The XblocPlus is a new type of single layer armour unit for breakwaters. The key difference between earlier single layer armour units is that the unit is not only placed in a regular grid, but also with a regular orientation. The main benefit of this is that it can directly be seen whether the unit is placed correctly. Additionally, the placement always takes place with the same repetitive movement, as is preferred by crane drivers. The benefits to the placement procedure would however be reduced when the requirements for the under layer become very tight. Since the time that is saved during placement of the armour units, then would be lost during the profiling of the under layer. This has led this study to focus on the influence of irregularities in the under layer on the stability of the XblocPlus and the allowed tolerances for the placement of the under layer. In the process of obtaining a stable armour unit, multiple researches have been conducted. The final shape has been further optimised by adding a hole in the middle of the unit and increasing the interlocking capacity. Better interlocking increased the connection between the units and thereby improved the resistance. The hole increased the porosity and thereby reduced the overpressure underneath the armour layer. Which is a result of a difference in water level inside and outside of the breakwater. The increase in stability due to the enlargement of porosity, validated earlier findings that the acting failure mechanism is extraction due to the overpressure. The stability was expected to be mainly effected by the amount of interlocking. Subsequently, the amount of interlocking is determined by the relative angle between the armour units. For this research physical model tests have been performed to check that hypothesis. Multiple tests have been conducted with different radii of convex and concave shapes in both long shore and cross shore direction. The goal was to find the critical relative angles of each combination of shape and direction. The convex shape in cross shore direction was the only irregularity that caused failure and proved to be critical. The relation between the relative angle and the stability number resulted to be linear, instead of the expected drop of stability at a certain critical value. The relation showed signicant spreading, for which tests with small deviations from the design profile seem to form the upper bound and large deviations the lower bound. Thereby indicating that the level of stability is not only determined by the relative angle but also by the deviation from the design profile. In succession of the tests with specific shapes and directions, more realistic tests have been performed with micro irregularities and S-proles. The convex shape in cross shore direction proved to be critical for these congurations as well. Furthermore it was found that for large S-proles, sudden failure could occur without previous indication of loss of interlocking. Further analysis of the divergent failure behaviour of large S-profiles indicated that the arched shape of the profile enabled the lifting of the armour layer. A mechanism similar to the buckling of beams. The pressure inside the breakwater, the drag of the down-rush and the weight of the upper part of the slope, cause the initial distortion of the profile to be enlarged. The differences between the measurements of the profile before and after the tests, showed that the same movements occur for smaller S-proles and the tested convex shapes in cross shore direction. The movement could even be seen in tests that have not failed. Which implies that the arching mechanism that causes sudden failure for large S-proles, also induces the loss of interlocking for other convex shapes. A simplied model of the forces on the convex sections in the profile indicates that the enforcing of the arching mechanism mainly depends on the length and steepness of the downward part of the convex section and the  atness of the upward part of the convex section. These findings correspond with the test results and explain why the stability performance is the highest for the short length scale micro irregularities and lowest for the large scale S-proles with large deviations from the design profile. Evaluation of the effect of irregularities is performed with the tolerances of the regular Xbloc, which are also intended to be used on the XblocPlus. To prevent differences in stability due to the size of the under layer, the tolerances are expressed in the unit size (Dn) instead of the under layer grain size (Dn50). The resulting tolerances are maximum 0.25 Dn for the deviation from the design profile and maximum 0.1 Dn deviation between subsequent measurements along the profile. The profile is measured every 10m of the breakwater and subsequent measurements along the profile have a distance of 0.3 Dn. The requirements are a little more liberal than the tolerances of the regular Xbloc since the tolerances of the largest under layer grain size are taken as a starting point. The test results indicate that the tolerances are sufficiently safe, with potential for more liberal requirements.

In this MSc thesis it is investigated how the first version of concrete armour unit Xbloc+, Xbloc+ v1, acquires its stability. The stability mechanisms are investigated by conducting two type of physical model tests. First, 23 dry pull-out tests are done to obtain insights into the aspects and mechanisms that influence the armour layer stability. At 8 locations per slope, blocks are pulled out to determine the force needed to extract an armour unit. Tests are done on a 3:4 slope with 2 pull-directions; under an angle of 45 degrees with respect to the slope and perpendicular to the slope. Concrete as well as plastic armour units are tested, both having a different surface roughness. The conclusions of the pull-out tests are verified by means of the second type of model tests; small scale physical hydraulic model tests in a 2D wave flume. In total, 10 tests are conducted; 6 tests with plastic armour units and 4 tests with concrete armour units. Each test starts with a run with a small significant wave height which is increased stepwise in each run until failure occurs. All test sections have a 3:4 slope and are subjected to waves with a 4% steepness. Additionally, the influence of the significant wave height step size for successive runs is investigated. The combination of both physical model tests results in recommendations for a change in design which is expected to lead to a higher stability of an armour layer with Xbloc+ armour units.

Alkali activated concrete is seen as possible contender to alleviate the environmental footprint of the concrete industry. The goal of this research is to evaluate the extend to which ground granulated blast furnace slag and calcined clay-based alkali activated concrete can be utilized in concrete revetment applications with equal performance in freeze-thaw and sulfate attack resistance and lower environmental impact compared to blast-furnace slag cement concrete. This research uses a combination of ground granulated blast furnace slag and calcined clay as precursor blend which is combined with sodium silicate and sodium hydroxide activator solution. An upscaling methodology is used such that differences in material behavior between each upscaling step (paste, mortar, concrete) is explained. Mix designs are developed with the Taguchi method.The alkali activated concrete mix designs develop good compressive strength, where both mix designs reach over 12MPa after 24 hours of ambient curing and over 37MPa after 28 days of ambient curing. It fulfills the requirement for revetment products and outperforms cement concrete.The water absorption is on the high side. It does not fulfill the requirement, but the high value is attributed to non-optimal compaction as the concrete phase uses a special vibration and pressure compaction machine, which does not represent the compaction enabled in a factory process as the reference concrete also fails to meet this requirement.Freeze-thaw performance of the alkali activated mortar is sufficient as 5 of 9 mortar mix designs meet the requirement from the CDF test. Inclusion of calcined clay and the effect of the modulus clearly results in worse freeze-thaw performance due to more difficult compaction, higher absorption and more interconnected pores resulting in more scaling as the de-icing solution can penetrate further in the specimens. Freeze-thaw of the alkali activated concrete and reference concrete is insufficient with large amount of scaling at the end of the test, partially attributed to compaction. However, the retarding scaling behavior of alkali activated concrete indicates good long term performance.Sulfate attack performance is tested at mortar level where specimens are exposed to 10 % MgSO4 solution for 14 days. No degradation is visible in terms of scaling and compressive strength. Slight formation of ettringite is observed, thus it is recommended to extend the testing period.LCA is performed on product level and does not consider service life and recyclability. The alkali activated concrete mix designs show the potential to reduce the milieukostenindicator with 48 % to €5,72 and reduce the CO2 emissions with 63% towards 48kg per m3 produced concrete. These are significant reductions, but for full validation of environmental footprint performance of alkali activated concrete, service life and recyclability should also be involved in the calculations.The research proves that alkali activated concrete is a very interesting alternative for cement concrete in revetment products where the saturated Dutch GGBFS market can be alleviated partially by substitution of calcined clay. However, to apply the alkali activated concrete in revetment products, more research should be carried out with regards to durability, curing methods, recyclability and service life.