Bond Behavior of Structural Lightweight Concrete – Case of Prestressed Concrete Joists

The European standard for the design of concrete structures (EN 1992-1-1) imposes additional requirements in case of lightweight aggregate concrete (LWAC). This is reflected in the design process, by a reduction of the mechanical properties (tensile strength and modulus of elasticity) and an increase of the concrete cover to ensure an equivalent bond strength. The purpose of this paper is to explore whether these rules are adequate for structural LWAC with densities ranging from 1600 to 2000 kg/m3. To achieve this objective, bond tests are conducted on nine prestressed concrete beam specimens. Experiments are carried out by changing only one variable at a time, which is the type of aggregate. Expanded clay, expanded slate and normal weight aggregate concrete were tested. The initial strand slip, the prestress transfer length and failure modes of LWAC and normal weight aggregate concrete (NWAC) are compared. Results indicate that tested LWAC with densities greater than 1600 kg/m3 have tensile strength and modulus of elasticity in good accordance with the specifications EN 1992-1-1. However, the initial strand slip and the prestress transfer are slightly lower in the case of LWAC. This proves that structural lightweight concrete used in this study has at least the same bond behavior as NWAC.