UNIT-V A presentation ON

CONCRETEING EQUIPMENT & AGGREGATE PROUDCUTION EQUIMENT

ByB.MAHESHBABU

CONCRETING EQUIPMENT Before going to learn about concrete

equipment we have to study the concrete manufacturing steps

All the equipment prominently used in manufacturing process of concrete

Concrete is mixture of cement ,fine aggregate ,and coarse aggregates are in proper portions

A method for producing Portland cement was patented by Joseph Aspdin in 1824.

Reinforced concrete was invented in 1849 by Joseph Monier.

CONCRETE GRADES M-5- 1:5:10

M-7.5 -1:4:8

M-10 - 1:3:6

M-15 - 1:2:4

M-20 - 1:1.5:3

M-25 -1:1:2

M-30 - M-40 - Design Mix Followed

The 'M' denotes 'Mix' followed by a number representing the compressive strength of that mix in N/mm^2. A mix is a specific ratio in which cement, fine(sand) and coarse aggregate(gravel) are mixed.

CONCRETE PRODUCTION STEPS The various stages of manufacture of

concrete are: (a ) Batching (b) Mixing (c ) Transporting (d placing(e) Compacting (f ) Curing (g) Finishing.

BATCHING Batching is the process of measuring

concrete mix ingredients by either mass or volume and introducing them into the mixer .

To produce concrete of uniform quality,

The ingredients must be measured accurately for each batch

VOLUME BATCHING

Volume Batching: Volume batching is not a good method for proportioning the material because of the difficulty it offers to measure granular material in terms of volume.

for any small job, concrete may be batched by volume

This method is generally adopted for small jobs

Gauge boxes are used for measuring the fine and coarse aggregate. •

The volume of gauge box is equal to the volume of one bag of cement.

 Gauge box are also called as FARMAS They can be made of timbers or steel. They

are made generally deep and narrow While filling the gauge boxes the material

should be filled loosely, no compaction is allowed.

Weigh Batching: Weigh batching is the correct method of measuring the materials.

Use of weight system in batching, facilitates accuracy, flexibility and simplicity.

Large weigh batching plants have automatic weighing equipment.

On large work sites, the weigh bucket type of weighing equipment's are used.

Batching by weight is more preferable to volume batching ,as it is more accurate and leads to more uniform proportioning.

It does not have uncertainties associated with bulking. It’s equipment falls into 2 general categories :

I. Semi automatic, II. Fully automatic.

In case of semi automatic batching the aggregate bin gates are opened by manually operated switches . And gates are closed automatically when the material has been delivered. This system also contains interlock which prevents charging and discharging

FULLY AUTOMATIC

In case of automatic batching the material are electrically activates by a single switch and complete autographic record are made of the weight of each material.

The batching plant comprises 2,3,4 or 6 compartment bins of several capacities.

Over the conveyer belt the weigh batchers discharging are provided below the bins

MIXING The mixing should be ensure that the mass

becomes Homogeneous , uniform in colour and consistency .

Methods of Mixing : 1.Hands(using hand shovels) 2.Stationary Mixers 3.Ready mix concrete

HAND MIXING

HAND MIXING Mixing ingredients of concrete by hands

using ordinary tools like, hand shovels etc. This type of mixing is done for Less output of

concrete.

CONCRETE MIXERS (STATIONARY) Concrete mixers are two types Free fall mixers Power mixers

Again free fall are two types and power mixers also

Concrete is sometime mixed at jobsite in a stationary mixer having a size of 9 cubic meter

FREE FALL MIXERS Free fall mixing is suitable for the concrete with 2-inch minimum

slump and are not too hard

This type of mixers are used at site of construction

The drum of freefall mixer can be filled and emptied by changing the direction of rotation

There are two major type namely

TILTING MIXER

REVERSIBLE MIXER

TILTING MIXER

TILTING MIXER A concrete mixer  is a device that

homogeneously combines cement, aggregate such as sand or gravel, and water to form concrete

It was invented by Gebhardt Jaeger

A typical concrete mixer uses a revolving drum to mix the components.

For smaller volume works portable concrete mixers are often used so that the concrete can be made at the construction site, giving the workers ample time to use the concrete before it hardens

An alternative to a machine is mixing concrete by hand. This is usually done in a wheelbarrow; however, several companies have recently begun to sell modified tarps for this purpose.

Major parts are wheel and axes ,Drum(9 cu.m approx) ,engine, tilting hooper

Engine maybe powered by electric, diesel

Usually, the material is loaded manually into the drum from ground level and the Hooper dumps the material tilting up mechanically

REVERSIBLE MIXERS

In reversible mixer, The drum has one horizontal axis, around which the drum rotates

There are two openings to the drum, one for loading the material and other for discharging

Usually self loading Self operation Large size unit compared to traditional mixer Major parts, wheel barrow, tilting hopper, self

and loaders ( bucket) Electric operated and diesel operated

POWER MIXERS Pan mixer

POWER MIXERS Pan mixer is a type of mixer which has a

fixed pan or removable tub with a vertical mixer unit in it as opposed to a typical cement mixer which has a horizontal rotating barrel with fixed beaters.

A mixer  filled through an opening at its top; for concrete, usually a pan or drum within which mixing blades revolve about the vertical axis; 

for mortar, usually a trough within which mixing paddles revolve about the horizontal axis.

Some concrete batching plants use a large pan mixer to pre mix the concrete before it is loaded into mixer trucks(Transit mixer in USA) to be delivered to site.

British company Liner  introduced the first  Pan Mixer design in 1924

major parts are rotating drum and paddles and cap

These electrically operated

FACTORS EFFECTING THE OUTPUT OF MIXERS Rotating speed of mixer Capacity of mixer Including mixing time loading and unloading time Operation time

READY MIXED CONCRETE Ready mixed concrete is proportioned and

mixed off at the project site and is delivered to the construction area in a freshly mixed and unhardened state. It can be manufactured by any of the following methods:

1.Central-mixed concrete 2.Truck-mixed concrete

CENTRAL MIXED CONCRETE Central-mixed concrete : mixed completely

in a stationary mixer delivered in Agitator Trucks A non-agitating truck

AGITATOR TRUCKS A vehicle carrying a drum or agitator body, in

which freshly mixed concrete can be conveyed from the point of mixing to that of placing, the drum being rotated continuously to agitate the contents.

Advantages: Operate usually from central mixing plants

Watch for: Timing of deliveries should suit job organization. Concrete crew and equipment must be ready onsite to handle concrete.

Used for: Transporting concrete for all uses. Haul distances must allow discharge of concrete within 1½ hours.

NON AGITATING TRUCK

NON-AGITATING TRUCKS Used for: Transport concrete on short

hauls(small distance) over smooth roadways. Advantages: Cost of non-agitating

equipment is lower than that of truck agitators or mixers.

Watch for: Slump should be limited. Possibility of segregation

TRUCK MIXED

TRUCK-MIXED CONCRETE Used for: Intermittent (periodic) production

of concrete at jobsite, or small quantities. Advantages: Combined materials transporter and batching

and mixing system. One-man operation

1) Mortar Pan : Concrete is carried in small Quantities

 2) Wheelbarrows and Buggies : Short flat hauls on all types of onsite concrete construction

3) Belt Conveyors : Conveying concrete horizontally or higher/lower level.

4) Cranes and Buckets : Used forWork above ground level , Buckets use with Cranes, cableways,

5) Pumps : Conveying concrete from central discharge point to formwork.

6) Transit Mixer : used for transporting the concrete over long distance particularly in RMC plant .

MORTAR PAN

WHEEL BORROW

CONVEOYRS

CABLES AND CRANES

TRANSIT MIXER

COMPACTION OF CONCRETE  Compaction of concrete is process adopted

for expelling the entrapped air from the concrete

In the process of mixing , transporting and placing of concrete air is likely to get entrapped in the concrete .

It has been found from the experimental studies that 1% air in the concrete approximately reduces the strength by 6%.

If we don’t expel this air, it will result into honeycombing and reduced strength

Different Methods Of Concrete Compaction 1) Hand Compaction Roding,

Ramming ,Tamping 2) Compaction by Vibration

HAND COMPACTION Hand compaction is used for ordinary and unimportant

structures. Workability should be decided in such a way that the chances of honeycombing should be minimum. The various methods of hand compaction are as given below

Roding It is a method of poking with 2m long, 16 mm dia. rod at sharp corners and edges. The thickness of layers for rodding should be 15 to 20 cm.

Ramming • It is generally used for compaction on ground in plain concrete. It is not used either in RCC or on upper floors.

Tamping • It is a method in which the top surface is beaten by wooden cross beam of cross section 10 cm x 10 cm. both compaction and leveling are achieved simultaneously. It is mainly used for roof slabs and road pavements.

RODING

RAMMING

TAMPING

VIBRATION Vibration is imparted to the concrete by

mechanical means. It causes temporary liquefaction so that air bubbles come on to the top and expelled ultimately. Mechanical vibration can be of various types as given under.

Internal Vibration It is most commonly used technique of concrete vibration.

We follow different methods in vibration External Vibration Table Vibration

CURING Curing is the process in which

the concrete is protected from loss of moisture and kept within a reasonable temperature range. The result of this process is increased strength and decreased permeability. Curing is also a key player in mitigating cracks in the concrete, which severely impacts durability.

CURING BY GUNNY BAGS

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