RELATIVE HUMIDITY ON THE CORROSION IN REINFORCED CONCRETE STRUCTURES 

There seems to be little or no change to the moisture at depths greater than 30 mm. This agrees with Parrot (1988), who performed tests, proving that at depths greater than 20 mm the drying occurs relatively slowly. The first 40 mm of depth is the most important section for measurements, as this will act as the cover for most structures, protecting the steel from environmental effects.

 

The minimum cover depths for South Africa are 30 mm for carbonating environments and 50 mm for marine environments. From the results plotted in relevant graphs, the relative humidity at depths greater than 40 mm is above 90 %. This proves that most of the drying and variations in moisture takes place in the first 40 mm from the exposed surface. At depths greater than 40 mm the pores are almost saturated, impairing the movement of oxygen through the concrete. Saturated pores will help prevent the initiation phase. In terms of the propagation phase, the pores experiencing a relative humidity of above 90 % will face an accelerated corrosion rate. Making sure that the steel sits below the drying surface is important in meeting the service life requirements for any reinforced structure. A small increase in cover on the design of a reinforced concrete structure could have an exponential increase in service life. The improved durability will also decrease the future maintenance costs on the mentioned structure.