Measuring Device For Determining Dowel Positions on Concrete Slabs

Paper by NOSKE from ISCR 9th 2004 Instanbul Turkey

and to secure the height position of the individual slabs. They must be positioned in the middle of the slab thickness so that they do not prevent longitudinal motion of the slabs. In modern concrete pavement construction the concrete is poured over the entire cross section width using slip form pavers. As a rule it is not possible to preposition the dowels in support baskets due to the fact that the concrete is delivered from the front using dump trucks, which tip to the rear. In such cases the dowels are set in the already compacted concrete during the production process using special equipment. For various reasons setting according to requirements is quite difficult and from practical experience it is known that incorrect positioning occurs frequently. This is also obvious from subsequent damage in the area of the joints. Dowels can contribute significantly to the transfer of lateral forces to the lateral dummy joints in concrete roads. Their correct positioning is of great significance for proper function and durability of the slab construction. The definitions made in the German regulations regarding positioning accuracy allow the following individual requirements to be categorized for dowels: 1. Number and interval in longitudinal/lateral cross section 2. Height position in concrete pavements 3. Displacement perpendicular to lateral joint 4. Angular position Presently the following definitions apply: - Number and interval - The number and interval are specified in the construction contract depending on the construction class (load class). The interval is 25 or 50 cm as a rule. - Height position Dowels are to be positioned in the middle of the slab thickness. The deviations should not exceed max. ± 20 mm. - Displacement Dowels are to be imbedded symmetrically in the adjacent slabs. The lateral displacement perpendicular to the joint should not exceed a maximum value of ± 50 mm. - Angular position The maximum angular position may vary up to 20 mm in relation to the dowel length of 50 cm. Due to the absence of non-destructive instruments to date, control tests are not foreseen. Therefore, there are no specifications regarding the consequences when the positioning does not meet the requirements. During the last few years developments have been made in Germany on non-destructive measurements of dowels and anchors in concrete pavement construction. The development status achieved is reported below.

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