quality assessment

QUALITY ASSESSMENT OF DIMENSIONAL STONES & MINING PRACTICES IN DIMENSIONAL STONES

Surendra KDepartment of civil engineering National Institute of Technology Karnataka surathkal

NEED OF QUALITY ASSESSMENT To Improve Productivity To Improve Marketability-the Economic Viability Of Granite Mining Operations Is Dependent Directly On The Quality Of Stones. Rate Of Recovery And Control Huge Waste. To Prepare Proper Mine Planning Quality Assessment Helpful For Entrepreneurs To Compute In World Market.

Geological Aspects In Quality Assessment Of Commercial Rock Deposits:Geology of rock deposit is one of the most prominent factors in assessment of quality, quantity, exploration, exploitation and economy of exploration.Geological aspects such as topography , stratigraphic position, mineral composition, textural variation, weathering and alteration , colour variation, structural conditions like macro and micro discontinuities ,intrusive veins etc. plays significant role granite mining.Careful studying favourable and unfavourable structural features in mining activity is useful to cut down the production cost and improving the quality of the product.Studies of structural elements in rock deposits help in qualitative assessment and plan of appropriate method quarrying suitable to nature rock deposit.

Some Favorable Structures:Sheet joints : Sheet joints in rock deposit minimizes high cost equipment for bottom cutting in granite mining.Vertical joints : Vertical joints facilitated easy and smooth splitting of rock deposit and also presence of this joints in rock deposits produce stone blocks with minimum waste, high rate of recovery and minimizes cost of production.Steep dipping foliation planes: foliation is the property of rock where they can break along parallel planes. deep foliation planes helps in economic exploitation of rock blocks. Migmatic structure: . Migmatite rocks are less affected by natural defects like cross hair line fractures, quartz and pegmatite veins which may spoil beauty of polished rock.

Unfavorable Geological StructuresThe unfavorable structures like closely spaced joints, minor faults, low dipping foliation planes, folds and shear cracks are adversely effects the quality of commercial stones. Some structures of regional phenomena like lineament zone, major shear zones, active fault zone etc. may not be suitable for exploitation. In certain cases it is difficult to get even blocks of cobble size.Unfavorable geological structural discontinuities influences size of rock blocks getting from quarries. Many quarry owners suffer loses not getting export size blocks from quarries due to presence of unfavorable structures.

Natural Defects In Decorative Dimensional StonesDetection of defects in dimensional stone industry plays a significant role in quality assessment. Natural defects stone industry adversely effects the quality and quantity of rock blocks.Macro defects like colour variation, texture variation ,structural discontinuities, inclusions, intrusions and contact zones etc. are can be identified by careful visual examination of stone deposits. Micro fractures, stress minerals, alterations of minerals are can be identified by systematic micro Petrographic analysis of entire stone deposits.Entrepreneurs took quarries leases, exploited rock deposits initially and abandoned quarry in midway due to bad quality of stone blocks.

Defects Which Affect The Quality And Exploitability Of A Dimension Stone Deposit

Colour variations Textural characteristics and textural variation Structural and macro-discontinuities Micro-discontinuities IntrusivesQuartz veinsFeldspar vein and reefsPegmatite rocksAplite veinsEpidote veinsDykes Inclusions Accessory minerals Contact zones Alterations

Weathering of stone depositIntrusive in stone depositDefect to due to water percolation

Quartz veins on stone depositColour variation in stone depositFractures present on stone depositSheet joints

Colour variation

Structural Discontinuities

Multiple joints

Microfolds and Minor foldsMicrofolds in charnockite Minorfolds in Hornblende Gneiss

IntrusivesQuartz veins Pegmatite vein with the Gneissic banding

Petrographical AspectsPetrography involves in Identification of the minerals, composition, fabric, and structure of a rock specimen is a necessary step towards recognition of the properties that may be expected to influence the behavior of the material in its intended use.Petrographic examinations will require the use of optical microscopy.Petrographic examination identify constituents or minerals and the extent to which they may lead to staining and color change of the surface of the stone.Petrographic examination identify weathered or altered constituents or minerals and describe the extent of that weathering or alteration.Petrographic analysis of litho units gives invaluable data on their sawing and polishing capabilities.Common Petrographic characters in commercial granite grain size, degree of uralitisation of pyroxenes, sasuritisation of plagioclase feldspars, cloudiness in feldspars, presence of opaque ores, presence of free quartz and micro pegmatite.

Microscopic imagesPhoto micro graph of gabbroPlagioclase exhibiting alterationshypersthene, Plagioclase and quartz with magmatic texturesModel analysis of gabbro

Mineral Sample-1Sample-2Opx(hypersthene.brozite)45%35%Cpx(augite)15%15%plagioclase38%55%magnetite-biotite-3%apatite-2%

Geochemical Aspects : Geochemical parameter is more essential to evaluate characteristics of the granite deposits. The colour of the deposit is controlled by the proportions of major oxides and trace elements.The microfabric and mineralogical aspects of samples usually carried out using X-ray diffraction (XRD) analysis for crystalline structure, differential thermal analysis (DTA) for chemically and physically unstable minerals, infrared spectroscopy, scanning electron microscopy (SEM) energy dispersive X-ray analysis (EDX) etc.The quality of quarry materials is to a large extent dependent on the geochemistry and mineralogy of the rock.Geo chemical examinations provide identification of type and varieties of minerals and structures present in the specimen.The Petrographic examination establish whether the specimen contains chemically unstable minerals or volumetrically unstable materials.X-ray microanalysis using energy-dispersive X-ray spectrometers with scanning electron microscopy (SEM/EDX) or wavelength-dispersive X-ray spectrometers in electron microprobes (EMPA/WDX) may provide useful information on the chemical composition of minerals and rocks

Scanning electron microscope image of stone sampleMinerological composition by edax

ZAF Method Standardless Quantitative AnalysisFitting Coefficient : 0.1552Element (keV) mass% Error% At% Compound mass% Cation KO K 0.525 36.91 0.15 50.79 34.9094F KNa K 1.041 5.02 0.09 4.80 5.4047Mg K 1.253 0.05 0.08 0.05 0.0427Al K 1.486 15.16 0.07 12.37 15.4100Si K 1.739 36.19 0.08 28.37 35.3476K K 3.312 0.80 0.10 0.45 1.0102Ca K 3.690 5.51 0.11 3.03 7.4496Cr K 5.411 0.16 0.19 0.07 0.1844Mn K 5.894 0.00 0.23 0.00 0.0034Fe K 6.398 0.20 0.24 0.08 0.2381Total 100.00 100.00

Physico-mechanical Strength PropertiesDimensional and ornamental stones for engineering applications have to satisfy not aesthetic needs but also technical characteristics. Physico-mechanical strength properties of rock is very important for optimal use of stones as a structural material.The index properties of rocks play a crucial role in the planning and design of civil and mining excavations, including the stability of dump and rock slopes.Physico-mechanical parameters (Density, Sp.Gr, Hardness, porosity, Adsorption, compressive and tensile strength, slake durability etc.) are carried out on representive samples.

Physico Mechanical Properties To Be Analyzed

s.nopropertiesTest typeApplications 1colourVisual and microscopicobservationTo establish technical name of the rock, to identify micro-fracture.2Mineral composition3Texture and grain size4Density and specific gravityLaboratory method (IS 1122-1974)To determine the weight of rock for handling. Density is a measure of mass per unit of volume.5Porosity and water adsorptionLaboratory method (IS 1124-1974)To determine the degree of decomposition rock.Porosity describes how densely the material is packed.. Water content is a measure indicating the amount of water the rock material contains.6Ultrasonic pulse wave velocityUltrasonic Non- Destructive digital tester(ISRM method)Useful to determine soundness of the block . The velocity measurements provide correlation to physical properties in terms of compaction degree of the material.7HardnessSchmidt Impact Hammer (ISRM method)Hardness is the characteristic of a solid material expressing its resistance to permanent deformation.Useful to assess quality of mineral constituents 8DurabilitySlake durability test (IS 10050-1981) Essential for assessing granites used in the chemical industries & labs. 9Protodykonov strength indexProtodykonov apparatus To find compressive strength by indirect method10Point load indexPoint load strength test(IS 8764-1998)11Unconfined compressive strengthCompression test(IS 9143-1979)Useful to rock suitable for engineering purpose. Compressive strength is the capacity of a material to withstand axially directed compressive forces.12Tensile strengthBrazilian test(IS10082-1981)Useful in calculating thickness of slab. Tensile strength maximum tensile stress the rock material can withstand.

Indian Specifications For Structural Granite.

Phases of a Dimensional Stone Exploration1. Desktop Study2. Field evaluation3. Detailed mapping4. Drilling5. Geophysical methods6. Bulk Sampling7. Test Quarrying

DIMENSIONAL STONE MININGIn Mining of dimension stone it is necessary to split or cut the stone into successively smaller pieces until the final desired block size is achieved, and saleable blocks are produced.The Mining stage of dimension stone extraction conforms to one of two general strategies. In the first of these, large volumes of rocks are loosened by means of primary cuts, and then divided stepwise into smaller pieces until commercial blocks are obtained, discarding waste material as the process is performed. This method employed in most granite and marble quarries.Under the second strategy, commercial blocks are directly cut from the rock body. This strategy is often employed in the production of sandstone.

Different Extraction Methods For Dimensional StoneCutting: Blocks separated by means of kerfs Sand wire (helicoidal wire) , Diamond wire, Chain saw, Disc cutter ,Diamond belt cutter ,Flame jet ,Water jet etc.Splitting: Blocks separated by fractures induced in pre-determined planes Explosives: Detonating cord, NG based explosives, Blasting gunpowder ,Plug & feather ,Expansive mortar ,Hydraulic wedgesCautious Blasting: Blasting with minimal breakage suitable pieces selected from muck pileExplosives

Splitting TechniquesEarliest techniques involved chipping a V-shaped groove in the stone using hand tools, and then either filling this groove with wooden wedges which expanded when wet, or in colder climates filling this groove with water which froze to ice overnight in order to split the stone.Today, all of the splitting techniques involve drilling of a series of small diameter co-planar holes in the stone in order to introduce a splitting agent.Plugs and FeathersMechanical SplittingExpansive MortarExplosive Splitting

CUTTING TECHNIQUESThe Techniques of cutting stone have been developed in relatively recent times. They were developed initially in response to the problems incurred when splitting.One of the earliest developed techniques, the use of helicoidal wire sawing was the forerunner of the development of diamond wire sawing which is now the most prevalent of the cutting techniques.Jet Flame CuttingSlot DrillingDiamond Wire SawingWater Jet CuttingChain CuttersDiamond Belt Cutters