## 3 Results and Discussion
### Mass Loss and Water Absorption  
According to the results of previous studies [14; 22], the normalized amount of water absorbed is proportional to the square root of time, and after immersing in water for 7 days, the slope is between 0.026 and 0.033 [14]. Thus, the change of water absorption in this study may be seen as a consequence of FT damage. The recorded masses and calculated solution-filled pore volumes at different FT cycles and exposure conditions are listed in Table 3. The calculated saturated and oven-dried mass losses at different FT cycles are shown in Figure 4. It is clear that saturated and oven-dried specimens exposed to water have more mass loss than those exposed to sulfatesolution. This result indicates that FT cycles under water exposure may cause more serious damage to the concrete. However, the oven-dried mass loss (Figure 4B) for both groups of specimens increased with the increase of FT cycles, which is in accordance with the damage accumulation caused by FT cycles increasing. However, the saturated mass loss (Figure 4A) was not stabilized during the FT tests. This indicates that oven-dried tests are more suitable for assessing FT damage than the saturated mass one. In addition, FT causes the development of micro-cracks, which eventually results in the change of solution absorption [33]. The relative solution-filled pore volume, i.e., the ratio of solution-filled pore volume after being subjected to FT cycles to the one before FT cycles, is shown in Figure 5. For water-exposed specimens (W), the relative solution-filled pore volume was always larger than one, which confirms that FT results in an increase in solution-filled pore volume. A similar phenomenon was also recorded in sulfate-exposed specimens (S) after being subjected to 120 FT cycles or more. However, for sulfate-exposed specimens, there was hardly any decrease in their pore volumes from 60 to 90 FT cycles. This may be attributed to the precipitation of the synthesized ettrinigite and thuamasite, a common phenomenon of sulfate attack, which results in the decrease of pore volume [38; 39; 40]. Figure 4: Saturated mass loss (**A**) and oven-dried mass loss (**B**) at different FT cycles of water saturated (W) and sulfate attack (S) RAC. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Specimen** & **FT Cycles** & \(m_{1s}\) **(g)** & \(m_{1d}\) **(g)** & \(m_{2s}\) **(g)** & \(m_{2d}\) **(g)** & \(V_{1}\) **(mm\({}^{3}\))** & \(V_{2}\) **(mm\({}^{3}\))** \\ \hline
0 (W0/S0) & 0 & - & - & - & - & - & - \\ W60 & 60 & 9306 & 9217 & 9270 & 9178 & 89 & 92 \\ W90 & 90 & 9087 & 8999 & 9023 & 8931 & 88 & 92 \\ W120 & 120 & 9539 & 9474 & 9474 & 9399 & 65 & 75 \\ W150 & 150 & 9101 & 9018 & 9041 & 8924 & 83 & 117 \\ W180 & 180 & 9047 & 8955 & 8976 & 8813 & 92 & 163 \\ \hline S60 & 60 & 9143 & 9048 & 9116 & 9029 & 95 & 87 \\ S90 & 90 & 9298 & 9224 & 9273 & 9205 & 74 & 68 \\ S120 & 120 & 9106 & 9019 & 9083 & 8985 & 87 & 98 \\ S150 & 150 & 9060 & 8996 & 9031 & 8944 & 64 & 87 \\ S180 & 180 & 9206 & 9127 & 9146 & 9033 & 79 & 113 \\ \hline \hline \end{tabular} Note: “W” and “S” correspond to exposure of the specimens to water or sulfate solution, respectively, while numbers represent the FT cycles. \(m_{s}\), \(m_{d}\) and \(V\) are saturated mass, oven-dried mass and solution-filled pore volume, respectively; the subscripts 1 and 2 indicate before and after FT cycles, respectively.  
\end{table} 
Table 3: Mass and solution-filled pore volume of notched beams subjected to freeze–thaw cycles. Different from the mass loss, the differences in solution-filled pore volume between water- and sulfate-exposed specimens was small at lower FT cycles, while 180 cycles resulted in a 16.1% increase of pore volume in the water-exposed sample (Figure 5). For specimens subjected to 120 and 150 FT cycles, the pore volume changes of the sulfate solution exposure group were marginally higher (4.1% and 2.9%, respectively) than that of their water exposure counterparts.