Dear Md Daniyal

It is well known that in a concrete ,weather the concrete is in a pure block form or a steel embedded in the concrete, always has fraction of moisture in the surrounding environment. So, one would expect to have internal corrosion products at the interface between the concrete and the embedded steel as a result of the corrosion of the steel. It is expected with time that the internal corrosion products will increase as a function of the amount of moisture in the concrete. The worse case scenario is that when the volume of the internal corrosion products becomes large enough for the concrete to fracture as a consequence of a spread of cracks initiation and cracks propagation in the concrete .

according to the environmental condition and the corrosion increase due to presence of (H2O + O2)

The expansion of corroding steel creates tensile stresses in the concrete,

which can cause cracking, delamination, and spalling. So pattern of corrosion is in increasing trend.

The key issue is "aggressive environment" , looking at the corrosion propagation in reinforced concrete one can recall the following processes;

*Ingress of harmful compounds to concrete(the time depends on the porosity,always years)

*Lowering of the concrete pH to acidic state(after the reaction between harmful compounds i.e Cl-,SO2,CO2 etc) remember concrete is basic in nature

*Reaction between Fe,water and the compounds to form the corrosion products(these products are up to 6 times in volume as compared to steel volume) in acidic condition

*The additional materials to the steel rebar causes the tensile stress to the surrounding concrete which cracks easily due to lower tensile strength of concrete

*The cracks propagates more rusting because more rebar is exposed and this results to spalling

*After spalling nothing will stop corrosion propagation rate

So,as long as the structure is located in aggressive environment the above highlighted theory suggests that the pattern increase with time.

However field observations as well as theory have shown that the rebar /reinforcement section is decreasing with time as corrosion propagates, this brings us to the question of threshold for percentage of steel rebar necessary for corrosion formation.

corrosion

perhaps increasing

My opinion is:

Generally, the corrosion of rebar in concrete increases over time as appropriate conditions are available. However, this behavior represents the "trend line" of corrosion. Individual measured points may be fluctuated, especially for the corrosion rate test. Corrosion is affected by several parameters including relative humidity, temperature, exposure severity, concrete permeability and exposure mode (wetting-drying cycles or full immersed) as well as the thickness of the concrete cover. Many of these parameters may change over time that lead to fluctuation of the results.

Regards

Interesting question.

Aggressive environment makes it increasing.