Self-compacting concrete with high green strength for use in slipform pavers in concrete road construction

Duration: 2007 - 2010

In the production of concrete pavements, concretes of stiff to very stiff consistency have so far been placed with slipform pavers. Accordingly, it is inevitable to compact the concrete with internal vibrators firmly attached to the paver. This often results in an increased proportion of fine mortar in the vibrating lanes, which may alter the concrete properties in these areas compared with those of the surfaces outside. In such system-related weak points, cracks can then form in the course of use, whereby the vibrating alleys are not necessarily to be described as the cause of the cracks, but merely as localizing them. Self-compacting concretes (SCC) do not require external compaction energy and are capable of complete self-release under the influence of gravity alone. Self-compacting concrete could be used in the construction of pavements to facilitate paving, improve economy, and eliminate the vibration alleys outlined above as potential weak points. For this purpose, however, two more or less conflicting properties or their requirements must be reconciled. On the one hand, the concrete must be so free-flowing that it completely deaerates itself under the influence of gravity alone, and on the other hand, it must exhibit a very stiff behavior in the dormant state and within a very short time, so that when it leaves the slipform paver, i.e. after a few minutes, it has a sufficiently high green strength and the carriageway slab retains its shape even in the fresh state. In order to get closer to this question, rheological tests were mainly carried out on binder glues in this research project. These investigations focused on the behavior of different additives and admixtures, such as fly ash, quartz powder, metakaolin, thixotropic agents, thixotropic additives, etc., on the rheological and thixotropic properties of binder glues.