Alkali-activated Fly Ash Binders: Feasibility as a Sustainable Alternative to Ordinary Portland Cement for Pre-Cast Systems
Creators: name: Sierra, Kimberly 
Publisher: name: University of Nevada, Las Vegas
Year: 2015

description: Fresh, load-dependent, transport, and durability properties of alkali-activated fly ash mortars were studied. The influences of activator concentration, solution-to-binder ratio, curing condition, activator type, and sodium silicate-to-total solution ratio on the properties of the studied alkali-activated mortars were examined. This study was divided in two phases. The first phase dealt with the use of sodium hydroxide as the sole activator. The second phase of the study was divided into two parts, both of which used a combination of sodium hydroxide and sodium silicate as the activator solution. Part I of phase II used elevated temperature curing conditions, whereas part II utilized moist curing at ambient temperature. Fresh properties included workability and setting times. Load-dependent properties included compressive and flexural strengths, as well as modulus of elasticity. The evaluated transport properties were absorption, density, void content, and rapid chloride migration. Durability properties consisted of resistance to abrasion, sulfuric acid, freezing and thawing, and external sulfate attack. 
For the phase I of this study, workability and initial and final setting times were found to increase and decrease with increased solution-to-binder ratio and activator concentration, respectively. The effects of different curing conditions were found to be dependent on the concentration of sodium hydroxide. All mechanical properties tested were found to decrease and increased with increased solution-to-binder ratio and activator concentration, respectively. Absorption and rapid chloride migration were found to increase and decrease with increased solution-to-binder ratio and activator concentration, respectively. Results for density, on the other hand, produced the contrary.
For the phase II of this study, workability was found to decrease with increased sodium hydroxide concentration and sodium silicate-to-total solution ratio. Mechanical properties were found to increase with an increase in sodium hydroxide concentration, as well as increased sodium silicate-to-total solution ratio up to 7.5 M NaOH. Mechanical properties decreased with increases in sodium silicate-to-total solution ratio when 10 and 12.5 M NaOH were used. Transport properties, namely absorption, void content and rapid chloride migration, results were found to decrease with increased sodium hydroxide concentration as well as sodium silicate-to-total solution ratio up to 7.5 M sodium hydroxide. The named transport properties were found to increase with increased sodium silicate-to-total solution ratio for the mortars activated by 10 and 12.5 M NaOH. Mass losses induced by acid attack and freezing and thawing cycles experienced the same trends as transport properties, whereas the depth of wear results produced the contrary. Strength losses due to acid and sulfate attacks were minimal throughout the entire immersion duration; with the mortars having lower sodium hydroxide concentrations experienced larger losses as compared to the mortars containing higher sodium hydroxide concentrations.