The question is this: we have two concrete sample. we would like to know which one getting higher compressive strength. 1st sample: immersion in water 2nd sample: in air but does not let the sample to be dry and keep it wet all the time (let the sample to have air*, in common we say the sample has respire).
Usually, you will get a higher strength of concrete cured in water than that of air cured. To get a highest strength, you may cure specimen in elevated temperature in water or in oven.
Hi Bijan,
I totally agree with Md Rezaul. If you want higher strength, adopt curing at elevated temperature. You may cure in water at 90 degrees for example.
Consult this article:
http://www.cement.org/docs/default-source/th-paving-pdfs/soil_cement/rd113-the-influence-of-casting-and-curing-temperature-on-the-properties-of-fresh-and-hardened-concrete.pdf
Best wishes
The sample totally immersed in water will give you the best result it is important to place it in water as soon as possible after demoulding. the issue with curing in air but keeping it damp is ensuring it remains damp the entire time. elevated temprature curing will give you a higer early strength but it might detract from your ultimate strength.
I totally agree with Ms Des, The concrete retained in a 100% moist environment in water will give you a good mechanical strength as well as a good durability compared to a concrete conserved in the air. Hardening in a high temperature medium will give a higher resistance to short-term but long-term mechanical properties will be lower.
There are two main classes of curing concrete: the moist curing and the membrane curing. Moist curing, if applied continuously without any break, will give 10% to 20% more strength as compared to membrane curing. However, it is very difficult and impractical to keep a real structure moist continuously for at least 28 days. So, in practice, there will be no significant difference or sometimes, membrane curing may give even more strength than moist curing. So the practical conditions at site and the availability of good labour for curing at site is necessary, if moist curing is to be applied. Otherwise, membrane curing is more practical.
in case of curing concrete samples at 90 degrees, what about the retrogression of strength?
I agree with Prof. Des Vliestra. You will get the maximum earlier Strength via steam curing but the later Strength will be lower than that ontained via Water curing. The highest Strength at 28 days will be got submerging the specimens in water (21°C) or curing then in a humidity room.
In laboratoiry academic conditions, I suggest to use the totally immersed in water method for curing, as said Mr Des. Indeed, that method is efficient for NormalWeight as well as for Lightweight Concrete.
Dear
To represent the actual field condition, the curing in air with damp environment is suitable, it gives the actual obtained strength.
Best curing method is to immersed the sample in to the water tank at a constant temperature at 27 degree C as per Indian Standard.
In no case water temperature should fall below 4degree C
I agree with previous discussants who said that the maximum strength will be achieved by total immersion in water. The reason for this is that the gain in strength for cement is by hydration process and so long as water is available hydration will be continuous. The hydration process can be represented by the following simplified equations.
C2S + H= CSH
C3S + H = CSH
Any withdrawal of water (moisture) will stop the hydration process and will give a lower strength.
Lower curing temperatures will lead to lower early strengths but higher ultimate strengths because at lower temperatures shorter crystal fibers are formed during the hydration process leading to a denser gel and therefore higher ultimate concrete strengths.
Steam curing leads to longer fibers which give a high early strength but the intergrowth of the gel fibers is not as good as at low temperatures. This leads to a more porous gel and therefore a lower ultimate strength in comparison to a concrete cured at lower temperatures throughout.
Water curing, as it allows water to diffuse in innermost pores and hydration will be uniform. In air curing, there will be non-uniform water distribution in the matrix. So the properties will not be consistent.
In my opinion, the cement hydration process doesn't need to water from the outside. Because water which is used in the preparation of cement paste is enough to continue the hydration process. We put the specimen in the water to prevent evaporation of water into cement paste. If the specimen is fully coated with nylon after one day of casting, the best result is obtained for strength. However, It should be noted that temperature has an effect on increasing strength. Also, the pure water-curing may lead to the leaching of Ca(OH)2 from the specimen.
Another issue is the curing temperature, higher strength could be obtained with steam or hot water.
Compressive strength of concrete depends on moisture as well as temperature, to get more strength in air but continuously wet keeping water inside concrete constant/no evaporation
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