Development of Conservative Material Properties to Account for Concrete Degradation Mechanisms With Specific Emphasis on Rebar Corrosion Due to Chloride Ingress

Abstract

Abstract NPPs and research reactors built during the mid-20th century often have incomprehensive material characteristics of their concrete structures. This lack of quality records frequently leads to challenges when attempting to demonstrate safety during life extension projects or when specific modelling is necessary for portions of the plant when design regulations are updated with new or revised requirements. In the framework of LTO there is limited knowledge about ageing and the structural integrity of concrete structures. In order to increase the knowledge in the field of civil structures, this paper focuses on investigating the ageing mechanisms of civil structures at NRG, Petten, and determining an appropriate chloride ingress model together with the alteration of concrete material properties to account for possible degradation effects. Knowledge of the ageing mechanisms of civil structures, especially concrete, will improve concrete’s ageing management and assessment methods. The purpose of this research paper is to provide a methodology that can be used to account for possible concrete degradation. This will include a chlorine ingress model, calibrated to data obtained from the HFR chimney, that allows for the rebar reduction to be calculated. Furthermore, the design properties of concrete were determined in line with NEN-EN 1992-1-1:2004 [10] and NEN-EN 1990 [11] for specific concrete grades. The model generated will allow for user input if more detailed concrete properties are available for the area in question. This will allow the generation of area specific design properties for concrete that accounts for possible rebar reduction due to chloride ingress corrosion. The report illustrates a methodology to account for chloride ingress during modelling by reducing the rebar diameter. It further demonstrates the importance of the assumed concrete properties as starting inputs to the chloride model and the calculated rebar reduction and generated internal pressure. The determined concrete properties, together with calculated rebar diameter reduction, are used to update the previously completed FEA of the HFR [1] and provide a comparison of the previous results when considering reduced concrete strength and rebar diameter. The actual rebar corrosion due to chloride ingress within the HFR is expected to be less as surface corrosion conditions are expected to be less. In the future, more accurate material properties should be determined through physical measurement for the modelled slab. Further research and modelling can be completed to understand better steel corrosion failure in reinforced concrete with 3D FE analysis and measurements for chloride ingress in the HFR should be obtained.