164 / 2022-04-30 09:37:55

The influence of lightweight functional aggregates on the acidification damage in the external anode mortar during cathodic protection for reinforced concrete

Corrosion of reinforced concrete; Impressed current cathodic protection; Anode system; acidification mitigation

Impressed current cathodic protection (ICCP) is an effective corrosion protection and prevention technique for reinforced concrete structures served in chloride-contaminated environment [1]. However, the anodic reactions occurred during ICCP treatment will both reduce the catalytic activity of the primary anode and result in dissolution of hydration products in the secondary anode mortar (leading to more porous microstructure and reduced adhesion at the primary anode/secondary mortar interface) [2, 3]. Therefore, improving the acidification resistance of the external anode mortar is of great importance for the long term application of ICCP treatment. In this study, a novel type of lightweight functional aggregates (LFA) was proposed to mitigate the acidification damage in the external anode system (Fig.1). The influence of the prepared LFAs both on the electrochemical performance (Fig.2 and Fig.3) of the primary anode and morphology, mineral compositions and microstructure of the secondary mortar were investigated.

In this study, severe acidification damage happened in the mortar matrix within a distance of 300 μm from the primary anode; beyond this region, the acidification damage was mainly propagated along the interfacial transition zone around the aggregates and resulted in cracks in the mortar matrix (Fig.4). Because the lightweight functional aggregates maintained the high alkalinity in the secondary mortar by releasing OH^- from the aggregates (Fig.1), the acidification damage both in the vicinity of the primary anode and ITZ around aggregates was significantly halted (Fig.4). Meanwhile, LFAs efficiently mitigated the damage of MMO coating on the primary anode surface, thus maintaining the high stability and catalytic activity of the primary anode, e.g. lower anodic polarization potential (Fig.2) and charge transfer resistance of the primary anode. Therefore, the prepared LFAs can be potentially used for preparing the high performance external anode mortar, further improving the stability and efficiency of ICCP treatment and durability of reinforced concrete structures.