Research on alternative cement materials is active worldwide, and in terms of fire safety, research on the evaluation of high-temperature properties of alternative materials is very important. Studies on concrete mixed with hwangto have been conducted by several researchers, but studies on high-temperature properties are lacking. Therefore, in this study, we evaluated the mechanical properties of concrete by partially replacing cement with non-sintered hwangto (NSH) at high temperatures. Normal concrete without NSH mixing and non-sintered hwangto concrete (NSHC) with HNT replacement were prepared as the specimens. The W/B of the concrete was set to 41 and 33, whereas the NSH replacement ratio was 15 and 30% of the cement. The target heating temperatures were set to 20, 100, 200, 300, 500, and 700 °C, and the heating rate was maintained at 1 °C/min. The following were calculated to evaluate the mechanical properties of the specimens: mass loss, compressive strength, ultrasonic pulse velocity (UPV), and modulus of elasticity. After analyzing the correlation between residual compressive strength and UPV, we proposed a compressive strength prediction model using different values of W/B for NSHC. Experimental results suggest that mass loss (%) shows a decreasing trend as NSH increases. In terms of residual compressive strength, residual compressive strength at W/B 41 increased with NSH replacement, whereas residual compressive strength values for W/B 33 were observed regardless of NSH replacement. Residual UPV showed a similar trend, regardless of the NSH replacement ratio, and residual modulus of elasticity was low at all W/B ratios as NSH replacement increased. A linear equation with a high correlation coefficient (R2) was proposed to predict compressive strength, and the linear value of W/B 41 was slightly higher than that of W/B 33.

This study classified the strength of normal aggregate concrete (NC) and lightweight aggregate concrete (LC) into three levels (30, 45, and 60 MPa). In particular, the compressive strength, ultrasonic pulse velocity, and elastic modulus were measured and analyzed at the ages of 1, 3, 7, and 28 days to establish the correlation between the compressive strength and the ultrasonic pulse velocity and between the elastic modulus and the ultrasonic pulse velocity. In addition, this study proposed strength and elastic modulus prediction equations as functions of the ultrasonic pulse velocity. The developed equations were compared with previously proposed strength prediction equations. The results showed that the measured mechanical properties of NC tended to be higher at all ages than in LC. However, LC45 exhibited relatively high compressive strength compared to NC45. The relative mechanical properties of LC compared to NC were the highest at 45 MPa and the lowest at 60 MPa. The relative ultrasonic pulse velocity converged at all levels as the age increased. Moreover, the correlation between the compressive strength and the ultrasonic pulse velocity in LC exceeded that of NC, and in LC, the correlation coefficient decreased as the strength increased. The correlation coefficients between the elastic modulus and the ultrasonic pulse velocity were high at all levels except for LC45. Finally, this study proposed compressive strength and elastic modulus prediction equations as an exponential function of LC. The proposed equations outperformed the previously proposed strength prediction equations.

In this study, the mechanical properties of normal concrete (NC) and lightweight concrete (LC) were measured upon exposure to high temperatures (20, 100, 200, 300, 500, and 700 °C). Then, analysis was conducted to predict the residual modulus of elasticity through ultrasonic pulse velocity. Crushed granite aggregate was mixed as the coarse aggregate for NC and coal-ash aggregate for LC. The effect of the water-to-binder (W/B) ratio (0.41, 0.33, and 0.28) on the mechanical properties (residual compressive strength, residual ultrasonic pulse velocity, residual modulus of elasticity, and stress–strain) of concrete was determined. The residual compressive strength, residual ultrasonic pulse velocity, and residual modulus of elasticity were higher for LC compared to NC. The correlation between the ultrasonic pulse velocity and residual modulus of elasticity was also analyzed, which yielded a high correlation coefficient (R2) at all levels. Finally, equations for predicting the residual modulus of elasticity using ultrasonic pulse velocity with R2 values of 0.94 and 0.91 were proposed for NC and LC, respectively.

This study measured and analyzed the mechanical properties of normal aggregate concrete (NC) and lightweight aggregate concrete (LC) subjected to high temperatures. The target temperature was set to 100, 200, 300, 500, and 700 °C, and W/C was set to 0.41, 0.33 and 0.28 to evaluate high temperature properties at various intensities. Measurement parameters included mass loss, compressive strength, ultrasonic pulse velocity (UPV), and elastic modulus. We compared the residual mechanical properties between the target and preheating temperatures (20 °C) and then analyzed the correlation between UPV and compressive strength. According to the research findings, after exposure to high temperatures, LC demonstrated a higher mass reduction rate than NC at all levels and exhibited higher residual mechanical properties. The results of analyzing the correlation between compressive strength and UPV for concrete subjected high temperatures were very different from the compressive strength prediction equation previous proposed at room temperature, and the error range of the residual strength prediction equation considering W/C was reduced.

Most studies on fire properties, including smoke control, have been based on simulations. However, the results of simulation experiments have an average error rate of approximately 36.7%, and data with low reliability are obtained, compared to theoretical values and actual-scale measurements. In addition, experimental studies using scale models exhibit an average error rate of 6.9%, significantly lower than those of simulation experiments. In this study, a method for decreasing the error rate of simulation experiments was investigated by constructing a database using scale-model smoke control experiments.