Mechanical properties of CFRP and shrinkage compensating concrete actively confined and strengthened short columns under freeze-thaw cycles

This paper investigates the use of CFRP precast tubes filled with shrinkage-compensating self-consolidating concrete (SSCC) for strengthening columns. Compared to ordinary self-consolidating concrete (OSCC), SSCC can address the stress hysteresis issue caused by the poor cooperation between CFRP and concrete structures, while also enhancing the mechanical properties of columns. Experimental and theoretical studies were conducted to examine the tensile mechanical properties of CFRP materials and the axial compressive mechanical properties of CFRP precast tubes strengthened with OSCC or SSCC under freeze-thaw cycles. Various variables were considered, such as freeze-thaw cycles, types of strengthening concrete, and the number of CFRP layers. The results indicate that freeze-thaw cycles do not affect the ultimate tensile strength of CFRP but significantly reduce its ultimate tensile strain. SSCC-strengthened specimens exhibit higher load-carrying capacity and better ductility compared to OSCC-strengthened specimens. In addition, compared to the strengthening of two-layer CFRP and SSCC, the strengthening of one-layer CFRP and SSCC more effectively demonstrates the advantage of the post-tensioning effect. However, the ductility coefficient of the columns decreases with an increase in the number of freeze-thaw cycles, regardless of the number of CFRP layers or type of strengthened concrete. Modified theoretical model accurately predicts the normalized peak stress and strain of the strengthened specimens.