REPAIR OPTIMIZATION AND PERFORMANCE ANALYSIS OF THE ASPHALT PROTECTION LAYER OF THE SOUTHERN BREAKWATER IN FRONT OF THE PORT OF AMSTERDAM

Breakwaters provide shelter against waves and currents for safe navigation to port entrance by sea vessels. The breakwaters of IJmuiden, in front of the port of Amsterdam, were initially built in the 19th century and extended in the years 1961 – 1967. The extension reaches out into water depth of approximately 15 m and consists of a core with armour stone 300 – 1 000 kg grading. It has a protection layer being a mixture of stones up to 60 kg overfilled with bituminous grout. The thickness of the layer is approximately 2.25 m. The mixture was made on shore. The breakwater is designed for wave heights up to 7.5 m. Since construction the breakwaters were frequently and severely damaged by wave impact and compressed air in the core and have been repaired many times. In order to stabilize the protection layer, concrete cubic blocks were installed in different periods. In the period 2013 – 2022 the performance of the blocks in combination with the asphalt protection layer was closely monitored and, together with the maintenance regime, evaluated in 2023. In conclusion, damage of blocks and the protection layer are tolerable for large stretches of the breakwaters. Only a few blocks disappeared and small parts of the asphalt protection needed to be repaired. The situation at the roundhead of the southern breakwater is different. Multiple times damage occurred in this period. Therefore in 2020 the remains of the blocks at the roundhead were removed and a new protection layer was constructed above the original damaged layer. The slope was smoothened with armour stone and fully grouted with mastic asphalt. This new protection layer at the roundhead of the southern breakwater did not meet the requirements and damages still occurred, many due to erosion of the asphalt. Already after a year the new protection layer needed to be repaired (2021). Repair was difficult due to wave conditions and the application of asphalt around and below the water surface. In addition, the quality of materials and construction method was insufficient. In 2023 and 2024 new repairs took place. The working method and quality of materials were improved during these repairs in order to optimize the reconstruction. The strength increased resulted in less damage than other years, but the construction is still not resistant to its design loads.