earthquakes or severe weather events. Waste concrete has mainly been used for producing recycled aggregates; however, its full recycling is still not practiced. Alternative uses include applications as fine recycled aggregates, supplementary cementitious materials, filler, and feedstocks for clinker production. These technologies still face challenges concerning their adoption and eco-efficiency. Restricted knowledge and operational barriers have also prevented implementation of beneficiation technologies for complete re-recycling of waste concretes, particularly the fine fractions produced during crushing. Despite these issues, it is recognised that the complete utilization of waste concrete offers unique opportunities for supply chain security, reducing natural resources consumption and enabling to move towards a Circular Economy. Harmonizing current practices for the treatment of waste concrete and the by-products generated during their processing, is a first step toward policy and standards development to enable their widespread use. This critical discussion addresses challenges and opportunities, as well as facilitation strategies needed to progress the complete re-utilization of waste concrete as a valuable resource for creating sustainable future infrastructure

Cuantificación mineralógica de cementos mediante análisis Rietveld de DRX

Existen varias técnicas para conocer la composición mineralógica de los cementos, como las fórmulas de Bogue o el conteo con microscopía. En los últimos años la técnica que ha ganado mayor aceptación es la cuantificación mediante el método Rietveld para difracción de rayos X, por sus ventajas comparativas a los demás métodos (velocidad, precisión y la posibilidad de ser aplicado a cualquier tipo de cemento). Entre las variables que pueden afectar a la reproducibilidad de los resultados, se encuentra el conocimiento y la experiencia del operario que utiliza los programas de refinamiento. Para minimizar la incidencia del operario existen protocolos de refinamiento, a veces incluidos en el programa, o como en este caso elaborados manualmente. En este trabajo se analizaron muestras de cementos y adiciones minerales con dos programas de refinamiento y se compararon los resultados entre sí, y con ensayos de fluorescencia