Granite/Basalt/Marble/Limestone

Standard requirements for the testing of granite/basalt/marble/limestone

Samples for testing must be taken from the productive or prospective part of a quarry and the sampling should be done or supervised and properly documented by an experienced stone consultant

1. Petrographic analysis

(fundamental to all tests)   
At least two tiles of each type of finish  (honed, sawn, rubbed) no smaller than 300mm x 300mm showing expected range of textural/structural variation likely to occur for the project; bedding should be visible or at least marked 
2a. Modulus of rupture

(where the stone is likely to be used forpaving situations)
10 pieces of 200mm x 100mm x 60mm (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
    and/or
2b. Flexural strength

(where the stone is likely to be used forcladding)
10 pieces of 350 (long) x 75 (wide) x 30 (thick) preferably withhoned upper surface; both large axes parallel to bedding  10 pieces of 350 (long) x 75 (wide) x 30 (thick) preferably with honed upper surface; long axis is parallel to bedding; 75 mm 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)
3. Compressive strength

(for all projects)
10 pieces of 50 x 50 x 50 (preferably with polished upper surface but may honed, sawn, or exfoliated)
4. Absorption

(for all projects)
5 pieces of 50 x 50 x 50 (preferably with polished upper surface but may be honed, sawn, or exfoliated)

 

5. Abrasion resistance

(for all paving projects)
3 pieces of 100 x 100 x 10 (with sawn or honed upper surface preferably but may be polished)
6. Slip resistance

(for all paving projects)
5 pieces of 300mm x 300mm x 20mm (with upper surface finish that is to be used in the project)

OPTIONAL/ADDITIONAL

Coefficient of expansion:   3 pieces of 200 x 50 x 50 (with all surfaces the same finish)

Breaking Load: 10 pieces of 300 x 150 x 75 (any finish).  As for MoR test

Quarry examination: To be carried out ONLY by stone specialist experienced in dimensional stone quarrying

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, 60, 75mm) 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.  



For tests 2a, 2b, and 3 the requirement is for 10 pieces because the standard tests are done on the basis of 5 dry and 5 saturated.


For flexural strength tests it is usually necessary to cut another 10 sample pieces perpendicular to the first 10 if the stone has a preferred orientation of crystals or structural grain.

If the stone is exfoliated and to be used externally, in cladding especially, it must be tested in the exfoliated finish because of a common substantial reduction in strength (25-40%) resulting from the exfoliation process.

Most of the strength tests are destructive (because they must proceed to failure) and there is usually a systematic mode of failure which requires documentation.For this reason I generally require the tested samples to 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 

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.