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External anode mortar with superior performance based on lightweight functional aggregates for Impressed Current Cathodic Protection of reinforced concrete

Wenhao Guo 1, Jie Hu 1, 2, Suhong Yin 1, 2, Jiangxiong Wei 1, 2, Qijun Yu 1, 2

1 School of Materials Science and Engineering, South China University of Technology, Guangzhou 510640, Guangdong, China
2 Guangdong Low Carbon Technologies Engineering Center for Building Materials, Guangzhou 510640, Guangdong, China

Cathodic protection has proved to be an effective and reliable technique for the corrosion protection of reinforced concrete structures, especially in chloride-contaminated environment. However, its application can be constrained by unsatisfactory anode service life [Weale, 1992]. Many shortcomings reported in the literatures were related to low and non- uniform distributed conductivity and degradation of anode systems, mainly their cementitious overlay, due to the acidification in the vicinity of the anode metal during the treatment [Page, 2000]. Based on this electrochemical characteristic issue, the ideal anode overlay was suggested to be equipped with good ionic conductivity and possibly moderately influenced by the environmental humidity variations [Pedeferri, 1996]. In this paper, a novel type of lightweight functional aggregate (CA) was prepared by impregnating an alkaline modified agar solution (changed into a solid gel after cooling) into the porous structures of ceramsites. An external anode mortar with superior performance was then prepared based on these functional aggregates, aiming at improving the conductivity of the mortar embedding the anode and halting the negative effects induced by anodic reactions. On one hand, the resistivity of the prepared conductive mortar in the presence of CA was in the range from 15.3 to 14.2 Ωm at the curing age of 28 days, basically 70% lower than plain mortar prepared with 45 vol.% of river sand. The high conductivity was related to the establishment of an effective conductive network formed by CA. On the other hand, the capacity for maintaining an alkaline environment was improved by 53% - 132% in presence of 15 ~ 40 vol.% of CA compared to that of the reference specimen. Meanwhile, the presence of CA in anode cell also contribute to the maintenance of catalytic activity in low polarizing state (0.6~0.8 V vs. SCE), which was beneficial for the long term performance of anode system.

Key words: External anode mortar, lightweight functional aggregates, conductivity, acidification erosion, cathodic protection