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Concrete - An Overview
- 1. CONCRETE : A Brief Overview By Dr. Abhishek Jindal Ph.D., IIT Roorkee A TEACHING DEMO PRESENTATION ON
- 2. • “Concrete” word originates from the Latin verb “concretus”, which means to grow together. • Most widely used construction material in the world. Roadways/ transportation systems Airstrips Infrastructure (bridges, dams) Harbor protection (breakwalls) Water distribution (pipes & conduit) Buildings Concrete
- 3. Advantage of Concrete • We have the ability to cast desired shapes • Arches, piers, columns, shells • Properties can be tailored according to need (strength, durability, etc.) • Ability to resist high temperatures • Will maintain structural integrity far longer than structural steel • Does not require protective coatings • Can be an architectural & structural member at the same time
- 4. Nature of Concrete • It is a composite material, considered as homogenous. • It consists of different ingredients carefully batched together to achieve desired results. • Aggregates are 65% - 80% of the volume • Fine aggregate: sand • Coarse aggregate: stone • Cement: General term & applies to any binder • Portland cement • fly ash • ground slag • silica fume • Water • Admixtures (if required)
- 5. Materials Aggregates Inert materials that form body of concrete Coarse Aggregates – size : 4.75 – 40 mm Forms body of concrete Provides strength Fine Aggregates – size < 4.75 mm Fill small voids between large aggregates Increases strength of the cement binder Tests : Crushing test, Impact test, Abrasion test, soundness test, water absorption test, specific gravity test, shape test
- 6. Materials – contd… Cement binds aggregates together produces a crystalline structure Water causes chemical reaction to occur water/cementitious “react” produces workability
- 8. Cement • Material that has hardening properties on coming in contact with water. • Consists of siliceous and argillaceous materials. • Different types: • Ordinary portland cement • Portland pozzolana cement • Quick setting cement • Rapid hardening cement • Low heat cement etc.. • Tests: Consistency test, setting time test, soundness test, strength test, fineness test, chemical composition test.
- 9. Cement Composition Compound Formula Percentage Calcium Oxide Cao 60 - 67 Silicon Dioxide Sio2 17 - 25 Aluminium oxide Al2O3 3 - 8 Iron Oxide Fe2O3 0.5 - 6 Magnesium Oxide Mgo 0.5 - 4 Alkalis Alkalis 0.3 – 1.2 Sulphur Trioxide So3 2 – 3.5 • Materials, are proportioned to produce a mixture with the desired chemical composition • Ground and blended by one of two processes - dry process or wet process. • The materials are then fed through a kiln at 1500º C to produce grayish-black pellets known as Clinker. • Gypsum, CaSO4.2H20 is later added to clinker to control setting time of cement.
- 10. Clinker Composition of clinker – 4 major components C3S – Tri Calcium Silicate (3Cao.Sio2)– Hydrates rapidly, initial set & early strength C2S – Di Calcium Silicate (2Cao.Sio2)– Hydrates slowly, strength gain after 1 week C3A – Tri Calcium Aluminate (3Cao.Al2O3)– lot of heat of hydration, less strength contributor C4AF – Tetra Calcium Alumino Ferrite (4Cao.Al2O3.Fe2O3)– fluxing agent, reduces melting temperature of raw materials.
- 11. Hydration • Chemical reaction taking place when cement comes in contact with water. • Starts the moment water comes in contact with cement. • Liberation of heat of hydration. • A crystalline structure grows to form bonds. • Rate of hydration increases with increased cement fineness. • Can continue till moisture is present in concrete.
- 12. Hydration - Reactions • For C3S 2C3S + 6H2O = C3S2H3 + 3Ca(0H)2 + Heat • For C2S 2C2S + 4H2O = C3S2H3 + Ca(0H)2 + Heat C3S2H3 – Calcium Silicate Hydrate (3Ca0.2SiO2.4H2O)
- 13. Fresh to Hardened State • Fresh State • Plastic, workable, can be modeled and manipulated. • Transition State • Workability reduces, setting begins, strength is slowly developed. • Hardened State • Stiff, able to support, has strength
- 14. Concrete
- 15. Curing • Maintaining desired moisture content in concrete for complete hydration. • To prevent or compensate for evaporation of water added for hydration. • Atleast 7 – 10 days duration Steam Curing Curing by gunny bags Shade Curing Curing by Sprinkling Membrane Curing Curing by Ponding
- 16. Tests • Fresh state • Slump test for workability • Hardened state tests • Strength tests: Compressive strength test, Flexural strength test, splitting tensile strength test. • Durability tests: water absorption test, chloride ion penetration test, resistance to sulphate attack, carbonation test, freezing thawing test etc.
- 17. Concrete - types • Normal concrete – usual ingredients, strength 10 – 40 MPa, less durable against extreme conditions. • High strength concrete – strength > 40 MPa, w/c < 0.35, pozzolanas as mineral admixture. • High performance concrete - strength 70 – 100 MPa, w/c – 0.25, superplasticizer, mineral admixtures. • Air entrained concrete – used where extreme freezing and thawing, less strength, air – entraining admixtures. • Light weight concrete – strength 7 – 40 MPa, density 1850 – 2400 kg/m3, no extra load.
- 18. Concrete - types • Self compacting concrete – self flowing, more finer content, superplasticizer. • Shotcrete - concrete conveyed through a hose and pneumatically projected onto a surface, no need for formwork, used as a quick fix for weathering and seepage issues. • Pervious concrete - 15% and 25% of the concrete volumes are voids, allowing water to drain, formed by leaving out some or the entire fine aggregate. • Roller compacted concrete -high density, low-cement-content stiff concrete placed using heavy rollers typically used in earthwork.
- 19. Concrete - Shortcomings • Low tensile strength • Brittle • Variable • Low Strength / weight ratio