CEMENT AND CONCRETE RESEARCH (Elsevier)
Mechanism of drying-induced change in the physical properties of concrete: A mesoscale simulation study
Sasano, H; Maruyama, I
CEMENT AND CONCRETE RESEARCH, Vol.143, 2021, MAY.
(https://doi.org/10.1016/j.cemconres.2021.106401)
Abstract
Although many studies have found that drying alters the mechanical properties of concrete, the mechanism behind this change remains unclarified. The aim of this study is to elucidate the mechanism of change in properties of concrete after drying through the numerical calculation: a 3D mesoscale rigid-body-spring model (RBSM) with three phases, i.e. mortar, aggregate, and the interfacial transition zone while considering the properties changes of mortar due to drying. Based on the RBSM results, it is concluded that the change in compressive strength due to drying and heating is determined by a balance of the impact of drying-induced microcracking around coarse aggregates and the change in mechanical properties of the mortar due to drying. These mechanisms change the applied load required to reach the critical crack width and distribution, at which rim of the specimen begins to isolate from the core region and the load sustained by the rim decreases.
Influence of the distribution of expansive sites in aggregates on microscopic damage caused by alkali-silica reaction: Insights into the mechanical origin of expansion
Miura, T; Multon, S; Kawabata, Y
CEMENT AND CONCRETE RESEARCH, Vol.142, 2021, APR.
(https://doi.org/10.1016/j.cemconres.2021.106355)
Abstract
The origin of damage in concrete due to the alkali-silica reaction (ASR) is attributed to the expansion site in the aggregate. To investigate the cracking process of the aggregate during ASR and its consequences on concrete damage, the effect of the distribution of the expansive sites in the aggregate on ASR expansion and the crack patterns must be evaluated. Thus, in this study, a mesoscale discrete model was applied to ASR modeling to represent the propagation of cracking during ASR accurately. The distribution of the expansive sites in the aggregate was based on the gel pocket and reaction rim models, which are two ASR mechanisms reported in the literature. These two expansion models highlight the different crack patterns obtained based on the aggregate characteristics. Further, the expansion cracking processes determined based on the gel pocket and reaction rim models are consistent with the evolution of cracking with the expansion level.
Cs retention and diffusion in C-S-H at different Ca/Si ratio
Duque-Redondo, E; Yamada, K; Manzano, H
CEMENT AND CONCRETE RESEARCH, Vol.140, 2021, FEB.
(https://doi.org/10.1016/j.cemconres.2020.106294)
Abstract
Cement and concrete are commonly used in the construction of repository sites for radioactive wastes. The correct isolation of those contaminants requires good adsorption and low diffusion rates. Both parameters are highly affected by many factors, such as pH, temperature or composition. The large variability of experimental conditions and formulations makes it extraordinarily difficult to tackle the influence of each of them independently in experimental samples. To this effect, molecular dynamics simulations have been employed in this study to investigate the role of the composition in the capacity to retain Cs and diffusivity of these ions in calcium silicate hydrate (C-S-H) gel pores. The results indicate that the adsorption of Cs ions is worsened at high Ca/Si ratios due to a lower interaction of the cations with the C-S-H surface, while hydrophilicity of the C-S-H nanopore rises, resulting in higher long-range ordering and lower diffusion coefficients of Cs ions.