Dear Sirs,
I have a problem with defining a unit when calculating the moisture diffusion coefficient in a concrete.
PROBLEM EXPLANATION:
research:
- I prepared cubic samples with a 150 mm edge, insulated from 4 sides, unidirectional movement of moisture.
- measuring RH on the surface, at a distance of 30 mm and 75 mm from the surface, assume a symmetrical distribution of moisture relative to the center of the sample.
- Initially about 90% RH in the whole sample,
- drying at a temperature of 65 degrees until the RH at a distance of 30 mm from the surface reaches 65%.
- tight sample wrap (no change of mass to the environment) and RH alignment in the sample.
- obtained RH distribution in the sample after drying and after stabilization in the drawing, approximation to the polynomial of the 4th degree. (Image1)
calculations:
- constant temperature, calculations based on the equation and RH dependance shown in Model Code 2010, (Image2)
alpha0=0,05; RH=0,8; n=15.
- iterations corresponding to the number of days during the stabilization period.
- a sample divided into "slices" of a thickness of 10 mm.
- In each iteration I placed the moisture flow from the slice with the higher RH to the neighboring lower RH. The flow depends on the gradient RH and the coefficient D (dependent on D0 and RH).
- determination of the coefficient D0 using Excel - Solver.
- measure of fit is the difference between the function of the RH distribution obtained from the iteration and determined from the fit to the experimental results (the sum of the squared differences in 8 points).
Examples of iterations in the Excel file,
QUESTION?
I get the coefficient D0. Assuming RH gradient in% / cm and the time in days D0 unit is cm / day?
How to determine from this calculation the moisture transport coefficient in [cm ^ 2 / day]?
Best Regards,
Wojtek
please find the link:
http://www.tandfonline.com/doi/abs/10.1080/07373937.2010.528106?src=recsys&journalCode=ldrt20
please find the link:
http://www.tandfonline.com/doi/abs/10.1080/07373937.2010.528106?src=recsys&journalCode=ldrt20
nice paper here:
http://www.tandfonline.com/doi/abs/10.1080/07373937.2010.528106?src=recsys&journalCode=ldrt20
another one:
https://www.google.iq/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwiauumG0YHVAhXH2xoKHWJoCV0QFgg2MAQ&url=http%3A%2F%2Flibrary.jsce.or.jp%2Fjsce%2Fopen%2F00670%2FNo25%2FCLI-25-0077.pdf&usg=AFQjCNFI2KD5My4WGNTZlBfzM9LNCbT9gg
here a numerical study:
http://ascelibrary.org/doi/pdf/10.1061/41096%28366%29346
Dear Ghassan Fadhil Smaisim,
Thank You for interest and answers. I have read several articles on modeling and calculation of moisture transport coefficient. The ones you gave, will study right away.
I still can't "feel" what the coefficient values should be:
In Model Code 2010 there is dependance between concrete strength and D1 coefficient. (Image1). For example for 50 MPa D1 is 0,206 [cm^2/day]
And in "AN ANALYTICAL METHOD OF MOISTURE TRANSFER WITHIN CONCRETE DUE TO DRYING" - Fig 9 values range from 10 [cm^2/day].
Perhaps the values I received are correct. In me, D1 has a range of 2 to 9 [cm ^ 2 / day]. In the concrete after drying at 65 degrees and with a high RH gradient at the beginning.
Best Regards, Wojtek Kubissa
Thank you Ghassan Fadhil Smaisim for sharing thess papers.
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