INTRODUCTION TO RC.pdf
- 1. INTRODUCTION TO REINFORCED CONCRETE CE 535 /D
- 2. CONCRETE AND REINFORCED CONCRETE CONCRETE Rocklike Material Ingredients Portland Cement Course Aggregate Fine Aggregate Water Admixtures (optional) REINFORCED CONCRETE It is a combination of concrete and steel wherein the steel reinforcement provides the tensile strength lacking in the concrete.
- 3. ADVANTAGES OF REINFORCED CONCRETE AS A STRUCTURAL MATERIAL 1. High compressive strength 2. Great resistance to the actions of fire and water. 3. Very rigid. 4. Low-maintenance material 5. Very long service life 6. Only economical material available for footings, floor slabs, basement walls, piers, and similar applications. 7. Formed into different shapes. 8. Inexpensive local materials. 9. Lower grade of skilled labor is required for erection
- 4. DISADVANTAGES OF REINFORCED CONCRETE AS A STRUCTURAL MATERIAL 1. Very low tensile strength 2. Formwork is very expensive. 3. The low strength per unit of weight of concrete leads to heavy members. 4. The properties of concrete vary widely because of variations in its proportioning and mixing.
- 6. COMPATIBILITY OF CONCRETE AND STEEL Concrete: high compressive strength, low tensile strength Steel: high tensile strength, low compressive strength Concrete + Steel: • Economical structural material, strong in compression & tension • Concrete provides corrosion protection and fire resistance
- 7. STRUCTURAL DESIGN Process of determining, selection of and determination of for the structure to be built Aim: ensure that the structure will perform satisfactorily during its design life
- 8. STRUCTURAL DESIGN PURPOSES Fitness for purpose Safety and reliability Economy Maintability
- 9. FITNESS FOR PURPOSE Arrangement of spaces, spans, ceiling height, access and traffic flow must complement the intended use. The structure should fit its environment and be aesthetically pleasing
- 10. SAFETY AND RELIABILITY Structure must be strong to safely support all anticipated loadings Structure must not deflect, overturn, tilt, vibrate or crack in a manner that impairs its usefulness
- 13. ECONOMY Overall cost of structure should not exceed the client’s budget Designer should take into account: cost of materials, buildability, construction time, cost of temporary structures and maintenance costs
- 14. MAINTAINABILITY STRUCTURE SHOULD BE DESIGNEDTO REQUIRE A MINIMUM MAINTENANCE, CAN BE MAINTAINED IN A SIMPLE FASHION
- 15. STRUCTURAL ELEMENTS Beams: horizontal members carrying lateral loads Slabs: horizontal plate elements carrying lateral loads Columns: vertical members carrying primarily axial loads but generally subjected to axial load and moment Walls: vertical plate elements resisting vertical, lateral or in-plane loads Foundations: pads or strips supported directly on the ground that spread loads from columns or walls to the ground Stairs: plate elements consists of a flight of steps, usually with one or more landings provided between the floor levels
- 17. DESIGN CODES
- 18. TYPES OF PORTLAND CEMENT Type 1 Standard Portland cement - Used for general purposes; air entrained Type II Modified Portland cement - Used when sulphate resistance and/or generation of moderate heat of hydration are required; air entrained Type III High early strength Portland cement - Used for early strength and cold weather operations; air entrained Type IV Low heat Portland cement - Used where low heat of hydration is required; air entrained TypeV High sulphate- resistant concrete - Used where sulphate concentration is very high; also used for marine and sewer structures; air entrained
- 19. ADMIXTURES ADMIXTURES ARE THOSE INGREDIENTS IN CONCRETE OTHER THAN PORTLAND CEMENT,WATER,AND AGGREGATES THAT ARE ADDED TO THE MIXTURE IMMEDIATELY BEFORE OR DURING MIXING (FIG. 6-1).ADMIXTURES CAN BE CLASSIFIED BY FUNCTION AS FOLLOWS:
- 20. MOST USED ADMIXTURES Air-entraining admixtures Water-reducing admixtures Plasticizers Accelerating admixtures Retarding admixtures Hydration-control admixtures
- 21. MOST USED ADMIXTURES Corrosion inhibitors Shrinkage reducers Alkali-silica reactivity inhibitors Colouring admixtures Miscellaneous admixtures such workability, bonding, damp proofing, permeability reducing, grouting, gas-forming, and pumping admixtures
- 23. THE MAJOR REASONS FOR USING ADMIXTURES ARE: To reduce the cost of concrete construction To achieve certain properties in concrete more effectively than by other means To maintain the quality of concrete during the stages of mixing, transporting, placing, and curing in adverse weather conditions To overcome certain emergencies during concreting operations
- 24. AIR-ENTRAINING ADMIXTURES used to purposely introduce and stabilize microscopic air bubbles in concrete.Air- entrainment will dramatically improve the durability of concrete exposed to cycles of freezing and thawing (Fig. 6-2). Entrained air greatly improves concrete's resistance to surface scaling caused by chemical de-icers
- 25. AIR-ENTRAINING ADMIXTURES The primary ingredients used in air-entraining admixtures are salts of wood resin (Vinsol resin), synthetic detergents, salts of petroleum acids, etc.
- 26. WATER-REDUCING ADMIXTURES used to reduce the quantity of mixing water required to produce concrete of a certain slump, reduce water-cementing materials ratio, reduce cement content, or increase slump. Typical water reducers reduce the water content by approximately 5% to 10%.
- 27. WATER- REDUCING ADMIXTURES MATERIALS: LIGNOSULFONATES. CARBOHYDRATES. HYDROXYLATED CARBOXYLIC ACIDS. The effectiveness of water reducers on concrete is a function of their chemical composition, concrete temperature, cement composition and fineness, cement content, and the presence of other admixtures.
- 29. SUPERPLASTICIZERS (HIGH-RANGE WATER REDUCERS) These admixtures are added to concrete with a low-to-normal slump and water-cementing materials ratio to make high- slump flowing concrete. Flowing concrete is a highly fluid but workable concrete that can be placed with little or no vibration or compaction while still remaining essentially free of excessive bleeding or segregation.
- 30. APPLICATIONS WHERE FLOWING CONCRETE IS USED: thin-section placements, areas of closely spaced and congested reinforcing steel, pumped concrete to reduce pump pressure, thereby increasing lift and distance capacity, areas where conventional consolidation methods are impractical or can not be used, and for reducing handling costs.
- 31. FLOWABLE CONCRETE WITH HIGH SLUMP
- 32. IS EASILY PLACED
- 33. EVEN IN AREAS OF HEAVY REINFORCING STEEL CONGESTION
- 34. Low water to cement ratio concrete with low chloride permeability--- easily made with high- range water reducers- is ideal for bridge decks
- 35. Plasticized, flowing concrete is easily placed in thin sections
- 36. SUPERPLASTICIZERS (HIGH-RANGE WATER REDUCERS) Typical superplasticizers include: Sulfonated melamine formaldehyde condensates. Sulfonated naphthalene formaldehyde condensate. Lignosulfonates. Polycarboxylates.
- 37. SUPERPLASTICIZERS (HIGH-RANGE WATER REDUCERS) bleed significantly less than control concretes of equally high slump and higher water content. High-slump, low-water-content, plasticized concrete has less drying shrinkage than a high-slump, high-water-content conventional concrete. has similar or higher drying shrinkage than conventional low-slump, low-water-content concrete. The effectiveness of the plasticizer is increased with an increasing amount of cement and fines in the concrete.
- 38. RETARDING ADMIXTURES used to retard the rate of setting of concrete at high temperatures of fresh concrete (30°C or more). One of the most practical methods of counteracting this effect is to reduce the temperature of the concrete by cooling the mixing water or the aggregates. Retarders do not decrease the initial temperature of concrete. The bleeding rate and capacity of plastic concrete is increased with retarders.
- 39. RETARDING ADMIXTURES The typical materials used as retarders are: Lignin, Borax, Sugars, Tartaric acid and salts.
- 41. RETARDING ADMIXTURES Retarders are used to: 1. offset the accelerating effect of hot weather on the setting of concrete, 2. delay the initial set of concrete when difficult or unusual conditions of placement occur, 3. delay the set for special finishing processes such as an exposed aggregate surface.
- 42. RETARDING ADMIXTURES some reduction in strength at early ages (one to three days) accompanies the use of retarders. The effects of these materials on the other properties of concrete, such as shrinkage, may not be predictable. Therefore, acceptance tests of retarders should be made with actual job materials under anticipated job conditions.
- 43. ACCELERATING ADMIXTURES used to accelerate strength development of concrete at an early age. Typical Materials are: • Calcium chloride: most commonly used for plain concrete. • Triethanolamine. • Calcium formate. • Calcium nitrate. • Calcium nitrite.
- 45. CORROSION INHIBITORS The chlorides can cause corrosion of steel reinforcement in concrete. Ferrous oxide and ferric oxide form on the surface of reinforcing steel in concrete. Ferrous oxide reacts with chlorides to form complexes that move away from the steel to form rust.The chloride ions continue to attack the steel until the passivating oxide layer is destroyed.
- 46. CORROSION INHIBITORS Corrosion-inhibiting admixtures chemically arrest the corrosion reaction. Commercially available corrosion inhibitors include: • calcium nitrite, • sodium nitrite, • dimethyl ethanolamine, • amines, • phosphates, • ester amines.
- 47. SHRINKAGE- REDUCING ADMIXTURES Shrinkage cracks, such as shown on this bridge deck, can be reduced with the use of good concreting practices and shrinkage reducing admixtures.
- 48. CHEMICAL ADMIXTURESTO REDUCE ALKALI-AGGREGATE REACTIVITY (ASR INHIBITORS) Expansion of specimens made with lithium carbonate admixture
- 49. COLORING ADMIXTURES (PIGMENTS) Red and blue pigments were used to color this floor