VCAS source in the UK - VCAS vs Silica Fume - A few other bits and bobs too.

Hi All,

The title says it all really. I've searched in the forums, but not seen any UK VCAS sources listed. However a UK based member (Johnny Rosh) stated in a 2016 thread that he was using VCAS in his concrete mix, so there must be some available (in non industrial quantities) somewhere!

Do any of you current active forum members know of any UK/European sources for VCAS pozzolan?

My second query is do any of you have any insight into the pros and cons of VCAS vs silica fume? The things that I believe to be true from my research so far are that:

  • silica fume is a more reactive pozzolan
  • silica fume will give higher early strength gain
  • silica fume will make the mix less workable (more SP required)
  • VCAS will make the mix more workable (less SP required)

I am new to working with concrete and am building up to making kitchen countertops and shower panels. The face coats of both the countertops and the shower panels will have glass aggregate and will be ground to expose the glass aggregate. The backer coats will be GRC/GFRC. I am aware that I need to use a pozzolan to nullify ASR between the cement and the aggregate in the face coats.

I am currently undecided as to which manufacturers admix products I will be using. The products I have found available in the UK thus far are:

  • Fishstone - Super6 Admix & SP
  • Oscrete - Flowcast (polymer & SP admix) (would use with Cemcraft SP if required)
  • Fibre Technologies - Polycure FT Polymer and Flowaid SP
  • Cemcraft - White Silica Fume
  • Cornish Lime - Metakaolin and fine (0.3mm-0.6mm) light coloured silica sand
  • Specialist Aggregates - Glass aggregates (also sand)

If any of you have any experience with using any of the above products, I would be very interested in your thoughts on your experiences.

My last question is to do with Polymer loading. My research thus far has suggested that 6% of cementitious components by weight is the minimum recommended loading of polymers for GRC/GFRC, going up to 12% for pieces destined for wet environments ie. my shower panels. However it seems that many of the all in one admix blends dose around 5% polymer loading, with some going as low as 2.5%. Do any of you have thoughts on this?

Thanks in advance!

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Hey James, Glad to see a fellow brit dipping his toe into the stressful world of concrete!!!

I can personally vouch for Fishstones Super-SIX and Optimimum 380 from House of Concrete in the UK. Very helpful and great customer service.

Super-SIX is an amzing product  and produces an amazing SCC mix which is perfect for wall panels. Keeps it simple equipment wise as no need for spray setup.

The Optimum 380 is fantastic and a 1 gallon jug will last you for ages.

As far as your polymer loading question goes, surely you will be sealing your worktops and shower panels and that is what will provide you with your protection from moisture in the shower area!

Hope this helps and good luck with your projects.

Hi Mostin,

I have started making samples using Oscrete's Flowcast. My primary reason for using the Oscrete at this stage is I was able to obtain sample quantities of it. So far my test pieces have come out very well. I'm not 100% sold on the Oscrete though. The main thing that is putting me off is the multi component nature of it. I think in the long term I want complete control of mix proportions. Also with the published literature from Oscrete I don't actually know what dosage of polymers I'm adding to the mix! I'll be giving them a call to see if they will divulge that information.

This ties in to to your query about sealing the panels/worktops. Yes, I will be sealing the panels and worktops. However, in scouring all the information sources I can find, I've found a couple of references which state that for GFRC applications destined for wet environments, polymer dosage of over 10% of the cementitious is recommended. Apparently the increased polymer loading decreases the permeability of the GFRC while also increasing flexibility. It does not eliminate the permeability so sealing is still required. The increased flexibility would, I believe, improve the handling characteristics of components such as shower panels which are essentially large think sheets and as such highly susceptible to cracking during handling.

Going back to my wariness of multi component admixtures, I believe that by the time I'd have added enough of the admix (be it Super Six or Flowcast) I would have overdosed the mix with SP and would end up with an unusable mix. 

I think I may go in the direction of using a mix based on either the Forton or Fibre Tech Polycure. However in my costing breakdowns the Forton based mixes end up with quite a high unit cost and the Fibre Tech Polycire is a straight polymer solution/suspension with no added defoamer. I think I have a little bit more figuring out to do to determine my best compromise. Truth be told what I would really like is a "dry" powdered polymer rather that a liquid but I've yet to find one that isn't a part of a polymer/SP mix.

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