Several interesting results and dependencies can be observed when looking at the chloride deposition rates measured:
• There is a clear link between the amount of deposited chlorides and the winter maintenance using de-icing salt. The chloride deposition rates during the winter maintenance period significantly exceed the values measured during the spring months. The difference is evident especially with bridge No. 1, which is affected by the intense traffic on the D1 highway underneath. The drop in deposition rate at the end of the winter maintenance period is rather steep. The chloride deposition rate during the winter period amounts to 5 mg·m−2 ·day−1 . The gradual decline in the deposition rate over approximately two months after the end of winter maintenance, reported in the literature, has not been observed.
• Comparing the results from sampling devices located at bridge No. 1 with results from bridge No. 2 shows the significant influence of the specific microclimate found under the bridge structure. It is quite evident that the road traffic under the bridge structure is the main source of chloride deposition upon the bridge’s supporting elements. The results from bridge No. 2 show, on the other hand, that a suitable design of the bridge (girder bridge with an upper deck and sufficient overhang over the external main girders), significantly reduces the amount of chloride deposits originating from the road traffic on the bridge.
• The method used for measuring the dry deposition of chlorides significantly affects the resulting values. For most measurements, the highest chloride deposition rates are obtained using the wet candle method (maximum deposition rate measured was 90 mg·m−2 ·day−1 ). In some cases, however, the highest chloride deposition rate was measured with a dry plate method in a horizontal position. Dry plate vertical measurements provided in all cases significantly lower values when compared with other measurement methods (approximately four times less than the dry plate in the horizontal position).
• The results indicate that the external surfaces of the supporting steel structure are exposed to higher levels of chloride deposition when compared to internal surfaces (this observation is in line with the results presented). However, dust deposition (including chlorides) on the external surfaces of bridge No. 1 is regularly washed by rainfall or wind. Non-protective corrosion products only form on the internal flanges, despite the fact that the chloride deposition rate on the internal surfaces is lower compared to the external ones.