Influence of slag powder on the mechanical and electrical properties of CECM

Abstract

Applying conductive cement-based anode is one of the commonly used methods to achieve uniform electrochemical protection for concrete structures. However, anodic acidification is a critical challenge limiting the effectiveness of electrochemical protection in concrete. Therefore, carbon fiber (CF) and expanded graphite (EG) were used in the current study as conductive materials to reduce the resistivity of cement-based anode by creating a “multi-scale” conductive grid within the anode, while slag powder was employed to enhance the anode resistance to chloride intrusion. This paper investigated the influence of slag powder on the mechanical properties, resistivity, and hydration products of carbon fiber-expanded-graphite conductive mortar (CECM) anodes. The results indicated an inverse relation between the slag powder content and the mechanical properties and resistivity of cement-based anodes. In general, the optimal dosage of slag powder is 20%, at which the compressive strength and resistivity of CECM decrease by 14.8% and 2.75%, respectively. Furthermore, a cubic function relation could be applied to correlate the slag powder content to the mechanical properties and electrical conductivity of the anodes. CF, EG, and slag powder created a composite structure within the hardened cement paste, and formed a multi-scale conductive grid that reduced the cement mortar’s resistivity. Through XRD and FT-IR tests, it was found that during the testing period, the pozzolanic effect of slag powder was insufficient to compensate for the loss of strength resulted from the reduced amount of cement clinker. In addition, TGA-DTG results showed that the total amount of C-S-H in Group A increased from 14.31% to 22.86%, while in the Group B this amount increased from 20.74% to 25.94%. The optimal group had an increase from 20.21% to 24.59% in C-S-H content. These results confirm the similar hydration effect of slag powder on EG cement slurry compared to that on ordinary cement. It also indicates that the chloride ion resistance of cement-based anodes can be enhanced through the pozzolanic effect of slag powder, ultimately achieving long-term stable operation of cathodic protection system.