Abstract
The rise in atmospheric [CO2] globally has consequences on economic infrastructures of concrete such as buildings, bridges, silos, amongst others. The present study employed a natural carbonation prediction (NCP) model to analyse carbonation progression and the service lifespans of concrete infrastructures, based on the forecasted global [CO2] levels for years up to A.D. 2100 (IPCC, 2013). The environmental factors considered comprise the inland and coastal subtropical climate conditions focusing on the South African cities of Johannesburg and Durban, respectively. In most developing countries, concretes of relatively low strengths are widely used in structural constructions. It was found that the carbonation depths for concrete infrastructures located in Johannesburg are consistently 1.5 times higher than those for the structures in Durban. For normal strength concretes, carbonation depths increase by up to 31% while service lifespans correspondingly reduce by up to 24%, owing to the rise in [CO2] levels between the years A.D. 2000 and A.D. 2100. Future use of higher strength concretes ≥ 40 MPa appears to be necessary for these adverse effects to be avoided. Unfortunately, this counter measure is paradoxical, as it promotes CO2 emissions due to employment of higher clinker contents in concretes, while attempting to hinder carbonation progression. For existing infrastructures, the resulting shorter lifespans imply an earlier onset of corrosion problems, which in turn imposes higher repair and rehabilitation costs. In order for future infrastructures to achieve the same service lifespans presently attained, it would be necessary to specify higher concrete strength grades and larger cover depths, relative to those presently recommended in the design guidelines. Ultimately, the unit costs for new concrete constructions would increase, as a result.