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Compression Tests for the Strength of Stone

Man has used stone as a construction material since the days of the earliest empires. The Great Pyramids of Egypt and Colosseum of Rome stand as testaments to the enduring property of this manufacturing marvel. However, until the modern era, builders had few means to ensure that their structures would pass the test of time. Recent technological tools and compression techniques allow engineers to analyze and measure the material strength of rock.

Standards
- Rules created by the American Society for Testing and Materials (ASTM) govern the use of construction materials in modern industry. This globally recognized organization of 144 committees from across the globe created more than 12,000 standards to define the way builders use various materials. ASTM C170 / C170M - 09 is the specific standard that defines the methods of testing by which testers analyze the compression strength of stone. Tests in the field and in the laboratory provide varying levels of measurement accuracy.
Field Tests
- Sometimes, an analyst needs to make a strength measurement of rock while it is still in a quarry or rock strata. The analyst can utilize a point load tester to compress the surface of the stone strata, a process that requires a parallel rock face. This portable tester creates index values that, on their own, are somewhat accurate, but require a comparison to accepted values of the same rock to fine-tune the results. Analysts can use other instruments, such as a Schmidt hammer or a cone indenter, to acquire rough measures of rock strength, though the latter is impractical for anything but fine-grained rock.
Laboratory Tests
- Analysts can perform various types of laboratory compression testing using professional grade machinery. One of the most common analyses is the uniaxial compression test, which applies pressure to a single axis of the stone. Engineers can use other tests, such as triaxial compression analysis, which applies pressure to all three axes of the stone, for a more thorough understanding of the stone's strength. While the latter method provides a clearer picture, it is costly and requires specialized and expensive equipment. Analysts generally perform these tests on both wet and dry stone.
Conclusion
- Compression testing is a vital part of evaluating how rock will perform in varying manufacturing roles; however, this is not the only way to determine its strength or how useful it will be in a particular application. Tensile strength and shear strength tests provide an even broader picture of performance factors. Petrographic study of stone reveals small defects or weaknesses that can render it useless. Ultimately, analysts should employ a broad spectrum of tests before deciding on the viability of a specific stone for a construction effort.

Rocks & Minerals