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Re: Sulfate Res Conc. & Waterproofing

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Norb Volny wrote:

> >I am reviewing the specs for the construction of a RC office building.
> >
>  The soil investigation shows no
> >presence of water for at least 25ft below foundation level and the soil
> >type is moderately fractured Limestone.
>
> >The specs also call for the waterpoofing membrane to continue below the
> >whole area of the 190" mat foundation (tanking.) IMHO there is no need
> >to do that, and waterproofing the basement walls would be enough.
>  Moni,
>
> Sounds like you could actually do just fine using a low w/c ratio type
> II/III cement and dispense with the submat waterproofing to me...unless
> someone expects 40 days and nights of rain or a Tsunami!! Using a pozz and
> air entraining admixture would render the mat relatively impermiable. Does
> the owner have something he wants to contain inside the building??..ie some
> noxious solvent or chemical?
>

Be careful with Type III, it has a high shrinkage rate due to the rapid
hydration of tricalcium aluminate and will be more susceptible to shrinkage
cracks..  Also, the sulfate resistance is not as good at II or V.   A low water
cement ratio is good anytime.

One thing to note CL will cause corrosion of the reinforcing steel and
subsequent spalling of the concrete.  Sulfates attack the cement paste directly
and cause real problems.  Type V is for sulfate resistance.  Without kowning
the analytical results for the soils I would be hesistant to recommend anything
else.  Most engineers only specify type V when and where it is needed since it
is usually hard to get and expensive.  There are some admixtures which can
help.

The waterproofing (it is a membrane or a visquene sheet?) may be necessary to
protect flooring which could be susceptible to moist conditions.  Moisture
contents tend to go up at the center of slabs.  Also, most buildings have
landscape and watering systems which can contribute to water problems.  In a
recent article in CE News I read where 90% of all functional problems in
buildings were related to water.

This is a case where reading the geotech report may be a good idea.

Arvel L. Williams, P.E.


> Hope this is of some use to you.
>
> Norb Volny, PE
>
>