Paper by BIRMANN from ISCR 10th 2006 Brussels Belgium
The precision and applicability of two non-destructive measuring methods for dowel bars alignment: Ground Penetrating Radar (GPR) and the Pulse Induction method (PI). was investigated. The project was sponsored by the German Federal Ministry of Transport, Building and Urban Affairs (Bundesministerium für Verkehr, Bau und Stadtentwicklung BMVBS). The precision of the two measuring methods is partly influenced by composition of steel, ferritic aggregates and other influences as neighbouring tie bars (PI) or moisture content (GPR). Therefore, a system of monetary penalty for dowel misalignments does not yet exist in the German specification ZTV Beton-StB 01. GPR can detect voids and irregularities in the concrete structure above the dowel bars, but requires drilling cores for calibration. The percentage of quantity of dowel bars showing misalignments and the resultant misalignment of dowels in several old concrete pavements indicated no influence to opening of joints or observed longitudinal cracking. However, dowels in a high position with low concrete cover initiated damage of the pavements. It can be concluded that the possibility of measuring dowel alignment already some hours after paving increases the quality in concrete pavement construction. The voluntary internal control enables the contractor to collect more experiences and already at the beginning of a project to optimize dowel setting by vibration techniques or to optimize the concrete mixture.