Behaviour of square panels under constant load (panel creep tests) The investigations were carried out in a cracked state. Initial crack widths corresponding to the state of use were generated in an interrupted square panel test (SIA 162/6). At the age of approximately 90 days, the Durability performance of bi-component polymer fibres under creep and in aggressive J. Kaufmann and M. Manser environments 588 Ground Support 2013, Perth, Australia test panels (600 × 600 × 100 mm3) were loaded while regulating the expansion until a deflection of δ = 2 mm was achieved and then unloaded in controlled manner immediately after reaching this limit. Then, the specimens were mounted into a frame representing the same test set-up as in the square panel test (central load, square support) were it was possible to apply a constant load. Load application was performed hydraulically via gas expansion vessels, which guaranteed the stability of pressure. The pressure was controlled by pressure gauges and readjusted if necessary. The load level was adjusted according to the test plan reaching 50 or 60% of the load measured at the limit deflection of δ = 2 mm. By means of a dilatometer (having an accuracy of one micron) the deformation as a function of time δ(tx) was determined by measuring the distance between two plugs situated at each side of the panel.