3.4 Future needs in durability design
and service life modelling
3.4.1 Calibration of service life models and
test methods against field performance
of concrete structures
The design against chloride ingress, using chloride
conductivity indexes, is based on service life models
that were developed at the University of Cape Town
(Mackechnie, 2001). The relationship between conductivity
index values and the potential field performance
of reinforced concrete structures was established
from 2 different techniques:
- Correlation between 28-day conductivity index
values and chloride ingress in structures in the
Western Cape Province.
- Laboratory-based experimental correlations between
28-day conductivity index values and chloride
diffusion coefficients.
Further work is necessary to test 28-day conductivity
index values against chloride ingress in various
marine environments in South Africa, taking into
account that chloride ingress is dependent on environmental
conditions such as water and air temperature
and relative humidity. In a current study at the
University of Cape Town, chloride ingress into various
different types of concrete is being investigated,
based on site exposure in the Cape Town and Durban
harbours, which, from a temperature and relative
humidity point of view, represent very different
environmental conditions. Measurements taken on
site-exposed samples are correlated to laboratorybased
measurements of chloride conductivity index
values and diffusion coefficients, in order to refine
existing service life models for application in various
regions in South Africa. This project is described in
more detail in another paper presented at ICCRRR
2008 (Heiyantuduwa, 2008).
The design against carbonation using oxygen permeability
indexes is based on empirical relationships
between 28-day OPI values and carbonation depth
measurements on actual structures and laboratorycured
samples (under accelerated carbonating conditions).
Carbonation depth measurements, particularly
on real structures, show large variations, making statistical
evaluations of test results difficult. It is therefore
important to collect more data to calibrate the
service life models used for the prediction of carbonation.
This needs to be done taking various climatic
conditions into account and researching fundamental
influences on carbonation of concrete.