Most of the standards suggest to use potable water for making concrete or curing of hardened concrete. Due to scarcity or non availability of potable water, it is observed that tendency of contractors or owners is growing to use treated water from sewage treatment plant or even effluent directly for making concrete or curing of hardened concrete. Sometimes, polluted water from industry or river is also used for concrete. Quality of water supplied for the construction works by "tanker system" can not be guaranteed. This will affect setting property of cement, hydration process, strength properties of concrete, durability of concrete and reinforcement . Few references are available and results are variable. Hence, A project is given to Under Graduate students at College of Engineering Pune (India) on this topic.
Mostly portable water is used for concrete preparation and curing.
The reason behind is portable water have the pH value of 6 to 8. It denotes that it does not belong to the of acid or base. Human body will be seriously affected when we consume water as a base or acid. Similarly concrete has some properties.
For cement integrity, to effectively hold the various components within it, it should have a pH of around 11. The problem is that Portland cement alone does not resist many acidic compounds well.
In road work, if the concrete’s pH is between 9 and 11, the surface can withstand salting in the winter and variable weather conditions. If the pH is between 7 and 9, the concrete is starting to break down and may exhibit signs of early damage. As the pH of acids decrease below 6.5, concrete deterioration increases. The more concrete deteriorates, the more porous it becomes. If the pH drop around 6, there will be problems and certainly visible damage. As cement cures the pH can rise, however if it is too low initially, the structural integrity will be compromised from the start.
Dear Ishwar,
It would depend on the contaminants. Organics may retard hydration. Phosphates would similarly retard hydration. Chlorides meanwhile will accelerate hydration.
We're just about to start a project on the same topic. It would be good to keep one another informed as to the outcomes.
regards,
Leon
I agree with Leon Black that the primary effects of contaminants will have to do with the hydration processes. A change in hydration rates (and therefore in initial and final set times) may affect construction schedules and methods.
I would also add that some salts may negatively affect the durability of the concrete. Chlorides can accelerate the corrosion of steel rebar. Sulfates (especially depending on their speciation) may affect the durability of aluminate phases in the cement. Finally, suspended solids may introduce weak zones into the concrete or even cause later release of contaminants or pH changes as they decompose.
The use of recycled water in curing presents a much greater challenge than in mixing/casting, because the concrete may go through cycles of wetting and drying (especially in a dry, hot climate), leading to the accumulation of salts in the pore spaces and eventually to damage. If curing water is acidic or contains nitrates, it may decompose and leach key cementitious phases (espcially calcium hydroxide, but potentially also C-S-H). If curing water contains dissolved carbonate or bicarbonate, it may accelerate the carbonation of the concrete. If curing water contains sulfates, then there is a prospect of sulfate attack.
If you're trying to represent field curing in a lab environment, I would suggest representing a cycled wetting/drying condition of curing, besides a continuous immersion condition.
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