Thermo-mechanical properties of Penly reactor envelope at temperatures up to 200 degrees C

This paper reports on an experimental investigation conducted to study the effects of high temperatures of up to 200 degrees C on the phase compositio n, pore structure development and physico-mechanical properties of concrete at the PENLY nuclear power plant (France). The concrete specimens were man ufactured under laboratory conditions from identical materials used at the construction site in PENLY, and then stored at 20 degrees C/100% R.H. for 2 8 days and exposed to temperatures of 40 degrees C, 60 degrees C, 100 degre es C, 200 degrees C, and 20 degrees C/60% R.H., respectively. Test results revealed that an intense structural integrity degradation of P ENLY concrete occurs between 100 degrees C and 200 degrees C due both to a loss of water bound in hydrated cement minerals and to subsequent air void formation. This phenomenon is related to an increase in the median pore rad ius and total porosity values, as well as to a decrease in the dynamic and static moduli of PENLY concrete. The reduction in volume of the hydrate pha se is believed to be the reason behind the rapid expansion, over a short ti me interval, due to a time-limited moistening of the specimen by released w ater with a sudden rise in temperature, followed by a stabilised period of shrinkage and creep.