Understanding the enhanced strength, waterproof and reduced shrinkage of alkali-activated slag/metakaolin incorporating SiC whiskers grafted organics

Abstract

As sustainable and green cementitious materials, alkali-activated materials have a wide range of applications. However, considerable drying shrinkage and poor waterproof hinder their development and scope, especially deteriorating durability. This study investigates the strength improvement, waterproof modification, and drying shrinkage mitigation of alkali-activated slag/metakaolin(AASM) using SEM-EDS, XRD, XPS, FTIR, BET, and isothermal calorimetry. The novel types of modified matrix are synthesized using beta-silicon carbide whiskers(β-SiCw) grafted silane. Two silanes, including KH550 and KH560, are successfully grafted onto β-SiCw through chemical methods. The study investigates the reaction kinetics and mechanism of specimens modified with two β-SiCw grafted silane. Results indicate silanes grafted onto β-SiCw reduce the capillary pressure and introduce functional groups, which mitigate 42 %-48 % drying shrinkage and improve waterproof of matrix. Despite diminishing early strength and prolonging setting time, the matrices incorporating modified β-SiCw ultimately obtain improved mechanical strength, enhanced wettability, and reduced porosity and water absorption. More C(N)-A-S-H gels are formed after the addition of suitable modified β-SiCw. The matrix reaction is affected by a synergistic effect at different periods. The matrix shows better shrinkage mitigation using β-SiCw-KH550, while better strength is performed using β-SiCw-KH560. The mechanism of modified matrix is revealed.