Study On The Effect Of Saturation Degree And Creep Damage On Transport For Cement-based Materials

The degradation process of construction materials is largely governed by transport of various deleterious agents including liquid water, gas and ions, which is significantly affected by the saturation degree for porous concretes. More importantly, most concrete materials under real service are unsaturated and damaged. For quantitative study of the durability of concrete structure in actual service, this paper finishes in-depth theoretic and experimental research on the transport properties such as water permeability and gas permeability of the mortar and concrete(damaged / undamaged), focusing on the influence of saturation and damage degree on transport properties of cement-based materials, and studies the variation of different levels the transport properties of cementbased materials in different levels.High level loading is used to prepare concrete specimens with different degrees of damage, and we drys specimens in an oven at 60℃ to get moisture-equilibrious concrete(damaged/undamaged) or mortar specimens with different saturation degrees. By measuring the gas permeability and capillary water absorption rate of each specimen, we analyze the variation of transport properties of cement-based materials, and compare every phase’s influence on transport properties in multiphase components of concrete and the interactions between them.Except for few mortar specimens with low water-cement ratio, the intrinsic gas permeability and the capillary sorptivity of the mortar specimen increases first and then decreases with the increase of saturation degree, the maximum intrinsic gas permeability and the capillary sorptivity of the mortar specimen occurs in the saturation degree 10%~25% state. The intrinsic gas permeability and the capillary sorptivity of mortar specimens is mainly controlled by the water saturation, while adding of fly ash shows little influence on the intrinsic gas permeability and the capillary sorptivity. The intrinsic gas permeability and the capillary sorptivity of the mortar specimen increases gradually with the increase of water-cement ratio.The intrinsic gas permeability and the relative capillary sorptivity of undamaged concrete specimens according to the characteristics of exponential decays with the increase of saturation degree. The relative gas permeability for the damaged concrete specimens obeys the exponential law with respect to the increase of saturation degree. The capillary sorptivity of the damaged concrete specimens increase first and then decrease with the increase of saturation degree, showing obvious nonlinear characteristic, the maximum capillary sorptivity of the damaged concrete specimen occurs in the saturation degree 15% state. With the creep strain increasing, the intrinsic gas permeability and the capillary sorptivity of damaged concrete increases at first and then gradually remains stable.