Title: Design for Avoiding Damage Due to Carbonation-Induced Corrosion

Author(s): P. J. Parrott

Publication: Symposium Paper

Volume: 145

Issue:

Appears on pages(s): 283-298

Keywords: carbonation; compressive strength; concretes; corrosion; cover; curing; humidity; permeability; service life; structural design; Structural Research

DOI: 10.14359/4466

Date: 5/1/1994

Abstract:
A design method for avoiding damage due to carbonation-induced corrosion of steel reinforcement in concrete is described. It accounts for the initiation period, during which a carbonation front penetrates the cover concrete, and a propagation period, during which the reinforcement corrodes and produces visible cracking of the concrete. The initiation period is controlled by diffusion of carbon dioxide through the carbonated concrete and is dependent upon the depth of cover, the gas permeability of the carbonated cover concrete, and the quantity of cement hydrate available to buffer the carbonation reaction. The rates of carbonation and reinforcement corrosion are dependent upon the relative humidity within the cover concrete. Estimates of carbonation depth give a reasonable upper bound to a wide range of field measurements. Corrosion rates are estimated on the basis of an upper bound to a range of published laboratory and field data. A sensitivity analysis showed that the main factors influencing the choice of concrete quality were the exposure conditions, depth of cover, and the notional service life: the effects of curing period and cement type were less significant. Estimates of concrete quality for selected combinations of exposure, cover, and service life were compatible with those being considered for European codes and standards. The design method can be used to examine alternative combinations of cover, concrete quality, cement type, and curing period for providing a given notional service life under selected exposure conditions.