Permeability of Sulfate Ions in Cementitious Materials Containing γ-Ca₂SiO₄ after Autoclave Curing and Accelerated Carbonation

Abstract

Sulfate attack on concrete structures is a serious problem around the world, particularly in the Middle East, where sulfate is abundant in soil. Design of a cementitious material with high sulfate resistance is thus required, leading to research on the high durability of cementitious materials containing γ-Ca 2 SiO 4 (γ-C 2 S). The authors have proposed the following material design for high durability: a cementitious material mixed with γ-C 2 S and subjected to autoclaving and accelerated carbonation, to give 1.1nm tobermorite in the autoclaved hardened body, and densification at the surface. However, the sulfate resistance of this new material has not been investigated. Therefore, the purpose of the present research is to understand the effect of adding γ-C 2 S, autoclaving and accelerated carbonation on the permeability of sulfate ions (crucial for sulfate resistance), from the viewpoint of the reaction products and porosity. The smallest sulfate ion penetration was a sample with 80% replacement ratio of OPC with γ-C 2 S. Generation of vaterite following accelerated carbonation suppressed sulfate ion penetration. In addition, dissolution of 1.1nm tobermorite in the hardened body was inhibited. Also, low-Ca/Si C-S-H at the surface may reduce the porosity of this surface and thus contribute to the suppression of sulfate ion penetration.

Effect of duration and pressure of carbonation curing on the chloride profile in concrete

“…The carbonation cure contributed to the reduction of porosity, permeability, and ettringite formation [10], [16], [23]- [25]. Also, the carbonation cure increased the resistance to attack by external sodium and magnesium sulfates [15], [22], [26], acids [17], carbonation by weathering [5], damage from freeze-thaw [22], drying shrinkage [11], [27], [28], and penetration of chloride ions [5], [16], [20]. The main applications for carbonation curing are related to the production of precast concrete and concrete blocks [23], [27], [28].…”