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using metakaolin
16main	04-10-2008 18:56:34
Member Posts: 10 Joined: 02-20-2008	I am casting small mosaic pieces with a mortar mix and I've started replacing 10% of my cement with meta K and am trying to deal with the gumminess that is making it hard to place the concrete into the molds. My mix is cement rich: 1 part cement: 1.5 part sand (mostly fines) 5% pigment max I'm up to a .38 water/cement ratio from a .35 but I find I have to overdose with superplasticizer to get my mix to move now and that has the consequence of prolonging my cure time. I was used to a 24 hr cure cycle before the metakaolin and I was basically able to slip cast my mix into the molds. Does anyone else have problems with the consistency of their mix with metakaolin? Is upping my water ratio the only choice I have? It probably doesn't help that I don't have much gradation to my sand but I'm polishing my pieces and I don't want a heavy aggregate exposure. I'm not into the terrazzo look. And my pieces are as thin as 3/8". I've tried upping my sand but I can't do that without more water either. I don't want to counteract the strength benefit of the metakaolin by dosing my mix with too much water. I'd appreciate any input, Libby

consci	04-13-2008 07:19:11
Member Posts: 64 Joined: 04-02-2008	What strength are you gaining if you need to increase w/c ratio. metakaolin is used in mixes to cut down on the amt. of cement needed to obtain desired psi. i guess what i am getting at is, why are you using kaolin in you mix? i understand you need a tight surface for final polish, it sounds like you had that already. What about not using meta-k? Instead apply a densifier after pieces are removed from mold? If asr is your concern then leave the meta-k in and try other water reducers/supers. Too much super will also make the mix like marshmallow puff

FISHSTONE	04-13-2008 08:08:45
Member Posts: 26 Joined: 02-09-2008	Hi Libby, We use Power Pozz Metakaolin in all of our mixes. You are correct that it is a thirsty product and we too increase our plasticizer and W/C%. We use Metakaolin at a 15% replacement mainly because it makes the mix easier to work with, improves surface and reduce efflorescence. We do keep our concrete in the mold and hydrated for at least four days as opposed to your 24hour turn time. If you need to start processing your concrete within 24 hours you could always add some accelerator to speed up the set time… There is a good article on Metakaolin from CCI that has some great information you may find interesting. http://www.concretecountertops.net/library.item.51/how-to-use-metakaolin-in-concrete-countertops.html Tom

16main	04-17-2008 22:27:33
Member Posts: 10 Joined: 02-20-2008	I'm thinking you're right. For such tight, tedious pieces it's not worth it. I wanted to use the metaK especially for my larger pieces to reduce any shrinkage cracking etc. since my mix is so rich. to increase strength, for a finer finish, for everything that I've read about metaK...but workability is key. I'm casting into sheet rubber, stencil molds, and some of the shapes are less than 1" square. thanks

aaron2u	04-18-2008 08:45:51
Member Posts: 25 Joined: 02-20-2008	I'm sure you know that you don't have to adjust your w/c ratio when you use metakaolin..... You add in the metakaolin to your cement and throw it all against water content... Metakaolin is considered cementitious.... Water/(C+M) Mix it in, use your .35 against the total, then evaluate performance.

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