In recent years, an increasing number of diaphragm walls has been built in the Netherlands. Studies have shown that the quality of the concrete in these D-walls is not comparable to that of compacted concrete poured in formwork, as is often assumed. There are known incidents of bentonite inclusions and insufficient concrete cover of the reinforcement. Less well-known problems are the presence of cavities around the reinforcement and porous zones in the concrete cover. Such defects limit the suitability of D-walls for use in aggressive environmental conditions, like the tidal and splash zone of marine structures.
The problems mentioned above are either fully or partly caused by insufficient workability and/or stability of the fresh concrete. An extensive research program has been carried out to improve the properties of D-wall concrete both in the fresh and hardened phase. The introduction of a stabilizing admixture proved to be a breakthrough to obtain high flowability and excellent stability in the fresh state. Whereas conventional D-wall concrete typically has F5 consistence, the innovative concrete mix (developed under the name: X10) has a consistence in the self-compacting concrete (SCC) range (SF1, SF2). Full scale trials have shown that this high flowability results in a quite even pouring front up to relatively large distances from the tremie pipe. As a result, the risk of bentonite inclusion in D-walls is considerably reduced. Investigation on cores revealed a very dense concrete cover with nearly no defects, leading to a high durability.
In 2015 X10 has been used in D-walls for strengthening of a river embankment. At present, it is being used for construction of the walls of a large sea lock for the port of Amsterdam in IJmuiden (NL). Experiences from the research program and the projects are shared in this paper.
Subjects: None provided
Author: M. M. R. Boutz, B. J. Admiraal, R. van Berkel and P. R. B. van der Werff
Publisher: DFI, EFFC