Bio‐derived sodium silicate for the manufacture of alkali‐activated binders: Use of bamboo leaf ash as silicate source

Abstract

Alkali activated binders are a promising alternative to the use of Portland cement in the manufacture of concrete for curbing CO2 emissions. Novel sources of silicates have been investigated in recent years for reducing cost and environmental impacts associated with the use of chemical activators. This study describes the production of solid sodium silicate (SS) activating powder from bamboo leaf ash (BLA). Bamboo leaves were calcined at 550–800°C, mixed with NaOH pellets, and heated in an oven at 300°C. The obtained silicate powder was used for activating blended fly ash/slag samples. Mechanical and microstructural properties of BLA‐based samples were compared to those of samples made with commercially available chemicals. The strength of BLA‐activated mortars matched the commercially‐sourced activators, being 25–30 MPa at 7 days and exceeding 40 MPa at 28 days. The microstructural analysis suggested that BLA‐based SS showed a lesser degree of dissolution of precursors at 7 days, but the quality of the matrix was higher than that of NaOH‐activated samples. These results confirmed that the reactivity of BLA‐silicate powder was similar to that of commercial SS solutions, and show the potential valorization of future biomass renewable waste in the production of low carbon, alkali‐activated concretes.

Acid resistance of alkali-activated binders: A review of performance, mechanisms of deterioration and testing procedures

“…In addition, the majority of studies used commercially available activators. No studies reported on the acid resistance of AABs prepared with novel low-carbon activators, such as those developed using rice husk ash, bamboo leaf or waste glass [11][12][13]. The effect of the curing regime on acid resistance was also rarely considered.…”

“…The most commonly used activators are alkali hydroxide or silicate solutions (usually Na or K) [8]. Unfortunately, the alkaline activators generally have a much greater environmental footprint than the aluminosilicate source materials, which has resulted in a search for alternative low-carbon activators to enhance the environmental credentials of AABs further [9][10][11][12][13].…”

Chemical and Microstructural Properties of Fly Ash and Fly Ash/Slag Activated by Waste Glass-Derived Sodium Silicate

“…WG-based activator gave lower early strength (1-day) but equal or superior 7 and 28-day strengths than the commercially available activating solutions. Since the method was proposed, it has been replicated and verified by several researchers (see, e.g., [16]), using other silicate sources (e.g., [17,18]), and providing environmental analysis confirming a potential for a 70% reduction in CO 2 emissions when compared to Portland cement-based concrete [19,20]. However, a detailed investigation of the microstructure of the reaction products when a WG-based activator is used has not been carried out yet.…”

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.…”

“…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].…”