Carbonation And Service Life Of Concrete Structures Under Combined Mechanical And Environmental Action

In many cases, concrete structures are exposed to combined environmental loads (such as carbonation and freeze-thaw cycles) and mechanical loads (such as compression, tension and shear simultaneously or subsequently. It is necessary to study the synergetic effects of deteriorating mechanisms under combined environmental and mechanical actions with respect to durability and importance to service-life of reinforced concrete structures.Three different types of concrete have been produced under four different conditions which included untreated concrete, concrete related to 50, 100 and 200 frost cycles, concrete treated with mechanical compression of 85%, concrete after surface waterproofing with silane. Then the experimental test series were described in every condition. Then accelerated carbonation, natural carbonation indoor and outdoor, capillary absorption had been imposed to three different types of concrete. Then CaCO₃ and Ca(OH)₂ content, amount of absorbed water and coefficient of capillary suction after mechanical and environmental loads were determined. Finally the reliability index was calculated and service-life was determined so as to study influence of combined environmental and mechanical actions on carbonation of concrete structure and its service-life.Results showed that the bigger water-cement ratio, the more CaCO₃ content and the less Ca(OH)₂ content after carbonated. When concrete structures were in tunnel circumstance and under combined environmental and mechanical actions, the service life of T was 80 years. Service life of T was 130 years when it was only suffered from carbonation. Therefore service-life reduced under combined actions of carbonation and mechanical load. Also, damage induced from freeze-thaw action accelerated the carbonation process. Influence of frost action became more evident with increasing number of freeze-thaw cycles. Service life of T after freeze-thaw cycles has reduced much more. So, service-life reduced under combined actions of carbonation and freeze-thaw cycles. And the more number of freeze-thaw cycles the more service life reduced. It has also been found that the amount of capillary absorbed water increased moderately after carbonation but strongly after imposed frost cycles. The coefficient of capillary suction increased after carbonation, mechanical loads and frost cycles but most after frost cycles. The ability of anti-carbonation of concrete after surface waterproofing with silane was better than untreated concrete. Natural carbonation depth indoor was bigger than outdoor.