記述言語：英語   出版者・発行元：Japan Concrete Institute  

<p>The 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.</p>

DOI： 10.3151/jact.21.869

Open Access

CiNii Research

記述言語：英語   出版者・発行元：Japan Concrete Institute  

<p>This 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.</p>

DOI： 10.3151/jact.21.851

Open Access

CiNii Research

出版者・発行元：Construction and Building Materials  

In this study, the fracture process of concrete in the presence of alkali silica reaction (ASR) cracks under compressive stress was evaluated. Concrete specimens damaged by ASR expansion at various expansion levels were tested under monotonic, stepwise cyclic, and sustained compressive loadings to evaluate the change in mechanical properties. The evolution of expansion cracks under these loading conditions was assessed using digital image correlation (DIC). In stepwise cyclic and sustained loadings, the elastic and plastic strains generated under different stress levels were separately investigated to elucidate the stress resistance mechanism and the impact of expansion cracks on mechanical properties. An increase in the expansion level was found to remarkably decrease the elastic modulus of concrete but only slightly reduce the compressive strength. Using DIC, expansion cracks were observed with the accumulation of principal strain development even at low stress level. Elastic strains linearly developed in specimens with and without ASR damage, whereas plastic strains increased non-linearly with expansion. Despite the high plastic strains observed before reaching the peak load under stepwise cyclic and sustained loadings, the compressive strength and elastic modulus of concrete remained unchanged regardless of the loading pattern. Based on this evidence, the stress resistance mechanism in the cross-section of ASR-damaged concrete was explained.

DOI： 10.1016/j.conbuildmat.2023.132099

Open Access

Web of Science

Scopus

記述言語：英語   出版者・発行元：Japan Concrete Institute  

<p>The involvement of expansion cracks in reducing compressive properties was experimentally evaluated. Concrete specimens deteriorated by delayed ettringite formation were subjected to three loading patterns (monotonic, stepwise cyclic and sustained loadings) and digital image correlation was performed to observe the behavior of expansion cracks during compressive loading. As a result, while significantly large plastic deformation was generated in the pre-peak, the reduction in compressive properties was hardly influenced by the loading patterns. The elastic strain, obtained from the loading hysteresis, increased linearly until a maximum load was reached. Consequently, two possible stress-bearing mechanism of concrete damaged by delayed ettringite formation under compressive stress was proposed to explain the development of elastic and plastic strains and the reduction in the compressive property.</p>

DOI： 10.3151/jact.21.294

Open Access

CiNii Research

出版者・発行元：Life Cycle of Structures and Infrastructure Systems Proceedings of the 8th International Symposium on Life Cycle Civil Engineering Ialcce 2023  

In this study, the effect of the expansive site ratio on the anisotropy of expansion due to delayed ettringite formation (DEF) was numerically evaluated considering creep. In this analysis, aggregates and mortar were separately modeled using 3D-Rigid Body Spring Model. The expansion strain was applied to the expansive site for 200 days. Each analysis was conducted under stress-free and restraint conditions. As a result of the 1 % expansive site, the expansion under restraint condition was smaller than that under stress-free condition. In the case of a higher expansive site ratio, the expansion under restraint condition was larger, and the larger compressive stress was generated in the restraint direction. The reason why the expansion under restraint condition was smaller for the 1 % expansive site case is the less accumulated compressive stress due to the localization of expansion origin. Consequently, the expansion origin may be scattered in the actual phenomenon.

DOI： 10.1201/9781003323020-144

Scopus

出版者・発行元：Cement and Concrete Composites  

This study discusses the mechanism for the changes in the compressive properties of internally cracked concrete due to expansion phenomena. The internal crack patterns due to alkali-silica reaction (ASR) and delayed ettringite formation (DEF) are reproduced using the model concrete with artificial cementitious aggregate. The compressive behaviors are clarified using a uniaxial compressive test with digital image correlation. As a result, in terms of ASR, the trends for reduced mechanical properties in model concrete differ from the expansion phenomena under stress-free condition and the anisotropy of change in mechanical properties due to the aggregate crack orientation changes is observed. For DEF, the reduction in mechanical properties is independent of thickness of a debonding crack. Consequently, the mechanism for reduction in compressive strength and elastic modulus by the aggregate cracking and gap formation due to ASR and DEF based on the compressive stress transfer path at the cross-sectional area was proposed.

DOI： 10.1016/j.cemconcomp.2022.104441

Web of Science

Scopus