CEMENT CONCRETE

PROPERTIES
High compressive strength
Lower tensile strength
Negligible change when temp changes
Develops cracks over time

1. CEMENT CONCRETE

2. PROPERTIES

3. COMPOSITION

4. Requirements of water Used in mixing and curing. Potable water should be used. Sea water is not permitted. pH value of water should not be less than 6. Disadvantages of using more water and advantages of using less water

5. Disadvantages of using more water Creates a diluted paste. Excess water bleeds out onto the surface. This affects the compressive and tensile strengths. Loss of cohesiveness and homogeneity. Harmful to strength and durability. Advantages of using less water Increased strength. Lower permeability. Increased resistance to weathering. Better bond between concrete and reinforcement. Reduced shrinkage and cracking. Less volume change from wetting and drying.

6. Aggregates FINE AGGREGATE COARSE AGGREGATE Size more than 4.75mm. Includes gravels and crushed stones. Obtained by crushing various types of granites, hard lime stones and sand stones. Harsh concrete. Size less than 4.75mm. Includes natural sand or crushed stone with most particles passing through a sieve. Obtained from pits, lake, river or sea-shore. Thoroughly washed before use.

7. Reinforcement Reinforced concrete  is a  composite material  in which  concrete's  relatively low  tensile strength  and  ductility  are counteracted by the inclusion of reinforcement having higher tensile strength and/or ductility. . Reinforced concrete may also be permanently stressed (in compression), so as to improve the behaviour of the final structure under working loads. In the United States, the most common methods of doing this are known as  pre-tensioning  and  post-tensioning .

8. Properties of reinforcement For a strong,  ductile  and durable construction the reinforcement needs to have the following properties at least: High relative  strength . High toleration of  tensile strain . Good  bond  to the concrete, irrespective of pH, moisture, and similar factors. Thermal compatibility, not causing unacceptable stresses in response to changing temperatures. Durability in the concrete environment, irrespective of corrosion or sustained stress.

9. Characteristics Two physical characteristics give reinforced concrete its special properties: The  coefficient of thermal expansion  of concrete is similar to that of steel, eliminating large internal stresses due to differences in  thermal  expansion or contraction. When the cement paste within the concrete hardens, this conforms to the surface details of the steel, permitting any stress to be transmitted efficiently between the different materials. Usually steel bars are roughened or corrugated to further improve the  bond  or cohesion between the concrete and steel

10. Common failure modes of steel reinforced concrete: Mechanical failure Carbonation Chlorides Alkali silica reaction Conversion of high alumina cement Sulphates

11. CARBONATION :

12. 12 Cement Production, Composition & Types

13. 13 Raw Materials in Cement

14. Production of Cement Acquisition of raw materials. Preparation of raw materials. Burning. Addition of Gypsum and Distribution. 14

15. 15 Compounds in Cement

16. Cement Types General Purpose Ordinary Portland Cement Sulphate Resisting Cement High Early Strength Low Heat Cement Air Entraining Cement White Cement 16

17. Ordinary Portland Cement Variety of artificial cement. On hardening , its color resembles to the rocks near Portland in England. Main constituents : Lime , Silica , Alumina. 17

18. Chemical Composition of Cement : Lime 63% Silica 22% Alumina 06% Iron Oxide 03% Gypsum 01-04% 18

19. Functions of Cement Manufacturing Constituents Lime : Sufficient quantity forms di-calcium silicate and tri-calcium silicate. Silica : Gives strength. Alumina : Sets cement quickly ; lowers clinkering temperature. 19

20. Iron Oxide : gives color to cement. Magnesia : helps in giving color to cement. Gypsum : added to increase the setting of the cement. 20

21. Sulphate Resisting Cement Modified form of O.P.C. Used when O.P.C. is liable to disintergrate. Uses : Hydraulic structures , canals. 21

22. High Early Strength Cement Provides strength at early stage. Reason : finer grinding , burning at high temperature , increased lime content. Strength by Rapid Hardening Cement in 4 days = strength by O.P.C. in 14 days. Uses : Highway Slabs. Suitable in Cold weather areas. 22

23. Low Heat Cement Heat of hydration is reduced by tri-calcium aluminate. Less % of Lime. Uses : Mass Concrete Works : Damns. 23

24. Air Entraining Cement Produced by grinding minute air entraining materials with clinker. Improves workability , durability. Uses : Natural raisins , fats , oils. 24

25. White Cement Keeps the content of Iron Oxide as low as possible. Costlier than O.P.C. Uses : Architectural finishing in buildings. 25

26. Characteristics of Cement Proportion of sand and cement decides the strength of mortar. Richer mixture than 1:3 proportion is prone to shrinkage. When water is added to initiate the cement and sand mixture , hydration starts and binds sand particle and surface of masonry and concrete. 26

27. Advantages Strong. Creates large structures easily. Has high thermal mass. Disadvantages Subjected to cracking. Difficult to provide idoneous curing conditions. Not ideal when settlement is expected. 27

28. ADMIXTURES

29. CONCRETE MIXTURES: Concrete admixtures are used to improve the behavior of concrete under a variety of conditions. There are two main types of Admixtures: Chemical admixture Mineral admixture

30. CHEMICAL ADMIXTUES : reduce the cost of construction, modify properties of hardened concrete, used to improve the quality of concrete during mixing, transporting, placement and curing.

31. They fall into the following categories: A ir entrainers W ater reducers S et retarders S et accelerators Super plasticizers S pecialty admixtures: which include corrosion inhibitors, shrinkage control, alkali-silica reactivity inhibitors, and coloring.

32. MINERAL ADMIXTURES: Mineral admixtures affect the nature of the hardened concrete through hydraulic or Pozzolanic activity. Pozzolans are cementations materials and include natural Pozzolans (such as the volcanic ash used in Roman concrete), fly ash and silica fume. They can be used with Portland cement, or blended cement either individually or in combinations.

33. Properties of mineral admixtures: make mixtures more economical, reduce permeability, increase strength, influence other concrete properties

34. CONCLUSIONS: Plasticizers, super plasticizers , & Air-entraining admixtures is mostly used. Super plasticizers is widely used all over the world . India is catching up with the use of super plasticizer in the construction of high rise buildings, long span brides because i t reduced cement content, increased workability, & increased strength.