Greenbuilding Archive for May 2001

One would be mixing unrelated units ( ie sq feet, inches) 
in order to arrive at a third unrelated unit (gallons).

Logically, the calculation would appear to be:

(1000 sf)  x (.75) x (.9) x (20 inches / 12 inches per foot)  
     =  1125 cu feet.

Then if one needed to convert from cubic feet to US liquid gallons, 
the multiplier would be  7.48 

       7.48 x 1125 cu ft = 8,415 gallons (before reduction for usage)

The difference in resultant volumes (over 5000 gallons) is no big deal
(except to  nit-picker such as I) since over-capacity is probably a Good
Thing when it comes to ability to store water.

Re: use of volcanic ash as a waterproofing admixture:

Some pozzolanic materials may reduce the permeabilty of low-cement-
content or fines-deficient mixes but their use in well-proportioned mixes
may increase the amount of mixing water required, ultimately increasing
rather than decreasing the permeability of the concrete.

That being said, I suspect that the composition of volcanic ash would 
vary with location and recognising that pozzolans vary considerably in their
effect when reacting with the  calcium hydroxide (released by the hydration
of Portland cement) I think that it would be difficult if not impossible to
predict the effect of your specific volcanic ash on the permeance of the
concrete mix. 

I suspect that in the absence of an analysis of the ash, only testing 
of the specific mix would tell.

But generally-speaking, keeping the mixing water to a minimum
(ie water - cement ratio of less than 0.45 by mass),  
length of moist curing period (longer = better) and incorporating 
an air-entraining admixture will do much to achieving a watertight
concrete ... and in the absence of the above, Xypex.

                 ===    *     ===

Robert  W. Tom          Kanata, Ontario, Canada       
Rob_Tom@ErehwonDesignGroup.intranets.com 

please visit:  http://www.theHungerSite.com daily






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