According to this model, there are two distinct
periods in deterioration caused by corrosion. The first is
the initiation period,T0, which represents the time required
for CO2or Cl
ions to diffuse to the steel-to-concrete interface and activate corrosion. The second is the propagation
period,Tcr, which represents the time between corrosion
initiation and corrosion cracking.
Weyers[3] reported that not all corrosion products contribute to the expansive pressure on the concrete; some of
them fill the voids and pores around the steel reinforcing
bar and some migrates away from the steel-to-concrete
interface through concrete pores. The researcher concluded
that the conceptual model presented by Tuutti [2]
underestimates the time to corrosion cracking compared
with times obtained from field and laboratory observations. The researcher reported that there is a porous zone
around the steel reinforcing bar caused by the transition
from cement paste to steel, entrapped/entrained air voids,
and capillary voids in the cement paste into which corrosion products diffuse. Fig. 2shows a schematic diagram
of the corrosion-cracking process as proposed by Weyers
[3]. Fig. 3shows a modified service life model in which
the propagation period, Tcr
, is divided into two different
periods. The first one is the free expansion period,Tfree
,
corresponding to the time required for corrosion products
to fill the porous zone around the corroding steel reinforc