CEMENT AND CONCRETE RESEARCH (Elsevier Ltd.)
Direct observation of the local bond behavior between corroded reinforcing bars and concrete using digital image correlation
Avadh, K., Jiradilok, P., Bolander, J.E., Nagai, K.
CEMENT AND CONCRETE RESEARCH, Vol.123, 2021, OCT.
(https://doi.org/10.1016/j.cemconcomp.2021.104180)
Abstract
Corrosion induced rebar deterioration and concrete cracking alter the local bond interactions in reinforced concrete. An experimental methodology for investigating changes in the local deformation at the interface, caused by rib height reduction and corrosion layer is proposed. The effect of concrete cracking is eliminated by re-casting corroded rebars into new specimens. Local bond interaction is examined using uniaxial tensile tests and recorded through an observation window. The recorded interaction was analysed using Digital Image Correlation (DIC). Prior to visible crack formation, strain distribution maps revealed diagonal cracks indicating that the bond failure is associated with mechanical anchorage until a degree of corrosion of around 12%. Measurements of local opening and sliding behavior at the interface confirm that the slipping interactions become dominant with increase in corrosion. Differences in the shape of individual rib tips and flat lengths in specimens with higher corrosion cause significant variation in local bond
Hinderance of C-S-H sheet piling during first drying using a shrinkage reducing agent: A SAXS study
Maruyama, I., Igarashi, G., Matsui, K., Sakamoto, N.
CEMENT AND CONCRETE RESEARCH, Vol.144, 2021, JUN.
(https://doi.org/10.1016/j.cemconres.2021.106429)
Abstract
The role of a shrinkage reducing agent (SRA) in the hardened cement paste during a first desorption process was investigated by measuring the small-angle X-ray scattering (SAXS). Fractal disc analysis and Guinier approximation were adopted to interpret the SAXS profiles. We experimentally confirmed that the presence of SRA molecules mitigated the piling of calcium-silicate hydrate (C-S-H) sheets, which could be monitored by the increase in the thickness of the disc, representing the agglomeration of C-S-H sheets. In addition, the basal spacing of C-S-H did not change during the drying. By contrast, the diameter of the discs monotonically decreased and showed a similar trend to that of samples lacking SRA. Based on these findings, we concluded that SRA molecules were on the surface of the C-S-H sheets and mitigated the piling, facilitating water removal from the C-S-H agglomeration in the RH range of 80?40%.
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.