Improved chloride binding capacity in sustainable metakaolin blended seawater cement mortar: Effect of external alternative electric field

Seawater is a promising substitution of fresh water in concrete production to relieve the resource crisis, especially for the concrete fabricated in harsh environment with less freshwater supply, while the excessive chloride ion (Cl⁻) in seawater may induce severe durability issue. In this work, metakaolin (MK) was used as supplementary cementitious material to prepare seawater cement mortar (SWCM), and ohmic heating (OH) curing was utilized to fabricate MK-SWCM at −20 °C by creating high temperature curing condition, with conductive carbon fibers (CFs) as electrical reinforcement media. The CFs fraction was numerically and experimentally obtained as 1.0 vol%, the electrical resistivity, electric voltage and curing temperature change during OH process was disclosed. Results showed that MK inclusion and OH curing both contributed to enhancing the Cl⁻ binding capacity with higher hydration degree and denser pore structure. To be specific, OH cured SWCM with 10 % MK content endowed the Cl⁻ binding ratio of 35.4 %, meeting the increase of 97.8 % compared to that of room temperature cured SWCM with no MK addition. Moreover, the mechanical strengths were further proven excellent for winter production in cold environment, which were all above 60 MPa with the aid of OH curing. A systematical analysis was conducted to roundly clarify the benefits for MK-SWCM fabrication in cold region from the aspects of Cl⁻ binding capacity efficiency, environmental benefits and mechanical strength.