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

Effect of metallic aggregate and cement content on abrasion resistance behaviour of concrete

Many concrete structures are required to have sufficient abrasion resistance, such as dams, canals, roads and floors. The abrasion resistance of concrete may be defined as its ability to resist being worn away by rubbing. Compressive strength and aggregate type are also important factors affecting the abrasive behaviour of concrete. However, very little information on the properties of haematite containing concrete has been reported. The authors report on the abrasion resistance of concrete with four different cement contents (300, 350, 400 and 450 kg m(-3)) and with haematite as a metallic aggregate with replacement ratios of 15, 30, 45 and 60\% under 5, 10 and 15 kg loads. The water/cement ratio was kept constant at 0.40 to evaluate the effects of haematite and cement content. Slump tests were conducted to evaluate the workability of fresh concretes. For hardened concrete samples, mechanical tests such as compressive strength, splitting tensile strength, unit weight and wear resistance were performed. Along with the physical and mechanical properties of concretes, haematite was studied as a mineral. Increasing both cement and haematite content has substantial effects on the strength of the concrete. Polarising microscopy views of the interfaces show that haematite aggregates exhibit greatly improved bond strength. Wear loss of concrete decreases with increasing concentration of haematite, while it increases with increasing cement content. An equation representing wear as a function of cement content, compressive strength and also applied load provides virtually perfect agreement with the experimental results

Casting position effects on bond performance of reinforcement bars

The phenomena associated with the consolidation of fresh concrete (bleeding and plastic settlement) are commonly considered significant for the bond performance of reinforcement. However, rules to take care of such influence for design are not consistent amongst design recommendations and may lead to notable differences. With this respect, two failure modes generally govern the bond failure, namely the spalling of the concrete cover (also called splitting failure) and the pull-out of the reinforcement. In this paper, a detailed investigation is presented on the influence of bleeding and plastic settlement on both failures modes, in an effort to understand their conceptual differences and to clarify how shall consistent design recommendations be formulated. Such investigation is based on a comprehensive experimental programme, comprising 137 pull-out tests on specimens with different casting conditions, embedment lengths, loading arrangements and concrete covers. On the basis of the test results, the phenomenological differences between pull-out and spalling failures are clarified, as well as the main influencing phenomena (particularly the potential presence of cracks and voids under the reinforcement and the mechanical properties of concrete). On this basis, a physically-consistent approach is presented to consider the casting conditions on the bond performance and failure modes