Q. We are on a job where the only source of potable water for curing concrete is about a mile away. The general contractor plans on using a deep well as a water source for curing. While waiting for water quality test results, however, we noticed red iron stains, a strong sulphur odor, and a salty taste. Can we use this well water for curing? We are concerned about discoloring the concrete and the possible introduction of chlorides.
A. First a little background on the issue of water in general. Until recently the specific requirements for mixing water—let alone curing water—were open to broad interpretation. The basic reference has been to ASTM C94, “Standard Specification for Ready-Mixed Concrete.” Section 5.1.3 of that document says questionable water should not be used as mixing water unless “service records of concrete made with it or other information indicates that it is not injurious to the quality of the concrete.” Two tables give some additional guidance, but it is still a judgment call.
Last June, however, ASTM approved a new document, ASTM C 1602, “Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete,” that contains specific guidelines defining water's acceptability for this purpose. While it still does not directly address water for curing, water suitable for mixing concrete should also work for curing. A more complete description of the standard can be found in the January 2005 issue of Concrete Construction (“A New Water Standard for Concrete,” page 71).
In terms of dealing with the water source you describe, you can install some sort of filtration system, similar to what is used in cure room systems. If discoloration is an issue, test a small section that will receive a floor covering. Trowel-finish concrete (that is, a warehouse burn) is less susceptible to stains, but the additional chloride may be detrimental to long-term durability.
ASTM C511 has the specifications for moist cabinets, moist rooms, and water storage tanks. ASTM C192/C192M covers making and curing concrete test specimens in the laboratory. If it's an architectural issue, the use of filters will be mandatory.
However, if you have a potable water source for making the concrete, using a questionable water source for curing is not the best approach. Look at alternate curing methods such as covering with plastic to maintain the original moisture from the concrete mixture or curing compounds. There are various good resources available on concrete curing practices.
The U.S. Army Corps of Engineers lists several test methods that deal with water for curing at www.wes.army.mil/SL/MTC /handbook/handbook.htm. Once there, scroll down to the “400” series that deals with water. Some are ASTM test methods that you will have to get from ASTM (www.astm.org). But the majority are U.S. Army Corps of Engineers' Test Methods that you can access directly.
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