Strengthening and shape modification of fire-damaged concrete with expansive cement concrete and CFRP wrap

This paper reports the results of an experimental study where the axial capacity of fire-damaged specimens repaired by expansive cement concrete and CFRP wrap were investigated. Specimens were subjected to axial compressive loading and their resulting stress-strain curves were recorded. Since the flat sides of the square samples remained unconfined then the cross sections of the tested specimens largely remained unconfined. The FRP jacket was effective only along the two diagonals of the cross-section. Confinement is generally more effective in specimens with circular cross-section than those with square cross-section. The change in cross section for some of the specimens from square to circle was implemented. To modify the shape, expansive cement concrete has been utilized to fill the gap between the circular and the square cross sections. The test results indicated that heating up to 500 °C caused a severe decline in compressive strength and the elastic modulus of concrete.  Two layers of CFRP wrap around the concrete not only compensated the drop in compressive strength but furthermore it increased the strength beyond that of unheated specimen. However, the effect of wrapping alone on the stiffness and the elastic modulus is negligible. The heated square specimens that were first subjected to shape modification and then wrapped by CFRP sheet, experienced increase in the strength and the elastic modulus. Therefore, the stiffness and the compression strength of fire-damaged square concrete specimens could be compensated fully by the use of shape modification and CFRP wrapping of the cross section.