INTRODUCTION OF THE PRODUCT

Cement concrete hollow/solid blocks have an important place in modern building

industry. They are cost effective and better alternative to burnt clay bricks by

virtue of their good durability, fire resistance, partial resistance to sound, thermal

insulation, small dead load and high speed of construction. Concrete hollow/solid

blocks being usually larger in size than the normal clay building bricks and less

mortar is required, faster of construction is achieved.

Also building construction with cement concrete hollow/solid blocks provides

facility for concealing electrical conduit, water and sewer pipes wherever so

desired and requires less plastering.

MARKET & DEMAND ASPECTS

Cement concrete hollow/solid blocks are modern construction materials and as

such are used in all the constructions viz. residential, commercial and industrial

building constructions. Construction industry is a growing a sector. The demand

for this product is always high in all cities and other urban centres due to

construction of residential apartments, commercial buildings and industrial

buildings.

Growing public awareness of the advantages of the product coupled with increase

in the government and financial institutions support for housing which is a basic

human necessity would ensure a healthy growth in the demand.

RAW MATERIALS

Concrete is a mixture of ordinary Portland cement, mineral aggregate (sand and

stone chips) and water. The water used in preparing the concrete serves two

purposes:

(1) It combines with the cement to form a hardened paste

(2) It lubricates the aggregates to form a plastic and workable mass

The water that combines with the cement varies from about 22 to 28% of the total

amount of mixing water in concrete.

Mineral aggregates (sand and stone chips) are normally divided into two fractions

based on their particle size. Aggregate particles passing through the No.4 or 4.7

mm Indian Standard sieve are known as fine aggregate. The particles retained on

this sieve are designated as coarse aggregate. Natural sand is often used as fine

aggregate in cement concrete mixture. Coarse aggregate are crushed stone chips.

Crushed stone chips broken into particle sizes passing through the 4.7 mm sieve

may also be used as fine aggregate. The maximum size of the coarse aggregate that

may be used in cement concrete hollow blocks is 12.5 mm. However, the particle

size of the coarse aggregate should not exceed one third thickness of the thinnest

web of the hollow blocks.

Ordinary Portland cement is the cementing material used in cement concrete

hollow blocks. Cement is the highest priced material per unit weight of the

concrete. Hence, the fine and coarse aggregates are combined in such proportions

that the resulting concrete is workable and has minimum cement content for the

desired quality.

MANUFACTURING PROCESS

The process of manufacture of cement concrete hollow blocks involves the

following 5 stages;

(1) Proportioning

(2) Mixing

(3) Compacting

(4) Curing

(5) Drying

(1) Proportioning:

The determination of suitable amounts of raw materials needed to produce concrete

of desired quality under given conditions of mixing, placing and curing is known

as proportioning. As per Indian Standard specifications, the combined aggregate

content in the concrete mix used for making hollow blocks should not be more

than 6 parts to 1 part by volume of Portland cement. If this ratio is taken in terms

of weight basis this may average approximately at 1:7 (cement : aggregate).

However, there have been instances of employing a lean mix of as high as 1:9 by

manufacturers where hollow blocks are compacted by power operated vibrating

machines. The water cement ratio of 0.62 by weight basis can be used for concrete

hollow blocks.

(2) Mixing

The objective of thorough mixing of aggregates, cement and water is to ensure that

the cement-water paste completely covers the surface of the aggregates. All the

raw materials including water are collected in a concrete mixer, which is rotated

for about 1 minutes. The prepared mix is discharged from the mixer and

consumed within 30 minutes.

(3) Compacting

The purpose of compacting is to fill all air pockets with concrete as a whole

without movement of free water through the concrete. Excessive compaction

would result in formation of water pockets or layers with higher water content and

poor quality of the product.

Semi-automatic vibrating table type machines are widely used for making cement

concrete hollow blocks. The machine consists of an automatic vibrating unit, a

lever operated up and down metallic mould box and a stripper head contained in a

frame work.

Wooden pallet is kept on the vibrating platform of the machine. The mould box is

lowered on to the pallet. Concrete mix is poured into the mould and evenly leveled.

The motorized vibrating causes the concrete to settle down the mould by

approximately 1 to 1 inches. More of concrete is then raked across the mould

level. The stripper head is placed over the mould to bear on the leveled material.

Vibration causes the concrete come down to its limit position. Then the mould box

is lifted by the lever. The moulded hollow blocks resting on the pallet is removed

and a new pallet is placed and the process repeated. The machine can

accommodate interchangeable mould for producing blocks of different sizes of

hollow or solid blocks.

(4) Curing

Hollow blocks removed from the mould are protected until they are sufficiently

hardened to permit handling without damage. This may take about 24 hours in a

shelter away from sun and winds. The hollow blocks thus hardened are cured in a

curing yard to permit complete moisturisation for at least 21 days. When the

hollow blocks are cured by immersing them in a water tank, water should be

changed at least every four days.

The greatest strength benefits occur during the first three days and valuable effects

are secured up to 10 or 14 days. The longer the curing time permitted the better the

product.

(5) Drying

Concrete shrinks slightly with loss of moisture. It is therefore essential that after

curing is over, the blocks should be allowed to dry out gradually in shade so that

the initial drying shrinkage of the blocks is completed before they are used in the

construction work. Hollow blocks are stacked with their cavities horizontal to

facilitate thorough passage of air.

Generally a period of 7 to 15 days of drying will bring the blocks to the desired

degree of dryness to complete their initial shrinkage. After this the blocks are ready

for use in construction work.

Quality measurement:

Casting Platform

The blocks are produced on a smooth, level and hard surface of 30 mm. thick 1:3:6

cement concrete platform simultaneously finished smooth with 1:3 mortar. A base

of brick soling of 12 cm thick lean concrete 1:8:16 may be used as a sub grade.

The platform shall be cast in bays of 2m to avoid random surface-cracks. A

casting platform of about 80 m (10m x 8m preferably) is required for production

of 500 blocks per day.

Mould

A battery of single moulds fabricated with mild steel plate is used to cast the

blocks. Steel moulds yield clean, sharp edged blocks with prefinished faces. It is

advisable to use 8 to 20 moulds arranged in a row with no gap in between to form a

battery. Moulds are provided with handles to facilitate lifting.

Concrete mix

Properly selected, clean ingredients of concrete should be used in appropriate

proportions. Mixing of concrete should be done preferably in a mixer. Basically

two types of mixes are proposed to carter for situations (i) where coarse sand is

available and (ii) where coarse sand is not available. Although it is advisable to do

precise mix design with the available ingredients at a place, the following two

mixes could be followed in general with local modifications.

Release Agents

Before starting and also after completion of the work, the platform and the moulds

are cleaned properly. Lubricating oil is applied inside the moulds and on the area

of platform under the moulds, to act as release agent. This helps in an easy, clean

release of blocks and avoids the breakage of platform. The blocks may also be cast

over alkathene sheet for easy release from the casting floor.

Dimensional Tolerance

Deviation in the block length should not be more than () 5mm, and that in the

height and width of the block should not be more than (3mm) these tolerance

limits can be achieved without any difficulty with the help of steel moulds

fabricated to an accuracy of 3.0mm in length and 1.5mm in height and width.

Masonry Strength using solid blocks:

The wall made of solid concrete masonry blocks is designed like other masonry

wall. The values of basic permissible stresses given in IS: 1905-1980. "Structural

Safety of Building Masonry Wall" hold good for solid concrete masonry blocks

also. (Although the actual values achieved are about 30% higher). Provision of

vertical reinforcement at corners and opening to impart desired protection to the

structure in seismic regions can easily be made by using special blocks with recess.

Masonry Construction of solid blocks:

Mortar Composition

Commonly used 1:6 cement sand mortar is compatible to solid concrete blocks.

However, it is preferable to use 1:2:9 composite mortars if good quality lime is

available. The composite mortar has a quality of autogenous healing of shrinking

cracks. In case the mortar should be such that the minimum flow after suction

should be 60% to 70% of that before suction.

Masonry Bonds

Typical 'T' and 'L' junctions occurring generally in various combinations of wall

thickness are illustrated in figure. Alternate courses are clearly indicated in the

sketches. The figures illustrate two typical wall to pilaster junctions. These also

indicate how bonding for 20cm thick wall with special grooved blocks is provided,

which facilitates introduction of vertical reinforcement at opening and corners,

wherever desired.

Pictures of masonry bond

Advantages of using concrete block:

The solid Concrete Block Masonry has following advantages

1) It is a labour intensive appropriate technique and hence does not call for heavy

capital investment.

2) It is suitable for site oriented production. Thus transportation cost can be

eliminated.

3) Quality control is easy.

4) The wall thickness is reduced to 20 cm for load bearing wall and 10cm for

partition walls. Thereby reducing the cubic contents of the material, obviously

resulting in to saving in substructure as well as superstructure. It also offers larger

floor area for the same plinth area as compared to conventional random rubble

masonry or even non modular brick walling.

5) Internal plaster can be eliminated with proper care during production and laying.

When plastered, the thickness of the plaster required is also lesser as compared to

that in the case of brick wall.

6) Can be produced in remote areas without power supply by using a portable 1

KW generator.

Do's and Don'ts for making concrete blocks:

1) Plan the building to a 10 cm module to avoid cutting of the blocks.

2) Check the accuracy of new moulds before starting the production. Check

accuracy of the angles of the mould every day, before starting the work.

3) Keep strict watch on quality and the proportions of ingredients used in concrete.

4) Modify the mix to suit the local sand and coarse aggregate. Confirm result of the

trial mixes before commencement of the production of blocks. It is a must.

5) Do not forget to use release agent or alkathene sheet on the platform before

casting.

6) Clean the moulds, alkathene sheet and, the production floor as soon as the day's

production is closed.

7) Do not disturb the freshly cast blocks before 24 hrs, in any case.

8) Do temporary stacking near the casting yard on a level ground provided with

sand cushioning. Each day's production is accommodated in not more than 2 tiers.

9) Cure the blocks by sprinkling water for three weeks and then air dry for two to

three weeks depending upon weather conditions.

10) Do not use a partially dry block in masonry.

11) Do not soak the block before using in the masonry. It should be only surface

wet. So, a light water spray, about half an hour an hour before use, is enough.

12) Do not use harsh mortar in masonry.

13) Fill up the vertical joints with extra care.

14) Provide control joints at appropriate locations for wall more than 10 meter

long.

Block Making Machine:

Design Parameters

Compaction of concrete in mould depends on frequency. Amplitude and duration

of vibration, these in turn depend on the conditions of vibrating system comprising

the mould and the concrete to it. For concrete having coarse fraction of aggregate,

a lower frequency of vibration and high amplitude are required whereas for

concrete containing fine fractions, the high frequency with low amplitude is

necessary. Since concrete normally contains particles of varying sites, the most

satisfactory compaction is obtained by using vibrators with different speed of

vibration as in case of poly frequency vibrators. This however, makes the vibrating

system costly. The vibrators used in practice therefore work only at single

frequency suitable for average particle size of the concrete to be compacted. By

using increased frequency of vibration, it is possible to obtain high values of

exciting forces with a much lighter vibrating system, but with increased vibration

frequencies, the resistance of wear of the vibrator is markedly reduced. The most

widely used form of vibrators therefore have vibration frequencies varying from

2800 to 6000 VPM and amplitude of vibrations correspondingly varying from 1.0

to 0.1 mm. Besides frequency and amplitude, the acceleration of vibration is also

an important factor. For external vibration of concrete (as in case of block making

machines in general), the criterion for effective compaction at constant workability

and constant time of vibrations acceleration with the provision that at frequencies

up to 6000 VPM, the acceleration is greater than 1.5 g and at frequencies greater

than 0.04 mm. The available block making machines work at higher side of

frequency range, 6000 VPM and lower amplitudes and are therefore more suitable

for concrete with smaller aggregates. Since the new block making machine was

required to primarily cast the stone blocks and the large aggregate concrete block

wherein lean mixes of concrete with larger size aggregates are involved, a lower

frequency of 3000 VPM and a corresponding higher amplitude of 1.5 mm with an

acceleration of about 7 g were considered desirable in the light of the

recommendations of IS: 4656 1968 Specifications for Form Vibrators for Concrete.

A top pressure of 30 to 100 gm/cm2 has been reported to improve the flow ability

of concrete during vibration and is particularly helpful in handling stiff mixes. A

top pressure of about 50 to 80 gm/cm2 was found effective in case of stone blocks

and large aggregate blocks respectively.

Features

The block making machine comprises a four wheel trolley with front pair of

wheels having steering arrangement and a portal frame which its top carries a

horizontal power shift connected to an electric motor through V belt and pulleys

mould block with a number of mould cavities placed centrally inside the portal

frame. Two vertical power screws, onset each end of the mould block are used to

raise or lower down the mould block. The lower end of the power screw after

passing through the edge of mould block is supported in a bearing which in turn is

supported with the trolley. The top end of power screw is connected with the

aforesaid horizontal power shaft through gears. The arrangement helps in lifting or

lowering down the mould block by motor power. The mould block has a number of

cavities or moulds for castling more than one block at a time. On form vibrator is

rigidly fixed with each opposite face of longer side of the mould block. A bridge

arranged just above the mould block carries as many number pressure platens as

there are mould cavities in the mould block. The pressure platens keep the concrete

pressed in the mould during vibration and later help during ejection of the new

casts blocks from the moulds. The bridge also carries a system which provides

required amount of to pressure through the pressure platens on the concrete in

moulds at the time of the compaction of concrete. The vertical upward movement

of the bridge is achieved through the mould block when the later is lifted up with

the help of two power screws. The connection between the power screws and the

mould block is through two lifting pads each fitted on the edge of opposite shorter

faces of the mould block. The lifting pads have built-in vibration isolating devices

that help in confining the vibrations (during compaction of concrete) only to the

mould block. Salient features of the machine are given in the following:

A portable egg laying type machine.

Six blocks of size 30x20x15 cm case in one operation.

Output of 120 to 150 blocks of above size in one hour.

Better compaction ensured through pressure vibration.

Two vibrators each of 0.5 KW capacity and frequency 3000 VPM used for

consolidation of concrete.

Suitable for casting stone block, large aggregate concrete blocks traditional

concrete block and hollow blocks.

Operator's access right upto the moulds help in easy placement of stone

spalls in casting stone blocks and screeding of concrete in the moulds while

casting large aggregate blocks.

Power required: 3KW

Working and trials

The machine is placed on the casting platform which should be a leveled and well

finished concrete floor. Waste newspapers or polythene sheets are laid on the

platform for easy removal of the block next day. The mould block is first made to

rest on the platform by operating the powers screws. Concrete prepared in a

concrete mixer is received in special trolleys and brought to the block making

machine and dumped in the moulds. Screeding of concrete is done manually to

bring the concrete to the same level in all moulds. The operator then allows the

bridge to drop freely. These results in sudden impact which passes through the

pressure platens on the concrete filled in the moulds. Vibration of concrete is later

carried out by switching vibrators simultaneously. The vibration is maintained till

the full height of the compacted block is achieved. The height of the compacted

block is achieved. The mould block is the lifted up leaving cast concrete blocks on

the platform. During upward moving when mould block completely clears the cast

blocks, the former comes in contact with the bottom face of bridge. From this stage

onwards. the bridges also lifted up along with the mould block resulting in

simultaneous breaking of the contact between all pressure platens and the top face

of the cast blocks. When both the mould block and the bridge are raised to a certain

height, their upward movement is automatically stopped with a limit switch. The

machine is then moved forward on its wheels to a new position of casting while

leaving the newly cast blocks behind on the floor.

Concrete Block Making Machine

Types of Concrete block making machines:

Heavy duty concrete block making machine

The product is used in the construction and civil works. This range of high density

paver blocks are widely used in swimming pools, petrol pumps, parking areas,

courtyards, container yards, road side foot-path. Due to this heavy duty, the blocks

have to be built according to the nature of use. Heavy Duty Paver Block Machine

are developed to bring about looking into this requirement. This machine on an

average can produce 1400 to 1500 nos per day of 8 hrs. The latest model machine

are highly specialized with Total Motor 7.5 HP, 3 Phase 1440 RPM Pressing Load

40 to 50 Ton Cylinder Bore Size 125 mm Hydraulic Oil 120 Ltr. Same size mould

or any different two types mould can be used simultaneously. Any type mould as

per customers specification can be manufactured.

Cover block making machine

Cover Block Making Machine offered by us are widely used in the construction

industry to making high quality cover blocks. In this process highly flowing

pigments with concrete is poured in to the rubber moulds and compacted in vibro forming vibrating tables. The various customized size & thickness with design and

attractive.

Technical Specifications:

Power Consumption: 1.5 HP / single phase

Mixer Muller Machine: 2 hp / single phase

Vibrator cum manual machine

Designed and developed by the professionals using advanced technologies and

quality raw material in adherence with the international standards. The offered

machines are widely used for making blocks that are suitable for construction

purposes.

Features:

Easy operations

Minimum maintenance

Excellent performance

Interlock soil block making machine

Interlock Soil Block Making Machine machines can be availed by the customers in

varied capacities and are widely used at construction sites to reduce the labor cost.

Before the end delivery, these machines are stringently checked by the quality

analyzers on varied parameters to ensure their flawlessness.

Features:

Optimal performance

Compact design

Low power consumption

Precise engineering

Economy in production

It has been observed in the field that the contractors normally employ a gang of

about 20 persons to produce 1000 large aggregate concrete blocks of size

30x20x15 cm in one shift of 8 hours with manual, method of casting. The gang

includes labour for mixing concrete in moulds vibrating the concrete with two

plate vibrators. Demoulding the blocks and preparing moulds for next filling.

Normally the labour cost of production estimated in the manual method at Rs. 0.50

per block. An estimate was also prepared for labour charged for making blocks

with newly developed machine. The operating charges for the machine are Rs.

160.00 per day per shift of eight hours. Considering a production rate of 1000 large

aggregate concrete blocks of size 30x20x15 cm in one shift and using concrete

mixer of 200 liters capacity with Rs. 80.00 per day labour charges the total cost of

labour was estimated at Rs. 0.24 per block which is 50 percent of the labour cost of

manually made blocks. Since in the field the labour charges are about 20 % of the

total cost of a block, the mechanized production of blocks brings in substantial

savings in the labour charges in addition to improving strength and other properties

of the block.

Labour cost per a single block is

Rate of cement per bag(50kg) =Rs 280

Sand or crushed stone per 1 ton = Rs 350

Crushed stone chips per 1 ton =Rs 600

As a single cube size is 30cmx20cmx15cm the volume is 0.009cum per

cube and for M10 (1:3:6) the required mass of

1. cement is 2kg (Rs 5/kg)

2. sand or crushed stone sand is 6kg (Rs 0.35/kg)

3. crushed stone chips is 11 kg (Rs 0.60/kg)

Then the cost of materials per cube is

1) cement = Rs 10

2) sand or crushed stone sand= Rs 2

3) crushed stone chips= Rs 7

---------------------------

Total Rs 19/per block (30cmx20cmx15cm)

Then we can say the total cost of a single block including labour cost &

material cost is Rs 19.24