With the opening of the world stone trade through the internet stone is now readily available to anyone – from anywhere. But what does the purchaser know about the technical characteristics of the stone and how do those characteristics impact on the immediate and long-term performance of the stone in its intended applications?
Where the stone is a structural element in any construction it is necessary to assess a number of engineering parameters to establish its limitations – much the same as other construction elements. However, being a natural material, as opposed to manufactured, the range of variation in stone is much greater and often unpredictable. And with over 12,000 stones available on the world market the differences in stone are considerable. Establishing the limitations of each stone is critical for successful construction.
To achieve this it is necessary to test the natural material. Over the years a number of properties have been defined as being important in assessing the performance of stone, namely the mineralogical, textural and structural make-up (petrography), compressive strength (for load bearing), flexural strength (for vertical applications), impact strength (modulus of rupture for paving), absorption, slip resistance, stain resistance, salt resistance, and degree of expansion. Collectively, these properties will determine where and how the stone can be successfully used. A wide number of international standards are in place to provide the necessary guidelines for testing to ensure consistency during the testing and also between laboratories.
Importantly, stone is not a uniform product. Sedimentary rocks such as sandstone are bedded, granitic rocks may contain veins, basaltic rocks may contain vesicles, felsic volcanic rocks may contain a mineralogy that is reactive to cements, and metamorphic rocks may contain unusual minerals with properties that require careful investigation. A stone scientist or stone specialist is required to organize and conduct the tests that will be appropriate for the intended construction. Sending random samples of stone to a laboratory is a total waste of time and money; a laboratory technician does not know anything about the stone and its properties and its intended application – he/she only has to know how to use the testing apparatus and compile the results.
Hensel Geosciences has a long history of stone, rock and mineral testing – from the most sophisticated geochronological techniques (rock dating, isotopic characterization), through mineral investigations (electron microprobe, scanning electron microscope, X-ray diffraction, FTIR, XAS, ICP, XRF and petrological studies), to the more fundamental tests required for stone and rock analysis. Knowing what tests are required is important not only to the client (in terms of costs) but also to the engineer (in terms of suitability to facilitate construction). Additionally, knowing which laboratories provide the most reliable results, at a good turn-around and at the most reasonable price is advantageous in construction.
Hensel Geosciences also has a long history in the evaluation of the test results. Many test results of stone are manipulated and it is therefore important to be able to discern the erroneous/inconsistent results. This requires a long-term in-depth knowledge of the natural product that only comes with experience. The most common form of data manipulation is in sample selection; therefore it is fundamental that the stone scientist selects the product and conducts the testing programme.