Performance‐based durability design, carbonation part 2 – Classification of concrete

Abstract

Performance-based durability design, carbonation part 2 -Classification of concreteAt present, prescriptive regulations with regard to concrete cover and composition are applied to provide sufficient durability of reinforced concrete members under exposure conditions with different degrees of severity. In view of current knowledge on deterioration mechanisms and their modelling, it is planned to change from these deemed-to-satisfy specifications to a performancebased design approach in future standards. In such specifications, concrete durability design is based on the statistically characterized performance of concrete, determined in standardized tests with respect to defined classes of concretes with similar performance. This paper presents the results of a study in which concrete mixes were tested and analysed with respect to their carbonation resistance. Compositions with similar performance are grouped into carbonation resistance classes. These classes are described statistically and requirements for performance testing are given. In addition, composition requirements are introduced in order to determine concrete performance depending on mix composition prescriptively. Finally, an example is given for the assessment of concrete performance with regard to carbonation. This work was carried out at the request of JWG under CEN TC 250/SC2 and CEN TC 104/SC1 as an input and starting point for the ongoing committee work to implement the methodology from the fib Model Code for Concrete Structures 2010 in the next generation (2021) of European concrete standards.

FE-Study on the Effect of Gradient Concrete on Early Constraint and Crack Risk

“…In a performance-based design concept, the aim is to predict the carbonation depth in concrete depending on the concrete age. One concept that is based on experimental observations and theoretically derived by diffusion theory can be found in the literature [4][5][6]39]. In this theory, carbon dioxide is diffused into concrete and reacts with non-carbonated calcium minerals in the concrete at the "moving carbonation boundary".…”

“…According to [4][5][6] the performance-based resistance to carbonation is highly dependent on the cement type. Cement CEM I (high hydration energy) has good carbonation resistance while CEM III (low hydration energy) has a poor one.…”

“…To account for environmental conditions (humidity, CO2 concentration, curing, wetting effects) additional factors are applied in [4][5][6].…”

“…The curves are calculated assuming a carbonation rate for CEM I of kNAC = 2.5 mm/year 0.5 and a carbonation rate for CEM III/B of kNAC = 4.5 mm/year 0.5 . Additionally, an execution tolerance of Δc = 10 mm, according to [4][5][6] and standard test conditions (ke = ka = kc = W(t) = 1) for carbonation rate were assumed. The following equation (10) was used:…”

“…The main influences are corrosion induced by carbonation of the concrete, corrosion induced by chloride, freeze-thaw attack, chemical attacks or abrasive wear as already stated in present codes such as [2]. In recent years, performance-based design concepts for durability of reinforced concrete structures against carbonation of the concrete have been developed (e.g., [3][4][5][6]). …”