Proper understanding of the fracture mechanism of lightweight concrete (LWC) after exposure to high temperatures has a significant role in LWC proportioning design which provides a better comprehension of the structural behavior during a fire event. In this study, the effect of high temperatures (250, 500, and 750 °C) on the fracture parameters of LWC and its brittleness compared to normal-weight concrete (NWC) was experimented using a total of 120 notched beams subjected to the three-point bending test. For this purpose, the size effect method (SEM) and the work of fracture method (WFM) were employed to analyze and explain the fracture parameters. The results demonstrate a reduction of 85 and 77% in the size-independent total fracture energy (G_F) and a decrease of 37 and 28% in the characteristic length (L_ch) based on WFM, respectively for NWC and LWC with increasing temperature up to 750 °C. As the temperature reaches 750 °C, the size-dependent initial fracture energy (G_f), fracture toughness (K_IC), and fracture process zone length (C_f) based on SEM, are reduced by 73, 64 and 76% for NWC. The corresponding reduction values for LWC are 68, 47 and 69% compared to specimen at ambient temperature. However, the brittleness number ($\beta$) based on SEM is increased. The results of the parameters of effective size of the process zone (C_f) in SEM and characteristic length (L_ch) in WFM indicated that normal-weight concrete is more brittle and its ductility is reduced compared to lightweight concrete exposed to high temperatures. Based on the size effect phenomenon, the behavior of normal and lightweight concrete became closer to the linear elastic fracture mechanics (LEFM) criterion with increasing temperature. Finally, the average ratio of G_F obtained from WFM to G_f obtained from SEM for NWC and LWC at elevated temperature exposure show 1.82 and 1.7, respectively.

正确理解轻质混凝土 (LWC) 暴露于高温后的断裂机制在 LWC 配比设计中具有重要作用，可以更好地理解火灾期间的结构行为。在这项研究中，与普通混凝土 (NWC) 相比，高温（250、500 和 750 °C）对 LWC 的断裂参数及其脆性的影响使用总共 120 根缺口梁进行了试验-点弯曲试验。为此，采用尺寸效应法（SEM）和断裂功法（WFM）对断裂参数进行分析和解释。结果表明，与尺寸无关的总断裂能 ( G _F)降低了 85% 和 77%) 和基于 WFM的特征长度 ( L _ch ) 分别减少 37% 和 28% ，对于 NWC 和 LWC，随着温度升高至 750 °C。当温度达到 750 °C 时，基于 SEM的尺寸相关初始断裂能 ( G _f )、断裂韧性 ( K _IC ) 和断裂过程区长度 ( C _f ) 分别降低了 73%、64% 和 76%新华网。与环境温度下的试样相比，LWC 的相应减少值为 68%、47% 和 69%。然而，脆性数（$\beta$) 基于 SEM 的增加。SEM中加工区的有效尺寸( C _f )和WFM中的特征长度( L _ch )参数结果表明，与暴露在高温下的轻质混凝土相比，普通重量混凝土更脆，延展性降低。基于尺寸效应现象，随着温度的升高，普通混凝土和轻质混凝土的行为变得更接近线弹性断裂力学（LEFM）准则。最后，在高温暴露下，NWC 和 LWC从 WFM 获得的G _F与从 SEM 获得的G _f的平均比率分别显示为 1.82 和 1.7。