Optimizing Precursors and Reagents for the Development of Alkali-Activated Binders in Ambient Curing Conditions

Abstract

Alkali-activated binders (AABs) are developed through the activation of aluminosilicate-rich materials using alkaline reagents. The characteristics of AABs developed using a novel dry-mixing technique incorporating powder-based reagents/activators are extensively explored. A total of forty-four binder mixes are assessed in terms of their fresh and hardened state properties. The influence of mono/binary/ternary combinations of supplementary cementitious materials (SCMs)/precursors and different types/combinations/dosages of powder-based reagents on the strength and workability properties of different binder mixes are assessed to determine the optimum composition of precursors and the reagents. The binary (55% fly ash class C and 45% ground granulated blast furnace slag) and ternary (25% fly ash class C, 35% fly ash class F and 40% ground granulated blast furnace slag) binders with reagent-2 (calcium hydroxide and sodium sulfate = 2.5:1) exhibited desired workability and 28-day compressive strengths of 56 and 52 MPa, respectively. Microstructural analyses (in terms of SEM/EDS and XRD) revealed the formation of additional calcium aluminosilicate hydrate with sodium or mixed Ca/Na compounds in binary and ternary binders incorporating reagent-2, resulting in higher compressive strength. This research confirms the potential of producing powder-based cement-free green AABs incorporating binary/ternary combinations of SCMs having the desired fresh and hardened state properties under ambient curing conditions.

Strength, Fracture and Durability Characteristics of Ambient Cured Alkali—Activated Mortars Incorporating High Calcium Industrial Wastes and Powdered Reagents

“…The experimental program involved a comprehensive evaluation of geopolymer/alkaliactivated mortars developed from the optimized paste mix compositions produced by the authors [31,32], incorporating a constant amount of silica sand. The performance of the developed mortars has been assessed in terms of mechanical (dry density, compressive strength, elastic modulus, fracture toughness, crack tip toughness and fracture energy), durability properties (drying shrinkage in water and ambient/air curing regimes, sorptivity and freeze-thaw resistance) and microstructural characteristics through scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD).…”

“…High calcium fly-ash class C (FA-C), low calcium fly-ash class F (FA-F), ground granulated blast furnace slag (GGBFS), silica sand (maximum particle size 600 µ), as well as two types of powder-based reagents were used to develop AAM mixes using the dry mixing technique [31,32] 6, 14 and 7, respectively. All the reagents were of lab-grade quality procured from Westlab, Canada., having a purity of 95−100%.…”

“…The eight optimized alkali-activated paste binders resulting from four binary/te combinations of SCMs and two powder-based reagents having two different do from authors' research [31,32] were used to develop AAMs with a constant amo…”

“…The eight optimized alkali-activated paste binders resulting from four binary/ternary combinations of SCMs and two powder-based reagents having two different dosages from authors' research [31,32] were used to develop AAMs with a constant amount of silica sand. The objective was to achieve comparable fresh, and rheological characteristics to the control cement-based mortar (FP C M), with a high volume of fly ash previously developed for producing fibre-reinforced engineered cementitious composites [33,34].…”

“…The reagent 1 has a reagent component ratio (calcium hydroxide to sodium metasilicate) of 1:2.5, while reagent 2 has a reagent component ratio (calcium hydroxide to sodium sulphate) of 2.5:1. These component ratios were superior performing in terms of compressive strength from authors' research on AABs [31,32]. 43.5 1937 SCMs: Supplementary cementitious materials; In mix designation-numerical value denotes reagent type, C: FA-C, F: FA-F, S: GGBFS, N denotes mixes with equal mass of fly ash (class C + class F) and GGBFS.…”