Ice-concrete bond analysis

Abstract

In regions which experience arctic conditions, structures like offshore wind turbines, oil-platforms, light houses, piers and bridges suffer from abrasion by moving ice sheets. This results in challenging maintenance and repair works. At the ice-structure interface, several mechanisms exist which are responsible for the wear of concrete such as: freeze-thaw cycles, chemical effects of sea water, and mechanical loading of concrete. The main cause of concrete abrasion is however thought to be the flow of ice floes together with a layer of crushed ice, which is partly controlled by friction and adhesion between the two interfaces. Adhesion is thought to be the main component of the static friction and is, under certain circumstances, also directly responsible for concrete abrasion. It is yet not well known to what degree ice adhesion contributes to concrete abrasion, and how extrinsic parameters such as: pressure, hold time and submergence relate to the ice-concrete bond strength. This research aims to better understand the physical phenomena happening at the ice-concrete interface by shearing an adhesive ice-concrete bond to get a better understanding of the role of ice adhesion in concrete abrasion processes. To achieve this goal, a double shear apparatus has been designed and ice-concrete shear tests have been performed in a thermal laboratory. The apparatus was designed to be relatively simple compared to conventional soil shearing machines. The design allowed for the ability of submergence, accurate and sustained application of normal load, improved implementation of standardisation procedures, and easy portability. The temperature during the test was remained relatively constant at around - 9° for dry the ice-concrete adhesion test, and around 0° C for submerged tests. The influence of hold time, varying from very short (6 seconds) to overnight, and pressure (51, 316 and 682 kPa) on the force required to break the ice-concrete bond has been investigated following a series of five test sequences. In sequence 1, the applied pressure was remained when shearing the ice. In test sequence 2, the shearing was initiated immediately after removing the applied pressure. In sequence 3, the time between removing the pressure and shearing has been varied. In sequence 4, different materials have been used to clamp in the ice and sequence in 5, both the concrete and the ice has been fully submerged before shearing. The force required to shear the ice has been measured using a load cell. The results show a positive influence of holding time on the force required to perform the shearing, and although a higher normal load results in a higher shearing force, it is unclear what the result of a higher normal load is on the adhesive force. These result are found for both the remained and released pressure tests. The bond strength also appeared to increase when waiting after removing the applied load. Submergence showed to have a negative influence of the bond strength compared to the dry tests. When using a different surface as the concrete specimen, a pure paste surface showed to give the highest bond strength and a pure sandstone surface resulted in the lowest bond strength. The force required to break a bond between ice and a cut-concrete surface, as used in all other tests, was in between the pure paste and sandstone surfaces. All three types of failing mechanism have been observed. And the failing mechanism is dependent on hold time and pressure. Visual observations show an increase of ice stuck to the concrete surface for both higher normal loads and longer holding times. It is concluded from the experiments in this research, that mechanical adhesion theory seems to be the main mechanism of ice-concrete bonding. The failure type of the ice-concrete bond is dependent on holding time and pressure. The bond strength is strongly dependent on holding time and it is unclear what the influence of pressure is on the bond strength. Ice adhesion has many mechanisms by which it can contribute to the abrasion of concrete.