1.Aggregate_Intro.ppt
- 2. Materials for Concrete • Occupy 70-75% of the total volume of concrete • Defined as an inert mineral filler for OPC – BIS, ASTM, ACI & BS 882 codes
- 3. Aggregates(Combined) Aggregates are the inert filler materials, such as sand or stone, used in making concrete
- 4. Aggregates • Coarse Aggregates (4.75mm-80mm) Broken Stones & Gravels • Fine Aggregates (<4.75mm) Gravel, Sand, Silt & Clay
- 5. Fine & Coarse Aggregates • Fine Aggregate - <4.75mm (5mm) • Coarse Aggregate - >4.75mm & up to 80mm • Boulders – Beyond 80mm • Grading: Fine Aggregate Coarse Aggregate C-Coarse 40, 20, 14mm down M-Medium till 4.75 mm F-Fine
- 6. Sizes • Coarse aggregate e.g. Gravel – 4.75mm or more (5mm) • Fine aggregate e.g. sand – less than 4.75mm • Silt – varies from 0.02mm – 0.06mm • Clay – much finer than 0.02mm
- 7. Classification • A) Petrological – BS 812 • B) Density • C) Shape & texture
- 8. A) Petrological 1.) Igneous rocks - Granites, basalts dolerites, gabbro & porphyries – Hard, tough, dense – Excellent aggregates 2.) Sedimentary rocks - Sandstones - When hard & dense suitable - Siliceous better than calcareous which are liable to acid attack Limes Stones - Sedimentary rocks chiefly composed of calcium carbonate Harder, denser types are suitable
- 9. A) Petrological Shale - Poor aggregates – weak, soft, laminated & absorptive 3.) Metamorphic rocks - Variable characters – marbles & quartzite usually massive, dense & adequately tough & strong Schist & slates are often thinly laminated & therefore unsuitable
- 10. B) Density 1.) Heavy – SG>4.0 i) Magnetic, natural iron ore (Fe3O4) ii) Barytes (BaSO4) 2.) Normal SG 2.5-3.0 i) Sands & gravels – division is arbitrarily on size – sands pass 4.76 mm BS sieve ii) Granites & basalts – hard & tough iii) Sandstone – hard & dense types iv) Limestone – hard & dense types v) Broken bricks – must be free of plaster – low sulphur content vi) Air cooled blast furnace slag
- 11. B) Density 3.) Lightweight - SG<2.5 i) Sintered PFA ii) Foamed slag iii) Vermiculite iv) Expanded polystyrene v) Pumice vi) Wood waste
- 12. C) Shape & Texture • Particle shape classified to BS 812 : 1975 • Terms used: • Well rounded, rounded, sub-rounded, sub-angular, angular
- 13. • Surface texture classified to BS 812 : 1975 • Relates to the degree of polish or dullness, smoothness or roughness of particles surfaces • Depends on hardness, grain size and pore character • Note: BS 812 & BS 882 have been replaced by BS EN 12620 C) Shape & Texture
- 14. Bond of Aggregate • Partly due to interlocking • Partly due to physical & chemical characteristics of the aggregate • Other factors include the cement paste
- 15. Aggregate Properties • Ideally should be chemically inert, durable, hard & tough • Should be capable of being compacted to the appropriate density & provide good bonding with the cement paste
- 16. A) Chemical Properties • Soluble salts – sulphates - cause problems with hydrated cement or chloride which accelerate hydration & increase risk of corrosion of steel reinforcement. • Reactive aggregates of lime stone or rock based vulnerable to Alkalies in the cement resulting with formation of AAR (Alkaline Aggregate Reaction) – an expansive compound or ASR (Alkaline Silica Reaction) – ‘concrete cancer’ – not common now but has been a problem in the past.
- 18. • Clay & silt – defined as materials passing a 75 micron sieve – harmful to concrete in substantial amounts – increase specific surface & hence water requirements • Weak (unsound particles) – lower the strength of the concrete Other Harmful Substances
- 19. B) Physical Properties • Strength • Porosity • Thermal • Bonding • Moisture • Density - relative (SSD) & solid (x1000) - bulk (packing air)
- 20. Relative Density - Calculation • Relative Density or Specific Gravity(SSD) = Mass of sample of SSD aggregate Volume of water displaced SSD sample x 1000 Where, SSD = saturated surface dry – all accessible pores are full of water, but the aggregate surface is dry
- 21. Bulk Density(Unit Weight) • Stockpiles of loosely packed aggregates contain large volumes of air trapped between particles, usually many times that of the volume of air present within the particles – ‘Bulking’ • Coarse aggregates – 30-50% of total space occupied • Fine aggregate – approx 20% - varies with moisture content
- 22. Batching of Aggregates • Bulking of aggregates produce uncertainty in the solid content of aggregates batched by volume • Batching by weight (mass) is therefore preferred, hence most concrete mixes are batched by weight
- 23. Grading of Aggregates • Refers to the size & distribution of the aggregate • Sieve analysis – BS 410 : 1976 • Grading limits – BS 882 : 1983 Note: The Euro-standard BS EN 12620 now covers testing & specification for aggregates
- 24. Graded Aggregate • Uniform Graded – equal weights of each particle size present • Gap graded – several consecutive particle sizes missing • Single graded – consist predominantly of a single particle size
- 25. Aggregate Durability • Soundness – degradation through interstitial crystallisation • Organic matter – act as retarders • Mica – Muscovite or Biotite • Chalk – affects strength (freeze/thaw) • Shell – strength
- 26. • Sulphates – limited to 4% overall • Chlorides – corrosion (<0.06%) • Metallic Pyrites – Lead, Zinc, Iron impurities Aggregate Durability
- 27. Coarse Aggregates (Broken Stones) Procurement process: Quarrying of Stone 1. Excavating 2. Heating 3. Wedging 4. Blasting
- 28. Coarse Aggregates (Broken Stones) Characteristics of Coarse Aggregate based on 1. Appearance 2. Strength 3. Hardness, Toughness and Resistance to Abrasion 4. Durable 5. Porosity and Absorption 6. Workability
- 29. Profile of different stones S. No Name of Stone Characteristics Uses Places of Occurrence 1 Granite Un-stratified and has crystalline granular structure – Very Heavy and Hard. Used in the construction of bridges marine works etc. Widely throughout in INDIA 2 Gneiss Stratified – can be split into thin slabs Used for paving the floors and roads Tamil nadu, Kerala Karnataka,AP, Bihar 4 Slate Can be split into thin sheets – found in variety of colors Used for roof covering, flooring, sills of doors and windows AP, MP, Punjab 5 Sandstone Found in variety of colors Used for jali work, ashlar work and carving work. Trichy, mysore, Karnool 6 Marble Crystalline and compact – found in variety of colors – dressing and carving can be easily done. Used to beautify buildings Kadappa, Kurnool, Rajasthan, 7 Limestone Consists of mainly CaCO3 Used for the manufacturing of lime and cement. Used in building construction. Tamil Nadu, AP, Maharashtra 8 Quartzite Compact, hard and brittle – strong and durable Used as road metal, railway ballast, concrete aggregate Coimbatore, Salem, Karnataka
- 30. Fine Aggregates Size: (<4.75mm) Types of Fine Aggregates 1. Gravel 2. Sand 3. Silt 4. Clay
- 31. Sand & Gravel • Sources – pits or dredging from river or sea bed – screening & washing • Marine aggregates Problems with Marine Aggregates • Liable to contain impurities of shell & salt • Granites, sandstones or lime stones – generally unconsolidated sedimentary deposits • 50% of aggregates came from sand & gravel deposits • Emphasis has now shifted to hard rock sources
- 32. Fine Aggregates - Sand (<4.75mm) Important Properties 1. Permeability 2. Consolidation 3. Shear Strength
- 33. Aggregate Uses • Concrete • Mortar • Renders • Screeds • Unbound pavements
- 34. • Bituminous Materials • Railway ballast • Filter media - biological Aggregate Uses