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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.

In this study, we made examinations by means of experimental and analytical methods for the purpose of grasping the shear characteristics of RC walls with corroded reinforcement and verified the validity of analytical models and constitutive laws by making comparisons between the analysis results and the test results. First of all, we conducted two kinds of element tests on the bond strength of reinforcement greatly affected by corroded reinforcement and tension stiffening of concrete around the reinforcement. Regardless of the diameter of the reinforcement, we found that the bond strength could be assessed using past equations and, for tension stiffening, proposed an equation in consideration of the effect of corrosion weight loss by obtaining data of constitutive laws for FEM analyses. Then, we conducted in-plane shearing tests on the RC walls with corroded reinforcement and found that the effect of the corrosion weight loss of reinforcement on the shear strength of the walls was low. Finally, we found that the analyses almost follow the test results through FEM analyses of the RC shear walls with corroded reinforcement using the constitutive laws obtained through element tests and past constitutive laws.

This paper provides a part of the series “Development of an Evaluation Method for Seismic Isolation Systems of Nuclear Power Facilities.” This part shows the fundamental properties of full-scale lead rubber bearings with 1600 mm diameter based on break tests. The following results are mainly obtained. One: The deformations and the acting loads of the full-scale specimens were accurately obtained up to break by the measurement system for the break tests. Two: The fundamental properties for the full-scale lead rubber bearings with a large-diameter lead plug were obtained by the basic property tests. The load-displacement relations were stable and similar basic properties were obtained among the specimens. Three: The result of shear break tests showed that the hardening property of the specimens had a certain harmony with the hardening stiffness model which was used in the seismic response analysis to investigate the safety margin for severe earthquakes beyond design basis earthquakes of nuclear power facilities. The effect of axial pressure on hardening property was not specifically observed. The evaluated linear strain limit was larger than 250% for every specimen. Four: The softening property of the specimens was obtained from the tensile break tests. The axial stress of tensile yield was approx. 1.4 MPa and the axial stress did not show any negative gradient at least up to approx. 10% axial strain after the tensile yield even with offset shear strains. Five: The tensile force acting on the bolts which secure the specimen to the testing machine was lower than the estimated tensile force at shear break, which indicates tensile force was conservatively calculated to maintain safety in the design for foundation of lead rubber bearings.