Effects of corrosion on the behaviour of precast concrete floor systems

Corrosion is the most deteriorating phenomenon causing structural deterioration of both prestressed and nonprestressed reinforced concrete structures. Precast and pretensioned concrete floor elements, as solid joists and solid and hollow-core planks, are widely used worldwide for structural floor of small to medium size buildings, including car-parking garages. Although usually considered as secondary structural elements, these are particularly vulnerable to corrosion as they are designed and produced using neither longitudinal nor transverse ordinary reinforcements. In this paper the structural behaviour of pretensioned concrete solid joists is experimentally investigated. A set of joists specimens is subjected to accelerated corrosion by subjecting it to an impressed electrical current, in order to achieve (theoretical) reinforcement area reductions between 2.5% and 40% of the initial area. Corrosion levels are then experimentally assessed including their variability along the prestressing wire length. The crack development is observed and the equivalent prestressing losses are evaluated based on the counter deflection variation. The mean tensile stresses and strains of the prestressing wires, depending on the corrosion rate, are assessed. Finally, the ultimate loading capacities of the concrete joist specimens are evaluated based on a three point loading protocol. Results show that the service and the ultimate performance of pretensioned concrete joists are not affected for corrosion levels below approximately 2%. For higher degrees, concrete cracking starts developing resulting into bond degradation and consequent loss of effective prestressing force and counter deflection reduction. Tensile tests of corroded prestressing wires suggest a more relevant reduction of the material average maximum strain than strength. Loading tests of the joist specimens show that for corrosion levels above 15%–20% the ultimate loading capacity can be reduced up to 10% of that of the uncorroded specimens.