Validation of FEM models describing moisture transport in heated concrete by Magnetic Resonance Imaging

Fire safety of buildings and structures is an important issue, and has a great impact on human life and economy. One of the processes negatively affecting the strength of a concrete building or structure during fire is spalling. Many examples exists in which spalling of concrete during fire has caused severe damage to structures, such as in the Mont Blanc and Channel Tunnel. Especially newly developed dense types of concrete such as HPC and SCC, have shown to be sensitive to spalling, hampering the application of these new concrete types. To reduce risks and building costs, the processes behind spalling need to be understood. Increasing our knowledge allows us to reliably predict the behaviour and take effective and cost friendly preventive measures. Moisture present in concrete is one of the reasons for spalling. When concrete is heated water will evaporate, which results in a high gas pressure inside the pores of concrete. This high gas pressure can induce spalling. To attain a better understanding of this process, a first step was taken to develop a finite element model (FEM) describing this transport of moisture in heated concrete. However, the validity of all current models (including our own) is unknown because of debatable input parameters and lack of experimental techniques to follow the transport process in situ. In cooperation with the Eindhoven University of Technology moisture transport in heated concrete can now be investigated with a home built dedicated 1D Magnetic Resonance Imaging (MRI) setup. Using the results of the MRI experiments the validity of our FEM models has been assessed for the first time. A general correspondence is observed. The FEM model described in this paper is a simplified FEM model compared to literature models. Already this simplified model shows a good correspondence with the MRI measurements

Monitoren duurzaamheid van betonconstructies

In prefab segmenten van de Groene Hart tunnel zijn sensoren ingebouwd voor het monitoren van aspecten van de levensduur. Corrosie-initiatie en -snelheid en elektrisch

AC en DC beinvloeding van pijpleidingen

Invoering van AC tractie in Nederland en het bundelen van leidingen in leidingenstraten en -corridors, kan consequenties hebben op de AC en DC beïnvloeding van ondergrondse pijpleidingen, en naar mee op hun duurzaamheid. DC beïnvloeding heeft plaats, omdat het bestaande spoor of andere DC bronnen, lekstromen naar de bodem vertonen. Deze stromen kunnen als deel van hun retourpad buisleidingen gebruiken vanwege hun relatief lage Ohmse weerstand. AC beïnvloeding vindt op dezelfde wijze plaats, echter bij AC is er nog een andere manier van beïnvloeding door middel van inductie. AC en DC beïnvloeding kunnen, o.a. afhankelijk van hun grootte, de coating op de leiding en van de werking van het KB systeem, corrosie veroorzaken. Verder wordt de controleerbaarheid van effectieve KB door de aanwezigheid van deze stromen bemoeilijkt

Stability and reactivity of oxygen, nickel and cobalt species in molten carbonates

Applied Science

Durability assessment of concrete sheet piling in the 'De Betuweroute' railway line

Assessment of the durability of prestressed concrete sheet piles under the interference of CP gas pipeline system current, established that due to their low magnitude, these currents do not compromise the required 100-year service life of the structures. The sophisticated numerical modelling tools being developed, are important in assessing durability of concrete in underground structures. Prestressed concrete sheet piles are equipped with monitoring devices consisting of sensors such as reference electrodes. To assess the expected life of interference in terms of steel piles, the level of of interference expressed as the maximum interference current density at the entrance and exit points on the steel must also be known

Advanced numerical design for economical cathodic protection for concrete structures

Concrete structures under aggressive load may suffer chloride induced reinforcement corrosion, in particular with increasing age. Due to high monetary and societal cost (non-availability), replacement is often undesirable. Durable repair is necessary, e.g. by Cathodic Protection (CP). CP involves an electrical current through the concrete to the reinforcement from an external anode. The current causes steel polarisation, electrochemical reactions and ion transport. CP systems are designed from experience, which results in conservative designs and their performance is a matter of wait-and-see. Using numerical models for current and polarisation distribution, CP systems can be designed for critical aspects and made more economical. This paper presents principles and results of preliminary numerical calculations for design of CP systems, applied to protection of local damage in bridges (e.g. at leaking joints)

Risk based management of concrete structures using advanced corrosion monitoring

Reinlorced concrete is a very cost elfective construction material, used for a large part of the world's physícal ínfrastructure. The durable collaboration between steel and concrele is essential for its safe and serviceable funclioning. Normally, the physícal and chemÍcal nature of concrete protects the ernbedded reinforcing steel against corrosion. Hornrever, in the coursa of time, this protection can be reduced or completely lost due to the ingress of aggressive substances from the environment, for example chloride ions from seawaler and de-icing salts and carbon dioxide from the atmosphere, resulting in reinforcement corrosion. Corrosion creates expansive corrosion producls, which crack and subsequently spall off the concrete cover: eventually corrosion tvill reduce bar diameters to unsate values and collapse cannol be exclude

Throwing power of the zinc-hydrogel anode for sacrifical protection of steel in concrete

The throwing power of the Zinc-Hydrogel Anode for sacrificial protection of steel in concrete was studied in the laboratory under controlled environments. The anode to steel ratio in the specimens was 1. The corrosion state of the rebar is moderate. The results indicate that for a concrete resistivity of 600 Qm and higher the ohmic drop in the concrete is an important factor in the lateral protection of steel with diameter of 8 mm and a cover of 15 mm. For 600 Qm a lateral throwing power of 220 mm or more was obtained, while for 1900 SZm this decreases to less than 120 mm. Our results on the throwing power in the depth direction indicate that for a concrete resistivity between 600 and 1000 Qm protection of two corroding rebar layers of 8 mm diameter at two different depths between 0 and 150 mm can be obtained. The measurements show that for a higher concrete resistivity proper protection is questionabl