Autogenous shrinkage and maturity concept

[awolfgang]

Hello,


I want to introduce autogenous shrinkage data into a finite element model to determine stresses.

I have experimental data for the shrinkage as a function of time. But I cannot feed this information directly into the finite element model because shrinkage is actually a function of temperature or degree of hydration, which can change in the finite element domain depending on initial and boundary conditions of temperature.

I understand that one could convert shrinkage as a function of time to shrinkage as a function of so called maturity, which in turn is a function of temperature and time. Could anyone explain to me how I can do this conversion.

Thanks a lot for your help.


Regards,
Wolfgang

 

[IDS]

The Reinforced Concrete Design Functions spreadsheet which you can download from:

http://newtonexcelbach.wordpress.co...ete-moment-curvature-–-2-shrinkage-and-creep/

has an Adjustedage function, which calculates an effective age allowing for any specified time-temperature history, using the method specified in Eurocode 2.

Please let me know if that is suitable for your application, or if you have any problems with it.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[awolfgang]

Dear Doug,


Thank you very much for your positive response.

Unfortunately, the link is not downloadable. Is the link still active?

I saw a screenshot of adjusted age input and output on your website. What was not clear is the temperature vs time curve. I do not have temperature vs. time that corresponds to autogenous shrinkage measurements. Instead, I only have the temperature vs. time from adiabatic experiment. But this information is available only for 100 hours. However, the information of autogenous shrinkage is available for 32 days. Is it the standard approach that during the autogenous shrinkage experiments, temperature is also recorded simultaneously. I do not have the EC2 code with me, but I faintly remember that one could use Arrhenius type equation (of temperature) which is integrated over time to obtain maturity. But the question is where do you get the temperature vs. time from.

I appreciate your willingness to help me.


Regards,
Wolfgang

 

[IDS]

Wolfgang - thanks for letting me know about the link not working. I have now fixed that and updated it to the latest version. I have also attached a direct link to the file below.

For the temperature-time history, that would depend on the details of the project, type of concrete, size of member, type of curing etc. Normally I would just use the rate of shrinkage given in the code, recognising that the actual shrinkage rate might be significantly different, but if you need a better estimate I think the first step would be to get your own temperature information, either from measurements if possible, or from computer modelling.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[awolfgang]

Dear Doug,


Thanks again for your time.

I may need a bit more help please. Am I right in assuming that you used Arrhenius equation to convert time to adjusted age in your excel sheet?

The only information I have is shrinkage vs. time from measurements. The experimenters state that they did measure temperature as a function of time, but no data is made available (this is some 10 year old data). So am I right in assuming that in this situation there is no way to evaluate shrinkage as a function of adjusted age (i.e. maturity)?

I did not understand when you state that I should get the temperature information from modelling. What do you mean by this? Do you mean model the temperature evolution of the autogenous shrinkage experiment or did you mean simulate temperature evolution of a concrete wall through finite element analysis. The latter is already done and I have simulated temperature vs. time data for the wall. During the finite element analysis, What I do is obtain adjusted age (or maturity) from this temperature history at every point in my domain. Corresponding to this maturity, I need the corresponding shrinkage strain. But as I stated above I only have a table containing shrinkage strain vs. time (not maturity).

Any suggestions would be helpful. I must confess I am not well conversant in this subject.


Regards,
Wolfgang

 

[IDS]

Dear Wolfgang,

The adjusted age in my spreadsheet is taken straight from the Eurocode. I am not sure of the background, but it looks like it probably comes from the Arrhenius equation. I have attached an extract from the code where the adjusted age is defined.

Reviewing the wording in the code, this adjusted age is specifically intended for use with creep calculations. It is not clear to me whether it is intended that this adjusted age should be used in shrinkage calculations, and if so if it should be applied to both the autogenous and drying shrinkage components. In "Time-Dependent Behaviour of Concrete Structures" it states:

"Chemical shrinkage (often called autogenous shrinkage) occurs rapidly in the days and weeks after casting and is less dependent on the environment and the size of the specimen than drying shrinkage.

Gilbert, Raymond Ian; Ranzi, Gianluca (2011-02-18). Time-Dependent Behaviour of Concrete Structures (Kindle Locations 1372-1373). Taylor and Francis CRC ebook account. Kindle Edition. "

This suggests that it would be reasonable to use the un-adjusted time for autogenous shrinkage, and the adjusted time (based on the EC 2 equation) for creep and drying shrinkage.


Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[awolfgang]

Dear Doug,


Sorry for the late acknowledgement.

Thank you for your further insights, it is helpful. I will look into those references in greater detail. As I see from the experimental data, autogenous shrinkage continuous for about 2 years with nearly 150 micro strains.

Can you also please suggest how to calculate the amount of hydrated or adsorbed water after hydration is complete. Are there any references?


Regards,
Wolfgang