Corrosion in cracked and uncracked concrete – influence of crack width, concrete quality and crack reopening

TLDR

Cracks accelerate corrosive agent ingress, compromising reinforced concrete durability in aggressive environments. The study aimed to determine how crack width, binder type, water‑to‑binder ratio, and crack reopening influence chloride‑induced corrosion in reinforced concrete. RC specimens with 40 mm cover were tested over 31 weeks, varying crack widths (0.7 mm, 0.4 mm, incipient), binder types (OPC and 50/50 OPC/slag), w/b ratios (0.40, 0.55), and crack reopening conditions. Over 31 weeks, corrosion rates ranged from 0.01 to 1.50 µA/cm²; rates increased with crack width, were higher for OPC than Corex slag, decreased with lower w/b ratio, and rose further after crack reopening, especially when corrosion was already active.

Abstract

Cracks influence the durability of reinforced concrete (RC) structures in aggressive environments by accelerating the ingress of corrosive agents to the embedded steel. This study investigated the influence of crack width (0·7 mm, 0·4 mm and incipient cracks), binder type (100% CEM I (ordinary Portland cement – OPC) and 50/50 OPC/Corex slag blend), water-to-binder (w/b) ratio (0·40 and 0·55) and crack reopening on chloride-induced corrosion in RC specimens with constant cover of 40 mm. Over the study period (31 weeks), corrosion rates varied from passive values of 0·01 μA/cm 2 to active values of 1·50 μA/cm 2 . Results indicate that corrosion rate is sensitive to crack width, concrete quality (i.e. binder type and w/b ratio) and crack reopening. For a given binder type and w/b ratio, corrosion rate increased with increasing crack width; however, this increase was smaller in Corex slag specimens (increases of 40% or more) than in OPC specimens (increases 210% or more). Corex slag specimens generally had lower corrosion rates compared to OPC specimens. For both OPC and Corex slag specimens, corrosion rate decreased with decreasing w/b ratio. Crack reopening increased the corrosion rate in the cracked specimens. This increase in corrosion rate was higher if the specimen was actively corroding prior to the crack reopening.