Mariusz Jaśniok Tomasz Jaśniok Evaluation of maximum and minimum corrosion rate of steel rebars in concrete structures, based on laboratory measurements on drilled cores

Variability of corrosion current density during one year 0,51 0,04 The diagram presents the variability of corrosion current density during the seasons of the year. On the horizontal axis is time, but on the vertical axis corrosion current density As we can see on the diagram in very short time the values of corrosion current density may drop from 0.51 to 0.04 uA/cm2. It is recognized that the variability of the corrosion rate is influenced by the following factors: Parameters variable over time Temperature Resistance of concrete cover (depending on air humidity) Concentration of free chloride ions The parameter is relatively constant over a long period of time

Corrosion rate dependence on temperature and humidity Laboratory measurements on drilled cores A single in situ measurement of the corrosion rate of the reinforcement is insufficient Corrosion rate dependence on temperature and humidity Our research has shown that rapid changes in T and RH also result in a sharp change in the rate of corrosion Temperature Resistance of concrete cover (depending on air humidity) Concentration of free chloride ions Parameters variable over time

The method discussed in the presentation was patented by the authors Laboratory measurements on drilled cores Drilling of cores containing a piece or pieces of rebars The method discussed in the presentation was patented by the authors

Laboratory measurements on drilled cores Drilling of cores containing a piece or pieces of rebars Arranging of three-electrode system on the cores

Laboratory measurements on drilled cores Drilling of cores containing a piece or pieces of rebars Arranging of three-electrode system on the cores Assuming two pairs of (humidity-temperature) parameters for the tested construction Highly favourable values of temperature and relative humidity Extremely adverse values of temperature and relative humidity Conducting of polarization measurements in climatic chamber

Laboratory measurements on drilled cores Drilling of cores containing a piece or pieces of rebars Arranging of three-electrode system on the cores Assuming two pairs of (humidity-temperature) parameters for the tested construction Highly favourable values of temperature and relative humidity Extremely adverse values of temperature and relative humidity Conducting of polarization measurements in climatic chamber Determination of two values of corrosion current density ikor max ikor min

Example no. 1 First attempt of use the method in practice was on cement silos built in the 1970s in the south of Poland.

Example no. 1 Silos with a diameter of 17 m, were 42 m high. Concrete cores for corrosion tests were drilled from concrete areas without visible damage and with noticeable fractures and cracks. Used for over 40 years, their structure shown signs of noticeable corrosion damage, numerous damage and cracks in the reinforced concrete outside shell.

Example no. 2 The second attempt of use the method in practice was on two underground reinforced concrete tanks for potable water The dimensions in plan view are 60 × 40 m. The tanks were placed ca. 7 meters below ground level. For corrosion tests were drilled six cores with rebar pieces.

Example no. 1 and 2 Measurement methods: EIS i LPR For each drilled core a three-electrode system was arranged and connected to a potentiostat. A piece of rebar drilled with the core was used as the working electrode. A metal disk from stainless steel was used as the counter electrode placed on one of cylindrical core bases. A wet felt pad was placed between these two surfaces. A typical electrode of known and constant potential was used as the reference electrode. Visible core damage were filled with cellulose fibres wetted with water.

Example no. 1 and 2 Conditions favourable to corrosion RH = 99% Conditions adverse to corrosion RH = 40% T = 10° Water T = 8° For each construction were assumed individual favorable and adverse values of temperature and relative humidity. The parameters were set in climatic chamber and the cores with the counter and refrence electrodes were put into the chamber

Example no. 1 and 2 This slide presents bar charts of corrosion hazard for both analyzed structures. According to the corrosion criteria for RC Structures we can point out the level of corrosion hazard: below 0.2 uA/cm2 there is no corrosion, above 0.5 uA/cm2 we have corrosion. Looking at the bar charts we can easily localized areas on the structure with different level of corrosion hazard.

Conclusions The novelty of this technique lies in a method of conducting such measurements in the climatic chamber, for which possible temperature and humidity conditions, favourable and adverse for reinforcement corrosion, are set individually for each tested structure By defining extreme values for two pairs of T-RH parameters typical for the structure surrounding, the range of extreme values of corrosion rate can be determined. It is worth mentioning that tests on drilled cores not only with reference to corrosion rate of reinforcement, but also concrete pore solution (pH, chlorides) and compressive strength of concrete make the most rational use of the presented diagnostic technique.

Mariusz Jaśniok Tomasz Jaśniok Evaluation of maximum and minimum corrosion rate of steel rebars in concrete structures, based on laboratory measurements on drilled cores