冻融介质及温度阈值对混凝土快速冻融试验试件温度历程的影响

Influence of Freeze Thaw Medium and Temperature Threshold on Temperature History of Concrete Rapid Freeze Thaw Test Specimen

国内普遍采用快速冻融试验机、按照GB/T 50082—2009《普通混凝土长期性能和耐久性能试验方法标准》中快冻法开展混凝土抗冻试验。该方法中规定用于控制冷冻、融化过程的测温试件以防冻液为冻融介质,而用于测量混凝土抗冻性能的冻融试件以水为冻融介质。两种试件冻融介质的差异必然会造成其中心温度变化历程不同。本文以测温试件冻融介质的种类、测温试件和冻融箱内防冻液的温度阈值作为影响因素,试验研究冻融试件在冻融循环过程中的温度变化历程。结果表明:冻融循环过程中混凝土冻融状态会因水—冰相变而在0℃短暂滞留;以水代替防冻液作为测温试件的冻融介质时,冻融过程中冻融试件中心温度上限值的持续时间更长;通过调整测温试件和冻融箱内防冻液的温度阈值,可实现对冻融试件中心温度变化历程、冻融循环周期时长的调控。因此,须调整测温试件和冻融箱内防冻液的温度阈值,确定冻融试件温度变化历程满足冻融循环标准要求后方可开展抗冻试验。

Rapid freeze thaw test machine is widely used in China to carry out concrete frost resistance test according to the rapid freezing method in GB/T 50082—2009 Standard for Test Methods of Long Term Performance and Durability of Ordinary Concrete.The method specifies that the temperature measurement specimen used to control the freeze thaw and melting process should take antifreeze as the freeze thaw medium,while the freeze thaw specimen used to measure the frost resistance of concrete should take water as the freeze thaw medium.The difference between freeze thaw medium of two specimens will inevitably lead to the different change process of core temperature.In this paper,the type of freeze thaw medium of temperature measurement specimen,the temperature threshold of temperature measurement specimen and antifreeze in freeze thaw chamber were taken as influencing factors to experimentally study the temperature change process of freeze thaw specimen during freeze thaw cycle.The results show that the freeze thaw state of concrete will be temporarily retained at 0℃due to the water-ice phase transition during the freeze thaw cycle.When water is used as the freeze thaw medium of temperature measurement specimen instead of antifreeze,the duration of the upper limit of the core temperature of the freeze thaw specimen is longer.By adjusting the temperature threshold of the temperature measurement specimen and the antifreeze in the freeze thaw chamber,the core temperature history of the freeze thaw specimen and the duration of the freeze thaw cycle could be controlled.Therefore,it is necessary to adjust the temperature threshold of the temperature measurement specimen and the antifreeze in the freeze thaw chamber,and determine that the temperature change process of the freeze thaw specimen meets the requirements of the freeze thaw cycle standard before the concrete frost resistance test can be carried out.