[Ferro List] more Tom's crud testings

[Keith Britton]

Tom

A micro-crack in fc is a "Griffith Flaw", Google that for more info than 
you want.  Flaws may or may not be tolerable depending on design and 
duty.  For OPC based mortars, if flaws are a concern, one mustn't forget 
that local tensile stresses may occur due to dimensional changes in 
curing and with thermal change.  Given a Griffith Flaw, all you need is 
local tension exceeding the critical value at the crack tip for it to 
propagate, hence cracks creeping with aging, diurnal or seasonal 
temperature swings - even when in an area not obviously under tension. 

I don't see Richard's PVA fibers as useful for reinforcement, do see 
them of great value in the few cases where fracture toughness may be 
critical, but see them as priceless and unrivalled for general Griffith 
Flaw suppression in early cure.

I can send you a small amount of a dichromate if you want to test that.  
For something like a tank, where you may worry about rust but actually 
need no bond, you might try an asphalt emulsion dip.

Flaws with surface expression might be healed by penetrating silicate or 
silane treatment, but, given the access to easily surfce coat or treat, 
is microcracking significant for a tank?

kb