Interface shear transfer of lightweight-aggregate concretes cast at different times

This study examined the direct shear transfer across an in- terface of lightweight aggregate concretes cast at different times. Increasing use of lightweight aggregate concretes prompted this investigation to determine the appropri- ateness of current shear friction design provisions with respect to all-lightweight and sand-lightweight concrete. The experimental investigation included 36 push-off specimens constructed with a cold joint along the shear plane. Test variables included concrete type (unit weight), compressive strength of concrete, and surface preparation of the shear interface. A constant amount of reinforcing steel (1.33%) was provided across the shear plane. Applied shear force–slip relations were presented and discussed. Peak and residual shear strengths were also compared. Results suggest that concrete type did not play a significant role in the shear strength of the specimens in this study. Shear strengths computed using the shear friction design provisions in the Building Code Requirements for Struc- tural Concrete (ACI 318-11) and Commentary (ACI 318R- 11) and PCI Design Handbook: Precast and Prestressed Concrete were conservative for the sand-lightweight and all-lightweight specimens.