Liu YongHe, Yang Bo, Guo Aojun
Civil Engineering Department, Lanzhou Jiaotong University, Lanzhou, China.
National and Provincial Joint Engineering Laboratory of Road & Bridge Disaster Prevention and Control, Lanzhou Jiaotong University, Lanzhou, China.
PLoS One. 2024 Dec 26;19(12):e0312890. doi: 10.1371/journal.pone.0312890. eCollection 2024.
The Belt and Road strategy has significantly advanced the scale of infrastructure construction in the Qinghai-Tibet Plateau permafrost area. Consequently, this demands higher requirements on the strength and frost resistance of concrete (FRC) cured under low-temperature and negative-temperature conditions. Accordingly, in this study, tests on the mechanical properties and FRC were conducted under standard curing, 5 °C curing, and -3 °C curing conditions. The pore structure characteristics of concrete subjected to freeze-thaw (F-T) damage (FTD) under different curing methods were analyzed using nuclear magnetic resonance. The study results show that when the air content is constant, the compressive strength of concrete (CSC) tends to decrease with the curing temperature. Moreover, the occurrence of an age lag phenomenon is evident. The compressive strength of concrete cured under standard curing for 28-d was comparable to that achieved by concrete cured at 5 °C curing for 56-d and at -3 °C curing for 84-d. Under the same curing conditions, the CSC decreases with increasing air content. Observations revealed that with the air content in the concrete set at 0.08%, the material's compressive strength was at its minimum. As the number of F-T cycles increases, the concrete transverse relaxation time (T2) curve shifts to the right, and the proportion of both harmful and multi-harmful pores increases. Based on the same CSC under different curing methods, the FRC under 5 °C curing and -3 °C curing conditions is considerably lower than that under standard curing conditions. Moreover, the FRC exhibits an increasing and then a decreasing trend with increasing air content. Concrete exhibits the best frost resistance when the air content is 3.6%. It was established that an optimal range exists for air content in concrete. If the air content is too low, there is only a slight improvement in the FRC. Conversely, if the air content was excessively high, it leads to a significant decrease in frost resistance. Further, this study establishes an FTD model for concrete under 5 °C curing and -3 °C curing conditions considering the compressive strength factors of concrete under standard curing conditions for 28-d. This study is anticipated to be used as reference for determining the FRC cured under different temperatures.
“一带一路”战略显著推进了青藏高原冻土区基础设施建设的规模。因此，这对低温和负温条件下养护的混凝土（FRC）的强度和抗冻性提出了更高要求。据此，本研究在标准养护、5℃养护和-3℃养护条件下对力学性能和FRC进行了试验。采用核磁共振分析了不同养护方法下遭受冻融（F-T）损伤（FTD）的混凝土的孔结构特征。研究结果表明，当含气量恒定时，混凝土抗压强度（CSC）随养护温度降低而降低。此外，龄期滞后现象明显。标准养护28d的混凝土抗压强度与5℃养护56d和-3℃养护84d的混凝土抗压强度相当。在相同养护条件下，CSC随含气量增加而降低。观察发现，当混凝土含气量设定为0.08%时，材料的抗压强度最低。随着F-T循环次数增加，混凝土横向弛豫时间（T2）曲线右移，有害孔和多害孔比例增加。基于不同养护方法下相同的CSC，5℃养护和-3℃养护条件下的FRC明显低于标准养护条件下的FRC。此外，FRC随含气量增加呈先增加后降低的趋势。当含气量为3.6%时，混凝土抗冻性最佳。研究确定混凝土含气量存在一个最佳范围。如果含气量过低，FRC改善不大。相反，如果含气量过高，则会导致抗冻性显著降低。此外，本研究考虑标准养护28d的混凝土抗压强度因素，建立了5℃养护和-3℃养护条件下混凝土的FTD模型。本研究有望为确定不同温度下养护的FRC提供参考。
