Let say we have a brick may fly ash or another one then I want to know the porosity distribution with respect to their position?
It all depends how much you want to spend to solve this problem.
If you are ready to spend some money on it then go for X-ray tomography. You will need a great computing power to collect data of 2D slices and produce the 3D image.
I hope the following article will provide you and example of the technique.
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H. Taud, R. Martinez-Angeles, J.F. Parrot, and L. Hernandez-Escobedo, "Porosity estimation method by X-ray computed tomography", Journal of Petroleum Science and Engineering, Volume 47, Issues 3–4, 30 June 2005, Pages 209-217, ISSN 0920-4105, http://dx.doi.org/10.1016/j.petrol.2005.03.009.
(http://www.sciencedirect.com/science/article/pii/S0920410505000586)
Abstract: In X-ray computed tomography imaging, the approaches used to determine the porosity of the rock from a single computed tomography scan are based on image segmentation techniques. When these techniques are applied to the same data, different results emerge and a threshold is needed at some level of the process. Consequently, the implication is that there is an uncertainty in the porosity measurement. Because of these sensibilities, a new method, called here the grey level method, is developed avoiding the use of these techniques. Considering the computed tomography image as a surface, the volumes required in porosity estimation are obtained by means of integrating this surface with simple operations applied to the image histogram. A porosity distribution which can reflect the properties of the studied rocks is developed given the value of the estimated porosity. The method is compared to two segmentation methods and is evaluated by a conventional one. A close agreement with the conventional method is found.
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Have a good day...
Porosity distribution can be determined by MIP (mercury intrusion prosimetry) analysis. It can provide information about the size and distribution of the pores present in the sample.
With Mercury porosimetry I think only average porosity can be calculated not its distribution.
I am not an expert in bricks so this answer may be off. But if I was asked to do this task, I would take 1-3 sections from a brick, scan the image(s) and conduct image analysis. As in many other materials, I would expect the pore sizes to have a lognormal distribution. So once I get the data from an digital image analysis software, I would use a statistical package to look into the distribution.
Whereas PORE SIZE is a measure of the diameter of the largest pore, PORE SIZE DISTRIBUTION is a measure of the range of pore sizes. The range of pore sizes may be normally distributed, and the spread can be quite narrow ( ratio of largest to smallest may be less than 2). On the other hand, pore size distribution can be very heterogeneous. In the case of large spreads and heterogeneity, the pore size will be far less predictive.
EXPERIMENT TO CALCULATE % POROCITY
The simplest method is given as follows:
Wash the clay brick with deionized water.Dry for 24hrs at 60C.Place it in a descicator over dry silica gel to cool off and wiegh.Repeat the drying process for another 24 hrs; cool and wiegh again to a constant weight ( difference between the two wieghings should not be more than 0.1% of the mass of the brick). Let this constant weight be [Mc].
Now place it in a container on a base of glass rods and slowly cover with deionized water untill the sample is totally immersed with about 2cm of water above it.Take this brick out of the container after 24 hrs. Blot it with damp cloth to remove surface water and weigh it. Repeat the process and weigh again so that the difference in two weights is less than 1% of the water absorbed in 24hrs. Let the constantweight be [Ms].
Put the brick in a graduated cylinder filled with deionized water and note the increase in volume indicated by the cylinder. Let this volume be [VApp]; App. stands for apparent.
Now VPore=Ms-Mc.
% porocity= 100.VPore/Vapp.
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