Civil Engineering Reference
In-Depth Information
effects of mix water impurities can be found in
Steinour
(1960)
and
Abrams (1924)
. Over 100 different compounds
and ions are discussed.
Following is a synopsis of the effects of certain impu-
rities in mixing water on the quality of normal concrete:
ALKALI CARBONATE AND
BICARBONATE
Carbonates and bicarbonates of sodium and potassium
have different effects on the setting times of different
cements. Sodium carbonate can cause very rapid setting,
bicarbonates can either accelerate or retard the set. In large
concentrations, these salts can materially reduce concrete
strength. When the sum of the dissolved salts exceeds
1000 ppm, tests for their effect on setting time and 28-day
strength should be made. The possibility of aggravated
alkali-aggregate reactions should also be considered.
Fig. 4-2. Laboratory analysis of water, in this case using an
atomic absorption spectrophotometer to detect concentra-
tion of elements. (44182)
alkalies, and solids in the mixing water or appropriate
tests can be performed to determine the effect the impu-
rity has on various properties. Some impurities may have
little effect on strength and setting time, yet they can
adversely affect durability and other properties.
Water containing less than 2000 parts per million
(ppm) of total dissolved solids can generally be used satis-
factorily for making concrete. Water containing more than
2000 ppm of dissolved solids should be tested for its effect
on strength and time of set. Additional information on the
CHLORIDE
Concern over a high chloride content in mixing water is
chiefly due to the possible adverse effect of chloride ions
on the corrosion of reinforcing steel or prestressing
strands. Chloride ions attack the protective oxide film
formed on the steel by the highly alkaline (pH greater than
12.5) chemical environment present in concrete. The acid-
Table 4-2. Acceptance Criteria for Questionable Water Supplies (ASTM C 94 or AASHTO M 157)
Limits
Test method
Compressive strength, minimum percentage of
90
C 109* or T 106
control at 7 days
Time of set, deviation from control, hr:min. from 1:00 earlier to 1:30 later C 191* or T 131
* Comparisons should be based on fixed proportions and the same volume of test water compared to a control mixture using city water or
distilled water.
Table 4-3. Chemical Limits for Wash Water used as Mixing Water (ASTM C 94 or AASHTO M 157)
Maximum
Test
Chemical or type of construction
concentration, ppm*
method**
Chloride, as Cl
ASTM D 512
Prestressed concrete or concrete in bridge decks
500
†
Other reinforced concrete in moist environments or containing
aluminum embedments or dissimilar metals or with stay-in-place
1,000
†
galvanized metal forms
Sulfate, as SO
4
3,000
ASTM D 516
Alkalies, as (Na
2
O + 0.658 K
2
O)
600
Total solids
50,000
AASHTO T 26
* Wash water reused as mixing water in concrete can exceed the listed concentrations of chloride and sulfate if it can be shown that the concen-
tration calculated in the total mixing water, including mixing water on the aggregates and other sources, does not exceed the stated limits.
** Other test methods that have been demonstrated to yield comparable results can be used.
† For conditions allowing use of CaCl
2
accelerator as an admixture, the chloride limitation may be waived by the purchaser.
