Experimental Study On The Physical Indicators For Durability Of Structural Concretes

The long-term durability of concrete structures is closely related to their transport properties. The durability of concrete depends on its physical and chemical properties.The relationships between the concrete durability properties and component, and pore structure, are the substance of the durability study.In this study, concrete specimens with different water/binder(w/b) ratios(0.3, 0.4, 0.5 and 0.6), and different fly ash or slag contents(30% and 50%, respectively) were prepared. The pore structure of materials was characterized by gravimetry method for porosity and mercury intrusion porosimetry(MIP) method for pore size distribution.Gas permeability, chloride diffusivity, electrical conductivity and surface sorptivity were measured by the Cem Bureau method, the(RCM) method, the alternative current method and ASTM C1585 method, respectively. On the basis of these data measured, the influence of the components of concretes on corresponding properties aforementioned is discussed. The relationships among previous four transport properties are explored according to Archie’s law and Katz-Thompson equation. In addition, the multi-scale simulations on the electrical conductivity and chloride diffusivity are further carried out. Moreover, the influence of pore saturation on gas permeability and electrical conductivity, two indicators for structural concrete, is investigated. Meanwhile, at different saturations, the relationship between these two indicators is also discussed.The results show that w/b ratio and the component of binding materials play vital roles in the properties of concretes. Both the fly ash and slag tend to refine the pore structure. However, the tortuosity of concretes increases owing to the addition of the fly ash, while it decreases due to the addition of the slag. Both gravimetry porosity and compressive strength are closely related to the four durability indicators.In unsaturated case, the stability of electrical conductivity and gas permeability is affected significantly by the saturation state. In saturated case, electrical conductivity, chloride diffusivity and sorptivity(dried) are three steady indicators with variation coefficients within15%.As Archie’s law described, the electrical conductivity is consistent with the chloride diffusivity, which implies that the two indicators can be replaced by each other. However, the Katz-Thompson equation can notwork well to characterize the relationship between gas permeability and conductivity. This may be attributed to different transport pathway for the gas and electric current. Moreover, the critical saturationsare found in both conductivity and gas permeability experiments. For a given pore structure, there exists a unique relation between electrical conductivity and gas permeabity.