Concrete behavior in reactor envelope of a nuclear power plant at temperatures up to 200 degrees C

In this contribution, the properties of concrete at Temelin nuclear power p lant (Czech Republic) are introduced. The concrete specimens from Temelin N PP were manufactured at the construction site, then stored at 20 degrees C and 100% R.H. for 28 days and exposed to temperatures of 40 degrees C, 60 d egrees C, 100 degrees C, and 200 degrees C. It was found that the loss in mechanical properties of concrete is influenc ed by its degradation through changes induced in basic processes of cement hydration and hardening of the bonding system in the cement paste under the action of elevated temperatures. At 200 degrees C, the bonding system of c oncrete has already lost approximately three quarters of the water content bound in C-S-H and C-A-H gel-like hydrate phase. The Ca(OH)(2) content, det ermined by the intensity of diffraction line at 4.91 Angstrom, is decreased by approximately 5 times at 200 degrees C compared to that at 20 degrees C /100% R.H. - 28 days - cure. This decrease in volume of the hydrate phase a nd Ca(OH)(2) is closely connected with the coarsening of the pore structure of concrete, because the bound water mass is replaced at elevated temperat ures by air voids. At 200 degrees C, the remainder of non-decomposed hydrat e phase and Ca(OH)(2) represents the binding material supply, giving concre te its residual utility properties.