Based on the following standard ASTM C 39 and C 192, the 28 curing time does it include the time at which the concrete is inside the mold?
If yes, which means it will be cured 1 day in the mold and the remaining 27 days in moist environment?
It wasn't clear in the standard.
I agree with Shafi and confirm what you have stated.
Based on my experience with casting cylinders (25x50, 50x100 and the standard 100x200 all in mm), 1 day is allocated for setting in the mold while it is covered to minimise evaporation and subsequently placed in the lime bath for 27 days.
Feel free to refer to my publications for further information and description of the whole process.
The 28-day period is the specimen age for testing the compressive strength of concrete. Therefore, I can say that this period starts from day one of sampling, and the concrete should be cured as required.
It is estimated that concrete reaches 75% of this 28-day compressive strength in seven days, and its strength will remain stable or even increase over the time.
Curing of concrete is basically the control of moisture content and temperature of concrete. The moisture content of concrete can be controlled either by sealing it so that its own water is not readily evaporated or, if not sealed, providing it water from external sources to compensate for evaporation.
During the initial period of approximately 1 day (24+-8 hrs), the concrete is in a sealed environment due to the mold over its cylindrical surface and a plastic sheet or other impervious plate/sheet over its top. Hence, the concrete specimen is under curing during the 1st day inside the mold. It will need further 27 days moist curing in a water tank or humid room.
Hope it works
You are right. In the hot weather, the concrete moisture should be prevented from evaporating by covering the concrete with some materials.
I agree with Shafi and confirm what you have stated.
Based on my experience with casting cylinders (25x50, 50x100 and the standard 100x200 all in mm), 1 day is allocated for setting in the mold while it is covered to minimise evaporation and subsequently placed in the lime bath for 27 days.
Feel free to refer to my publications for further information and description of the whole process.
After casting your samples in the mold, cover it with moist hessian cloth under polyethylene for 24 hours. Them de-mould carefully and cure in water till time of testing, say 7 or 28 days. Water curing is best for concrete prior to testing.
Your concrete sample is to be kept under high humidity immediatelyafter casting by either covering it with a polyethene sheet or putting it in a humidity chamber. This is also curing though it is not immersed in water (it prevents the concrete from losing its moisture).
After de-molding, the concrete sample is put to cure by immersion in a water tank for the remaining 27 days for the concrete to reach maturity in strength.
So the concrete spends one day in a mold (under a controlled moisture condition) and the remaining 27 days immersed in water.
28 days compressive strength of concrete means the strength of concrete in compression at the age of 28 days, means as soon as the concrete casted in the mould its age started.
28 days include 24hr. (1 day )in mould + 27 days moist curing
I am agreed with Shafi, furthermore, as per ACI 308, curing for;
7 days achieved 70% strength
14 days achieved 80% strength
28 days achieved 90% strength,
whereas, the specimens in the moulds may also be considered as curing time.
ASTM D 1632-07. Practice for Making and Curing Soil-Cement Compression and Flexure Test Specimens in the Laboratory.
San Ty ....Good question… Please check references below.. hope it will be helpful for you…
Regards…
https://www.ccanz.org.nz/page/Curing-Methods.aspx
https://civilblog.org/2014/05/16/6-methods-of-curing-of-concrete/
http://www.ccaa.com.au/imis_prod/documents/Library%20Documents/CCAA%20Datasheets/DS2006Curing.pdf
generally , cube is kept in mould for 24 hours then it is taken out from mould and cured in water or covered by moist jute sack for 27 days prior before 1 hour of testing to prevent heat of hydration
Standard grades of concrete will generally gain 16% of its strength after the first day, 40% after three days, 65% after seven days, 90% after 14 days and almost 100% after 28 days. This is why compressive strength tests are performed after 28 days. The concrete will be near-optimal strength and is unlikely to change much more after four weeks of curing.
It should be noted, however, that despite the above-mentioned percentages of maturation, these values are approximate and extremely dependent on the hygrometric conditions of the cures (temperature and humidity).
Please refer to the standard: ASTM D 1632-07. Practice for Making and Curing Soil-Cement Compression and Flexure Test Specimens in the Laboratory.
- Badges
- Science topic
- Similar topics
- Engineering
- Materials Engineering