Effect of temperature on the water retention properties of two high performance concretes

This contribution aims at (1) determining experimentally the first desorption isotherms of two high performance concretes (based on CEM I and CEM V cements), at three different temperature levels T=20, 50 and 80 degrees C, and (2) showing whether these may be simply described by adsorption and capillarity. Results at 20 degrees C compare well with recently published results: in particular, an important desorption is observed at high RH (>= 98%). A simple pore network model, based on Kelvin-Laplace's capillary theory, is implemented, and shows the existence of two main de-saturation modes, one at high pore radii (capillary pores), the other for pore radii on the order of a few nanometers (C-S-H porosity), where desorption is shown to occur. A complementary drying mechanism is evidenced at 80 degrees C. which is attributed to ettringite and/or C-S-H degradation. Finally, proper numerical fitting of all isotherm data is achieved using the well-known three-parameter BSB model. (C) 2011 Elsevier Ltd. All rights reserved.