There are many forms of analysis for testing the composition of mortars to render a formula for matching the old mortar. The two most commonly used methods of mortar analysis are acid digestion of mortar samples and the ASTM c1324 mortar test for testing hardened mortars. As with any individual method of analysis, these two methods have their limitations and drawbacks.
All forms of testing the composition of mortar require an understanding of the field use of masonry cement. This is the biggest restriction of the c1324 mortar analysis. If the results are not interpreted with an understanding of masonry by someone of experience in the field, the accuracy of the results is reduced, and under the best conditions is already limited.
The acid digestion mortar analysis can identify the amount of cementious materials, but not their proportions.
Because a mortar type can be based on its composition or crushing pressure but not both because the compressive strength can be adjusted by adding more or less sand to the mixture or other ad mixes like fibers or hairs, you cannot determine the composition formula of mortars by a compressive strength test alone either.
Due to these issues, it has been difficult to get any accurate form of mortar composition analysis. However, during each of these methods of testing there are details about the mortar that are not collected or used to determine mortar composition.
There are some more scientific or mathematic approaches to composition testing that are not used for this method with some exceptions.
This method of analyzing samples of mortar to determine their composition combines many of these tests and collects more data from their results to be used with a mathematic calculation of their compositions and ratio of proportions of binder materials.
Throughout the testing process, there are different visual inspections and analysis performed through magnification or microscopic analysis of mortar samples. The samples are crushed to determine compressive strength of mortar, and weighed to determine a starting reference point. Then, the samples are tested through acid digestion methods. Then the sample must be dried again and weighed to determine the amount of weight loss that occurs during acid digestion of the mortar sample. At this point, the sand is analyzed and gradation of particle sizes are determined. Then the amounts of weight loss are determined.
With all of these details about the mortar and how it performs, you can use the specific gravity weights of the identified binder materials to calculate the range of probabilities of possible mortar formulas for the composition of the sample. Then using the crushing pressure and known compositions you can limit the possible matches to a far more accurate composition than any individual mortar analysis method.
Source by James Nech
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