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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