Effect mechanism of slag activity on the basic tensile creep of alkali-activated slag mortar

Abstract

This study aims to investigate the effect mechanism of slag activity on the basic tensile creep of alkali-activated slag mortar (AM) using a combined activator of quicklime and sodium carbonate (molar ratio 1:1). Based on the results of setting time, compressive strength, dynamic modulus, autogenous shrinkage, basic tensile creep and microstructure, the basic tensile creep mechanism of AM with different activity slag is discussed. Results indicate that as slag activity increases, the degree of hydration increases and more C-A-S-H gel generates; meanwhile, the nominal crystal-binder ratio decreases, resulting in a high autogenous shrinkage of AM. Autogenous shrinkage is the driving force of the basic tensile creep. The increased amount of Q2(1Al) results that more Na+ is absorbed by C-A-S-H gel, which promotes the slippage of C-A-S-H gel. Moreover, the collapsing of C-A-S-H gel is easier with its shorter mean chain length (MCL). Therefore, the basic tensile creep increases as slag activity increases. Because of the higher autogenous shrinkage, smaller nominal crystal-binder ratio and larger amount of Q2(1Al), AM has larger basic tensile creep than ordinary Portland cement mortar (OM).