SECTION II. WATER
2-19. Water has two functions in the concrete mix--it affects hydration and it improves workability.
2-20. Mixing water should be clean and free from organic materials, alkalies, acids, and oil. Potable water is usually suitable for mixing with cement. However, water containing many sulfates may be drinkable, but it makes a weak paste that leads to concrete deterioration or failure. You can use water of unknown quality if concrete cylinders made with it have 7- and 28-day strengths equaling at least 90 percent of the control cylinders made with potable water. Test batches can also determine if the cement's setting time is badly affected by water impurities. Too many impurities in mixing water can affect not only setting time, but can cause surface efflorescence and corrosion of the steel reinforcement. In some cases, you can increase the concrete's cement content to offset the impurities. The effects of certain common water impurities on the quality of plain concrete are described below.
ALKALICARBONATE AND BICARBONATE
2-21. Carbonates, bicarbonates of sodium, and potassium can either accelerate or retard the set of different cements. In large concentrations, these salts can materially reduce concrete strength. A test must be performed to determine the effect on setting time if the sum of these dissolved salts exceeds 1,000 parts per million (ppm).
SODIUM CHLORIDE AND SODIUM SULFATE
2-22. A highly dissolved solid content in a natural water usually results from a high content of sodium chloride or sodium sulfate. Both can be tolerated in rather large quantities in the concrete mix. Concentrations of 20,000 ppm of sodium chloride are generally tolerable in concrete that will dry in service and have low potential for corrosive reactions. Water used in concrete that will have aluminum embodiments should not contain large amounts (more than 550 ppm) of chloride ion.
2-23. Carbonates of calcium and magnesium are seldom concentrated enough to affect the concrete's strength. Bicarbonates of calcium and magnesium in concentrations up to 400 ppm will not affect strength, nor will magnesium sulfate and magnesium chloride in concentrations up to 40,000 ppm. Calcium chloride accelerates both hardening and strength gain.
2-24. Although natural groundwater usually contains only small amounts of iron, acid mine waters can contain large amounts. Iron salts in concentrations up to 40,000 ppm are acceptable.
MISCELLANEOUS INORGANIC SALTS
2-25. Salts of manganese, tin, zinc, copper, and lead can greatly reduce concrete strength and cause large variations in setting time. Sodium iodate, sodium phosphate, sodium arsenate, and sodium borate can greatly retard both the set and the strength development. Concentrations of these salts up to 500 ppm are acceptable, whereas concentrations of sodium sulfide as small as 100 ppm can be harmful.
2-26. Up to 35,000 ppm of salt in seawater are normally suitable for unreinforced concrete. You can offset the degree of strength reduction that occurs by reducing the W/C ratio, but seawater can corrode the steel in reinforced concrete. The risk of corrosion is reduced if the steel has sufficient cover (4 or more inches), the concrete is watertight, and the concrete contains enough entrained air.
2-27. The acceptance of acid water is based on the concentration of acids (ppm) in the water, rather than on the hydrogen-ion activity (pH) of the water. Hydrochloric, sulfuric, and other common inorganic acids in concentrations up to 10,000 ppm generally have no harmful effect on concrete strength.
2-28. Concentrations of sodium hydroxide above 0.5 percent by weight of cement can reduce concrete strength. Potassium hydroxide in concentrations up to 1.2 percent by weight of cement has little effect on the strength of the concrete that is developed by some cements but can substantially reduce the strength of others. When making concrete with water having a pH greater than 11, test the concrete for strength.
INDUSTRIAL WASTE WATERS
2-29. Less than 4,000 ppm of total solids in industrial waste waters generally reduces compressive strength no more than 10 percent. Test any water that contains unusual solids.
SAMITORY WASTE WATER
2-30. Sewage diluted in a good disposal system generally has no significant effect on the concrete's strength.
2-31. Small amounts of sugar (0.03 to 0.15 percent by weight of cement) usually retard setting time, whereas larger amounts (about 0.20 percent by weight of cement) usually accelerate the set. However, sugar in quantities of about 0.25 percent by weight of cement can substantially reduce strength. Perform strength tests if the sugar concentration in the water exceeds 500 ppm.
SILT ORSUSPENDED PARTICLES
2-32. Mixing water can contain up to 2,000 ppm of suspended clay or fine rock particles without adverse effect. Higher concentrations may adversely affect other concrete properties and should be avoided.
2-33. Pure mineral (petroleum) oil probably affects strength development less than other oils. However, mineral oil in concentrations greater than 2 percent by weight of cement can reduce the concrete's strength by more than 20 percent.
2-34. Water containing algae is unsuitable for making concrete.
|David L. Heiserman, Editor||
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Revised: June 06, 2015