Structural Changes of C-S-H Phase During Leaching Alteration

Abstract

During leaching alteration of hardened cementitious materials, Ca/Si ratio of C-S-H phase will decrease following the disappearance of calcium hydroxide (CH). Though the progression rate of CH alteration front and decreasing rate of Ca/Si ratio in C-S-H phase depend on the type of cementitious material, chain structure of Si tetrahedron in C-S-H phase will extend with increasing Q²/Q¹ signal ratio in ²⁹Si-NMR analysis, regardless of the type of cement. When the leaching alteration of C-S-H progressed further to 1.0 in Ca/Si ratio, Q³ signal which indicates the status of three-directional bonding of the Si tetrahedron with other Si had generated. Granular substance with 10 to 30 nm diameter which was thought to be the unit of C-S-H phase would shrink during the leaching alteration with forming minor pore in C-S-H phase.