A POWERPOINT PRESENTAION ON READY-MIX CONCRETE

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A POWERPOINT PRESENTAION ON READY-MIX CONCRETE

RMC IN INDIA:In India RMC was first initially was used in 1950 during the construction sites of Dams like Bhakra Nangal, Koyna. At the construction the transportation of concrete is done by either manually or mechanically using ropeways & buckets or conveyor systems.

General introduction:

Ready Mix Concrete (RMC) is a specialized material in which the cement aggregates and other ingredients are weigh-batched at a plant in a central mixer or truck mixer, before delivery to the construction site in a condition ready for placing by the builder. Thus, `fresh' concrete is manufactured in a plant away from the construction site and transported within the requisite journey time. The RMC supplier provides two services, firstly one of processing the materials for making fresh concrete and secondly, of transporting a product within a short time

ADVANTAGES

A centralized concrete batching plant can serve a wide area.The plants are located in areas zoned for industrial use, and yet the delivery trucks can service residential districts or inner cities.Better quality concrete is produced.Elimination of storage space for basic materials at site.Elimination of hiring of plant and machinery.Wastage of basic materials is avoided.Labors associated with production of concrete is eliminated.Time required is greatly reduced.Noise and dust pollution at site is reduced.

ADVANTAGE OF RMCRMC is preferred to on-site concrete mixing because of the precision of the mixture and reduced worksite confusion. It facilitates speedy construction through programmed delivery at site and mechanized operation with consequent economy. It also decreases labor, site supervising cost and project time, resulting in savings. Proper control and economy in use of raw material results in saving of natural resources. It assures consistent quality through accurate computerized control

DISADVANTAGES:-

The materials are batched at a central plant, and the mixing begins at that plant, so the traveling time from the plant to site is critical over longer distances.Access roads, and site access have to be able to carry the weight of the truck and load concrete is approx 2.5tonne per comm.concretes limited time span between mixing and going-off means that ready-mix should be placed within 2hours of batching at the plant

Disadvantages of ready-mix concrete:-

The materials are batched at a central plant, and the mixing begins at that plant, so the traveling time from the plant to the site is critical over longer distances. Some sites are just too far away, though this is usually a commercial rather than a technical issue.Generation of additional road traffic. Furthermore, access roads and site access have to be able to carry the greater weight of the ready-mix truck plus load. (Green concrete is approx. 2.5 tone per m.) This problem can be overcome by utilizing so-called 'mini mix' companies which use smaller 4m capacity mixers able to reach more-restricted sites.Concrete's limited time span between mixing and curing means that ready-mix should be placed within 210 minutes of batching at the plant.[2] Modern admixtures can modify that time span precisely, however, so the amount and type of admixture added to the mix is very important.

Standard ready-mix concrete vs. site-mix

concrete centralized concrete batching plant can serve a wide area. Site-mix trucks can serve an even larger area including remote locations that standard trucks can not.The plants are located in areas zoned for industrial use, and yet the delivery trucks can service residential districts or inner cities. Site-mix trucks have the same capabilities.Better quality concrete is produced. Site mix can produce higher compression strength with less water than standard batching methods.

MIXING PROCESS:Thorough mixing of the materials is essential for the production of uniform concrete. The mixing should ensure that the mass becomes homogeneous, uniform in color and consistency. There are three methods adopted for mixing Ready Mix Concrete.Following are the three types of mixing process of RMC1. Transit Mixed (or "truck-mixed") Concrete2. Shrink Mixed Concrete3. Central Mixed Concrete

TRANSIT MIXING:-It is delivered to the worksite, often in transit mixers capable of mixing the ingredients of the concrete just before the delivery of batch. This results in a precise mixture, allowing specialty concrete mixtures to be developed and implemented on construction sites. The second option available is to mix the concrete at the batching plant and deliver the mixed concrete to the site in an agitator truck, which keeps the mixed concrete in correct form.

CENTRALLY MIX:-In the case of the centrally mixed type, the drum carrying the concrete revolves slowly so as to prevent the mixed concrete from "segregation" and prevent its stiffening due to initial set. However, in the case of the truck-mixed concrete, the batched materials (sand, gravel and cement) are carried and water is added just at the time of mixing. In this case the cement remains in contact with the wet or moist material and this phase cannot exceed the permissible period, which is normally 90 minutes.The use of the RMC is facilitated through a truck-mounted 'boom placer' that can pump the product for ready use at multi-storied construction sites. A boom placer can pump the concrete up 80 meters.

Transit Mixed (or "truck-mixed") Concrete:-In transit-mixed concrete, also called truck mixed or dry-batched, all of the raw ingredients are charged directly in the truck mixer. Most or all water is usually batched at the plant.

Concrete mixed at the job site:- While traveling to the job site the drum is turned at agitating speed (slow speed). After arriving at the job site, the concrete is completely mixed. Concrete mixed in the yard:- The drum is turned at high speed or 12-15 rpm for 50 revolutions. This allows a quick check of the batch. The concrete is then agitated slowly while driving to the job site. Concrete mixed in transit:- The drum is turned at medium speed or about 8 rpm for 70 revolutions while driving to the job site. The drum is then slowed to agitating speed.

Time in Transport:The general requirement is that concrete shall be discharged from the truck mixer within 2 hours of thetime of loading. However, longer period may be permitted if retarding admixtures are used or in coolhumid weather or when chilled concrete is producedSAMPLING AND TESTING OF READY-MIXED CONCRETE (As per IS 4926-2003):For the assessment of compliance of ready-mixed concrete, the point and the time of sampling shall beat the discharge from the producers delivery vehicle or from the mixer to the site or when deliveredinto the purchasers vehicle.

Volumetric concrete mixerAs an alternative to ready-mix concrete, volumetric mobile mixers may be used to provide metered concrete services. The volumetric mobile mixer is a truck that contains concrete ingredient materials and water to be mixed on the truck at the job site to make and deliver concrete according to the amount needed. The on-truck mixing at the job site eliminates the problems of ready-mix concrete such as delays that can cause the pre-mixed concrete to become unusable. This is a hybrid approach between ready-mix concrete and traditional on-site mixing.[3]

A volumetric concrete mixer (also known as volumetric mobile mixer and metered concrete truck) is a truck that contains concrete ingredient materials and water to be mixed on the truck at the job site to make and deliver concrete according to the amount needed.[1]

The mixer is a mixing device that measures the raw materials using volume rather than weight. The volumetric mixer blends the concrete mixture using an auger or a paddle or a drum device to mix the ingredients with water. The volumetric mixing process starts with a batch metering system that allows the volume of raw materials to be measured prior to entering the mixing chamber. This process can be as simple as using a measured bucket, to highly sophisticated and computerized batch plants that feed the correct volume.[2]

Standard ready-mix concrete vs. site-mix concrete

A centralized concrete batching plant can serve a wide area. Site-mix trucks can serve an even larger area including remote locations that standard trucks can not.The plants are located in areas zoned for industrial use, and yet the delivery trucks can service residential districts orinner cities. Site-mix trucks have the same capabilities.Better quality concrete is produced. Site mix can produce higher compression strength with less water than standard batching methods.

Table 1 Assumed Standard DeviationGrade of Concrete Assumed Standard Deviation N/sq.mmM 10 3.5M 15M 20 4.0M 25M 30 5.0M 35M 40M 45M 50

ADMIXTURE:

A substance added to the basic concrete mixture to alter one or more properties of the concrete; i.e. fibrous materials for reinforcing, water repellent treatments, and coloring compounds.Air-entraining admixtures (mainly used in concrete exposed to freezing and thawing cycles) Water-reducing admixtures, plasticizers (reduce the dosage of water while maintaining the workability) Retarding admixtures (mainly used in hot weather to retard the reaction of hydration) Accelerating admixtures (mainly used in cold weather to accelerate the reaction of hydration) Super plasticizer or high range water-reducer (significantly reduce the dosage of water while maintaining the workability) Miscellaneous admixtures such as corrosion inhibiting, shrinkage reducing, coloring, pumping etc.

BATCHING PLANT

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