Optimum percentage replacement of cement with flyash in casting of ferrocement cubes of dimension(7.07*7.07*7.07)cm so that it can be used in casting of panels.
In depend of type of Fly Ash, and type of environment factors.
From my experience , but the fly ash from Coal product is from 10-15 %
in my opinion an optimum percentage of fly ash doesn't exist since it depends on many factors. For instance, the percentage replacement of fly ash depend on the cement type and class. In fact, cements containing high clinker content (type I according EN 197-1) and with rapid hardening (42.5R and 52.5R) permit to use higher percentage of fly ash than that usable with Type II (A and in particular B) low strength class cement (32.5) having normal hardening (N). Temperature during hardening is also important. In fact the higher the temperature the higher the fly ash addition. Moreover, if the cementitious mixture is thermal cured the replacement of fly ash increases.
Of course the percentage of replacement depends even on the fly ash quality. Generally speaking the unburnt content influences the performance of fly ash. The higher the unburnt material in fly ash the lower rheological and mechanical properties.
For these reasons I suggest to carry out some preliminary tests consisting in manufacturing mortars with fly ash replacing cement in percentage of 10, 20, 40 and 80%. Flow and compressive strength up to 60 days should be measured to evaluated the optimum percentage of fly ash addition.
My experience suggests that if fly ash is a premium quality material (low unburnt content is possible to use fly ash in the same dosage of cement in combination with an HRWR admixture to reduce water/binder in order to produce durable structures.
In Jamuna Bridge Project, fly ash was used for the first time in Bangladesh. 30% was added.
It depends on the chemical composition of the fly ash. Also it depends of the pozzolanic activity of the fly ash. Replacements up to 25% can be used if fly ash is of high quality. For safety provisions, it is preferable (according to my experience) that the replacement ratio does not exceed 15% to 20%, especially if the 28-day strength is critical.
Dear Hisham Qasrawi,
Is it a better option to go for flyash based portland pozzolona cement in ferrocement panels instead of replacing(15 to 20)% cement with flyash?
Dear Hisham,
nothing will help you more than sending samples of your fly ash and your cement to the lab to make tests with different proportions....Anything between 10 an 30% could be the answer.
Dear William
I think you are addressing your last comment to Dhruv Sood who has the problem. I agree with you that he should test his fly ash before use. This is what I meant when I noted that the ratio depends on the pozzolanic activity and chemical composition.
Why do you want to use flyash in ferrocement construction? If it is because of enhanced durability, then go for flyash based composite cement. In that case you don't need to worry about the replacement percentages. However, be careful about the strength class of that composite cement. Don't use 32.5N cement.
Dear Kaish ,
Yeah, Durability concerns are there, but its more because we want to make it as green ferrocement panels that too hybrid panels (composed of different types of mesh layers and choosing the optimum combination of meshes based on flexural testing of panels for the optimum flyash content).
Depends on your strength and durability aspects...also on w/binder ratio....i think you have to do trial mixes to find out.....well concrete is complex materials its difficult to tell whats the optimum percentage.
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