Untersuchungen zu Betonabplatzungen an Brückenkappen infolge Frost-Taumitteleinwirkungen

Investigations of concrete scaling at edge beams of bridges due to freeze deicing salt attacks

Two nearly contrary requirements are set to the concrete of edge beams on bridges. On the one hand a low water-cement-ratio is sought with respect to a sufficient freeze deicing salt resistance (XF 4). On the other hand the same characteristic value should be not too low as the concrete strength and in sequence the crack-limiting reinforcement should be kept below certain ranges.
In the last few years at several times scaling at concrete surfaces of edge beams on bridges due to the attack by freeze and deicing salt has been observed. This casually is associated with the fact, that today also in concretes for these edge beams more and more CEM II- and CEM III-cements are used - contrary to the past, where traditionally CEM I-cement had been applied. To check the influence of the various parameters of concrete and execution on the freeze deicing salt resistance considering the specific random conditions of bridges appropriate lab tests (CDF-tests) had been performed. Amongst others it could be demonstrated that the w/c-ratio, with 0.50 set in ZTV-ING as maximum allowable value, seems to be marginal. Only a small exceeding of this value resulted in significant increased scaling. This was quite more evident in the concretes with CEM II-cements than in those with CEM I. Thus the specific adjustment between cement and water-cement-ratio is of very high importance in concretes for edge beams on bridges.