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Transcript of Concrete :)
Concrete is basically a mixture of aggregates and paste. The aggregates are sand and gravel or crushed stone; the paste is water and portland cement. Concrete gets stronger as it gets older. Portland cement is not a brand name, but the generic term for the type of cement used in virtually all concrete, just as stainless is a type of steel and sterling a type of silver. There are different types of concrete. One of the most popular concrete used is Portland cement, mineral aggregates and water. Concrete often solidifies as the cement hydrates and glues all the other components together. It has a high compressive strength and general uses of concrete include pavements, fences, gates, walls and more. In old times, concrete was often referred to as liquid stone. Sometimes external stabilizers are included to concrete to give it desired characteristics. Some of the major concrete types include, Self-compacting concretes
Reinforced concrete The Self-compacting concretes use superplasticizers that accounts for the excessive fluidity of the concrete. It acts like a sticky self-levelling fluid that is combined using vibration. Self-compacting concretes Pump concrete consist of more quantity of sand than normal concrete. It is specifically made smooth to allow easy pumping from roadside to the construction site. Due to the increased quantity of water to make the concrete wet, it also requires more cement to attain the appropriate strength. Pump Sprayed concrete or Shotcrete makes use of compressed air to cast it to a structure. There are two different kind of sprayed concrete—the dry-mix and the wet-mix concrete. Dry mixed concrete is a dry mixture of cement and aggregates that are shot using compressed air through hoses. The water required for hydration is added at the nozzle. The wet mixture is appropriately hydrated and pumped through hoses. Sprayed concrete is usually reinforced using fiber. Sprayed concrete * It is the most common concreting applications. The slump is + 15mm.
* The concrete in which common ingredients i.e. aggregate, water, cement .
* It is also called normal weight concrete or normal strength concrete. Normal concrete This concrete is used for casting columns and loads or any areas where concrete has to flow into position. Tremmie concrete Special class might be any concrete specifically required by customers like pre-stressed concrete and light weight concrete. Special concrete Chipping concrete is made by
passing the mixture between
very small spaces, small size
stones. Chipping No fines concrete as the name suggests is a concrete with no sand in its mixture. It is a porous mass also known as a washed-out concrete. It uses water so that minimum paste remains stay at the bottom during placing. Mortar Concrete mould wrapped in a mesh of iron rods is called reinforced cement concrete or RCC. Concrete with reinforced steel acquires the capacity to carry enormous loads. It is the most versatile material with a wide range of applications in construction. Reinforced concrete Properties of Fresh Concrete
Properties of Hardened Concrete Properties of Concrete Fresh concrete is that stage of concrete in which concrete can be moulded and it is in plastic state. This is also called "Green Concrete". Another term used to describe the state of fresh concrete is consistence, which is the ease with which concrete will flow. Fresh Concrete Setting
Bleeding and Segregation
Air Entrainment Properties of Fresh Concrete The hardening of concrete before its hydration is known as setting of concrete
The hardening of concrete before it gains strength
The transition process of changing of concrete from plastic state to hardened state. Setting of concrete is based or related to the setting of cement paste SETTING Factors affecting setting: 1. WaterCement ratio
2. Suitable Temperature
3. Cement content
4. Type of Cement
5. Fineness of Cement
8. Type and amount ofAggregate Workability Factors affecting concrete workability: Workability is often referred to as the ease with which a concrete can be transported, placed and consolidated without excessive bleeding or segregation. The internal work done required to overcome the frictional forces between concrete ingredients for full compaction. It is obvious that no single test can evaluate all these factors. In fact, most of these cannot be easily assessed even though some standard tests have been established to evaluate them under specific conditions. In the case of concrete, consistence is sometimes taken to mean the degree of wetness; within limits, wet concretes are more workable than dry concrete, but concrete of same consistence may vary in workability. Water-Cement ratio
Amount and type of Aggregate
Amount and type of Cement
Sand to Aggregate ratio Concrete Bleeding Bleeding in concrete is sometimes referred as water gain. It is a particular form ofsegregation, in which some of the water from the concrete comes out to the surface of the concrete, being of the lowest specific gravity among all theingredientsof concrete. Bleeding is predominantly observed in a highly wet mix, badly proportioned and insufficiently mixed concrete. In thin members like roof slab or road slabs and when concrete is placed in sunny weather show excessive bleeding. Segregation in concrete Segregationcan be defined as the separation of the constituent materials of concrete. A good concrete is one in which all theingredientsare properly distributed to make a homogeneous mixture. There are considerable differences in the sizes and specific gravities of the constituent ingredientsof concrete. Therefore, it is natural that the materials show a tendency to fall apart. Segregation may be of three types Coarse aggregate separating out or settling down from the rest of the matrix.
Paste separating away from coarse aggregate.
Water separating out from the rest of the material being a material of lowest specific gravity. Hydration in concrete Concrete derives its strength by the hydration of cement particles. The hydration of cement is not a momentary action but a process continuing for long time. Of course, the rate of hydration is fast to start with, but continues over a very long time at a decreasing rate In the field and in actual work, even a higher water/cement ratio is used, since the concrete is open to atmosphere, the water used in the concrete evaporates and the water available in the concrete will not be sufficient for effective hydration to take place particularly in the top layer.