A Review of Recent Advances in Alkali-activated Materials from Silica-rich Wastes Derived Sodium Silicate Activators

Abstract

Sodium silicate activators derived from silica-rich wastes have attracted increasing attention owing to their promotion on the sustainable production and development of alkali-activated materials (AAM). This paper presents the research progress on the feasibility of using silica-rich wastes-derived sodium silicate activator as an alternative to commercial sodium silicate activator in AAM. The basic factors affecting the quality of silica-rich wastes-derived sodium silicate activator are reviewed. The structure features between commercial sodium silicate and derivative sodium silicate are addressed and compared. Influences of the two different sodium silicates on flowability, mechanical properties, microstructure and durability are summarized and discussed. Previous studies reveal that utilizations of amorphously rich SiO 2 containing materials, together with proper preparation technology, enable to produce highly reactive sodium silicate activators and as a consequence to obtain materials with comparable or even better performances as compared to the commercially available sodium silicate-AAM. Recommendations for future investigation are provided eventually.

Research on Damage Evolution Law of Glazed Hollow Beads-Cement/Sodium Silicate Grouting Materials under Different Cycles of Loading and Unloading

“…During the cyclic load-unloading, the grouting material specimen always exchanges energy with the surrounding system. This energy is typically continuously input from the outside into the grouting material in the form of mechanical energy, a portion of which is accumulated inside the specimen as elastic energy, while the remainder is consumed to cause irreversible plastic deformation [ 31 ]. Energy dissipation effectively reflects the entire process of internal defect compacting and new cracks developing and expanding until the specimen loses its strength.…”

The Use of Solid Sodium Silicate as Activator for an Amorphous Wollastonitic Hydraulic Binder

“…Several studies have focused on the synthesis of this activator [13,14] using different silica-rich sources as raw materials. These sources include low-value, silicate-rich wastes [15][16][17][18], and bio-derived materials [19,20].…”

“…There are two main routes of synthesis that can be applied [21], a thermochemical method and a hydrothermal method. The thermochemical method consists of mixing the silica-rich powder with a sodium hydroxide powder using a temperature of 450-600 • C [14,19,21], and the hydrothermal method consists of dissolving the silica-rich materials in an alkaline solution at a temperature ≤ 100 • C [15][16][17][18]. Therefore, products produced using the hydrothermal method are liquid and require less energy for production [21].…”

“…Therefore, products produced using the hydrothermal method are liquid and require less energy for production [21]. In both cases, the concentration of the alkaline material [21], the particle size distribution, and the amorphous content of the silica source influence the reaction process [14], since smaller particles have higher SiO 2 extraction capabilities and amorphous phases display higher solubility [14]. Finally, to analyze the formation of condensed and uncondensed silica [18] and to confirm the characteristic bands associated with the sodium silicate spectra [17], the final product can be characterized by FTIR.…”

“…The different routes and raw materials used in the production of the activator may affect its application with the binder, since these factors influence the rate of silicate release in the system [14], and consequently the hydration kinetics, compositions, crystalline phases, and mechanical strength of the AAC [14].…”