Standard requirements for testing of sandstone/siltstone/quartzite
Samples for testing must be taken from productive or prospective part of quarry and sampling should be supervised and properly documented by stone consultant or testing authority
| 1. | Petrographic analysis (fundamental to all tests) | At least two tiles of each type of finish (honed, sawn, rubbed) no smaller than 300 x 300 showing expected range of textural/structural variation likely to occur for the project; bedding should be visible or at least marked |
| 2. | Modulus of rupture (where the stone islikely to be used for paving situations) | 10 pieces of 200 x 100 x 60 (preferably honed upper surface; top and bottom should be the bedding plane) Because of the hardness of some fused sandstone and siltstone it is strongly recommended that the slabs be made 250mm long to prevent premature shearing at the ends |
| 3. | Flexural strength (where the stone is likely to be used for cladding) | 10 pieces of 350mm (long) x 100mm (wide) x 30mm (thick) preferably with honed upper surface; both large axes parallel to bedding 10 pieces of 350mm (long) x 100mm (wide) x 30mm (thick) preferably with honed upper surface; long axis is parallel to bedding; 100mm axis is perpendicular to bedding. If the stone is to be used for cladding there is now also a common requirement to test the stone in its weakest direction (with long axis perpendicular to bedding so that flexing breaks across bedding) |
| 4. | Compressive strength | 10 off 50mm cubes or 50mm core (in minimum lengths of 150mm); top and bottom must be very flat and marked T or B |
| 5. | Water absorption/ effective porosity/ bulk density | 10 pieces of 50mm cubed (any finish) |
| 6. | Sodium sulphate soundness | 5 pieces of 50mm cubed (any finish) |
| 7. | Slip resistance | 1 piece of 300 (min.) x 300 x 20 (finish to be that of the paving); any lineation should be parallel to the long axis of slab |
| 8. | Abrasion resistance | 3 pieces of 100mm x 100mm x 10mm with 6mm hole in centre |
| 9. | Quarry examination | To be carried out ONLY by someone experienced in dimensional stone quarrying (not a geologist, mining engineer, accountant, etc.) |
IMPORTANT NOTES
Because of the range of thicknesses required for the test specimens it is best to cut slabs of the required thickness (10, 20, 30, 50, 60mm) straight from a block. Do not manufacture from small pieces such as off-cuts.
Reason: It is not easy to physically produce the sample pieces to the quality required for testing.
Any imperfections such as saw marks/ridges on the test samples will cause point loading and results can be much lower than the real values (by up to 90%). This will result in a meaningless scatter of results against your stone and because of the lower values may result in rejection of your stone.
A visual and binocular microscope inspection will be carried out by the stone specialist prior to testing to check for other defects, irregularities or natural features that might unduly influence the results. The better the quality of the test specimens the better the results.
To ensure consistent sample orientation it is suggested that the slabs are marked TOP and BOTTOM after cutting.
It is common for most companies to provide additional test specimens from which to choose the best specimens for testing. An insufficient number of specimens of the right size and quality will delay testing until new ones have been produced.
PLEASE NOTE A laboratory technician does not know anything about stone – only the equipment he uses. He relies on stone consultant like me to provide guidance for the testing. Only the stone consultant can provide the specialist interpretations – not the laboratory technician. DO NOT send stone samples directly to a testing laboratory.
In tests 2, 3 and 4 the requirement is for 10 pieces because the standard tests are done on the basis of 5 dry and 5 wet.
Non-standard tests that are requested at times often target a particular problem with the stone. These include X-ray diffraction analyses of clays or potentially deleterious minerals, SEM (scanning electron microscope) examination and analysis of potentially reactive or dangerous minerals, radon emission analysis, XRF (X-ray fluorescence) and gamma-ray spectroscopy to determine possibly excessive radioactive elements such as uranium and thorium, acid immersion to determine colour stability, pulse velocity measurements to determine the presence of cracks/discontinuities, and dimensional stability to determine the behaviour of stone slabs due to wetting and drying.
Most of the strength tests are destructive (because they must proceed to failure); however, there is usually a systematic mode of failure which needs to be established and documented. For this reason I usually request that the tested samples be retained for inspection.
For stone testing the following standards are used:
Modulus of rupture ASTM C-99
Flexural strength ASTM C-880
Water absorption ASTM C-97
Compressive strength ASTM C-170
Slip resistance AS/NZS 4586
Salt resistance AS/NZS 4456.10 (Sodium sulphate soundness)
Abrasion resistance ASTM C-1353
Note that the standards for stone differ from standards used for masonry blocks, bricks, concrete and other construction materials. Standards other than those specifically designed for stone are invalid for use on stone because the testing methods differ and therefore the results may differ. Furthermore, comparisons of results performed using inappropriate standards cannot be compared with results carried out using the correct procedures.