Concrete strength in old Swedish concrete bridges

In this paper the development and variation of compressive and tensile strength of concrete are presented for old reinforced concrete bridges in Sweden. The mean increase in concrete compressive strength was about 70% for twenty bridges built during 1931-1962 (a rather high dispersion must be taken into consideration). The increase is related to the original 28-day concrete compressive strength which varied between 18 and 51 MPa. The compressive strength within a typical reinforced railway concrete trough bridge was approximately 15% higher in the longitudinal beams than in the bottom slab (measured on drilled cores). The tensile strength showed a similar variation as the compressive strength, but the difference could not be statistically verified. Different equations to convert compressive strength into tensile strength have also been studied. The investigation shows that it is important which conversion equation that is used in an assessment situation.Validerad; 2006; 20070619 (thun