Comparison of Diffusion and Migration Coefficients Determined from Tests on Concrete in Prestressed Floor Slabs HC-500

摘要

Protective properties of concrete for steel can be assessed with a diffusion coefficient.This method refers to steel exposed to chloride ions present in sea water or deicing agents.However,the aggressive environment with chlorides hinders the determination of diffusion coefficient as they enter into electrostatic interaction with other ions present in concrete pore water,adsorb hardened cement grout on the surface of hydrated minerals,and react with concrete components.But Fick's laws can be used to express chloride ion flow in concrete regardless of complex physical,chemical and electrostatic processes.Fick's laws are predominantly used to calculate values of that coefficient values with reference to methods defined by standards AASHTO T 259 and NT BUILD 443.The main disadvantage of such methods is their duration.Therefore,an electric field is used to speed up a flow of chloride ions.On the basis of obtained results,we can either calculate a passed charge or a migration coefficient.The determined coefficient of migration according to NT BUILD 492 characterized chlorides ingress into concrete when exposed to the electric field.But this method did not specify the time,after which the critical value of chloride ions was achieved at the reinforcement.Also,the method described in the standard ASTM C 1202-97 is only useful for comparing protective properties of concrete.However,the migration of chlorides could be analysed with the theoretical model,which was the base to derive the equation of migration.This paper presents experimentally determined averaged results and values of diffusion coefficients determined from migration tests.It also compares results from diffusion tests performed in accordance with standards AASHTO T 259 and NT BUILD443,and results from migration tests conducted in accordance with standards ASTM C 1202-97 and NT BUILD 492.