Most sources agree that a water/cement ratio in the vicinity of 0.4 to
0.5 provides watertightness:
"Permeability to water is largely a function of the concrete
structure. Hardened cement always contains pores; concrete can
therefore never be absolutely watertight. It will always contain at
least 10 per cent by volume of pores of varying origin, possessing
differing properties.
Watertightness is, however, very dependent upon a high standard of
workmanship, avoiding honeycombing and the like. As a general rule, it
may be stated that all measures which result in a dense concrete with
few pores improve its watertightness. There is, however, no
relationship between the strength and the water permeability. If the
aggregates are well graded and river sand is used as fines, a concrete
containing 500 kg cement per m3 of concrete and having a water/cement
ratio of 0.4 is practically impermeable to water, even under high
pressure (2.4 MN/m2) and over a long test period."
VSL Technical Reports
http://www.vsl.net/downloads/VSL_technical_reports/PT_Pressure_Tunnels.pdf
"Reminder: for waterproof concrete, the water/cement ratio should be
no higher than 0.55."
MAPEI
http://www.mapei.it/pdfProd/ING/780_ING.pdf
"Water permeability increases exponentially when concrete has a water
cement ratio greater than .50."
Do It Yourself
http://doityourself.com/concrete/cement_water_ratio.htm
"Concrete which will be exposed to freezing and thawing shall contain
entrained air and shall have water-cement ratios of 0.45 or less.
Concrete which will not be exposed to freezing, but which is required
to be watertight, shall have a water-cement ratio of 0.50 or less if
the concrete is exposed to fresh water, or 0.45 or less is exposed to
brackish water or sea water. For corrosion protection, reinforced
concrete exposed to deicer salts, brackish water or sea water shall
have a water-cement ratio of 0.40 or less."
Precast Concrete Association of New York
http://www.pcany.org/info/nysdot/guidspc.htm
The document linked below contains a chart (on page 2) which compares
the water permeability of concrete at water/cement ratios of 0.6,0 .5,
and 0.44. From the chart:
" W/c ratio: 0.60 0.50 0.44
[...]
Water penetration (mm) according
To DIN 1048 after 28 days cure: 30 13 4
Impermeability to water according
to UNI 9858 and ENV 206: no yes yes "
As you can see from the results above, concretes with w/c ratios of
0.44 and 0.5 meet the standards of impermeability to water established
by two European technical bodies (UNI and ENV). Concrete with a w/c
ratio of 0.6 did not meet these standards.
Here's information on deriving the water/cement ratio:
"The water to cement ratio is calculated by dividing the water in one
cubic yard of the mix ( in pounds) by the cement in the in the mix (in
pounds). So if one cubic yard of the mix has 235 pounds of water and
470 pounds of cement- the mix is a .50 water to cement ratio.
If the mix lists the water in gallons, multiply the gallons by 8.33 to
find how many pounds there are in the mix."
Concrete Network
http://www.concretenetwork.com/concrete/slabs/ratio.htm
Google search strategy:
Google Web Search: "concrete" + "waterproof" + "water/cement ratio"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=concrete+waterproof+%22water%2Fcement+ratio
Google Web Search: "concrete" + "waterproof" + "w/c ratio"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=concrete+waterproof+%22w%2Fc+ratio
Google Web Search: "concrete" + "water-tight" + "water/cement ratio"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=concrete+water-tight+%22water%2Fcement+ratio
Google Web Search: "concrete" + "water-tight" + "w/c ratio"
://www.google.com/search?hl=en&ie=UTF-8&oe=UTF-8&q=concrete+water-tight+%22w%2c+ratio
I hope this is useful. If anything is unclear, or if a link doesn't
work for you, please request clarification; I'll be glad to offer
further assistance before you rate my answer.
Best regards,
pinkfreud |
