Micro-environment temperature and relative humidity response of fly ash concrete under natural climatic conditions

The internal micro-environment temperature and humidity, which depend on external climate and concrete material properties are important factors affecting the durability. In a natural environment, the diurnal and seasonal weather cycles lead to the fluctuations in internal climate in concrete. This paper is focused on the internal temperature and relative humidity of fly ash concrete under natural climatic conditions. Three fly ash replacement levels, namely, 15%, 30% and 45% are considered. The temperature and humidity inside and outside concrete specimens are recorded chronically by temperature and humidity sensors. The test shows that the internal temperature varies similarly to the external ambient temperature, and the content of fly ash has a little influence on temperature response. The internal humidity fluctuates more slowly than the temperature; in particular, it may remain almost constant for a long time during winter. The higher fly ash content (such as 30% or 45% replacement ratio) increases the fluctuation in internal humidity, especially during summer. Therefore, in the concrete durability studies involving impact of temperature and relative humidity, while the external environment temperature can be directly considered instead of internal temperature, the ambient humidity and the micro-environment humidity must be clearly distinguished.