Many researchers have investigated the mechanical properties of class F fly ash, and elevated temperatures were used to cure the class F fly ash concrete. From my reading, I reached to this conclusion : Alkali activated class F fly ash can not cure at room temperature which limit it's applications in-situ
FA has 3 main methods of activation:
- mechanical
- thermal
- chemical (Alkaline; alkaline earth; alkaline earth-sulfate)
Alkaline - the phases like N(K)-A-S-H or N-C-A-S-H
Alkaline earth - the phases like C-A-S-H
Alkaline earth-sulfate - the phases like C-A-S-SO4-H
100% FA can cure at room temperature. But it needs to FA has the hight surface
area - min. 600 m2/kg and hight alkaline activation (alkaline silicate solution and NaOH or KOH solution). The phases will be like zeolites N(K)-A-S-H.
Another way to achieve curing FA at room temperature is to use together Alkaline and Alkaline earth activation (hybrid cements). It will be the hybrids phases like N(K)-C-A-S-H. Maybe it's the best and the easiest way to cure FA at room temperature.
P.S. Sorry for my English, I tried!
Generally not
But curing is possible in the presence of a source of calcium (e.g. a calcium oxide bearing slag like slags from iron and steel operations) or for activated fly ash (e.g. after mechanical activation). See some of our publications on the subject.
yes, Geopolymer mortar / concrete with the addition of 6% colloidal nano silica shows appreciable improvement in mechanical strength at 28 days under ambient temperature curing.
Data Effect of nano-silica on strength and durability of fly ash ...
As far as my understanding goes, geopolymer is either alkali activated slag or alkali activated fly ash. While the former is effective even under ambient curing the later needs curing at elevated temp. In ether case, adding silica enhances.the properties.as mentioned by Dibyendu Adak.
Yes of course, any kind of pozzolans, like the fly ash type F with alcalis and water, may react without problems at any room temperature. The esential for this react is the presence of water!!
Yes of course, any kind of pozzolans, like the fly ash type F with alcalis and water, may react without problems at any room temperature. The esential for this react is the presence of water!!
Yes of course, any kind of pozzolans, like the fly ash type F with alcalis and water, may react without problems at any room temperature. The esential for this react is the presence of water!!
Can you please provide me with a scientific reason for not curing at room temperature?
Even though Metakaolin has almost the same chemical composition of Fly ash class F, but Metakaolin cures at room temprature, why.
thanks
The process of geopolymerisation primarily comprises of three stages : dissolution (including formation of polymeric species in solution), precipitation (main reaction) and reorganization of the structure (to minimise energy (surface/bulk)). For the second stage to take place, there has to be a build up of concentration (just like any precipitation reaction through homogeneous/heterogeneous nucleation and growth). The process of dissolution will depend on the experimental conditions (temperature, concentration, reactant present) and most importantly, nature (or reactivity) of solid. When the temperature is low, dissolution is slow (that means curing may take very long time). For solid you have to consider not just composition but also phases. Metakaolin reactivity is higher than kaolin and greater than the phases in fly ash (notably glass, which is the most reactive phase in fly ash); therefore low higher solubility at room temeperature. Based on this, you may try to visualize what exactly happens for kaolin/metakaolin/presence of lime/concentration increase/mechanical activation etc and you will hopefully get your answer.
Mr. Rakesh kumar garu,
Rightly said about Alkali activated flyash. But i observed that alkali activated GGBS can be cured at ambient temperature with satisfactory results. Can you explain this Sir.
yes, at least for two reason : amorphous (glassy character) and presence of CaO as an important constituents (not phase) in GGBS. The slag has latent hydraulic activity (all/most Si-O bond broken, Q4 structure); this is not true for FA which shows pozzolanic activity, means shows cementitious character only in the presence of lime. During alkali activation, silica and alumina present in slag can behave the way they do in FA. In fact both C-S-H and Na-S-H gels may form in the case of slag. see our papers on the subject
I assuming you are talking about 100% FA without OPC or lime in the mix. FA on its own, no matter which activation agent is used, it won't cure at room temperature. Even at high temperature it's curing will be limited as the CSH formation happens only on the surface of the fly ash particle. Probably you will have a better result if all the activation mechanism works in tandem - mechanical activation by fine grinding, thermal activation by elevated temperature and chemical activation by alkali attack.
I assuming you are talking about 100% FA without OPC or lime in the mix. FA on its own, no matter which activation agent is used, it won't cure at room temperature. Even at high temperature it's curing will be limited as the CSH formation happens only on the surface of the fly ash particle. Probably you will have a better result if all the activation mechanism works in tandem - mechanical activation by fine grinding, thermal activation by elevated temperature and chemical activation by alkali attack.
FA has 3 main methods of activation:
- mechanical
- thermal
- chemical (Alkaline; alkaline earth; alkaline earth-sulfate)
Alkaline - the phases like N(K)-A-S-H or N-C-A-S-H
Alkaline earth - the phases like C-A-S-H
Alkaline earth-sulfate - the phases like C-A-S-SO4-H
100% FA can cure at room temperature. But it needs to FA has the hight surface
area - min. 600 m2/kg and hight alkaline activation (alkaline silicate solution and NaOH or KOH solution). The phases will be like zeolites N(K)-A-S-H.
Another way to achieve curing FA at room temperature is to use together Alkaline and Alkaline earth activation (hybrid cements). It will be the hybrids phases like N(K)-C-A-S-H. Maybe it's the best and the easiest way to cure FA at room temperature.
P.S. Sorry for my English, I tried!
This might Help,
Article Current state of k-based Geopolymer cements cured at ambient...
- Badges
- Science topic