Chemomechanical assessment of beams damaged by alkali-silica reaction

International audienceThe alkali-silica reaction (ASR) is a chemical reaction that causes expansions and unexpected deformations of concrete structures. A methodology of assessment of ASR-damaged structures is required in order to evaluate their structural stability. Chemomechanical calculations have been performed in order to investigate the assumption of modeling ASR-induced expansions as imposed strains. The input data for the model comprises the moisture distribution in the damaged structures, ASR-induced potential strains, and the influence of ASR on the concrete mechanical properties. The results of calculations have been compared with experimental data obtained from ASR-damaged beam specimens. The role of water supply and reinforcement has been analyzed in comparing the deformations of plain and reinforced concrete beams subjected to a moisture gradient. Calculations show that cracking and compressive stresses (here induced by steel reinforcement) have a large influence on the anisotropy of the ASR swellings. This induced anisotropy is shown to be one of the main factors that should be considered while predicting the mechanical behavior of ASR-damaged structures

Influence of Reinforcing Rebar on Expansion due to Delayed Ettringite Formation along the Bonding Length – Part II: Bond Performance of Reinforced Concrete Affected by DEF Expansion

International audienceThe purpose of this study is to clarify the bond behavior between rebar and concrete during DEF expansion and pullout testing. The details of the expansion test and the influence of reinforcing bar on DEF expansion have been precisely described in Part I. In Part II, the data related to the bond test is described. The change in bond behavior due to DEF expansion is investigated via the one-end pullout test and the influence of DEF expansion on the bond behavior is discussed. The local bond behavior (slip and bond stress) during the pullout test of the specimens without stirrups is observed to be dramatically changed by DEF expansion. Regarding the specimens with stirrups, failure did not occur during the pullout test and the local bond behavior slightly changed as in the case without stirrups. From the experimental results, a conceptual diagram is proposed to explain the bond behavior during DEF expansion and the pullout test based on the general conceptual understanding of the bond. It can be considered that the direction of local slip and local bond stress during the pullout test is opposite to that during the expansion process. This results in the observed complex local bond behavior during DEF expansion and the pullout test and the effect of stirrups on DEF expansion

Influence of Reinforcing Rebar on Expansion due to Delayed Ettringite Formation along the Bonding Length – Part I: The Role of Bond on Expansive Behavior of Concrete

International audienceThis paper explores the effects of rebar as an internal restraint on the expansion of delayed ettringite formation (DEF) in concrete. Concrete specimens embedded with steel bars without end plates are subjected to heat treatment followed by immersion in water. The effect of stirrups on expansion is also investigated. The results show that the longitudinal expansion of specimens without stirrups differs depending on the longitudinal position, owing to the different degrees of restraint resulting from stress in the steel bar. The final transverse expansions of the specimens without stirrups are close to those measured for stress-free specimens. Conversely, longitudinal and transverse expansions are significantly reduced in the specimens with stirrups. This indicates that the combination of a longitudinal steel bar and stirrups induces three-dimensional confinement stresses that help to limit DEF expansion in both the longitudinal and transverse directions. Furthermore, possible debonding along the longitudinal bar is observed in specimens without stirrups when the transverse expansion of the prismatic specimens is 0.4 to 0.6%. This behavior is not observed in the specimens with stirrups, which demonstrates the effectiveness of three-dimensional restraints in significantly mitigating the risk of debonding, as well as DEF expansion