Long-term Material Properties of a Thick Concrete Wall Exposed to Ordinary Environmental Conditions in a Nuclear Reactor Building: the Contribution of Cement Hydrates and Feldspar Interaction

Rymeš, Jiří; Maruyama, Ippei; Shimamoto, Ryu; Tachibana, Akira; Tanaka, Yoshihito; Sawada, Shohei; Ichikawa, Yoshikazu; Kontani, Osamu

doi:10.3151/jact.17.195

Cited by 12 publications

(5 citation statements)

References 38 publications

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“…In the latter, after 16½ years under a relative humidity higher than 80% and a highly soluble alkali concentration, the cement hydrates reacted with the silica and alumina released from feldspar group aggregates and formed Al‐tobermorite. In contrast to the general cases where the concrete strength decreases over time, the strength and Young's modulus of the concrete wall of the Hamaoka nuclear power plant increased due to this reaction 66 and Al‐tobermorite formation. Maruyama et al 65 .…”

Section: Introductionmentioning

confidence: 67%

Micro X‐ray diffraction and elemental study on Al‐tobermorite formation in aged modern concrete

et al. 2022

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In modern Portland cement, calcium aluminum silicate hydrates (C‐A‐S‐H) do not generally form crystalline Al‐tobermorite. In this study, to identify the mechanism of Al‐tobermorite formation, synchrotron micro X‐ray diffraction and field‐emission scanning electron microscopy‐based energy‐dispersive X‐ray spectroscopy (EDS) investigations were performed on a slice of a thick concrete wall in a nuclear power plant, where the presence of Al‐tobermorite was previously confirmed. Rietveld analysis of the diffraction diagrams obtained from the 2D diffraction patterns showed that Al‐tobermorite was formed almost everywhere in the cement paste near sandstone aggregate and that Al‐tobermorite platelets were distributed across most of the cement paste area in a random orientation. The basal spacing d‐value of Al‐tobermorite was identical and equal to 11.39 Å. The ratio plots from the EDS maps indicated that the chemical composition of the mixture of Al‐tobermorite and C‐A‐S‐H was almost homogeneous all around the cement paste. The Al‐tobermorite in this concrete is probably formed via a dissolution–precipitation process. From the random orientation even next to the surface of aggregate, we infer that the Al‐tobermorite formation does not need the surface of aggregate to precipitate.

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Section: Introductionmentioning

confidence: 67%

Micro X‐ray diffraction and elemental study on Al‐tobermorite formation in aged modern concrete

et al. 2022

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“…To systematize the knowledge for long-term use, it is necessary to accumulate health monitoring data of actual structures, crack investigations, and detailed analysis of physical properties. For example, it has been reported that an additional reaction between hydrates and rock-forming minerals in thick concrete members contributed to a significant increase in strength [81,82]. This phenomenon cannot be observed in laboratory experiments.…”

Section: Discussionmentioning

confidence: 98%

Impact of drying on concrete and concrete structures

Maruyama

2022

RILEM Tech Lett

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This study reviews research showing changes in the performance of reinforced concrete structures and members caused by drying conditions, and aims to contribute to evaluating the structural safety in the long-term use of concrete. Additionally, to build a consensus on the changes in the physical properties of concrete materials after drying, the review focused on experiments intended to produce a uniform distribution of moisture-induced material property changes in the interior of the cross-section. There is generally no effect on the change in the maximum loading capacity of a structure when the design is based on the flexural performance of the components. However, in the case of structures dominated by members determined by the shear capacity of the components, the reduction of the maximum loading capacity can be a problem. The decrease in stiffness is largely due to the opening of shrinkage cracks and the reduction of the Young’s modulus of concrete after drying. The change in the compressive strength of concrete due to drying is governed by the specific strength change of hardened cement paste caused by the colloidal nature, but it is also affected by the shrinkage of the aggregate, which changes the damage in concrete under drying.

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“…The drying period took 93 days, ensuring a quasi-equilibrium condition [0.01%/day according to (Wu et al 2019)] for all samples. This 105°C was selected as the reference that is the most commonly used, and 20°C and 40% RH was selected since this drying state is similar to the drying condition on the surface of thick concrete walls in nuclear power plants [an estimation was made based on references (Rymeš et al 2019;Maruyama et al 2021)].…”

Section: Water Absorption Test Methodsmentioning

confidence: 99%

“…To assess the level of contamination in concrete structures accurately, it is important to consider water transport and microstructural changes within the material. The concrete in the Fukushima NPP buildings has a relatively low moisture content after many years of service (Rymeš et al 2019;Maruyama et al 2021). After the accident, part of the concrete surface was exposed to heat and drying conditions, then was subsequently exposed to seawater and contaminated water.…”

Section: Introductionmentioning

confidence: 99%

Water Uptake in OPC and FAC Mortars under Different Temperature Conditions

Kiran

Samouh

Matsuda

et al. 2021

ACT

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This experimental and numerical study aims to evaluate the penetration depth of contaminated water in the concrete structures involved in the Fukushima Daiichi nuclear powerplant. The influence of the mortar mixture on water absorption was investigated by varying the composition: mortars containing aggregates from river sand and crushed limestone sand were compared, and 15% of the cement in the mixture was substituted with fly ash. The effect of temperature in nuclear conditions is also significant; therefore, water uptake at temperatures of 20 and 60°C was considered. Finally, pre-drying conditions were studied by drying the sample at two different conditions: at 105°C and at 40% RH (relative humidity) and 20°C. Water uptake was monitored using x-ray computed radiography in combination with mass measurements. In all cases, anomalous sorption, or a nonlinear relationship between penetration depth and the square root of exposure time was observed, with the sorption curves showing bimodal behavior. The aggregate type had no significant effect on the water uptake results. However, the samples containing fly ash clearly had lower water uptake rates, which can be explained by the differences in the calcium silicate hydrate (C-S-H) structures. With increasing temperature, the penetration was slightly accelerated at the beginning of the experiment, with the rate of penetration then decreasing rapidly. The densification of C-S-H at higher temperatures could contribute to this phenomenon. Microstructural rearrangements can also explain why the highest uptake rates occurred for samples that were exposed to severe drying conditions (105°C). The experimental results were consistent when the microstructural rearrangement was considered, further confirming these conclusions.

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Long-term Material Properties of a Thick Concrete Wall Exposed to Ordinary Environmental Conditions in a Nuclear Reactor Building: the Contribution of Cement Hydrates and Feldspar Interaction

Cited by 12 publications

References 38 publications

Micro X‐ray diffraction and elemental study on Al‐tobermorite formation in aged modern concrete

Micro X‐ray diffraction and elemental study on Al‐tobermorite formation in aged modern concrete

Impact of drying on concrete and concrete structures

Water Uptake in OPC and FAC Mortars under Different Temperature Conditions

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