ASTM C1602 conserves resources

Some of us who live in arid parts of the world think about water with a reverence others might find excessive.—Joan Didion, “Holy Water”, 1977

Most of us learned in engineering school to use potable water in concrete. If you’re making concrete in the laboratory you just get your water from the tap. If you’re at a remote jobsite where potable water isn’t available, you try to make do with what you have on site. Now with the implementation of CALGreen, there’s growing interest in conserving water—for example, by reusing water from concrete production.  This is where ASTM C1602 comes in.

The West begins where the average annual rainfall drops below twenty inches. Water is important to people who do not have it, and the same is true of control.—Joan Didion, “Holy Water”

Having spent the first 30 years of my life in the western United States, I appreciate the need to conserve water. Over the last 30 years or so I’ve lived within a short distance of one or another of the Great Lakes, where people see little need to conserve what we have so much of. Yet even now, I can’t stand just to let water run. And while I do understand that too much water can be a really bad thing, I still view rain as a blessing.

Even where surface water is abundant, we still need to maintain its quality. We pay attention to runoff water and keep leaves out of our gutters because we don’t want nutrients washing into rivers and lakes. And we try to reuse wash water from concrete trucks rather than let it flow down the drain. It’s also possible to reuse fresh concrete in new concrete.

Common impurities and their effects in concrete

Sodium- and potassium carbonates and bicarbonates affect setting time in different ways. Sodium carbonate can cause very rapid setting, while bicarbonates may either accelerate or retard setting. In high concentrations these salts can reduce concrete strength. They may also contribute to alkali-silica reaction with susceptible aggregates.

Chlorides matter mainly in reinforced concrete, as chlorides act as catalysts to the corrosion reaction. Because prestressing steel is in tension at all times, it’s more prone to stress corrosion than mild steel. For this reason, acceptable chloride-ion contents are lower in prestressed- and posttensioned concrete. It’s important to note that mixing water is not the only potential source of chlorides. The steel doesn’t care where the chlorides came from, so be sure to check that the aggregates and admixtures don’t contribute chlorides to the mixture either.

Sulfates may contribute to sulfate attack, which results in expansive reactions and deterioration of the concrete. Sulfate attack is likely to be of concern in the western United States and Canada, where soils and groundwater are high in sulfates. Sanitary sewers also constitute a sulfate exposure, and sulfates may be present in some industrial environments.

Due to its high chloride concentration, seawater is not suitable for use in reinforced concrete. It may be acceptable in unreinforced concrete, but will reduce the strength. However, it is not suitable for use with alkali-reactive aggregates.

Organic impurities such as algae, sugars, and oils can all be problematic. Algae, which may also be present on aggregates, leads to lower strengths. Sugars in small quantities can retard setting, while in higher concentrations they may cause rapid setting. And oils can saponify in the presence of the alkalis from cement, entraining air and consequently reducing the strength.

Water from various agricultural and industrial environments may have other impurities we haven’t covered here. If you’re thinking of using this kind of water, ask us about it.

Provisions of ASTM C1602

concrete mixer at a ready mix plant
ASTM C1602 shows you how to safely use water from concrete production. Shutterstock image.

ASTM C1602, “Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete,” helps conserve resources by allowing us to make good concrete from less-than-pure water. ASTM C1602 defines non-potable water as not fit for human consumption or containing substances that make it taste or smell bad. It defines water from concrete production operations as wash water from concrete mixers, water collected from stormwater runoff at a concrete plant, and water that contains concrete ingredients. If you want to use any of these kinds of water in concrete, you need to test it first.

Impurities in water may affect strength, setting time, and/or durability. ASTM C1602 uses both performance- and prescriptive requirements for these characteristics. To test for the effect on strength, make mortar cubes with clean water and the proposed impure water. The 7-day compressive strength of mortar cubes made with impure water must be at least 90% of the strength of the control mortar cubes. Similarly, the setting time of mortar made with the impure water must be between 1 hour less and 1½ hours more than that of the control mortar.

On the other hand, the durability requirements are prescriptive. The limits on chloride (Cl) concentration are lower for prestressed concrete (500 ppm) than for reinforced concrete (1000 ppm). In addition, ACI 318 imposes limits on the total water-soluble chloride ion content of the concrete. These limits vary depending on the type of reinforcement and the exposure conditions.

ASTM C1602 limits the sulfate (SO4) concentration to a maximum of 3000 ppm and the equivalent alkali (Na2Oeq) content to a maximum of 600 ppm. In addition, the total solids content must not exceed 50,000 ppm. This corresponds roughly to water with a specific gravity of 1.03.

Additional words of advice

If you’re making concrete with several chemical admixtures, you should verify that the combination works with the proposed impure water. Particularly if the mixing water has organic impurities, you could see some unexpected—and unwelcome—interactions. Remember that the potential for incompatibility is greatest at elevated temperatures, so consider testing your concrete under those conditions.

Although we normally concern ourselves mainly with the strength and durability of concrete, other properties may also be important. In architectural concrete—or indeed any concrete that will not be covered or painted—the color may also matter. Even when we don’t care about the color per se, we may still want it to be uniform. If that’s the case, keep in mind that some impurities in the mixing water can alter the color of the concrete.