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Innovative fibrous concrete against fire spalling

Explosive concrete spalling at high temperatures results in
serious economic and human safety problems. A research
programme will study innovative concretes using new fibre
types able to exclude toxic effects and avoid spalling.

Concrete is the most commonly used construction material. In the majority of applications (such as buildings, bridges, nuclear reactors, tunnels, offshore structures) it faces the risk of exposure to high temperatures (e.g. nuclear reactor accidents or fire) and in this case its structural behaviour is jeopardised by one major problem, namely the likelihood of the occurrence of explosive spalling. Today, and in the future, the risk of explosive spalling of concrete at high temperatures will markedly increase - and the problems magnified - by the increasing use of high performance, low permeability, and concretes in construction. While such concretes are indeed 'high performance' under normal service conditions, they become 'low performance' at high temperatures because their dense structure does not allow moisture and vapour to escape readily, thus leading to the build up of high pore pressures, which contribute to explosive spalling. The main parameters influencing explosive spalling are thermal stresses associated with the build-up of pore pressures inside the material. Explosive spalling can, therefore, truly be described as the 'Achilles' heel' of concrete. The use of polypropylene fibres reduces and even eliminate this serious problem. The fibres melt at about 160 degrees C (new fibres have just been produced which melt at 130 degrees C) thus providing channels for the escape of water vapour during heating and avoiding the build-up of vapour pressure. The major problem in convincing industry to use this innovative new technique lies in the facts that: (a) little research has been carried out into this subject, (b) the use of pp fibres is far from being fully understood or optimized, (c) concrete durability under service conditions has been questioned, and (d) last but not least the toxicity of its products of combustion needs to be examined. An innovative research programme is proposed with the main purpose of studying the use of new types of fibres, to optimise on the positive effects on the permeability increase and on the same time to minimise any negative effects. Advanced laboratory tests will be conducted to analyse the two basic material parameters: dynamic permeability and sorption/desorption curves at high temperatures. Experiments will be conducted on concrete elements and the relevant experimental data used to validate an innovative software package able to numerical simulate associated phenomena. It is important that the explosive spalling problem is satisfactorily addressed and solved at both theoretical and practical levels, and the promising use of safe and reliable new pp fibres properly addressed and exploited. Keywords: spalling, fibre concrete, innovative fibres.
Acronym: 
NEWCON
Project ID: 
2 591
Start date: 
01-07-2003
Project Duration: 
48months
Project costs: 
910 000.00€
Technological Area: 
Building materials
Market Area: 
Construction

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