Water for Making Concrete
When water is to be used in concrete, it should be tested to ensure it doesn't negatively affect the strength, setting, or durability of the concrete. Adverse effects can occur if the water contains certain impurities in quantities beyond permissible limits. Here's a list of tests typically conducted on water for use in concrete:
pH Value: The water should be neutral or slightly alkaline. The typical range considered safe for concrete mixing is a pH of 6 to 8.
Organic Impurities: Organic impurities can delay the setting time of cement. A visual examination can be conducted, and if the water appears colored, it should be tested for the effect of organic impurities on the strength of mortar.
Inorganic Impurities: These include salts of sodium, potassium, calcium, etc. High amounts can affect setting, strength, and durability. Tests include:
Sulfate Content: Excessive sulfates can cause expansion and disintegration of concrete.
Chloride Content: Chlorides can cause corrosion of steel reinforcement in concrete.
Suspended Solids: These can interfere with the bond between aggregate and cement paste.
Hardness: Very hard water can affect the setting and hardening of concrete.
Oil, fats, and detergents: These should be absent as they can interfere with the development of concrete strength.
Sugar: Even small amounts of sugar can retard the setting of concrete.
Set Test on Cement Paste: A sample of water under investigation can be used to make a cement paste and checked for setting characteristics.
Compressive Strength Test: Concrete cubes can be cast using the water in question and tested for compressive strength after 7 and 28 days to ascertain the impact of water on the strength of the concrete.
Initial and Final Setting Time: The initial and final setting times of cement are affected by impurities in the water. Thus, testing the setting time of a cement paste using the water can help determine its suitability.
In many cases, if the water source is known to be potable (safe for drinking), it's also considered safe for use in concrete. However, even potable water can sometimes have high chloride or sulfate content that can be harmful for concrete, especially in structures where steel reinforcement is used.
Always refer to local standards and guidelines when assessing water quality for concrete to ensure that all specific requirements and conditions are met.
Test requirements
For the testing of water for use in concrete, both European and American standards have laid down specific methods and procedures. Here's a brief overview of the respective standards:
European Standards (EN):
EN 1008:2002 - Mixing water for concrete – Specification for sampling, testing, and assessing the suitability of water, including water recovered from processes in the concrete industry, as mixing water for concrete.
This standard provides the requirements for the suitability of water for use in the mixing of concrete. It covers aspects such as sampling and testing methods and sets out the criteria based on the effect of the water on the properties of fresh and hardened concrete.
American Standards (ASTM):
ASTM C1602/C1602M - Standard Specification for Mixing Water Used in the Production of Hydraulic Cement Concrete:
This specification covers the organic impurities, chlorides, sulfates, and other chemical contaminants and their allowable limits.
ASTM C94/C94M - Standard Specification for Ready-Mixed Concrete:
While primarily focused on ready-mixed concrete, this standard has provisions related to mixing water quality and references ASTM C1602.
ASTM C1580 - Standard Test Method for Water-Soluble Sulfate in Soil:
This test is specifically for determining the concentration of water-soluble sulfate ions in soils, but the concept is useful for understanding sulfate concentrations, which can be a concern in concrete water.
ASTM D512 - Standard Test Methods for Chloride Ion In Water:
One of the tests relevant to water for concrete is the test for chloride ion, as excessive chloride can lead to corrosion of reinforcement in concrete.
ASTM D1293 - Standard Test Methods for pH of Water:
pH is an essential parameter to ensure water doesn't negatively impact the setting and hardening of concrete.
Remember that while these standards lay out methodologies and limits for various properties and contaminants in the water, the final suitability of the water often depends on its effect on the setting time, strength, and durability of the concrete. Hence, empirical tests, where the water is used to produce concrete and the concrete is then tested for its properties, are critical in addition to these chemical and physical tests. Always refer to the full text of the standard when conducting tests or evaluations.