RMCREADY-MIX

CONCRETE

• VISHAL HIRWANI

• DHRUPAD NATH

• KULDEEP PANCHAL

CONTENTS1.RMC2.HISTORY3.GRADES OF CONCRETE4.ADV. AND LIM.5.EQUIPMENTS6.MANUFACTURING PROCESS7.RMC PLANT8.SAMPLING AND TESTING

RMC (READY MIX CONCRETE)Ready-mix concrete (RMC) is a type of concrete which is

manufactured in a cement factory, or specifically known as the

batching plant, according to a given set of proportions, and then

delivered to a work site, by truck mounted with mixers. This results

in a precise mixture, allowing specialty concrete mixtures to be

developed and implemented on construction sites.

IS-4926, the definition of Ready mixed concrete is: “Concrete delivered at site or in to the purchaser’s vehicle in a plastic condition and requiring no further treatment before being placed in position in which it is to set and harden”

READY MIX VS SITE MIXREADY MIX

1. Consistent Quality- concrete is made in high tech batching plants in a computerized environment.

2. Construction in double quick time.

3. Raw materials are chosen after strict quality checks

4. Large quantities of concrete can be ordered. This allows you to upgrade yourself and handle projects of any size.

5. No wastage of raw materials at your site. Everything is pre-mixed at our plants, based on your needs.

6. No hassle of managing labor on site. We supply ready-to-use concrete. well-equipped technical crew will handle the pouring and patching of concrete at the site.

7. Safe work practices – no disruption in your schedule

8. You don’t have to stock materials and watch over them. There’s no worry about pilferage as the concrete is directly supplied to your site when you need it.

SITE MIX1. Quality is inconsistent–because concrete is hand mixed.

2. Manual mixing is time consuming. Projects take longer time to finish.

3. Quality of raw materials is manually checked. Or not checked at all.

4. Takes more time. Repeated mixing needs to be done for large quantities as the mixer will be too small to handle the requirement

5. High wastage of raw materials due to manual mixing.

6. Involves the use of laborers for mixing the concrete on site. Management of labor means more time, efforts and money.

7. Highly unsafe. Unskilled and untrained laborers may work carelessly resulting in dangerous working conditions

8. Risk of pilferage of raw materials is high. Housekeeping could be poor due to piles of stocks lying at the site

HISTORY

•The Idea of Ready Mix Concrete (RMC) was first introduced by Architect Jurgen Heinrich Magens, he got his patent of RMC in Germany in 1903. In 1907, he discovered that the available time for transportation could be prolonged not only by cooling fresh concrete but also by vibrating it during transportation.

•The first concrete mixed off site and delivered to a construction site was effectively done in Baltimore, United States in 1913, just before the First World War. The first concept of transit mixer was also born in 1926 in the United States. In 1939, the first RMC plant was installed in United Kingdom. Between the years 1950 and 1980 considerable growth of RMC took place in the United States. In India RMC was first initially was used in 1950 during the construction sites of Dams like Bhakra Nangal, Koyna.

RMC PLANTS IN INDIACOMPANY PLANTS ACROSS INDIA

UltraTech - Ready Mix Concrete (RMC) Plants 103

LAFARGE 68

ACC LIMITED 92RMC Ready-mix India 50Relcon Infra Projects Ltd -RDC -Apollo Inffratech Private Limited -The Ramco Cements Limited -Wonder Ready-mix Concrete -

TOTAL IN INDIA 9000+ PLANTS

READY MIX CONCRETE - GRADES OF CONCRETECLASSIFICATION GRADE APPLICATION RATIO

ORDINARY M10 PCC (Plain Cement Concrete) e.g. Levelling course, bedding for footing, concrete roads etc. 1:3:6

M15 PCC e.g. Levelling course, bedding for footing, concrete roads etc. 1 : 2 : 4

M20 RCC (Reinforced Cement Concrete) e.g. Slabs, beams, columns, footing etc. (for mild exposure)

1 : 1.5 : 3

STANDARD M25 RCC (Reinforced Cement Concrete) e.g. Slabs, beams, columns, footing etc. 1 : 1 : 2

M30 RCC e.g. Slabs, beams, columns, footing etc.

M35 RCC e.g. Slabs, beams, columns, footing etc.

M40 RCC e.g. Pre-stressed concrete, slabs, beams, columns, footing etc.

M45 RCC e.g. Runways, Concrete Roads (PQC), Prestressed Concrete Girders, beams, RCC Columns

M50 RCC e.g. Runways, Concrete Roads (PQC), Prestressed Concrete Girders, beams, RCC Columns

M55 RCC e.g. Prestressed Concrete Girders & Piers

HIGH-STRENGTH

M60-M80

RCC work where compressive strength is required such as high rise building, long span bridges, ultra-thin white topping etc and constructions in aggressive e.g. Spilways of dams coastal construction

ADVANTAGE OF READY-MIX CONCRETE•Better quality concrete is produced in lesser time.

•Elimination of storage space for basic materials at site.

•Elimination of Procurement / Hiring of plant and machinery

•Wastage of basic materials is avoided.

•Labor associated with production of concrete is eliminated.

•Time required is greatly reduced.

•Noise and dust pollution at site is reduced.

•Organization at site is more streamlined.

LIMITATIONS OF READY-MIX CONCRETE• As the Ready Mixed Concrete is not available for placement immediately after preparation of concrete mix, loss of workability occurs. In addition, there are chances of setting of concrete if transit time involved is more. Therefore, generally admixture like plasticizers/ super plasticizers and retarders are used. Addition of retarders may delay the setting time substantially which may cause placement problems. In addition, it may also affect the strength of concrete. Therefore, it is necessary that the admixtures i.e. plasticizers and super plasticizers/ retarders used in Ready Mixed Concrete are properly tested for their suitability with the concrete. In case loss of strength is observed, the characteristic strength may have to be enhanced so that after loss of strength, required characteristic strength is available.

• Because of large quantity of concrete available in short span, special placing and form work arrangement are required to be made in advance.

EQUIPMENTS (RMC)• THE STORAGE SYSTEMThis System Stores The Cement, Fine Aggregates(sand), Coarse Aggregates(gravel, Limestone, Gypsum) And Also Generally Has A Tank

For Storing Compressed Air For Cleaning And Another Tank For Storing Chemical Additives For The Concrete Mix.

1. BIN TYPE:    

Consists Of A Metal Structure With Partitions Inside For Storing The Materials Except The Chemicals, Air And The Cement. Depending On

The Type Of The Batching Plant, The Bins Greatly Vary In Size. They Drop Materials Onto A Conveyor Belt Or Directly Into A Movable

Bucket( Called Skip Bucket/Charger Box) Via Pneumatically Or Electrically Operated Gates That Open For Specific Time Periods So

That Appropriate Amounts Of Materials Are Added For Different Concrete Recipes. They Are Common In Large Capacity Plants(ie

Plants With Capacities Over 60 Cu M Per Hour). The Bins May Be Arranged In-line Or Side-by-side.

EQUIPMENTS (RMC)• THE STORAGE SYSTEM2. STAR TYPE:       This system consists of the materials(except cement) stored in the open with partitions between the materials. The

aerial view roughly resembles half a star so hence the name. The partitions are made of metal, concrete blocks or

bricks. They are fed into a bucket for transporting to the mixer by means of a scraper( the long arm attached to the

cabin) which has a bucket attached and is controlled by an operator in the cabin. The number of partitions

depends on the requirement but is generally at least four.

EQUIPMENTS (RMC)• THE STORAGE SYSTEM3. COMPARTMENT BINS: Very Similar To The Bins Mentioned Above But The Difference Is That While The Bins Generally Feed Onto A Conveyor

That Feeds The Skip Bucket, The Compartment Bins Feed Directly Into The Skip-bucket. They Are More Common In Small Capacity And Vertical Plants.

EQUIPMENTS (RMC)• SILOS (Cement and Cement Supplement) UNLOADING OF CEMENT OR CEMENT SUPPLEMENT INTO ELEVATED

STORAGE SILOS FROM TRUCK, RAIL OR BARGE. DUE TO THE

SENSITIVITY OF CEMENT AND THE CEMENT SUPPLEMENT TO

MOISTURE, THIS IS ALWAYS AN ENCLOSED SYSTEM. THE

EMISSIONS THAT ARE GENERATED BY THIS PROCESS ARE

GENERALLY PASSED THROUGH A BAGHOUSE LOCATED ON TOP OF

THE STORAGE SILO, OR THROUGH A CENTRAL BAGHOUSE. THE

DNR RECOMMENDS THE EMISSIONS FROM EACH SILO BE MODELED

AS A POINT SOURCE USING THE STACK CHARACTERISTICS OF THE

BAGHOUSE THAT CONTROLS IT.

• Diameter of Silo Diameter is 2800/3200/3500 mm.• Shell Thickness 5 mm Premium Quality Plate Grade IS 2062-B.• Bottom Cone Section 6 mm Thick Premium Quality Plate Grade

IS 2062-B.• Top Shell in 5 mm Thick Premium Quality Plate Grade IS 2062-

B.

EQUIPMENTS (RMC)• TRANSIT MIXER (IS 5892-2004)The purpose of producing well mixed concrete is lost if concrete

loses its strength during transportation. Therefore, efficient

transit mixers constitute an integral part of the RMC plants as

well as concrete batching plant units.

• The geometrical volume of a 4 cum capacity mixer is around 8,000 liter and 10,500 liter for a 6 cum capacity mixer. Therefore, a 5 cum capacity mixer should have about 8,700 liter capacity. Filling volumes vary from 50 per cent to 60 per cent

• Mixer drum The transit mixers are made of sturdy, high wear resistance grade steel. Normally, the chrome and nickel content of steel should be more than normal.

• The thickness of drum should be more at the bottom than at the sides. A bottom thickness of 6 mm and shell thickness of 4 mm can be considered normal.

EQUIPMENTS (RMC)

EQUIPMENTS (RMC)• CONVEYANCE UNIT

1. SKIP-BUCKET/CHARGER-BOX:   This is a large steel box that receives the aggregates and transports it to the mixer for mixing. The box runs on rails pulled by 1 or 2 metal

cables which are attached to a motor or two motors. The box has steel rails to run along the track but polyurethane wheels are increase

becoming popular due to their longer life and quieter operation.

2. CONVEYOR BELTS:    Made of Buna-S or EP rubber they are used to convey materials from the bins to the skip-bucket or to the mixer. A modified form of

the conveyor belt is called a dip-bucket and it is used to carry materials to the mixer in place of the charger box. The dip-bucket

consists of two protective rubber layers at the sides to prevent spillage and the belt is partitioned to ensure correct quantities

are batched.

3. SCREW CONVEYORS:    Screw conveyors are used to carry cement from the silos to the mixer.

4. OTHERS:A batching plant also has a network of pipes to carry air-suspended oil droplets for circulation and for operating the various

pneumatic systems like batching gates etc. A water pump for adding water. Admixture pump for adding the chemical additives

from the admixture tank.

EQUIPMENTS (RMC)

SKIP-BUCKET/CHARGER-

BOX.

CONVEYOR BELTS SCREW CONVEYORS OTHERS

1. 2. 3. 4.

1 Aggregates, Which Make Up Roughly 60% To 75% Of Ready-mix Concrete’s Volume, Are Obtained From Quarries And Aggregate Banks.

AGGREGATES

• GRADING :- Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and maximum aggregate size are specified because these properties affect the amount of aggregate used as well as cement and water requirements, workability, pump ability, and durability of concrete.

• SPECIFIC GRAVITY :- It is the ratio of the mass of a substance to the mass of a reference substance for the same given volume.

• WATER ABSORPTION :- This test helps to determine the water absorption of coarse aggregates as per IS: 2386 (Part III) – 1963.

• MOISTURE CONTENT :- Water content or moisture content is the quantity of water contained in a material.

• ORGANIC IMPURITIES :- The Organic Impurities Test is used to determine the presence of injurious organic compounds in sand to be used in cement mortar or concrete

RAW MATERIAL USED TO PRODUCE CONCRETE

FINE AGG. TEST•GRADING•SPECIFIC GRAVITY •WATER ABSORPTION•MOISTURE CONTENT•ORGANIC IMPURITIES (IS 383 &2386

COARSE AGG. TEST•GRADING•SPECIFIC GRAVITY•WATER ABSORPTION•MOISTURE CONTENT•IMPACT VALUE•CRUSHING VALUE•ABRASION VALUE (IS 383 & 2386

1 Aggregates, Which Make Up Roughly 60% To 75% Of Ready-mix Concrete’s Volume, Are Obtained From Quarries And Aggregate Banks.

AGGREGATES

• IMPACT VALUE :-The aggregate impact value is a measure of resistance to sudden impact or shock, which may differ from its resistance to gradually applied compressive load. PROCEDURE: The test sample consists of aggregates sized 10.0 mm 12.5 mm. Aggregates may be dried by heating at 100-110° C for a period of 4 hours and cooled.

• CRUSHING VALUE :- This test helps to determine the aggregate crushing value of coarse aggregates as per IS: 2386 (Part IV) – 1963. The apparatus used is Cylindrical measure and plunger, Compression testing machine, IS Sieves of sizes – 12.5mm, 10mm and 2.36mm.

• ABRASION VALUE (IS 383 & 2386) :- The test sample and the abrasive charge should be placed in the Los Angles abrasion testing machine and the machine rotated at a speed of 20 to 33 revolutions/minute for 1000 revolutions. At the completion of the test, the material should be discharged and sieved through 1.70mm IS Sieve.

RAW MATERIAL USED TO PRODUCE CONCRETE

FINE AGG. TEST•GRADING•SPECIFIC GRAVITY •WATER ABSORPTION•MOISTURE CONTENT•ORGANIC IMPURITIES (IS 383 &2386

COARSE AGG. TEST•GRADING•SPECIFIC GRAVITY•WATER ABSORPTION•MOISTURE CONTENT•IMPACT VALUE•CRUSHING VALUE•ABRASION VALUE (IS 383 & 2386)

2The Reason Cement Is One Of The Most Common Construction Ingredients

Among Other Is Its Ability To Hold The Structure Together

CEMENT

3 Fly Ash Is Used As A Supplementary Cementitious Material (SCM) In The

Production Of Portland Cement Concrete. A Supplementary Cementitious

Material, when Used In Conjunction With Portland Cement, contributes To

The Properties Of The Hardened Concrete Through Hydraulic Or Pozzolanic

Activity, or Both.(The pozzolanic activity is a measure for the degree of

reaction over time or the reaction rate between a pozzolan and Ca2+ or

Ca(OH)2 in the presence of water.)

The major utilization areas of FLY ASH areas under:

•Manufacture of Portland Pozzolana Cement & Performance improver in

Ordinary Portland Cement(OPC).

•High volume fly ash concrete.

FLY ASHRAW MATERIAL USED TO PRODUCE CONCRETE

4 Additives Are Solid Or Liquid Chemical Substances That Can Be Added To Rmc

Before Or During Preparation. Most Commonly Used Additives Either Improve A

Hardened Concrete’s Durability Or Reduce A Concrete’s Water Content In An

Effort To Shorten Setting Times . EX-CHRYSO PLAST CRX

ADDITIVES/ADMIXTURES

5 The Amount Of Water In Concrete Controls Many Fresh And Hardened

Properties Of Concrete Including Workability, Compressive Strengths,

Permeability And Water tightness, Durability And Weathering, Drying

Shrinkage And Potential For Cracking

WATER

6 A Concrete Mixer Is Often Referred To As A Cement Mixer. The Function Of

A Concrete Mixer Is To Combine Cement With Aggregates Including Sand Or

Gravel, And Water To Form Concrete. The Most Common Type Of Concrete

Mixer Uses A Revolving Drum To Mix The Cement, Aggregates And Water

CONCRETE MIXING

RAW MATERIAL USED TO PRODUCE CONCRETE

MANUFACTURING OF CONCRETESTEP1: IMPLEMENTING THE PRODUCT RECEIVED• Receiving facilities for aggregates make it possible for trucks to unload their goods directly into a hopper (large funnel-like device) which feeds the product through a conveyor belt.

•The cement is delivered by tanker trucks that unload their cargo in silos via pneumatic pipes under compressed air pressure.

STEP 2: STORAGE OF AGGREGATES•Aggregates are stored in silos, in hoppers, or on the ground. The storage of aggregates allows the batch plant to have several days worth of storage.

STEP 3: ADJUVANTS (ADDITIVES)•Admixtures or additives are added at the time of manufacturing to obtain fluidity, and to accelerate or delay setting time…

STEP 4: STORAGE OF CEMENT•Cement is stored in silos equipped with a dust collection venting system. There are as many silos as there are types of cement.

STEP 5: MIXING •The mixer blends the cement, sand, gravel and adjuvants supplied by the PLC (Programmable Logic Controller). A mixer must contain up to 3 m3.

•The time and the quality of the mixing are important factors so as to produce a good product. They are controlled by a programmer.

MANUFACTURING OF CONCRETESTEP 6: CONTROL STATION •The batch plants are all equipped with PLC’s to automate control production. They allow for better selection with rigorous standards, of a formulation adapted to the concrete ordered by clients, and according to the dosage in water corresponding to the hygrometry of aggregates.

•Cement, sand, gravel, water and adjuvants are dosage (measured) and weighed with extreme precision

STEP 7: DELIVERY

•Fresh concrete is brought to the site via mixer-trucks with a capacity of 6 to 8 m3, in which it is generally mixed before delivery to clients. Delivery logistics constitute an essential part of the process because of cement’s setting time which is limited.

SAMPLING AND TESTING OF CONCRETE SLUMP TESTThis is a site test to determine the workability of the ready mixed concrete just before its placing to final position inside the formwork, and is always conducted by the supervisor on site.

1. Ensure the standard Slump Cone and associated equipment are clean before test and free from hardened concrete.2. Wet the Slump Cone and drain away the superfluous water.3. Request the mixer or concrete truck to well mix the concrete for additional 5 minutes.4. Place the Slump Cone on one side ( i.e. not in middle ) of the base plate on leveled ground and stand with feet on the foot-pieces of cone .5. Using a scoop and fill the cone with sampled concrete in 3 equal layers, each of about 100mm thick.6. Compact each layer of concrete in turn exactly 25 times with a Slump Rod, allowing the rod just passes into the underlying layer.7. While tamping the top layer, top up the cone with a slight surcharge of concrete after the tamping operation.8. Level the top by a “sawing and rolling” motion of the Slump Rod across the cone.9. With feet are still firmly on the foot-pieces, wipe the cone and base plate clean and remove any leaked concrete from bottom edge of the Slump Cone.10. Leave the foot-pieces and lift the cone carefully in a vertical up motion in a few seconds time.11. Invert the cone on other side and next to the mound of concrete.12. Lay the Slump Rod across the inverted cone such that it passes above the slumped concrete at its highest point.13. Measure the distance between the underside of rod and the highest point of concrete to the nearest 5mm.14. This reading is the amount that the sampled concrete has slumped.15. If the concrete does not show an acceptable slump, repeat the test with another sample.16. If the repeated test still does not show an acceptable slump, record this fact in the report, or reject that load of concrete.

SLUMP TEST

SAMPLING AND TESTING OF CONCRETECOMPRESSION TESTThe Compression Test is a laboratory test to determine the characteristic strength of the concrete but the making of test cubes is sometimes carried out by the supervisor on site. This cube test result is very important to the acceptance of insitu concrete work since it demonstrates the strength of the design mix.The procedure of making the test cubes is as follows: –1. 150 mm standard cube mold is to be used for concrete mix and 100 mm standard cube mold is to be used for grout mix.2. Arrange adequate numbers of required cube molds to site in respect with the sampling sequence for the proposed pour.3. Make sure the apparatus and associated equipment ( see Fig 7 – 6 ) are clean before test and free from hardened concrete and superfluous water .4. Assemble the cube mold correctly and ensure all nuts are tightened.5. Apply a light coat of proprietary mold oil on the internal faces of the mold.6. Place the mold on level firm ground and fill with sampled concrete to a layer of about 50 mm thick.7. Compact the layer of concrete thoroughly by tamping the whole surface area with the Standard Tamping Bar. (Note that no less than 35 tamps / layer for 150 mm mold and no less than 25 tamps / layer for 100 mm mold).8. Repeat Steps 5 & 6 until the mold is all filled. (Note that 3 layers to be proceeded for 150 mm mold and 2 layers for 100 mm mold).9. Remove the surplus concrete after the mold is fully filled and trowel the top surface flush with the mold.10. Mark the cube surface with an identification number (say simply 1, 2, 3, etc) with a nail or match stick and record these numbers in respect with the concrete truck and location of pour where the sampled concrete is obtained.11. Cover the cube surface with a piece of damp cloth or polythene sheeting and keep the cube in a place free from vibration for about 24 hours to allow initial set .12. Strip off the mold pieces in about 24 hours after the respective pour is cast. Press the concrete surface with the thumb to see any denting to ensure the concrete is sufficiently hardened, or otherwise de-molding has to be delayed for one more day and this occurrence should be stated clearly in the Test Report.13. Mark the test cube a reference number with waterproof felt pen on the molded side, in respect with the previous identification number.14. Place the cube and submerge in a clean water bath or preferably a thermostatically controlled curing tank until it is delivered to the accredited laboratory for testing

SAMPLING AND TESTING OF CONCRETECOMPRESSION TEST

SAMPLING AND TESTING CONCRETE

SAMPLING AND TESTING CONCRETE

THE END