particle size distribution is pivotal as smaller the particle size greater will be the workability of the concrete .
I am not sure about the second statement. With decreasing particle size (increasing fineness), the workability will also decrease. As for the color, the dark color will exclude architectural applications, where light concrete surface is desired. On the other hand, in some regions dark concrete is preferred because it seems more cement-rich
Hello,
Also important is the shape of the ash grains. Spherical particles of conventional ash from coal can improve consistency. Ash from lignite and fluidized ash bed have a much greater impact on reducing consistency.
I noticed that the effect of ash on the workability is not as clear as for consistency. The greater amount of fine particles can sometimes be a positive influence on the workability (not measured, the subjective assessment), despite the decrease in consistency.
When it comes to color concrete with CEM I 32.5 often brown while the one with CEM II 32.5 B-V is gray. Most people prefer, in my opinion gray concrete and believes that the opposite is true: the brown concrete is with ash and gray with pure cement.
Best Regards, Wojtek Kubissa
I think colour matters only when the cement is intended for architectural finese. Otherwise, most builders will prefer that the cement meets it's functional requirements.
In most cases, the colours of of the fly ashes are related to their C contents. The higher the C content, the darker the fly ash is. While higher C content has adverse effects on the properties of the fly ash.
Generally speaking color of fly ash is not a problem. The major problem related to the use of fly ash in concrete production is represented by inconstant properties and in particular in unburnt content and size.
The unburnt content and size are responsible for the workability of the mixture. The higher the unburnt concrete the lower the fluidity. At the same time increase in fa ash particle higher than 45 micrometer reduce concrete workability. Consequently, the concrete producer is obliged to change concrete mix design in order to obtain a constant workability. This means change in superplastizer dosage and/or water content. Variation in concrete composition inevitably produces changes in concrete color.
regards
luigi coppola
I would agree with the respondents who said that color is not an issue as long as the physical properties meet project requirements. Cement users are likely to be concerned when they see color changes in the flyash over time as these might indicate changes in physical properties. Users want a consistent product so they do not have to adjust their mix design every time they see some change in the flyash. The users most likely to be concerned about flyash color are the masonry industry and other architectural concrete users concerned about the color of the final concrete product.
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