Comparison of CEM I and CEM II/A-V in Certyd Lightweight Aggregate Concrete on Bond Strength Development to 15.7 mm Non-Pretensioned Steel Strand

The production of pretensioned concrete elements is significantly influenced by the ability to achieve required bond stress values shortly after the element is formed, which is essential for transferring prestressing force. Due to the complex testing procedure, bond strength is not directly measured in practice. Instead, decisions regarding the transfer of prestressing force to the concrete element are based on the tested compressive strength (typically 30–35 MPa). The literature contains studies and guidelines that define bond strength in normal concretes (generally dependent on the compressive strength of the concrete). Such relationships are lacking for lightweight aggregate concretes (LWAC). CEM I 52.5R is the most commonly used type of cement for prestressed concrete elements due to its rapid strength development. However, concrete with CEM II/A-V 52.5R-NA is characterized by better workability and a lower carbon footprint. This paper presents the results of experimental studies on the bond strength of LWAC made with artificial Certyd aggregate and cement CEM II/A-V 52.5R-NA. The obtained results were compared with results from similar previous studies on LWAC using cement CEM I 52.5R. The analysis encompassed bond stress–slip curves and the correlation between bond strength and free-end slip after 3 and 28 days of curing. The tests conducted and the final analysis of the test results pointed out that Certyd lightweight aggregate concrete made with a concrete mixture with cement type CEM I 52.5R, as well as with cement type CEM II/A-V 52.5R-NA, is appropriate for pretensioned concrete members.