Effect of Air-Entraining Agent on Hardened Properties of 3D Printed Concrete with Emphasis on Permeability and Air Void Structure

Abstract

Three-dimensional (3D) printing is proposed as a potential solution in construction. Therefore, it is necessary to examine different properties of these concretes. On the other hand, air entrainment is a well-established method to improve the resistance of concrete against freeze–thaw cycles. Although the primary purpose of using these materials in the concrete mixture is to increase its resistance to freeze–thaw cycles, it affects other properties of concrete, including its hardened properties, which have to be evaluated. This study investigates the effect of air-entraining agents (AEAs) on the hardened properties of 3D printed concrete, including its permeability, chloride penetration, and air void structure. Several mixes with various amounts of AEAs were used, all of which had the necessary specifications for pumpability, printability, and buildability. The results show that although the use of air-entraining agent reduced the compressive (2.7%–17.4%) and flexural (7.6%–21.2%) strength of the samples, the permeability decreased (e.g., 1.4%–15.5% decrease in 0.5-h water absorption at different ages), and the resistance against chloride attack increased (e.g., reduction of 12.5%–19.4% in chloride ion migration coefficient). An acceptable increase in the resistance against freeze–thaw cycles was achieved for all mixes containing AEA. Although the samples containing 0.12% air-entraining agent showed the highest resistance to freeze–thaw cycles, it seems that lower values were more suitable for reaching the lowest permeability.