Experimental Study on the Stability and Distribution of Air Voids in Fresh Fly Ash Concrete

Abstract

The air void system purposely introduced by an air-entraining admixture (AEA) is of great significance for the protection of concrete from freeze–thaw damage. Fly ash has been globally used in concrete, while the unburnt carbon in fly ash can adsorb AEA molecules and, thus, increase the AEA demand. Previous studies primarily focused on the air content of fresh fly ash concrete. This paper aimed to explore the stability and distribution of air voids in fly ash concrete at the fresh state. To achieve this goal, eleven different fresh fly ash concrete mixtures with an initial air content of 6 ± 1% were prepared in the laboratory. Samples were taken at various times within 75 min after initial mixing to investigate the air content and air void distribution in fly ash concrete at the fresh state using a super air meter (SAM). The results indicated that there was no significant correlation between loss on ignition (LOI) of fly ash and AEA demand to achieve the initial air content of 6 ± 1%. Class C fly ash concrete tended to have a better air content retention than Class F fly ash concrete. Compared with LOI, AEA demand had a stronger correlation with air content retention. Most of the fly ash concrete mixtures had a satisfactory air void system immediately after mixing, but the SAM number showed an increasing trend over time, suggesting the coarsening of the air void system with time.

Development of eco-friendly self-compacting concrete using marble powder, blast furnace slag and glass fibre-reinforced plastic waste: Application of mixture design approach

“…The air content measured using the pressure method provides insight into the air voids or bubble content in the fresh concrete. The majority of air bubbles are formed during the concrete mixing process and get entrapped between colliding fine aggregates (40). It can Fig.…”

“…Different parameters can contribute to the negative effect of MP addition on the air content. Zeng et al reported the low viscosity of fresh concrete facilitates the escape of air bubbles during mixing and placing (40). Puthipad et al also found that particles of spherical shape may promote the coalescence of fine air bubbles into larger ones, making their collapse easier (41,42).…”

Effect of Redispersible Latex Powder and Fly Ash on Properties of Mortar

“…Fly ash is a powdery substance with very fine particles that can flow in the air. It is a byproduct of coal combustion and has been widely used in concrete worldwide for many years, with economic, environmental protection, and technical benefits [5]. Zhang Lijuan et al showed that the addition of fly ash could improve the fluidity of cement mortar, but reduce its compressive strength, and this effect would be more significant with the increase in water-binder ratio [6].…”