Early-Age Shrinkage Effects in Precast Concrete Sandwich Panels

■ The results of the study show that using a bilinear shrinkage profile for each concrete layer in the analysis accurately predicts the shrinkage strains and that early-age cracking can occur in precast concrete sandwich panels that are not properly cured or that have a high reinforcement ratio. Precast concrete sandwich panels (PCSPs) are becoming popular because of their advantages in terms of rapid speed of construction, superior energy conservation, and flexible and diverse aesthetic options. PCSPs are widely used as structural members in residential buildings, hospitals, industrial warehouses, and schools. Traditional noncomposite PCSPs are commonly used and usually comprise one thick reinforced concrete layer and one thin layer of concrete cladding connected using mechanical anchors. Composite PCSPs that use shear connectors in the form of diagonal steel or fiber reinforced polymer (FRP) reinforcing bars to connect the two reinforced concrete layers are becoming popular due to their improved shear transfer mechanism and material savings. In composite PCSP applications, the two reinforced concrete layers are the same thickness, and the overall thickness of the panel is about 1⁄2 to ∕3 of a comparable noncomposite panel while still offering relatively similar structural and thermal insulation properties. No official standards have been established to date for designing PCSPs, and relatively little research has been reported on their early-age structural behavior. Because PCSPs are normally designed to ensure crack-free performance, a careful look at all potential causes of cracking is needed, especially at the panels’ early age, while concrete is still immature with relatively low tensile strength.