Then, the specimens were mounted into a frame representing the same test set-up as in the square paneltest (central load, square support) were it was possible to apply a constant load. Load application wasperformed hydraulically via gas expansion vessels, which guaranteed the stability of pressure. The pressurewas controlled by pressure gauges and readjusted if necessary. The load level was adjusted according tothe test plan reaching 50 or 60% of the load measured at the limit deflection of δ = 2 mm. By means of adilatometer (having an accuracy of one micron) the deformation as a function of time δ(tx) was determinedby measuring the distance between two plugs situated at each side of the panel.