Characterization of Alkali Activated Materials Prepared from Continuous Attrition and Ball Milled Fly Ashes

Abstract

Mechanical activation is known to greatly influence the reactivity of fly ashes. In this paper, we report a comparative study of the properties of alkali-activated geopolymer materials prepared using both ball-milled and attrition-milled fly ashes. Ball milling was carried out for 30 min and 60 min while attrition milling was carried out continuously in a high-speed attritor. The surface area of the raw fly ash decreased from 4017 cm2/g to 3999 cm2/g and 3912 cm2/g after ball milling for 30 min and 60 min, respectively. By contrast, the surface area of the continuously attrition-milled fly ash increased to 5545 cm2/g. Fly ash processed by continuous attrition milling showed a 50% particle size reduction to 25–38 μm, whereas fly ash ball-milled for 30 and 60 min was reduced in size by 33.4 and 42.9%. The milled fly ash samples were activated with 8 M NaOH solution and cured at 40 °C for 68 h. After curing, the samples were maintained at room temperature, and their 7-, 14-, and 28-day compressive strengths were measured. The compressive strength of the attrition-milled 28-day geopolymer paste was 24.6 MPa; that of the geopolymers ball-milled for 30 and 60 min was 23.37 MPa and 17.58 MPa, respectively; and that of the unmilled control geopolymer fly-ash-based paste was 17 MPa. The improvement in the mechanical properties is attributed to the increased gel formation resulting from the increased surface area (decreased particle size) in the fly ash glass starting material.

History of Developments in Geopolymer Science in New Zealand: A Brief Review

“…Following the work of Davidovits, most of our initial studies were on clay-based materials, produced by the reaction of an alkali or alkali silicate with deydroxylated kaolinite [3,4] or a mixture of silica fume and alumina [5], with the aim of producing pure products for advanced applications. However, we quickly realized that these clay-based materials are related to building materials reported much earlier, produced by reacting blast furnace slag or fly ash with alkali [6], and some of our later studies were on the formation and properties of geopolymers from fly ash [7,8,9], volcanic ash [10a,b] and water treatment residue [11]. A useful property of the geopolymers from water treatment residue was their ability to immobilize heavy metal contaminants in waste water [12].…”