Compressive Properties of Self-Compacting Concrete after Cooling from High Temperatures

Self-compacting concrete (SCC) has been widely used in building structures. However, previous research focused only on the mechanical properties and working properties of SCC at room temperature. Thus, there is limited research on the change of compressive strength of SCC after a fire. This paper aims to investigate the compressive properties of SCC after being cooled from high temperatures. The SCC specimens were firstly heated to a target temperature of 100-700 degrees C and were then cooled to ambient temperatures by water or in air. The heating and cooling damage to the SCC specimens was assessed by the mass loss and the ultrasonic pulse velocity (UPV) separately. Afterward, the axial compression tests were carried out to investigate the compressive properties of the fire-affected SCC specimens under uniaxial compression. The residual mass, UPV, stress-strain curves, post-fire failure characteristics, and compressive strengths of the SCC specimens were discussed in detail. The mass loss of the SCC specimens showed an obvious increase with the rising temperatures, while the UPV exhibited a converse pattern. The mass loss of the SCC specimens after being naturally cooled increased more significantly, while the two cooling methods used in this experiment had little effect on the UPV. When the SCC specimens were cooled from 100 degrees C, the compressive strength of the SCC specimens cooled in air or water dropped by 32.54% and 35.15%, respectively. However, while the heating temperature rose to 700 degrees C, the compressive strengths of the SCC specimens cooled in air or water dropped sharply by 72.98% and 86.51%, respectively. Finally, an improved mathematical model for SCC after cooling from high temperatures was proposed based on Jones and Nelson's equation. This improved material model matched the experimental results well, which demonstrates that the proposed constitutive model can provide better predictions for the SCC structures after a fire.