Civil Engineering Reference
In-Depth Information
WATERS CARRYING SANITARY SEWAGE
trations greater than 2.5% by mass of cement may reduce
strength by more than 20%.
A typical sewage may contain about 400 ppm of organic
matter. After the sewage is diluted in a good disposal
system, the concentration is reduced to about 20 ppm or
less. This amount is too low to have any significant effect
on concrete strength.
ALGAE
Water containing algae is unsuited for making concrete
because the algae can cause an excessive reduction in
strength. Algae in water leads to lower strengths either by
influencing cement hydration or by causing a large
amount of air to be entrained in the concrete. Algae may
also be present on aggregates, in which case the bond
between the aggregate and cement paste is reduced. A
maximum algae content of 1000 ppm is recommended.
ORGANIC IMPURITIES
The effect of organic substances on the setting time of
portland cement or the ultimate strength of concrete is a
problem of considerable complexity. Such substances, like
surface loams, can be found in natural waters. Highly
colored waters, waters with a noticeable odor, or those in
which green or brown algae are visible should be regarded
with suspicion and tested accordingly. Organic impurities
are often of a humus nature containing tannates or tannic
acid (Fig. 4-3).
INTERACTION WITH ADMIXTURES
When evaluating waters for their effect on concrete prop-
erties, it is important to also test the water with chemical
admixtures that will be used in the job concrete. Certain
compounds in water can influence the performance and
efficiency of certain admixtures. For example, the dosage
of air-entraining admixture may need to be increased
when used with hard waters containing high concentra-
tions of certain compounds or minerals.
SUGAR
Small amounts of sucrose, as little as 0.03% to 0.15% by
mass of cement, usually retard the setting of cement. The
upper limit of this range varies with different cements.
The 7-day strength may be reduced while the 28-day
strength may be improved. Sugar in quantities of 0.25% or
more by mass of cement may cause rapid setting and a
substantial reduction in 28-day strength. Each type of
sugar influences setting time and strength differently.
Less than 500 ppm of sugar in mix water generally
has no adverse effect on strength, but if the concentration
exceeds this amount, tests for setting time and strength
should be made.
REFERENCES
Abrams, Duff A.,
Effect of Tannic Acid on the Strength of
Concrete,
Bulletin 7, Structural Materials Research
Laboratory, Lewis Institute, Chicago,
http://www.port
cement.org/pdf_files/LS007.pdf
, 1920, 34 pages (avail-
able through PCA as
LS007
).
Abrams, Duff A.,
Tests of Impure Waters for Mixing Concrete,
Bulletin 12, Structural Materials Research Laboratory,
Lewis Institute, Chicago,
http://www.portcement.org/
pdf_files/LS012.pdf
, 1924, 50 pages (available through
PCA as
LS012
).
SILT OR SUSPENDED PARTICLES
About 2000 ppm of suspended clay or fine rock particles
can be tolerated in mixing water. Higher amounts might
not affect strength but may influence other properties of
some concrete mixtures. Before use, muddy water should
be passed through settling basins or otherwise clarified to
reduce the amount of silt and clay added to the mixture by
way of the mix water. When cement fines are returned to
the concrete in reused wash water, 50,000 ppm can be
tolerated.
ACI Committee 201,
Guide to Durable Concrete,
ACI 201.2R-
92, American Concrete Institute, Farmington Hills, Mich-
igan, 1992, 41 pages.
ACI Committee 222,
Corrosion of Metals in Concrete,
ACI
222R-96, American Concrete Institute, Farmington Hills,
Michigan, 1997, 30 pages.
ACI Committee 318,
Building Code Requirements for
Structural Concrete and Commentary,
ACI 318-02, American
Concrete Institute, Farmington Hills, Michigan, 2002, 369
pages. Available through PCA as LT125.
OILS
Bhatty, Javed I.,
Effects of Minor Elements on Cement
Manufacture and Use,
Research and Development Bulletin
RD109, Portland Cement Association, 1995, 48 pages.
Various kinds of oil are occasionally present in mixing
water. Mineral oil (petroleum) not mixed with animal or
vegetable oils probably has less effect on strength devel-
opment than other oils. However, mineral oil in concen-
