Limitations of the use of concrete resistivity as an indicator for the rate of chloride-induced macro-cell corrosion

An experimental setup was designed to study the impact of concrete resistivity on the rate of chloride-induced reinforcement corrosion. Small pieces of mild steel were used to simulate pits (anodes) that form when chlorides come into contact with the reinforcement. The galvanic current was measured between the simulated anodes and a cathode network. Comparisons were made between the galvanic current and the concrete bulk resistivity. The bulk resistivity was varied using two mortar mixes (made of plain Portland cement and a blended Fly ash cement) which were exposed in different temperature and moisture conditions. Despite a high scatter in the results, it was clear that the relationship between bulk resistivity and corrosion rate depended on the mortars tested. The findings presented in this paper and the accompanying work strongly indicate that concrete bulk resistivity alone does not provide sufficient information for assessment of the corrosion rate for chloride-induced macro-cell corrosio

Methods for characterising the steel–concrete interface to enhance understanding of reinforcement corrosion: a critical review by RILEM TC 262-SCI

The steel–concrete interface (SCI) is a complex, multi-phase and multi-scale system. It is widely known to influence the performance and long-term durability of concrete structures. However, a fundamental understanding of its properties and effects on corrosion initiation of embedded reinforcing steel remains elusive. This is attributed to its complicated heterogeneity and time-dependent nature, exacerbated by the lack of suitable techniques for systematic and detailed characterisation. This paper, prepared by members of the RILEM Technical Committee 262-SCI, critically reviews available information regarding current methods (laboratory or field-based) for characterising local properties of the SCI that have been identified as governing factors affecting corrosion initiation. These properties include characteristics of the steel such as mill scale and rust layers, and characteristics of the concrete such as interfacial voids, microstructure and moisture content. We evaluated over twenty methods and summarised their advantages, applications and limitations. The findings show a severe lack of well established, non-destructive techniques that are suitable for direct monitoring of the SCI at a representative scale with sufficiently high resolution (spatial, temporal), particularly for moisture related aspects. Several promising novel techniques with significant potential for further development and application were identified and discussed. Finally, we provide several recommendations for future research needs that are required to advance this critically important topic

The steel–concrete interface

Although the steel–concrete interface (SCI) is widely recognized to influence the durability of reinforced concrete, a systematic overview and detailed documentation of the various aspects of the SCI are lacking. In this paper, we compiled a comprehensive list of possible local characteristics at the SCI and reviewed available information regarding their properties as well as their occurrence in engineering structures and in the laboratory. Given the complexity of the SCI, we suggested a systematic approach to describe it in terms of local characteristics and their physical and chemical properties. It was found that the SCI exhibits significant spatial inhomogeneity along and around as well as perpendicular to the reinforcing steel. The SCI can differ strongly between different engineering structures and also between different members within a structure; particular differences are expected between structures built before and after the 1970/1980s. A single SCI representing all on-site conditions does not exist. Additionally, SCIs in common laboratory-made specimens exhibit significant differences compared to engineering structures. Thus, results from laboratory studies and from practical experience should be applied to engineering structures with caution. Finally, recommendations for further research are made

Characterisation of fibre content, distribution and orientation to predict Fibre Reinforced Concrete behaviour

This paper calculates the flexural behaviour (load-displacement and stress-crack opening distributions) of “real” beams where the contribution of every single fibre is considered. It therefore, allows clarifying to what extent a link between single fibre pull-out models and post-cracking behaviour can be established when the uncertainty about the actual fibre content, distribution and orientation is eliminated by using a computed tomography (CT) - imagery algorithm. The results were compared to three point bending tests of the same beams. The CT algorithm also presents a solution to the difficult problem of separating clusters that occur when fibres pack together within the concrete matrix

Mixing protocols for plant-scale production of concrete with superabsorbent polymers

Superabsorbent polymers (SAPs) have been investigated for their potential for internal curing, promotion of self-sealing, and self-healing of concrete structures. There has been a lack of publications concerning large-scale testing of structures with SAPs, and bringing this SAP-modified concretes from laboratory environment to plant-scale production might demand adaptations in the mixing protocols. In this paper, a reference mixture and a SAP-containing mixture were produced at a concrete plant scale and the influence of adding the polymers at different moments was investigated. The addition of SAPs directly in the truck, after the mixing procedure, showed no significant impact on the compressive strength of the concrete, but an agglomeration of particles was found in the air void analysis. The specimens with SAPs added directly in the truck presented an inferior performance in terms of shrinkage reduction when compared to the specimens with SAPs added on the materials belt, with the dry materials