1. CVL 2407 Faculty of Applied Engineering and Urban Planning Civil Engineering Department 2 nd Semester 2013/2014 Dr. Eng. Mustafa Maher Al-tayeb

2. 2 Chapter 6: Admixtures for Concrete Definition A material other than water, aggregates and hydraulic cement that is used as an ingredient in concrete or mortar and is added to the batch immediately before or during its mixing (ASTM C125). What are admixtures: Admixture are natural or manufactured chemicals which are added to concrete before or during mixing. the most often used admixtures are air- entraining agents, water reducers, water-reducing retarders and accelerators.

3. 3 Chapter 6: Admixtures for Concrete Why use admixtures:  Admixture are used to give special properties to fresh or hardened concrete.  Admixture may enhance the durability, workability or strength characteristics of a given concrete mixture.  Admixture are used to over come difficult construction situations, such as:  hot or cold weather placement.  pumping requirements  early strength requirements.  or very low water-cement ration specification.

4. 4 Chapter 6: Admixtures for Concrete Reasons for using Admixtures  reduce cost of concrete construction.  Achieve certain properties more effectively than by other.  Ensure quality of concrete during stages of mixing, transporting, placing and curing in adverse conditions.  Overcome certain emergencies during concreting.  Improve or modify some or several properties of Portland cement concrete.  Increase workability without increasing water cement or to decrease water content at the same workability.  Retard or accelerate the time of initial setting.  Create slight expansion.

5. 5 Chapter 6: Admixtures for Concrete Modification of fresh concrete:  To modify the rate, or capacity for bleeding or both.  To avoid segregation.  To improve pump ability.  Reduce the rate of slump loss. Modify Hardened concrete properties  Accelerate the rate of strength gain.  Increase ultimate strength.  Increase durability.  Reduce permeability.  Compensate for shrinkage.  Inhibit corrosion.

6. 6 Chapter 6: Admixtures for Concrete General Groupings of admixtures 1.Air-entraining agents group 2. Chemical Admixtures group. 3.Mineral admixtures group. 4.Miscellaneous admixtures group

7. 7 General Groupings of admixtures 1. Air-entraining agents group:  There are used primarily to improve freeze-thaw durability.  They are liquid chemicals added during batching concrete to produce microscopic air bubbles called entrained air, mixing state these air bubbles improve the concrete's resistance to damage caused by freezing and thawing plastic concrete state (improve workability, reduce bleeding and segregation)

8. 8 General Groupings of admixtures (Cont.) 2. Chemical Admixtures group: There are water soluble compounds added primarily to control setting and early hardening of fresh concrete or to reduce the water requirements. 1- Water reducer: are used to different purposes to lower the water content in plastic concrete and increase its strength. to obtain higher slump without adding water. 2- Retarders: are chemicals that delay initial setting of concrete by an hour or more ( are often used in hot weather to counter the rapid setting caused by high temperatures) 3- Accelerators: reduce the initial setting time of concrete and give higher strength. 4- High range water-reducers(HRWR): often called superlasticizers, HRWRs reduce the water content of a given concrete mixture between 12 and 25%. It are used to increase strength and reduce permeability of concrete by reducing the water content in the mixture.

9. 9 General Groupings of admixtures (Cont.) 3. Mineral admixtures group: There are finely divided solids to improve workability, durability, or provide additional cementing properties. (i.e. slags, silica fume, fly ash, and pozzolans). 4. Miscellaneous admixtures group: Those admixtures that don't fall under the above categories.

10. 10 Air Entraining Admixtures Air entrainment refers to the introduction of large quantities of tiny air bubbles in the concrete matrix. The main reason for air entrainment is to improve the durability of the concrete to freeze-thaw degradation.

11. 11 Air Entraining Admixtures

12. 12 Air Entraining Admixtures

13. 13 The Air-Void System:  As un-reacted water freezes it expands 9 % by volume on phase change.  This internal volume expansion causes internal stresses in the matrix.  It can generate cracks in the concrete, which may allow water to infiltrate and the process can get progressively worse.  It can lead to significant degradation of the concrete.  The formation of ice in the pore spaces generates pressure on any remaining unfrozen water.  Introducing a large quantity of air bubbles provides a place for this water to move in to relieving the internal pressure.

14. 14 The Air-Void System: (Cont.)  It's been determined that the optimum air content for frost protection is about 9% by volume of the mortar fraction.  With respect to the concrete volume, the air content should be in the range of 4- 8% by volume.  The concrete normally has entrained air, the admixture increases the total volume of the air voids by 3-4% of the concrete volume.

15. 15 Chemical Admixtures Type A: Water-reducing (WR) Type B: Set retarding (SR) Type C: Set accelerating (SA) Type D: WR + SR Type E: WR + SA Type F: High-range water-reducing (HRWR) Type G: HRWR + SR

16. 16 Mineral Admixtures  Raw or calcined pozzolans  Fly ash produced from burning bituminous coal  Fly ash normally produced from burning lignite (subbituminous) coal. (both pozzolanic and cementatious). Natural pozzolanIndustrial pozzolan Clay & Shaleالطين و الطفلةFly ashرماد متتطاير Opaltine materialsمواد أوباليةBurn oilزيت محروق Volcanic tuffsرواسب بركانية

17. 17 Placement of Concrete

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19. 19 Mixing: Thorough mixing is essential for the complete blending of the materials that are required for the production of homogeneous, uniform concrete. The optimum mixing time depends on: The type of mixer. The condition of the mixer. The speed of rotation. The size of the charge. The nature of the components. Lean, dry or harsh mixes require more mixing than those made with rounded gravels.

20. 20 Placement of Concrete

21. 21 Placement of Concrete

22. 22 Placement of Concrete

23. 23 Placement of Concrete

24. 24 Placement of Concrete

25. 25 Placement of Concrete

26. 26 Placement of Concrete

27. 27 Placement of Concrete