We received this from Kurt Rhyner of EcoSur;
Hello Geoffrey
Thank you for the docus
i have read them diagonally before giving them to our people in the field
I do have a couple of questions:
RHA....did you mill it or just use it the way it came ? How was it
burnt ?....in the text it is mentionned that RHA from clay brick burning
could be used, but that is unlikely, as there it is burnt at much to
high a temperature. We found that if you aplly controlled burning and
milling, RHA are totally uneconomical...we work only with natural
pozolans (mainly volvanic ashes)
saludos kurt
Brick Kiln Ash
We mill the pozolans in ball mills, but extremely light ashes are hard to mill, they take a long time to really get fine, natural pozolans (volcanic sands) are heavier and the output per hour is much larger. But even then it is a tight race for cost in Latin America. This will change when oil goes up in price and portland cement will follow fast. So prepare for the day......
I would not trust ashes from brick kilns too much.....after all you never know how hot it was in there, and if they are critslline they are not very reactive....and you will only know after the concrete has hardened...and you may never know it.....
RHA Cement vs. RHA Concrete Production
Thanks for your comment Kurt.
I think it depends on the scale of production. A large scale operation will produce cement for sale, certify it and bag it. A small scale operation can't afford the chemical lab analysis to certify it. But, they could use it in pre-cast concrete products and certify them. It is far easier to certify a concrete product for strength or porosity than it is to certify the content of a chemical powder.
So, a brick producer using rice husk as fuel can also produce cement for use in his/her own precast concrete products. S/he must regulate the temperature of her/his fire so s/he should have a good idea of which ash is appropriate.
A brick producer could also sell ash to a precaster.
In our RM2 rod mill, we grind our ash 20 minutes to acheive a fineness that passes our seive standard. How long do you grind your ash? You're correct that the lightness of the ash does make grinding a challenge.
Manufacturing Process of Pozzolanic Materials
I have been reading about Pozzolana as an excellent additive/Binding material for cement. What is the Manufacturing Process for Pozzolana obtained from Volcanic rocks?
Volcanic Rock processing for pozzolana use
Albey,
I believe that Kurt processes their volcanic ash with a ball mill. Any pozzolana needs to be fine to have a lot of surface area for good reactivity. I believe that only fly ash ('smoke' from coal-fired electric power plants) can be used directly. Here we use a rod mill to process rice husk ash.
Ash Processing
Rice Husk Ash has been known as a pozzolana for many years.
Kurt is refering to 'Recent Advances in Rice Husk Ash Cement,' a paper by 2 Cal Poly students. http://www.cvbt-web.org/uploads/Rice_Husk_Ash/Nick_Emmet_RHA.pdf
The rice husk ash is milled in our CVBT model RM2 rod mill. It must be fine in order to increase surface area so as to get a good reaction.
The ash is indeed from a brick kiln. This ash is actually from a field brick clamp. It is my understanding that brick firing in kilns goes through 3 stages; initial firing, intermdiate and final firing. The fire and temperature is different for each. The ash most appropriate for RHA cement comes from the initial firing.
The economics of RHA cement depend on the local cost of other cements, mainly ordinary portland cement. In Thailand RHA is not competitive with OPC either because we have high cement production and good infrastructure. In Cambodia RHA can be competitive because of high cement cost and poor infrastructure.
Thanks for your questions Kurt. We look forward to your comments.