Moisture Diffusion in Fly Ash Concrete Surface Layer in Constant Temperature and Humidity Environment

The effects of fly ash replacement and micro-environmental conditions on moisture diffusion in fly ash concrete surface layer were studied by humidification test(positive diffusion)and drying test(reversed diffusion)in constant temperature and humidity environment.The predicting model for equivalent moisture diffusion coefficients of fly ash concrete was created.The results show that in the humidification test and drying test,the micro-environment relative humidity response rate of fly ash concrete gradually slows down,while the moisture diffusion coefficient decreases gradually;15%(by mass)fly ash replacement reduces moisture diffusion coefficient of concrete under the same micro-environment relative humidity,but 45%fly ash replacement accelerates it.The reversed equivalent moisture diffusion coefficient is significantly smaller than the positive equivalent moisture diffusion coefficient in the same micro-environment temperature and initial relative humidity difference inside and outside the fly ash concrete.