As the construction industry moves towards reducing its carbon footprint, new low-carbon alternatives to Portland cement, such as alkali-activated cementitious materials (AACMs) and geopolymer concretes, are being explored. While these innovations hold promise in sustainability, they also introduce significant uncertainty in long-term corrosion performance, particularly in reinforced concrete structures.
Portland cement traditionally provides corrosion protection through its high pH environment, which passivates embedded steel. This protection is vulnerable to carbonation and chloride ingress, both of which reduce pH and destabilise the passive layer. Blended cements using supplementary cementitious materials (e.g., fly ash, slag) have shown good durability, but their alkali reserves can vary, affecting performance.
AACMs initially demonstrate high pH values (~14), but their lack of solid calcium hydroxide buffering capacity raises concerns about accelerated carbonation over time. Recent research suggests that some AACMs may form dense, pore-blocking matrices that resist further carbonation, but performance appears highly mix-specific and not easily generalised.
Field studies, such as those by RILEM and CRC Australia, reveal high variability in carbonation and chloride resistance among low-carbon concretes, stressing the need for performance-based standards and long-term durability testing. Additionally, the use of non-metallic reinforcements (e.g., GFRP, CFRP) complicates detection and corrosion assessment due to the lack of conventional testing methods.
While we all agree that low-carbon concretes are essential for sustainability, their corrosion resistance must be rigorously understood, tested, and specified to ensure structural durability over decades. This is critical to ensure that we are not simply pushing the problem down the line, where insufficiently tested materials could lead to premature corrosion, unexpected deterioration, and the need for extensive and costly repairs in the future.
Knowledge Base Articles Corrosion Control Technical Information
