Water as sprayed concrete constituent material in Mining Industry | South Africa
Mixing water
Water for mixing shall comply with the requirements of EN 1008 or the national standards and regulations.
As mentioned in EN 1008 [39], “The quality of the mixing water for production of concrete can influence the setting time, the strength development of concrete and the protection of the reinforcement against corrosion. When assessing the suitability of water of unknown quality for the production of concrete, both the composition of the water and the application of the concrete to be produced should be considered.”
Mixing water should not contain any substances that may be harmful to concrete or steel. Harmful substances include. sulfate, chloride, alkali (Na2O > 1500 mg/l), sugars, oil etc. Potable water should be used for mixing purposes. According to ACI 506R-05 [30], “If potable water is not available, the mixing water should be tested to ensure that compressive strengths of mortar cubes made with it are at least 90 % of that of mortar cubes made with distilled water (Section 3.4 of ACI 318). Cubes should be made of equal flow.”
According to ACI 506R-05, for the purposes of corrosion protection of the reinforcement in the sprayed concrete, maximum water-soluble chloride-ion concentration in hardened sprayed concrete at ages from 28 to 42 days should be limited to the values shown in the following Table 3-9.
![Table 3-9: Maximum water-soluble chloride-ion concentration in concrete for corrosion protection of reinforcement [30]](https://assets.construction-chemicals.mbcc-group.com/en-za/maximum%20water-soluble%20chloride-ion.jpg)
Table 3-9: Maximum water-soluble chloride-ion concentration in concrete for corrosion protection of reinforcement [30]
Curing water
Curing water is the amount of total water added, which is required for the full hydration process of cement. A theoretical value of the amount of water is in the range of a maximum w/c ratio of 0.24. This minimal amount of water however does not provide satisfactory workability required for placing. In order to fulfill all requirements, w/c ratios of 0.4 to 0.5 are commonly used. Evaporation of water, especially from the surface, should be avoided as it leads to insufficient hydration, resulting in higher water penetration and lower durability.