Please check the link for some papers
http://www.ijirset.com/upload/may/5_USE%20of%20FLYASH.pdf
http://www.ijesit.com/Volume%202/Issue%206/IJESIT201306_39.pdf
http://www.sciencedirect.com/science?_ob=ArticleListURL&_method=list&_ArticleListID=-638328781&_sort=r&_st=13&view=c&md5=d713d8bb058045942052ec6d9ab0b519&searchtype=a
Dear Krishnaraj,
Increase in flyash content increases the consistency of the fly ash concrete because of very small particle and high surface area, the volume of cementitious material to the same w/c ratio will increase thereby providing thicker consistency and very low to minimal segregation, depending upon the amount of fly ash content.
Increase the fly ash content in your mix will have corresponding decrease in concrete strength. This is because of its low reactivity and also due to the crystalline silica present in it which has negligible or no reactivity.
Flyash has spherical particle size, which provides ball bearing effect when used in a fly ash blended mix, thereby increasing its workability. Workability is directly proportional to the amount of flyash added to the mix. Higher the flyash content higher is the workability of flyash blended mix.
I recommend read a review paper that will cover many aspects of flyash's use in concrete. I have attached 1 reference for you:
http://www.concrete.org/Publications/InternationalConcreteAbstractsPortal.aspx?m=details&i=6991
Thanks mr.Rajeev Roychand,
I have High Calcium Flay ash with Spongy (Irregular and porous) particle shape. I want identify the Water to binder ratio, so that i prepared correlation between flow table spread value and water volumes. i got less workability compare with control mortars. If 0.4 is w/b ratio means for control mortar is 129 mm, 15% fly ash replacement is 116 mm,30% Fly ash replacement is 107mm spread value. In this case how could i refer and proceed further.
Hi Krishnaraj,
You have your answer, Fly ash from different sources will behave differently and be carefull of a generalized answer. You experienced it yourselve, some increase and some decrease the workability some increase later strengths and some does nothing.
So best advise to all, Test the representative sample of your sourse for your aplication. Don't do accelerated tests. (fly ash in general love heat and give a total scew answer for ultimate strength when heat is used)
Krishnaraj, i think the issue could be high content of unburnt carbon in your flyash. Unburnt carbon absorbs moisture, thereby reducing the actual content available for the workability and hydration reaction. Please check the content of unburnt carbon in your fly ash
Sir,
The unburnt carbon is 2.73% (LOI). In the reference, authors are mentioned like LOI is act as a Inert material. it will not influence.. any parameters. but SO3 i am getting like 4.21%.
Dear Krishnaraj,
Here is the link of one research paper related to the effect of unburnt carbon on workability.
http://www.sciencedirect.com.ezproxy.lib.rmit.edu.au/science/article/pii/S0958946502000987
Moreover i am also working on very high volume fly ash concrete and i have faced similar problem with one of the fly ashes i worked on.
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