Bonding of steel reinforcement in structural expanded clay lightweight aggregate concrete: The influence of failure mechanism and concrete composition

A comprehensive experimental study on the concrete–steel bond behaviour of structural expanded clay lightweight aggregate concrete (LWC) was carried out using different compositions, types and initial wetting conditions of lightweight aggregates, anchorage lengths, reinforcement arrangements, strength classes and failure mechanisms. For splitting failure, the bond strength of LWC was about 70% that of normal weight concrete (NWC). But when the confinement is sufficient and pull-out of the reinforcement occurs, the relative performance of LWC and NWC may vary widely. The reduction of the bond strength with LWC was roughly proportional to ρd/2200, where ρd is the concrete dry density. The addition of silica fume had little effect on the LWC bond strength. The bond was impaired when the LWA was pre-soaked. LWC seems to be less affected by the position and orientation of the reinforcement. It is shown that the water/cemet (w/c) ratio has a greater influence on the bond strength than on compressive strength. The bond strength was higher in the lower w/c concrete, regardless of the type of aggregate. Moreover, the bond strength of LWC was more than twice that of NWC of equal compressive strength. It is shown that the application of reduction factors to the LWC bond strength, as suggested in the main standards, may be too unrealistic. A new approach for estimating the LWC bond strength is suggested.