Mechanical behaviour and durability of high volume fly ash cementitious composites

Abstract

The purpose of this research is to separate different morphological particles of ASTM class F fly ash, and study their effect on mechanical behaviour and durability of high volume cementitious mixtures. In this research wet separation of raw fly ash is carried out, which resulted in three layers of different morphological particles. The first layer of particles float, comprise of about 1-5% of fly ash, is identified as cenospheres or hollow spheres. The second layer of particles is measured to be 55-60% of raw fly ash and consisting of porous spherical and rounded particles rich in Si and Al. The third layer particles is measured to be about 35-40% of raw fly ash. High volume fly ash cementitious composites containing second or third layer particles are tested under compression and bending, highlighting a higher strength and ductility in comparison to cementitious ones containing raw fly ash particles.

Effects of Wet Separated and High Speed Milling Fly Ash Added in High Volume to Cementitious Materials

“…In raw fly ash FE-SEM image of Fig. 3 (a), it is observed that raw fly ash consists of several type of particles including glassy hollow spherical, solid spherical, porous spherical, porous slaggy, compact slaggy particles, and some brighter particles as observed by the authors in [21]. However, in Fig.…”

“…Wet separation of ASTM Class F brown coal raw fly ash from Počerady power plant of Czech Republic was carried out as explained in [21] and [28] by the authors as shown in Fig. 1 (a) and (b).…”

“…shows second layer which consist of majority of submicron and ultrafine (<1µm) particles with few large slaggy and porous spherical particles. The origin of these porous particles of second layer takes place when brown coal is combusted in the boiler at temperatures between 1200-1500 °C, then coal is spontaneously combusted and absorbed water is released from the pores of these particles to produce porous particles [21]. Fig.…”

“…ASTM Class C fly ashes [19] if added to water reacts and rapidly hardens, however this phenomenon is rare in case of Class F fly ashes [20]. Therefore, ASTM Class F fly ashes can be mixed in water and consequently separation of its particles based on their densities relative to water can be carried out [21].…”

“…For brown coal ASTM Class F fly ashes research was carried out by the authors on different type of morphological particles separated by wet separation and its effects on mechanical strength when added in large volumes in cementitious materials [21]. But it is still to be determined how wet separated ASTM Class F brown coal fly ash particles would behave in high volume cementitious materials when milled/grinded by high speed milling with two counter rotors.…”