A Study on Factors Affecting Geopolymerization of Low Calcium Fly Ash

Abstract

This paper presents some factors affecting geopolymerization of low calcium fly ash for geopolymeric matrices. Low calcium fly ash samples were collected from two different coal-powered facilities: an Indonesian fertilizer plant and a Japanese power plant. Several series of tests were conducted using various ratios of fly ash to activator as well as ratios of activators to sodium hydroxide molarity. Each matrix consisted of a set molar ratio of three variations of Si/Al (1.5, 2, 2.5), Na2O/SiO2 (0.3-0.38), H2O/SiO2 (2.8 to 3.5), H2O/Na2O (9 to 10.6), and mass ratio of water/solid (0.31 to 0.45). The setting time of Japanese ash-matrices were longer than Indonesian ash. The compressive strength revealed that the Japanese and Indonesian matrices with activator ratios of 1.5 achieved 47.7 and 57.5 MPa respectively, while activator ratios of 2.5 reached 50.9 and 50.5 MPa. In addition, microstructural characterizations-XRF, XRD, SEM, EPMA-were performed. This study concludes that even ashes categorized as the same class, their mineral composition is different. Furthermore, coal combustion techniques modify ash particles, which in turn causes differences in setting time, while strength is not significantly affected.

Reliability of Alkali-Activated and Portland Cement Mortar Under Compressive Test by Acoustic Emission

“…AAM mortars are mixtures made from precursor materials (fly ash/GGBFS/micro-silica), mixed with a fixed alkaline solution (Na2SiO3+NaOH), and standardized sand. All of these materials are then compacted, demolded, cured as previous papers [10][11][12][13]. Fixed alkali solution ratio of Na2SiO3 to 8 M NaOH of 1.5 is used.…”

“…In previous work [10][11], the researcher investigated the utilization of low calcium fly ash for alkali-activated (geopolymer) matrices. Researchers developed low calcium fly ash, ground granulated blast furnace slag (GGBFS), and microsilica as binding materials for alkali-activated mortar [12][13].…”

Shear Behavior of Fly Ash-Based Geopolymer R/C Beam With Bauxites as Coarse Aggregates: Experimental Program

“…Fly ash-based geopolymer concrete had been developed since several decades ago [1][2][3][4][5][6][7]. Study of geopolymer reinforced concrete beam was also investigated by several researchers.…”

Effect of GGBFS and Micro-Silica on Mechanical Properties, Shrinkage and Microstructure of Alkali-Activated Fly Ash Mortar

“…Alkali-activated fly ash represent promising sustainable alternatives to ordinary Portland cement, with benefits including 70% lower CO2 emission than Portland cement [3], higher mechanical properties [4][5][6], fire resistance [7], thermal resistance [8], lower heat of hydration [9] and heat release [10], strength against chemical attack [11] [12] [11][12], durability in an aggressive environment [13][14], freeze-thaw resistance [15], lower shrinkage in fly ash-based geopolymer [6;16-18], and comparable shrinkage value in blended slag-fly ash geopolymers [19][20]. Conversely, drawbacks include setting periods [21][22], high shrinkage in alkali-activated materials [23][24][25], high salt efflorescence [5], higher carbonation [26], and cracking while curing [27][28]. A compilation of material regarding largescale application of alkaliactivated cement for materials, cements, concrete, structures, tests procedures, and system benefits is presented in [29].…”

“…A previous study [22] reported initial and final setting time of type II fly ash paste at 45 and 108 hours. However, initial setting time of OPC (Ordinary Portland Cement) with Vicat Needle by [58] at 30 min and final setting time should not be more than 10 hours.…”