Anhydrite subfloor opinions

Been to look at a job, (new build) I’m adamant it’s anhydrite. Spoke to site manager he assures me it’s concrete. It does look like anhydrite. It has fibres in it if that helps that I’ve never seen before. Any opinions appreciated

 

Had the same last month with a new build. Site agent telling me it's concrete then seen another agent further up the plots telling me its anhydrite....then the lady in reception its power floated

I knew it was anhydrite anyway.

Are there some fibre sticking up out the concrete?

 

Yea loads of fibres sticking out, never seen as many

 

Needs grinding and it can be a pig to do, or should I say the ones I have ground of have been

 

Yea, I get that. Have you ever seen anhydrite with fibres in or just concrete?

 

fibre-reinforced-screeds.pdf (nhbc.co.uk)
Both yes

 

Turns out the subfloor is concrete with GGBS in it, replacing 75% of the concrete. Never heard of it before, every days a school day

 

What the hell is GGBS

 

Ground granulated blast furnace slag

 

It’s a filler apparently that replaces the cement content

 

Helps the subfloor from cracking.