Admixtures-Overview.ppt
- 1. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Admixtures for Concrete Advanced Concrete Technology Natural Resources Ressources naturelles Canada Canada Overview
- 2. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Admixtures for Concrete • Admixtures are ingredients other than portland cement, water, and aggregates that are added to the mixture immediately before or during mixing. • Concrete admixtures are used to improve the behavior of concrete under a variety of conditions and are of two main types: chemical and mineral.
- 3. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Admixtures for Concrete • Chemical admixtures reduce the cost of construction, modify properties of hardened concrete, ensure quality of concrete during mixing/transporting/placing/curing, and overcome certain emergencies during concrete operations.
- 4. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET • Modify the rheology of fresh concrete • Increase workability without increasing water content or to decrease water content at the same workability • Retard or accelerate the time of initial setting • Entrain air bubbles in the fresh concrete • Prevent shrinkage, corrosion, expansion, evaporation; Enhance viscosity, … Admixtures for Concrete
- 5. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET ADMIXTURES for CONCRETE •1. Air-entraining admixtures (AEA) •2. Water-reducing admixtures (WR) •3. Retarding admixtures •4. Accelerating admixtures •5. Superplasticizers (HRWR) •6. Finely divided mineral admixtures •7. Specialty admixtures : such as •corrosion inhibitors, shrinkage control, Viscosity, alkali-silica reactivity inhibitors, coloring, curing, permeability-reducing, defoamers, etc.
- 6. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Action of concrete Admixtures • Physical action: – Do not affect directly cement reactions • AEA, defoamers, etc. • Chemical action: – Modify cement reactions • Accelerators, Retarders, Water-reducing admixtures N.B.: Many admixtures do both actions
- 7. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Air-entraining Admixtures
- 8. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Air-entraining Admixtures •Surfactants that ensure the stabilization of air bubbles in fresh concrete Anionic (most of the modern AEAs) Water soluble salts of Wood resins, Lignosulfonates, sulfonated hydocarbons, Wood rosins, Fatty acids proteanaceous materials Non-ionic (few) Water soluble low molecular weight ethylene oxide ploymers (weak stability of the air) Cationic Prohibitive cost and questionable air void system
- 9. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Product Group Type Products tested Sulfate Ether/ Carboxylate Ether Anionic 2 Ethoxylate Nonionic 3 Fatty acid Anionic 2 Imidazole Amphoteric 2 Phosphate Ether Anionic 2 Sorbitan Nonionic 3 Sulfonates Anionic 4 AEAAdmixtures Tested
- 10. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Air entraining admixtures
- 11. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Hardened concrete • Freeze thaw resistance • Resistance to sulfate attack • Water-tightness • Scaling resistance to de- icers Advantages of Air Entrained Concrete Fresh concrete • Improved workability • Reduced segregation • Easy finishing • Less water, less sand
- 12. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Disadvantages • For every 1 percent increase in air, the compressive strength will be reduced by 2-6%. Reduced Strength Dosage and Properties • Typical air entrainment ranges from 5% to 8% of the volume of concrete. •Spacing factor of ≤ 200 µm; surface ≤ 25 mm-1
- 13. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Well Distributed air bubbles in the concrete (5.2%; after Dodson)
- 14. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Accelerators
- 15. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Accelerating Mechanisms • Increased dissolution rate • Reduced pH • Catalytic effect • Change in surface area / morphology • Disruption of protective membrane • Osmotic pressure
- 16. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Common Chemicals Used in Accelerating Admixtures • Inorganic – Calcium Chloride – Calcium Nitrate – Calcium Nitrite • Organic – Calcium Formate – Triethanolamine
- 17. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Effect of Accelerators on Mortar Set Time 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 0.0 1.0 2.0 3.0 4.0 5.0 6.0 Calcium Chloride Calcium Nitrate Initial Set Time (Hours) Dosage % of Cement
- 18. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Cement CSH Accel Accel Accel Accel Accel
- 19. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Cement Hydration Products Semi permeable Membrane OH- Cl- Si
- 20. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Retarders
- 21. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Common Chemicals Used in Retarding Admixtures • Lignosulfonates • Carbohydrates – Polysaccharides – Corn Syrup – Molasses • Hydroxylated Carboxylic Acids – Salts – Gluconate – Glucoheptonate – Citrate
- 22. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET O C OH C H OH C H OH C H OH C H OH C H OH H Gluconic Acid Citric Acid O C OH C H H C HO OH C O C H H C OH O
- 24. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Cement Retardation mechanism Surface Adsorption
- 25. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Effect of Retarders:Mortar Set Time 0 2 4 6 8 10 12 14 16 18 0.00 0.20 0.40 0.60 0.80 sodium citrate Corn Syrup Lignosulfonate Initial Set Time ( Hours ) Dosage % of Cement
- 26. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Water Reducing Admixtures
- 27. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Water Reducing Admixtures • Conventional WR: (slump of 4-5”) – Reduce water content up to 5%. – Lignosulfonates, polysaccharides (glucose and corn syrup, molasses). – Hydroxylated carboxylic acids-salts: (Gluconate, Glucoheptanate, citrate). • Mid-range WR: (slump of 4-5”) – Reduce water content up to 12%. – Formulated admixtures: poorly purified lignins, modified sulfonated naphthalene or melamine, carboxylic acid-based polymers, etc.
- 28. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Water Reducing Admixtures • High-range WR: (Slump of 8-11”) – Reduce water content up to 30% – Sulfonated naphthalene, sulfonated melamine, purified lignin • New generation (third generation) WR: – Reduce water content up to 30% and more – Maintain slump for more than 90 minutes – Do not affect the setting time and the hardening of concrete
- 29. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Lignosulfonate Molecule
- 30. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Sulfonated melamine formaldehyde salts
- 31. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET SO3H SO3H Naphthalene Formaldehyde Sulfonate Salts (PNS) HRWR
- 32. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET CH3 C C = O O- Na+ CH2 H C C = O O-CH3 CH2 CH3 C CH2 SO3Na+ CH2 a b c H C CH2 O CH2 CH2 CH2 O CH3 N n C Polycarboxylates (Acrylic Ester Copolymer)
- 33. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Dispersing Mechanisms • Electrostatic Repulsion • Steric Repulsion • Chelation / Complexation • Inhibition of Nucleation • Modification of crystalline structure
- 34. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Surface Adsorption Cement pastes Dispersing action
- 35. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET ElectrostaticRepulsion Cement pastes Dispersing action
- 36. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Steric Repulsion Cement pastes Dispersing action
- 37. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Compatibility Cement/SP
- 38. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Some incompatibilities Bleeding and segregation Cements with low C3A and C3S Cements with low Blaine fineness Cement with low alkali content (overdosed)
- 39. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Other side effects • Too much air entrained • Setting retardation • Hardening retardation • Problems with other admixtures
- 40. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Cement C with naphthalene-base SP 50 100 150 200 Slump (mm) 0 25 50 75 100 125 150 Time (min) 0.8% N 1 + 0.2% Na 2SO4 0.8% N 1 + 0.1% retarder 0.8% N 1 Cement C W/C = 0.30
- 41. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Non-compatible or non-robust cement/SP 0 50 100 150 200 250 0 30 60 90 120 150 Time (min) Slump (mm) D1/PNS 0.8% D1/PNS 0.6% Cement D1 /PNS W/C = 0.30; T=22o C Excessive segregation
- 42. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Viscosity Modifying Admixtures
- 43. Materials Technology Laboratory Laboratoire de la technologie des matériaux CANMET Viscosity Modifying Admixtures (VMA) for Self-compacting Concrete • Water soluble polymers that increase the viscosity of mixing water and enhance the ability of cement paste to retain its constituents in suspension • Polysaccharides • Cellulose derivatives • Acrylic–based polymers • Mixture of HRWR and VMA