JMC Projects (I) Ltd.

CHAPTER ILINE-OUT OF THE STRUCTURE

Line-out is the first activity involved in constructing any type of civil structure in a project. It is to be done very carefully and accurately. Location of a single structure with respect to the total project is so important that if it is not done accurately then it shall have an effect on all other structure and other works, such as roads, storm water drains, lighting etc.

Instruments & tools required for line-out

1. Theodolite

2. Leveling Instruments

3. Steel tape

4. Ranging rods

5. Wooden pegs, wire nails, kg hammer

6. line Dori

7. Total Station

Accuracy of the Instruments

Theodolite and leveling instruments shall be calibrated by an approved Agency before start of every project. If they are calibrated for the previous project, they are to be again calibrated before the start of the next project.

Procedure

Normally, permanent bench mark and coordinates are available on projects like refinery, fertilizers, and petrochemicals and such like project on all Irrigation and hydro-electric project. This preliminary survey is done by Public works departments and contractor has to carry out survey for their works from these established points.

However, if they are not available (for smaller projects) then convenient base line is established for the location of the structures. Location of all structures shall be with reference to the base line. Similarly arbitrary bench is established in one of the corners of the plot at safe place so that it does not get disturbed by the movement of the workers and vehicle. Pillars are constructed for the base line and bench mark and the point for the base line and BM are established on the top of the pillar with very good finishing on the top of its surface. Area of the pillars shall be sufficiently large so that coordinates and BM can be written over it with paint.

Coordinates of the various structures are shown in the layout drawing of the project. From the permanent established bench mark, temporary bench mark is established nearer to the particular part of the project at a convenient place so that it is not needed to transfer the bench mark for establishing the different levels for the particular structure. Similarly temporary coordinates are also established .Care is to be taken in establishing those temporary points so that they are marked accurately without any error.

Establishing the centre line pegs for particular structure

Following is the typical example.

Centre line pegs are established at a convenient distance from the edge of the excavation line so that they are not disturbed while doing excavation. (Refer below sketch).Sketch showing wooden peg with wire nails with approximate size and length.

Pegs are driven in the ground to the extent they are not getting movement by hand. After driving the pegs center line is established on the peg as shown in the sketch and 1 long wire nails is fixed over it keeping above the top of the peg so that while checking line dori can be tied in between two such pegs. Alternate pegs shall be checked diagonally by calculating the diagonal by Pythagoras theorem.Every stage of works such as checking the excavation, marking the area of PCC, checking the shuttering for footing, marking the location of column over the footing already cast, checking of centre line by hanging the plumb bob from the crossing of the line dori as shown in the below sketch shall be carried out.

CHAPTER IIEARTH WORK

2.1 Basic knowledge of the trade:

The Earth work is a preliminary activity which involves large quantum of work as compared to the other activities in construction projects. The earthwork can be divided into the following main categories.

1. Excavation

2. Embankment.3. Back filling

4. Filling.5. Area Grading These are the major categories of earthwork.

Excavation: This is mainly required to rest the foundation of structure to reach to a level where required bearing capacity is available. Man excavation is required for reservoirs swimming pool etc.Embankment: Raising the ground to reach the required level such as for railways, roads, earthen dam etc. Level is being raised by filling earth with slopes varying from 1:1 to 1:2.

Backfilling: Filling the gap by earth between the line of excavation and line of foundation is known as backfilling .Suppose a pipeline of water supply is laid at about 1.5m from ground then first excavation is done , then line is laid there after the trench is filled by earth is known as backfilling.Filling: Normally building floor level is kept at about 500mm to 600mm above the surrounding ground level then depth between the ground level and floor level is filled by earth is known as filling.

Area-Grading: The plot where the building or factory is to be constructed is having ups and down at ground level. Secondly the plot is also required to be kept at a little higher level than the surrounding areas and a nominal slope is also required to be given so that rain water or spillage in the foundation can be easily drained out. This is called area grading where if the level is higher at a particular location than the required level then it has to be excavated and if any depression is there it is required to be filled up by earth.The knowledge about this activity particularly from the execution point of view is essential for synchronizing other activities to follow.

The excavation work is carried out in soils and rock. The planning for the excavation of this activity in a particular area depends on the following factors:

1. Type of soil / Rock

2. Depth of excavation

3. Quantum of work

4. Sub-soil Water table.

The correct analysis and interpretation of these factors coupled with proper resource planning and method of working will provide the desired output.2.2 Soil Classification:The classification of soils based on density and texture for execution purpose is as under:

Light

-(less than 1.44 g/cm3) muck, and humus.

Medium

- (1.44 g/cm3 to 1.6 g/cm3) loose sand, silty sand, silt etc.

Heavy

- (above 1.6 g/cm3) clay, clayey silt, dense sand etc.

The material to be excavated shall be classified as follows unless otherwise specified:

Soft/Loose Soil - Generally any soil which yields to the ordinary application of picks and shovel, or to phawra, rake or other ordinary digging implement; such as vegetable or organic soil, turf, gravel, sand, silt, loom, clay peat, etc

Hard/Dense Soil Generally any soil which requires the close application of picks, or jumpers or scrifiers to loosen; such a stiff clay, gravel and cobblestone.

Mud A mixture of soil and water in fluid or weak solid state.

The type of soil can be identified by visual inspection and laboratory test results.2.3 Field Method for soil identification:

Take a small soil sample

Place it on your palm

Add few drops of water

Mix it thoroughly and rub it between fingers.Observations:

Sandy soil Gritty sensation and non sticky, if squeezed in hand when dry will fall apart when pressure is released

Silty soil Some residual colour due to partial sticking of soil and less gritty sensation can be rolled into threads between fingers but crumbles when it dries.

Clayey soil No gritty sensation, soft and sticky.2.4 Rock classification:

1. Soft Rock Hard murrum, Kankar, disintegrated rock, sand stones

Soft rock can be excavated with less effort using pickaxe and crowbar etc.

2. Hard Rock

Rock not requiring blasting (NRB)

Rock requiring blasting (HRB)

3. Hard rock (NRB) is generally weathered, disintegrated, laminated rocks. Necessary precautions should be taken while excavating to avoid sliding and collapse. The excavation in such rock can be done either manually or using hydraulic excavator

4. The rock which cannot be excavated by above means fall in the category of HRB

The excavation in such rocks is in the following sequence:

1. Drilling

2. Loading with explosive material (like gelatin ,gun powder) and detonators (ED & OD)

3. Blasting

4. Removal of muck using hydraulic excavation / tipper combinations

Table: Safe bearing capacity of soils & Rock:Sr. No.Soil type Safe bearing capacity in tons / sqm

1Very soft, wet pasty clay0 to 5

2Black cotton soil4 to 10

3Red soil / Yellow soil10 to 20

4Loose gravel15 to 25

5Murrum25 to 45

6Soft rock40 to 90

7Hard rock >90

2.5 Material required

Lime, Shoring material, blasting material.2.6 Tools

Pick axe, spade, ghamelas, crow bar, chisels, hammers, line dori, and template2.7 Machinery and Equipments:

For Heavy Earth work (up to 40,000 m3 per month target)1. Hydraulic excavator with suitable bucket capacity

2. Tippers / Dumpers

3. Dozers capacity / model D-180. D-80, D-50

4. Water tankers

5. Vibratory rollers

a. Smooth wheel rollers

b. Sheep foot rollers

For medium Earth work (up to 10,000 m3 per month target)

1. Hydraulic excavation with 0.5 cum & 0.3 cum bucket capacity

2. Tippers / dumpers

3. Dozers capacity / model D-50

4. Water tankers

5. Road rollers 8 to 10 tone capacity

For Light Earth work (up to 5000 m3 per month target)

1. JCB excavator / loader or manual

2. Tractor with hydraulic tipping trolley3. Light rollers up to 3 MT capacity / Earth compactors/rammer2.8 Labour planning:

Depending upon the quantum of work and types of machineries available, the site incharge should judge and employ labour force so as to complete the task in scheduled time.

In excavation work labour requirement is governed by the following factors:

1. Type of soil and nature of work

2. Dewatering requirement

3. Quantum of work to be executed per day

4. Labour working capacity

5. Available working space required for each excavation labourRecord of work done per day and the resources engaged for the work shall be recorded and shall be compared with the derived work per day as per the work schedule and efforts shall be made to get the derived progress. One has to analyze and found out how to improve upon if derived progress is not being achieved.Table: The norms for Labour output:ItemUnitAvg. output/Day (Eight hours shift)

Excavation in soft soil

cum0.81

cum 0.65

cum 0.49

Excavation in hard soil

cum 0.38

Excavation in soft rock

cum 0.24

cum 0.21

Excavation in hard rockcum 0.20

Flow Chart for Resource Planning

2.9 Method of excavation.

Method of excavation depends upon the type of soil and quantum of excavation involved. Type of soil can be divided in the following groups.

Group I (Very soft soil, Black cotton soil, Red/yellow soil, loose gravel, Murrum)

Soil as per group I can be excavated manually by pick axe and spade or by mechanical device- mass excavation such as excavation for underground water tanks, swimming pool, then now days it is being excavated by engaging hydraulic Excavator with suitable bucket size of 0.5 m3 & 0.9 m3. 0.5 m3 bucket can do 300 to 400 m3 per day and excavation with 0.9 m3 per day can do 600 to 800 m3 per day. When the earth is to be dumped by the sides of excavation no casting arrangement are required just as excavation for pipe line but when the earth is required to be casted at a specific distance then tippers/dumpers are required . Number of Tippers or dumpers shall depend upon the distance to be casted. Small excavation for column footings or trench for wall foundation etc can be excavated by excavators.

Black cotton soil

This is grayish black in colour with a clay contents with unreliable quality, swells when wet and shrinks when dry. Wide cracks are developed when dry and termed as poor soil for foundation. Hence the depth foundation has to go beyond the depth of black cotton soil by about 300 mm when it interacts with yellow soil having bearing capacity of at least 10 to 15 ton/m2 . Such type of soil is available beyond karjan and toward south in Gujarat.

Excavation in black cotton soil is to be done carefully because of its properties as explained above. Proper slope in excavation is to be given and a berm of about 300 mm to be given when the depth of the soil is more than 1.5m. If this slope is not properly maintained lumps of soil may collapse. In such cases shoring & strutting is required to be done as shown in the figure.Existing Ground level

1.5 m300 mm 1.5 m

1.5 m

300 mm 4.5 m

600 mm

2.0 m

Formation Level

Sketch showing excavation details for RCC retaining wall for a depth of 4.5m below ground level.Group II (Soft Rock)

Excavation in soft rock may be done by excavators and some times by pavement breakers which are operated by pneumatic air through compressors.Group III (Hard Rock)

When the rock is hard enough and is not coming out by pavement breakers then series of holes are drilled in rock with jack hammers which are operated by pneumatic air and then holes are loaded with dynamite (gelatin) and electric detonators. To have this blasting procedure effective rock face is developed by removing over burden of murrum & soft rock, so that hard rock is fully exposed.

Layer of Soft Rock

Holes drilled for blasting

Hard Rock

Face has to open

From one side

Cut holes

Easer

Drilling Pattern

Holes are to be drilled to form a wedge which will make easier to blast effectively which will give more output with less explosive. Explosive is the costliest operation in rock cutting. Site-Engineer by his experience can develop the drilling pattern in such a way that with minimum consumption of explosive maximum output shall be obtained with 32 mm drill rod. Holes are drilled by jack hammer then gelatins along with detonators are inserted in the hole. All detonators wires are joined in series and then wires are taken out at a safer distance and then connected with exploder which on by charging manually explodes and rock is blasted to pieces. About 100 Rmt is the radius of this blasted zone. Utmost care is required to be observed so that the blasted pieces dos not hit any human being and the other materials lying

near by are not damaged. Warning by whistling is given in advance and red cloth is provided if any road is crossing the area. Traffic is not allowed to pass through till the whole blasting operation is completed. Formerly this was being done by using gunpowder & fuse coil. By using gelatin & electric detonators blasting operation has become safe

2.10 Work operations:

2.10.1 Excavation

1. Check the gridline and dimensions of the trench/foundation with the drawing provide allowance for working space as per requirement. Dont allow to disturb the pit during excavation2. Take proper care to check R.L. of bottom of pit / foundation grade3. Ensure removal care of all loose earth, roots of plants / trees etc.4. Check the dimensions at bottom of foundation pit before proceeding to the next activity5. Provide sufficient working space for workman when work is to be executed from outside. Maximum 600mm working space is sufficient for shuttering of R.C.C. walls basement, UGT, waterproofing etc. For more excavation depths, adequate side slope / berms must be considered to retain the sides. Get this extra working space requirements approved by site engineer for payment purpose

6. Take care to dump the excavation earth away from the edge of excavation or to suit the site requirements.

7. Proper barricading, shoring, shuttering must be provided for safety where ever required8. Ensure technical safety, by maintaining proper slope of cut depending upon the soil characteristics9. Any kind of water flooding near the pit is to be avoidedMass and Deep Excavation like Basement. For Basement, swimming pool etc. Strata is not the only criteria for deciding the depth of excavation, the formation level plays the important role and leads to mass or deep excavation

This type excavation needs special attention

1. The Quantity being large, more than one gang can be engaged for the job.

2. Allocation of work to different gangs should be such that maximum output in minimum time is achieved.

3. Levels should be taken prior to and after the completion of work for billing purpose.4. If the excavation goes below the ground water table, adequate arrangement should be done to pump out the water.

5. For lifting out the excavated material either ramps or steps should be provided at the time of excavation only.6. One corner pit is excavated for further more depth than require, to collect all the water at one place only.7. De-watering pump required in such cases is of higher capacity with long suction and delivery hose pipes, as shifting from place to place is not possible .Excavation by well point method where very heavy flow of subsoil water occurs.

Water table Bore Formation Level

If the excavation depth is below the ground water table and seepage water is not controlled by the dewatering pump then this method is adopted. Here bore or bores are drilled outside the excavation area and below the formation level. Screen Riser

Jet Point

Elevation

SectionA well point is a perforated pipe about 1m long and 5 cm in diameter. A jetting nozzle is provided at its lower end. The spacing of the well points depends upon the type of soil and depth of water, generally it varies between 1 to 3 m.Well points are generally installed by jetting. Water is pumped through the riser pipe in downward direction. As it discharges through the nozzle, it displaces the soil below the tip till required penetration is achieved. Pumping is started after well points have been installed. Well points are suitable for lowering the water table by 5 to 6 m in soils.

Riser PipeValve

Header

Clay

Water table

Sand

Well Point

2.10.2 Earth Filling Under Floor & In Plinth.From Sources within the Site.1. The earth for filling shall be free from salts, organic or any other foreign materials, roots, grass, rubbish and oil.

2. Lumps and clods exceeded 80 mm in size shall be broken. Each layer shall be 300 mm thick or as directed by Project Manager. Breaking of clods and watering shall be done along with ramming and consolidation.3. The consolidated earth filling within the plinth, which has been leveled and sloped shall be dressed to about 25 mm lower than the required finished earth level and thoroughly soaked with water for about 24 hours. While still wet, surplus or discarded building materials, available at site of work like cinders, gravel, stone or brick ballast , set cement or cement concrete , etc all broken into pieces not exceeding 40 mm shall be spread on the fill and rammed well till a uniform surface at required level is obtained.

4. The surface of the finally finished area shall be neatly dressed with a thin layer of clean sand to fill up the depressions and hollows, keeping in view the slopes required.

5. The work shall be taken up after the building has reached up to the plinth level or up to the floor level, as the case may be. The space between the walls shall be first filled in with the earth in layers and consolidated with an iron rammer. Filling in basement, over the raft foundation shall also be included under this item. The measurement shall be for depths after consolidation. The earth, as approved, shall first be obtained from the directly excavated earth of the foundations of from a source within a 30 meters lead. If the leads are more than 30 m, extra payment shall be made. Whereas the available earth is black cotton soil, the same should not be used as a filling unless permitted by the project Manager. Sand, gravel or cinder if specified shall be used, and shall be measured and paid separately. The slopes shall be kept as required.Earth Brought From Outside1. If the earth has to be brought from outside the job site, the rate shall include the purchase cost of the earth, its carting from the outside source to site, octroi, levy, royalty or any other form of tax (es) as per prevailing rules, loading, unloading, screening as necessary, and filling and/or spreading in 300 mm thick layers or as directed by project Manager and watering, ramming and/or consolidating. 2. The measurement shall be for depths after consolidation. If the original levels of the area to be filled are uneven, the depth between the top or the filled up and consolidated earth and the average original level shall be used for the volume calculations.3. If the floors as specified are to be provided with proper slopes, as directed, for easy and quick disposal of water the required slopes shall be provided for fully in the plinth earth filling or in the sand filling itself. It shall be the full responsibility of the agencies to ensure that this has done before concreting of the floor. If slight adjustments of slopes are required to be done, the same shall be allowed in the floor concrete but at the agencies cost. This shall mean that the thickness of the floor concrete shall be measured and paid for a uniform thickness or as directed, without any consideration to increased thickness, if provided by the agency for adjustment of slopes. Filling Flow chart

2.11 Provision of Transport to take away excess soil1. Estimate the excavated stuff to be re-utilized in filling, gardening, preparing roads, etc.2. As far as possible try to carry excavation and filling simultaneously to avoid double handling.

3. Select and stack the required material in such a place that it should not obstruct other construction activities.

4. The excess or unwanted material should immediately be carried away and disposed off by employing any of the following methods.

Department labour Tractor

Trucks2.12 Preparation of embankment:

1. The surface should be thoroughly stripped off vegetation, bushes, shrubs etc and thoroughly cleaned, scarified and watered before starting the new filling / embankment work

2. The earth is excavated using hydraulic excavation from the defined source outside the working area or within the working area having usable earth for disposal

3. The excavated earth is directly loaded in the dumpers/tippers and transported to the disposal point. The dumping of earth should be done systematically to avoid formation of large heaps and should be distributed within the area so as to have the specified thickness of layer when spread over by the dozers

4. The spreading of earth will be followed by using suitable capacity to get the earth layer of required thickness. For mass earth work layer thickness up to 500mm is allowed in IS and reduces the layer thickness up to 150mm for smaller works

5. The uniformly leveled earth layers will then be adequately sprinkled with water to obtain Optimum Moisture Content.

6. This would then be followed by compacting the earth layer by using suitable compactors / rollers to achieve the desired Maximum Dry Density normally 95% dry density needs to be achieved by proper consolidation procedures

7. The number of passes by the rollers may be decided by trial and error in the initial stage of work.

8. The edges of the earth for each layer has to be at least 200mm to 300mm more on either side than the required width at that level. This is required so that the edge of the wheel of the roller can go up to the edge of the required width for that level. After the final level is reached edges are required to be dressed to get the correct slope.

Extra Width

Theoretical line

2.13 Dewatering:In some cases during excavation, subsoil water is encountered at intermediate stage of excavation due to the depth of water table being higher than the required depth of excavation

In such conditions the inflow and outflow of water is to be balanced in order to have proper conditions conducive to excavation activities. The percolation of water while excavation depends on two factors:

Permeability of soil

Hydraulic gradient

So, above factors must be considered to calculate the quantity of water coming out per minute. Discharge can also be estimated using field method of estimating.Following points should be attended, while dewatering:

1. Select the pump of adequate capacity (Suction and delivery)

2. Provide suction and delivery pipes as specified

3. Check the availability of fuel or electricity

4. Provide gate valves for proper control

5. Provide a suction pit at suitable location so that water inflow is diverted to the small pit where suction is planned. This can give dry surface for excavation work

6. Check the working of foot valve. Clean it before use

7. Cover the foot valve with chicken mesh as a filter media

8. Install the pump on proper foundation

9. Check the electric connection and earthling10. Do not run the pump dry

11. Priming should be done if needed

2.14 Safety:1. Proper barricading should be provided around the excavated pit and caution sign/boards should be placed reflecting the on going activity2. Proper access should be provided by means of ladder / steps in cutting in deep excavation work3. Proper grading should be provided according to the soil condition e.g.: In cohesive soil steep slope can be allowed whereas noncohesive soils requires relatively flat slope or even berms4. Adequate berms should be provided in case of expansive dis-integratable soil.5. Proper shoring and strutting should be provided in case of sandy soil or water inflow is observed.6. Helmets should be provided to labours working. 7. Sufficient lighting arrangement should be made to carry out work at night.8. Adequate measures to be taken to see that the excavation operations do not damage the adjoining structures or dislocate the services like water supply pipes, sluice valves, chambers, sewage pipes, manholes, drainage pipes & chambers, communication cables, power supply cables etc. met within the course of excavation , shall be properly supported and adequately protected , so that these services remain functional.

9. Excavation shall not be carried out below the foundation level of the adjacent buildings until underpinning shoring etc. is done.

10. Blasting work: For the safety of persons red flags shall be prominently displayed around the area where blasting operations are to be carried out. All the workers at site, except those who actually ignite the fuse, shall withdraw to a safe distance of at least 200 meters from the blasting site. Audio warning by blowing whistle shall be given before igniting the fuse. Blasting shall not be within 200 metes of an existing structure, unless specifically permitted.Check points before / during / after Excavation:

1. Is excavation area checked against?

a. Any under ground cabling?

b. Any under ground piping?

c. Any under ground gas line or plumbing line or sewage?2. Is excavation checked for?

a. Slope / step cut / shoring?b. Approach / stair way?c. Safe barricading?d. Disposal and stacking method?3. Are mobile equipments checked for? a. Competent operator with valid license?

b. Light horns, back lights, reverse horn, brakes etc.?c. Properly maintained and fit for use?

4. In case of dewatering pump, is it checked for?

a. Proper earthing mechanism?

b. Safe connections/ improper joints / Improper splice cable / switches etc.

5. Is proper lighting arrangement done in case of night work or darkness?

6. Are proper PPE being used by the workers?

7. For Blasting operation :

a. Is license obtained from the competent authority for undertaking blasting work as well as for containing and storing the explosives as per the latest Explosive Act Rules 1983?b. Are Explosives, Fuses, and Detonators etc. are purchased from licensed dealer.

c. Transportation & storage of explosive at site shall confirm to the Explosive Act & Explosive rules. Fuses & detonators shall be stored separately and away from Explosives

Termite Proofing Destroy termites before they destroy your house.

Introduction

Termite Control of buildings is very important as the damage likely to be caused by the termite is huge. Wood is one of the cellulosic materials which termite damage, cellulose forming their basic nutrient. They also damage materials of organic origin with a cellulose base, household articles like furniture, furnishings, clothings, stationery, etc. Termites are also known to damage non-cellulosic substances in their search of food. Rubber, leather, plastics, neoprene, as well as lead coating used for covering of underground cables are damaged by termites. The widespread damage by termites, high constructional cost of buildings have necessitated evolving suitable measures for preventing access of termites to building.

Chemicals and rate of Application

Basic Principle: Chemicals toxic to subterranean termites may be used effectively to check termite infestation in the soil. These are useful in the treatment of new building sites and may also be used to eradicate existing infestation in buildings and to prevent reinfestation. The effectiveness and/or residual activity depend upon the choices of the chemicals, the dosage adopted and the thoroughness of application. The chemical solutions or emulsions are required to be dispersed uniformly in the soil and of the required strength so as to form an effective chemical barrier which is lethal and repellent to termites.

Mound Treatment: If termite mounds are found within the plinth area of the buildings these should be destroyed by means of insecticides in the form of water suspensions or emulsions which should be poured into the mounds at several places after breaking open the earthen structure and making holes with crow-bars. The quantity to be used will depend upon the size of the mound. For a mound volume of about 1 m3 , 4 litres of an emulsion in water of one of the following may be used.

a. 0.25 percent aldrin.b. 0.25 percent heptachlor.

c. 0.5 percent chlordane.

Soil TreatmentTreating the soil beneath the building and around the foundations with a soil insecticide is a preventive measure. The purpose of the treatment is to create a chemical barrier between the ground from where termites come and woodwork or other cellulosic materials in the building. Any one of the following chemicals conforming to relevant Indian Standards in water emulsion is effective when applied uniformly over the area to be treated.

Sr.NoChemicalsRelevant Indian StandardsConcentration by Weight,%

1Aldrin emulsifiable

concentrateIS : 1307-19880.5

2Heptachlor emulsifiable

ConcentrateIS : 6439-19780.5

3Chlordane emulsifiable

concentrateIS : 2682 - 19841

Time of Application: Soil treatment should starts when foundation trenches and pits are ready to take mass concrete in foundations. Laying of mass concrete should start when the chemical emulsion has been absorbed by the soil and the surface is quite dry . Treatment should not be carried out when it is raining or when the soil is wet with rain or subsoil water. The foregoing requirement applies also in the case of treatment to be filled earth surface within the plinth area before laying the sub grade for the floor. Once formed, treated soil barriers shall not be disturbed. If, by chance, treated soil barriers are disturbed, immediate steps shall be taken to restore the continuity and completeness of the barrier system.

Site preparationThe removal of trees, stumps, logs or roots from a building site reduces the hazards from subterranean termites. Similarly, the sub floor area should be kept free from all debris in which new colonies of termite might be established. In order to ensure uniform distribution of the treating solution and to assist penetration, some site preparation may be necessary.

Heavy soils and sloping sites: On clays and other heavy soils where penetration is likely to be slow and on sloping sites where run off of the treating solution is likely to occur , the surface of the soils should be scarified to a depth of at least 75 mm.Sandy or porous soils: On loose, sandy or porous soils where loss of treating solution through piping or excessive percolation is likely to occur, preliminary moistening to fill the capillary spaces in the soils is recommended.

Leveling, Excavation and filling: All sub floor leveling and grading should be completed ; all cuttings, trenches and excavation should be completed with backfilling in place; borrowed fill must be free from organic debris and should be well compacted. If this is not done supplementary treatments should be made to complete the barrier.

Concrete formwork:

All concrete formwork, leveling pegs, timber off cuts and other builders debris should be removed from the area to be treated.

Treatment for R.C.C Foundations and basement

1. Any one of the chemical emulsion described above shall be applied uniformly at the prescribed rate in all the stages of the treatment. A suitable hand operated compressed air sprayer or watering can should be used to facilitate uniform dispersal of the chemical emulsion. On Large jobs, a power sprayer may be used to save labour and time.2. In the event of water logging of foundation, the water shall be pumped out and the chemical emulsion applied when the soil is absorbent.

3. In the case of R.C.C. Foundations, the concrete is dense, the termite are unable to penetrate it. It is therefore unnecessary to start the treatment from the bottom of excavations.4. The treatment shall start at a depth of 500 mm below the ground level except when such ground level is raised or lowered by filling or cutting after the foundations have been cast.

5. In cases, the depth of 500 mm shall be determined from the new soil level resulting from the filling or cutting mentioned above, and soil in immediate contact with the vertical surfaces of R.C.C foundations shall be treated at the rate of 7.5 lit/sq.m. The top surface of the consolidated earth within plinth wall shall be treated with chemical emulsion at the rate of 5 litres /sq.m of the surface before the sand bed or sub grade is laid.

6. If the filled earth has been well rammed and the surface does not allow the emulsion to seep through, holes up to 50 to 75 mm deep at 150 mm centers both ways may be made with 12 mm diameter mild steel rod on the surface to facilitate saturation of the soil with the chemical emulsion.

2.15 Mode of Measurements (for detail refer SP 27 -1987)Unless otherwise stated, hereinafter all the work shall be measured net in decimal system, as fixed.

1. Each dimension shall be measured to the nearest 0.0 1m, where any dimension is more than 25 m it should be measured to the nearest 0.1 m.

2. Areas shall be worked out to the nearest 0.01 m2.and

3. Cubical contents shall be worked out to the nearest 0.01m3

4.The measurement of earthwork shall be done in cubic meters, unless otherwise mentioned. The measurements to be taken shall be those of the authorized dimensions from which soil has been taken out and shall be measured without allowance for increase in bulk.

5. Lead The distance for removal shall be measured over the shortest practicable route and not necessarily the route actually taken. Distance not exceeding 250 m shall be measured in units of 50 m. Distance exceeding 250 m and not exceeding 500m shall be measured as a separate item.6.Lift - Lift shall be measured from ground level. Excavation up to 1.5 m depth below ground level and depositing excavated material on the ground shall be included in the item of earthwork for various kinds of soil. Extra lift shall be measured in unit of 1.5 m or part thereof. Obvious lift shall only be measured; that is lifts inherent in the lead due to ground slope shall not be measured except for lead up to 250 m.Water Rating Chart

Out Put in Liters of water per minute

Speed 2880 RPM

NoKW / HP of motorSize Sucsiom x Delivery in mm Total Head in meters from all causes

81012.51517.52022.52527.53032.53537.54042.54547.5

12.2/362x50700670615550450340

22.2/375x62960940810650400300

32.2/362x62910860775650510250

43.7/575x62108010401000990875755550

53.7/562x62825810775680540325

63.7/562x50925850600450300225

75.5/7.575x62105010451020930810650350

85.5/7.575x751275123010601030880650

95.5/7.562x50900895870785670470

107.5/1075x62128010651025850575150

117.5/1075x751300128512051085725

127.5/1062x5011501050950885830770720610

132.2/362x50760700660600550460370230

Speed 1440 RPM

143.7/562x621260123011651030900660410

153.7/575x62138012501115930675

165.5/7.5100x75177016801560144012601080810

175.5/7.5100x100179017001580146012801100830

187.5/10100x75230021752000184016001175

197.5/10100x100234022002040186016201200

Conversation Factor : 1 gallon 4.54 liters. 1 meter 3.28 feets

CHAPTER III

CONCRETING

3.1 Brief knowledge of the trade:Concreting is one of the most important activities in the construction activities, hence utmost care is required to get good quality of concreting. The quantum of concreting depends on the size of work but the quality does not depend on the size of work. Everybody expects good quality of concreting even for a small work. For economy and good quality, Design Mix should be used instead of Ordinary mix i.e. volumetric mix. Aggregate size and grading plays a major role for good and homogeneous concrete. Concrete is the most widely used man made construction material in the world and is adopted in the construction works like:-

a) Industrialb) Bridges

c) Dams

d) Canal Lining

e) High rise Buildings

f) Public Building Hospitals, Town-halls, Hotel, educational institutes,g) Underground and overhead water Tanks

h) Road

i) Beautiful And Artistic Buildings

It shall therefore be realized that how much is the importance of this trade in Civil Engineering. Design Engineers has to design the structure economical as well as good enough to take all the loads necessary for which the structure is to utilize. It is to be design as per the locally available materials.

Concrete as a product made out of cement, coarse aggregates, fine aggregates and water. Product can be moulded to any shape as per the requirement of designer / architect. With addition of reinforcement to supply needed tensile strength, it has become the foremost structural material. Fine aggregate (sand) is filled up in the voids of coarse aggregates, held together by a hardened paste of hydraulic cement and water upon hydration of the cement by the water, concrete becomes stone like in strength and hardness with utility for much purpose as explained earlier. With different proportions of binding material (cement) we get a desired strength of concrete.

3.2 Standard of consumables:Cement, coarse aggregates, fine aggregates, water, admixtures

3.2.1 Cement:

Cement is a well known building material and has occupied an indispensable place in Construction Industries. The function of cement is first to bind the sand and coarse aggregates together, and second to fill the voids in between sand and coarse aggregate particles to form a compact mass. There are different types of cement to be used under certain conditions due to its special properties. Followings are some of the special cements.

1. Portland cement For massive construction

2. Sulphate Resistance Cement For use in sulphate soils and water

3. Pozzolona cement Introduction of Pozzolonic materials to reduce cost

4. Rapid Hardening cement

Good Qualities of cement 1. The colour should be uniform.

2. Cement should be uniform when touched. Cement should be cool when felt with hand. If a small quantity of cement is thrown into a bucket of water, it should sink.

3. Cement should be free from lumps.

4. Cement mortar at the edge of three days should have a compressive strength of 11.5 N/mm2 and tensile strength of 2 N/mm2. Also, at the age of seven days compressive strength should not be less than 17.5 N/mm2 and tensile strength should not be less than 2.5 N/mm2.

5. When ignited, cement should not loose more than 4 percent of its weight.

6. The weight of insoluble residue in cement should not be grater than 1.5 percent.

7. The specific surface of cement as found from the fineness test should not be less than 2250 mm2/gm 8. The initial setting time of cement should not be less than 30 minutes and the final setting time shall be around 10 hours.

9. The expansion of cement should not be greater than 10 mm when soundness test is conducted.

Precaution in storage of cement.1. Use cement of approved quality as per specification and ensure that it is fresh and not older than 90 days.2. Cement must arrive rite from the production Unit in the shortest time with minimum numbers of handling.3. Store cement bags in a completely water proof go down, free from moisture content.

4. Issue & consumption of cement bags shall be on First come & first go basis.5. In case cement bags are required to be stored in open as a temporary requirement, ensure that they are stacked on a dry platform made of wooden planks or railway sleepers resting on a brick masonry / concrete / dry sand / aggregate platform about 150 mm above the ground. The number of bags must be just sufficient for days consumption.6. Stacking of cement bags should not touch the wall of the godown.7. A godown has to be leak proof. During monsoon moisture enters the go downs then heater shall be provided .Ensure that entire stack is covered by tarpaulin or polythene sheet, with an adequate overlap. This procedure is to be adopted during cloudy or rainy season.8. Gangways shall be provided horizontally and vertically in between the stacks of cement.

3.2.2 Aggregates (Coarse aggregate & Fine aggregate):

The size of the aggregate used in concrete range from few centimeters or more down to a few microns. According to size the aggregate is classified as fine aggregate & Coarse Aggregate.Definition:

Fine Aggregate Aggregate most of which passes through 4.75 mm IS sieve and contains only that much coarser materials as is permitted by the specification.Sand is generally considered to have a lower size limit of about 0.07 mm. Material below 0.06 is classified as silt and still smaller particles are called clay. The fine aggregate may be one of the following types.1. Natural sand Fine aggregate resulting from the natural disintegration of rock and which has been deposited by streams or glacial agencies.

2. Crushed stone sand Fine aggregate produced by crushing hard stone

3. Crushed Gravel sand Fine aggregate produced by crushing natural gravel.

Coarse Aggregate Aggregate most of which is retained on 4.75 mm IS sieve.

The coarse aggregate may be one of the following types.1. Stones are being quarried and are crushed to much smaller sizes and screened to sort out different sizes as 63mm, 40 mm, 12mm etc2. At Places different sizes of gravel ranging from 75 mm to 125 mm or even some times 160 mm are available on the bank of river. Here crushers are installed very near to bank of river. Gravels are transported to crusher from the bank of a river and are being crushed to have smaller size as 63 mm, 40 mm, 12mm etc. Here one operation of quarrying is eliminated and subsequently quarrying cost is reduced.

3. Gravels of much smaller size are available on the bank of a river. Hence screens are installed on the bank of a river, and available gravels are screened to have coarser aggregates of various sizes as 63mm, 40 mm, 12mm etc. Here two operation of quarrying and crushing are eliminated and the coarse aggregate cost is further reduced..

All-in-Aggregates Material composed of fine aggregate and coarse aggregate.

Good Qualities of Aggregate

1. Aggregates shall comply with the requirement of IS 383. As far as possible preference shall be given to natural aggregate.

2. Use aggregates which have been tested and approved by Q.C. labs

3. Aggregate shall consist of naturally occurring (crushed or uncrushed) stones, gravel and sand or combination thereof.

4. Aggregate should be chemically inert , hard , strong, dense, durable of limited porosity, clear and free-from veins and adherent coating ; and free from injurious amounts of disintegrated pieces, alkali, vegetable matter and other deleterious substance. As far as possible, flaky, scoriaceous and elongated pieces should be avoided.

5. It should contain no organic or other admixtures that may cause corrosion of the reinforcement on impair the strength or durability of the concrete. Refer IS 383.

Size of Aggregate

1. Size of the coarse aggregate shall be 20 mm and below, well graded for concrete which normally we come across. This means that size of the aggregate shall pass through 20 mm x 20 mm sieve (screen). i.e. Sizes shall be from 20 mm to 4.75 mm. the proportion of different sizes ranging from 20 mm to 4.75 mm shall be uniform i.e. well graded. Here suppose particles below 12.5 mm are not available in required proportion, grit is being added in such conditions, to till up the voids below 12.5mm. This can be decided by performing sieve analysis. Suppose grit I not added then voids shall be filled up by (sand) and cement and as such not only consumption of sand and cement shall be on higher side. And concrete produced shall not be that compact as produced by adding grit.2. The nominal maximum size of coarse aggregate should be as large as possible within the limits specified but in no case greater than one-fourth of the minimum thickness of the member, provided that the concrete can be placed without difficulty so as to surround all reinforcement thoroughly and fill the corners of the form. In concrete elements with thin sections, closely spaced reinforcement or small cover, consideration should be given to the use of 10 mm nominal maximum size.3. For heavily reinforced concrete members as in the case of ribs of main beams, the nominal maximum size of the aggregate should usually be restricted to 5 mm less than the minimum clear distance between the main bars or 5 mm less than the minimum cover to the reinforcement whichever is smaller.

4. Coarse and fine aggregate shall be batched separately .All-in-aggregate may be used only where specifically permitted by the engineer-in-charge.5. Adequate quantity of aggregate is required before start of work

6. Necessary correction for bulking of sand to be done on day to day basis.Shape of Aggregate

The particle shape of an aggregate is generally classified as rounded, irregular, angular, or flaky. Experience indicates that angular aggregate do not produce as smooth and workable a mixture as materials having more rounded and smooth particles grading and other conditions being similar. The sharp angular fragments of crushed rock required more sand and more cement to produce workable concrete, where coarser grading can be used with gravels with consequent decrease in mortan requirement

Uniform Size more Voids Various size less voids3.2.3 Water:

1. Ensure that potable water for construction is available.2. Water used for mixing and curing shall be clean and free from injurious amount of oils, alkali, salts, sugar, organic materials, or other substances that may be deleterious to concrete or steel.3. In case of doubt regarding development of strength, the suitability of water for making concrete shall be ascertained by the compressive strength and initial setting time of cement.

4. The sample of water taken for testing shall represent the water proposed to be used for concreting, due account being paid to seasonal variation. The sample shall not receive any treatment before testing other than that envisaged in the regular supply of water proposed for use in concrete. The sample shall be stored in clean container previously rinsed out with similar water.

5. Average 28 days compressive strength of at least three 150 mm concrete cubes prepared with water proposed to be used shall not be less than 90 percent of the average of strength of three similar concrete cubes prepared with distilled water. The cubes shall be prepared, cured and tested in accordance with the requirement of IS 516.6. The PH value of water shall be not less than 6.

7. Water found satisfactory for mixing is also suitable for curing concrete. However, water used for curing should not produce any objectionable stain or unsightly deposit on the concrete surface. The presence of Tannic acid or iron compound is objectionable.

3.3 Basic Tools required for Concreting:

Concrete mixer machine (min. 3nos of blades and 15 to 20 rpm.) weigh-batchers, measurement box (30 cm x 30 cm x 38 cm), Vibrators, Needles, Electric Pump motor set, Cube moulds, Slump cones Shovels, Ghamellas, Gumboots, Hand gloves, Buckets, halogens, Hand lamps, garden hose pipes, barrels, D.G. Set if required, etc.

3.4 Work Procedure:3.4.1 Batching:1. Do not overload a batch.2. Carry out batching of materials by weight. If it is required to batch materials on volumetric basis, make use of measurement boxes in units of 0.035 m3 equivalents to 50 kg cement bag. Weight to volume can be worked out suitable boxes can be made for doing the volumetric batching.

3. Batching of cement must be done by weight considering 50 kg per bag.4. Exact measured quantity of water to be added to the batch as per w/c ratio.5. Apply necessary correction for bulkage of aggregate.6. Carry routine checks of weights as well as sensitivity of balance.7. Addition of admixtures Ensure addition of recommended admixtures in specified proportion.3.4.2 Mixing:a) Hand Mixing

This method of mixing concrete manually is almost not adopted now a day except for small buildings where quantum of work is of very small magnitude such as casting of lintels, coping etc. There may be occasions when the concrete has to be mixed manually. Particular care and efforts are necessary as in this case uniformity is more difficult to achieve. Aggregate should be spread in uniform layer on a hard and clean surface. Cement is then spread over this surface of aggregates and the dry materials are mixed by turning over from one end of the heap to another and cutting with a shovel until the mix appears uniform the water is gradually added and the mix is turned over until homogeneous mixture and consistency is obtained generally extra cement of 10% of the volume is added here to overcome the difficulties in mixing as recommended by I.Sb) Mixing by mixer Machine

Different capacities of mixers are available one bag mixer, two bags mixers, four bags mixers. Capacity of a mixer to be deployed on the project depending upon the quantum of works at a time and on frequency of such quantum. Concrete mixers are either diesel driven or electrical driven.

Ingredients that is cement and aggregates either measured by volume or weight (depending upon the mix design) are placed in hopper and thereafter it will go to mixing drum here required quantity of water is added and the mixtures rotates in the drum which has got the blades for mixing. Drum is continuously rotating and mixture is taken out from the drum by tilting the drum. Mixture is allowed to rotate for about one and a half to two minutes @ 15 to 20 RPMPrecautionary measures to be taken to take care of mixer machine.

1. Machine should be properly leveled by giving supports from the firm ground by providing wooden logs of size 10 x 5 in such a way that wheels of the machines remains free from the ground so that load in either empty condition or loaded condition is not transferred to ground through the wheel.

2. Hopper and drum should be absolutely clean i.e. free from dry set mortar.

3. Check fuel and engine oil before the start of the concrete.

4. See that proper grees is applied to the gear of the drum and to the wire rope of the

hopper.

5. Provide sand bags on the ground where the hopper is resting on the ground for

loading the aggregates and cement.

6. Provide experienced driver.

7. After concreting is completed wash the mixing drum in such a way that inner surface of drum and the blades for mixing are free from coating of mortar.

8. See that there is no dry mortar left in the hopper after concreting is completed.

9. When mixer machine is used check for rpm of mixer, number of blades inside the drum, discharge chute and hopper, breaks and tilting of drum.

10. Get the mixer machine checked by the machine once in a week.

This is very important and the Site Engineer has to see that the persons deployed by the management to perform above duties are following. This shall definitely reduce the maintenance cost and sudden break down of machine during concreting, ultimately helping in achieving time schedule.

3.4.3 Handling transporting and placing in position of concrete. Through carelessness or ignorance in manufacturing and placement of concrete, fails to give the services that can be expected. It is the responsibility of those in charge of construction work to make sure that concrete is of uniformly good quality. The extra effort and care required to achieve these objectives are small relation to the benefits. Good engineering dictates acceptance of only the best when the best is procurable at no greater cost. Understanding of the basic principles of making good concrete is to be provided during construction practice.

Initial setting time of concrete is 30 minutes. Mix therefore should be placed at the placing points within this period. Placing point may be either in horizontal direction at the ground level or in vertical direction. Proper and leveled walkway shall be provided for the labours to walk safely to avoid slipping. Incase of vertical directions platforms at different levels shall be provided for easy lifting and transporting of Ghamelas. Appropriate safety measures shall be provided to labours so that they are very much comfortable. Site engineer should see that accident does not take place. Mix shall be placed in such a manner that segregation of the mix does not take place. Experience worker at placing point will place the mix properly from Ghamelas. Requirements to be fulfilled during transporting and placing concrete in position:

a) No segregation or separation of materials

b) Concrete delivered at the points of placing should be uniform and of proper consistency

If the distance of placing point is far from the mixer, transportation of concrete shall be by following methods.

a) Wheel barrows and handcart.

b) Tippers and lorries

c) Truck mixers and agitators lorries Transit mixer

d) Conveyer belts

When the concrete is to be placed much below the general ground level a wooden or steel chute may be used for chuting the concrete to level and then placing in position manually.

If the vertical height is more than 5 meters transportation shall be by using hoist.

Method of placing concrete in its final position has an important effect on its homogeneity. The same which has been used to secure homogeneity in mixing and the avoidance of segregation in transporting must be exercised for placing also.

To secure good concrete it is necessary to make certain preparation before placing

a) Forms (work) must be examined for correct alignment and adequate rigidity to withstand the weight of concrete, impact loads.

b) Forms must be checked for tightness to avoid loss of mortar which may result in honey combing.

c) Forms from inside shall be cleaned and treated with a release agent to facilitate their removal when the concrete is set.

d) Any coating of hardened mortar on the forms should be removed. Coating of the mortar of previous poured concrete on reinforcement shall be removed and rods to be exposed clean to get proper bond between reinforcement and concrete.e) The reinforcement should be checked for proper binding with binding wire so that it does not get displaced while pouring concrete. It should be free from rusting, oil etc.

f) Reinforcement should be checked weather it is provided as per detail engineering drawing

g) Reinforcement should also be checked for proper cover as per drawings.

h) Please check that proper lap length is provided.

i) The surface of the previously poured concrete shall be cleaned and mortar layer shall be provided over it before pouring the fresh concrete.

j) Concrete in walls of thinner section and beam of larger depths, concrete shall be provided in layers

3.4.4 Compaction and consolidation

The objective in consolidating concrete is the elimination of voids within concrete. Well consolidated concrete is satisfactorily free of rock pockets and bubbles of entrapped air and it is in close contact with form work, reinforcement, and other embedded parts such as insert plates, pipe sleeves etc. Accomplishment of this objective is easier if segregation and slump loss are avoided during transportation and deposition of concrete.

The presence of 5 % voids in hardened concrete left due to incomplete compaction may result in a decrease in compressive strength by about 35 %.Compaction is achieved by using vibrators. The principal advantage of vibratory compaction is that it allows the use of stiff mixes. In addition, the vibratory compaction of concrete has following advantages.

a) The concrete produced is more impermeable and dense.

b) Bond between steel and concrete is improved.

c) Shrinkage and creep are reduced.,

d) An increase in the speed of placing is possible by the ready flow of vibrated concrete into difficult position.

e) A better finish is imparted to the surface of the concrete.

f) Vibrators are petrol driven, electrical driven or pneumatically driven. They are immersion type or form vibrators.

Immersion type vibrators- needle of 25 mm, 40 mm or 60 mm is coupled through flexible shaft and when the machine is operated needle vibrates. Vibrators are being operated at an oscillation frequency of at least 7000 vibrations per minute when immerse in the concrete. Window is also provided in the shuttering at particular place/height to immerse needle of the vibrator of the section & height to be concreted is not accessible from the top. Vibrators should be inserted vertically at points 450 mm to 600 mm apart and slowly withdrawn.

In shallow concrete needle has to be sloping on horizontal positions. Vibration period of 5 to 15 seconds for each penetration are usually sufficient. Systematic spacing of the points at vibrators should be established to ensure that no portions of the concrete are missed.

Steps to ensure good results from vibration of concrete

a) All forms to be as tight as possible to avoid leakage of mortar and consequent honey combing. Form to be rigidly braced to prevent displacement resulting in bulging g of concrete.

b) Vibration must be carefully controlled.

c) In order to avoid air being trapped, the lift of concrete should be as shallow as practicable. Damage of trapping air increases with depth, and a 60 cm layer is the maximum advisable.

d) The vibrator should be used only to aid compaction. It should never be used to push concrete laterally in the forms as this may lead to segregation

e) The vibrator should be allowed to penetrate of its own weight and should be withdrawn quite slowly.

f) The vibrator should be immersed through the entire depth of freshly deposited concrete and into the layer below, if this is still plastic or can be brought again into a plastic condition. In this manner a plane of weakness at the joint between the two layers can be avoided and monolithic concrete can be obtained.

g) The vibrator should be used not less than 10 cm to the form surface in order to obtain uniform appearance.

h) Please see that no over vibration is done when over vibrations occurs, the surface concrete not only appears very wet, but it actually consists of a layer of mortar containing practically no coarse aggregate.

Please mind that efforts to avoid over vibrations often results inadequate vibrations.

3.4.5 Finishing:Finishing is carried out after a little stiffening of concrete has occurred with suitable tools

Provide green cut immediately after finishing a particular layer of concrete by using wire brush and small brooms and clean it thoroughly. In case of preceding concrete surface being old, chipping must be done with 10-15mm depth and should be thoroughly cleaned using air or water jets before placing the subsequent layer of concrete. Cold joints can be formed with cement slurry spraying or with cement slurry spraying or with bonding agent

3.4.6 Removal of form work

From the point of view of curing and the protection of concrete at early ages it is advantageous to leave forms in place as long as possible. Under normal circumstances where temperatures are above 20oC and ordinary Portland cement is used forms may be struck after expiring of the following periods:

a) Vertical sides of slabs, beams, columns and walls

24 to 48 hours

b) Slabs (props left under)

3 days

c) Beam soffits (props left under)

7 days

d) Bottom of slabs to a span of 4.5 meters

7 days

e) Bottom of slabs above 4.6 meter span

14 days

f) Bottom of beams up to 6.0

21 days

With rapid-hardening cement, three-sevenths of the above period will suffice except for the vertical sides of the slabs beams and columns for which the forms should be retained for at least 24 hours.

3.4.7 Curing

The purpose of curing is twofold. Firstly, it is required to prevent or replenish the loss of water which is essential for the purpose of hydration for hardening. Secondly it prevents the exposure of the concrete to a hot atmosphere and to drying winds which would lead to a quick drying out of moisture in the concrete and subject it to contraction stresses at a stage when the concrete would not be strong enough to resist them. Loss of water by evaporation from the surface affects hydration to proceed in the interim members. Therefore curing of water is highly desirable.

Methods of curing.

a) Application of water directly to the concrete or by means of continuously saturated covering with a layer of soaking Hessian materials.

b) By Ponding water

c) Membrane curing in which proprietary compounds are sprayed to form an impervious film on the surface of concrete or where the concrete is covered with polyethylene sheet or water proof paper.

d) Surface application of calcium chloride which not only absorbs moisture from the atmosphere but also prevents the evaporation of a part of the mixing water.

Period of CuringAs per IS 456: 2000 concrete to be cured for at least 7 days. This requirement applies to ordinary Portland cement and if rapid hardening cement is used the period may be reducing to half. With low heat cement this curing period should be extended to 21 days.

1. The permeability of surface layers increases five to tenfold when curing is inadequate or interrupted

2. Curing sensitivity of concrete increases with water cement ratio.3. Blended cement with high % of replacement of cement ( more than 50 % slag, 15 % fly ash or 8 % silica fumes) hardened slowly initially but gains strength later on .Such cement require greater care in curing than OPC. However when properly cured, blended cement results in concrete of lower permeability and better protection cover against chloride penetration than OPC. Concrete is like baby in its early days as it is very delicate. Curing helps to protect the concrete and also help in developing a strong surface.As hydration of cement proceeds (assuming that water is supplied as necessary) gel development reduces the size of the voids and there by generally increases the water tightness of the concrete. For this reason prolonged and thorough curing is significant factor in securing impermeable water tight concrete.

3.4.8 Cover:Keep various thickness cover blocks ready as per the requirement of the structural drawings well in advance. Use proper mould and mortar mix for casting the cover blocks of various thicknesses with a two legged binding wire. Cover blocks needs to be strong enough so that it is not crushed after placing

3.5. Testing for Concreting

The most common test for hardened concrete is the compressive strength, at particular period of time, from the time of casting the concrete cubes. The concrete strength is generally specified by compressive strengths and the structural design is worked out on that basis.

It is very important for the Engineers and Technicians to obtain accurate results of compressive strengths of concrete. Compressive strength over the period of time also indicates the extent of Quality control being exercised at site.

a) Parameter Affecting Compression Strength

It is extremely important to know the significance of the various parameters that can lead to low compression strength of concrete or result in failure minimum specified strength.

The most significant parameters are as under.

i) Cement

Chemical Composition

Fineness of cement

Variation in compressive strengths of concrete can also occur to a considerable extent if the supply of cement is received from different brands or from different production units of the same brand. Therefore cement shall be obtained from the same sources.

ii) Water

Water cement (W / C) ratio by weight plays a VERY significant role in concrete strength and DURABILITY Lower the ratio higher is the strength and durability. Slight variation in W / C can cause considerable reduction in strength and very significant reduction in durability.

iii) Cement Storage & Transportation

To be stored in such a manner it does not come in contact with moisture or water.

Stack of cement should not touch the wall of godown.

Stack of cement should not directly rest on the floor. Wooden planks resting on wooden sizes to be provided below the stack of cement.

Godown has to be leak- proof. During monsoon if moisture enters the godown then heater shall be provided

Cement must arrive at site from the production unit in the shortest possible time with minimum numbers of handling.

Gang-ways to be provided in between the stacks of cement .

iv) Cement Packing

Packing Material should not be very porous.

v) Aggregate

Size of the aggregate

-Larger the maximum aggregate size lesser is

the cement pastes required

Shape of the aggregate-Rounded aggregate have lesser surface area

than crushed cubical aggregate. Aggregate should not be flaky. Grading of Aggregate

-Presence of finer fines causes increase in

Surface area.

Porosity - Porous aggregate may crush when compressive loads are applied before the failure in the mortar bond between the aggregate can occur.

vi) Workability

vii) Transportation & Placement

viii) Compaction

ix) Curing

b) Sampling

Samples from which the test specimens are moulded be representative of the concrete entering the structure. Following points must be considered.

i) Samples must be taken at random to ensure that each concrete batch shall have a reasonable chance of being tested. Sampling should be spread aver the entire period of concreting. Each sample shall contain 3 Nos. of cubes to be tested for 28 days or of 6 Nos. of cubes if 7 days test are required to be tested.

ii) Frequency

The minimum frequency of sampling of concrete of each grade as recommended by IS 456 2000 shall be in accordance with the following.

Quality of concrete

Number of Set

In the work cum.

Of samples

1 to 5

1

6 to 15

2

16 to 30

3

31 to 50

4

51 and above 4 plus one additional sample for each addition 50 cum. Or parts

iii) Cube mould for Test Samples are either made up from steel or C.I. They are in three parts. Two halves which constitutes the vertical sides of cube and base plate. Two halves are bolted and then fixed on the base plates by clamping inside face of these units must be planed and machine finished to high degree of accuracy.

iv) Cubes as cast, most commonly have sides 15 cm each the standard cylinder specimen is 15 cm in diameter and 30 cm in height.

v) Mould to be filled in 3 layers of about 5 cm and its top leveled off with a trowel.

vi) Compaction by hand is carried out by tamping each layer with a rod. The number of strokes to be applied to each layer shall 35 for 15 cm size cube mould.

Vibratory compaction is also carried out with either electric of pneumatic hammer.

vii) The tamping rod shall be of MS rod of 16 mm dia. 60 cm long with bullet nosed end.

viii) After finishing, the concrete cube mould should be immediately covered with damp Hessian cloth & transferred to room where relative humidity is 90% and temperature is 27+ 2oC.

ix) Coding / marking / identification This shall be given on the surface of the cube so that sample can be easily correlated to the concrete mix, casting date.

x) Strip the mould after 16 to 24 hours gently without damaging the edges of surface or

xi) Submerge the specimen in the curing tank containing clean water till such time it is due for testing.

xii) At least three cubes of the same batch be tested at a time and average of test results be considered for the compressive strength. Individual test results should not vary by + 15% from the average. If more, the test results on the sample are invalid as per IS 456-2000

3.6. Grade of Concrete

The concrete shall be in grades designated as under as per IS 456. Specified characteristics.

Grade Designation N/mm2 Specified Characteristic compressive strength at 28 days

M 1010

M1515

M2020

M2525

M3030

M3535

M4040

1 M refers to mix and number the characteristic compressive strength of 15 cm cube at 28 days expressed in N/mm2

2. M5 and M7.5 grade of concrete used for lean concrete bases and simple foundations for masonry wall. These mixes need not to be designed.

3. Grade of concrete lower than M20 shall not be used in reinforced concrete.

3.7. Workability

IS 6461 (Part VII)-1973 defines workability as that property of freshly mixed concrete or mortar which determines the ease and homogeneity with which it can be mixed , placed , compacted & finished

Workability has been defined as the ease, with which a given set of materials can be mixed into concrete and subsequently handled, transported and placed in position with minimum loss of Homogeneity. The importance of plasticity and uniformity are emphasized because these essentials to workability and appreance of finished structure.

Workability is dependent on the proportions of the ingredient materials. The degree of workability required for proper placement and consolidation of concrete is governed by the dimensions and shape of the structure and by the spacing of reinforcement.

Consistency or fluidity of concrete is as important component of workability and can be measured with reasonable accuracy by means of the slump test. The slump of mass concrete is usually restricted to maximum of 2 inches. If concrete cannot be placed without exceeding specified slump limitations then it may be concluded that the mix proportions are in need of adjustments. The minimum slump that can be used, commensurate with desired workability requires the least amount of cement and water.

The use of entrained air has minimized the effect of harshness in a concrete. It reduces bleedings and segregation and facilitates the placing and handling of concrete reduced bleeding permits finishing of concrete surfaces earlier and usually with less work. Each percent of entrained air permits with some improvement in workability and with no loss of slump. Workability can be enhanced by adding admixtures.

Concrete Admixtures Plasticizers

There are essential forms of ingredients in concrete i.e coarse aggregate, fine aggregate, cement and water. However, to improve certain properties of concrete both in plastic and bonded state, it is necessary to add the fifth ingredient in the cement mix. This fifth ingredient can be a chemical admixture.

There are several types of admixtures but the most popular and most often used one is the plasticizer.

Plasticizers is also called water reducing admixtures and are classified as follows:

c) Ordinary water reducing plasticizers which enable upto 15 percent of water reduction.

d) High range water reducing super plasticizers which enable upto 30 percent of water reduction. Some plasticizers also cause air entrainment in concrete. Plasticizers are generally used to achieve the following

In fresh concrete:

a) Increase workability and/or pump ability without increasing the water / cement ratio.

b) To improve cohesiveness and thereby reducing segregation or bleeding

c) Improve to some extent set retardation.

In hardened concrete

a) Increase strength by reducing the water / cement ratio, maintaining the same workability

b) reduce permeability and improve durability by reducing the water cement ratio

c) Reduce heat of hydration and drying shrinkage by reducing cement content.

3.8 Durability

Since prevention is better than cure, sufficient attention should be paid at the design stage (structural as well as architectural), and ensure high quality construction by adopting good engineering concreting practices. There is no substitute for well compacted, dense concrete of adequate strength in order to ensure durable structure with long service life.A durable concrete is one which will withstand in satisfactory degree, the efforts of service conditions to which it will be subjected such as weathering chemical action and wear.

a) Weathering Resistance

Disintegration of concrete by weathering is caused mainly by the disruptive action of freezing thawing and by expansion and contraction under restraint .Concrete can be made that will have excellent resistance to the efforts of such exposures if careful attention is given to the selection of materials and to all other phases of job control. The entrainment of small bubbles of air has helped to improve concrete. Provision is made for adequate drainage of exposed concrete surfaces. Freezing and thawing is affected by water tightness because the free water within the pores by capillary action inflow under pressure on the extent to which the pores have been filled with water at the time each freezing occurs. The more watertight the concrete the more difficult for water to gain entrance and to fill the voids.

b) Resistance to chemical deterioration

Concrete deterioration attributable in whole or in part to chemical reactions between alkalis in the cement and mineral constitutes of concrete aggregate is characterised by the following observable conditions.

3.8.1 Cracking, usually of random pattern on a fairly large scale.

3.8.2 Excessive internal and overall expansion.

3.8.3 Cracks that may be very large at the concreting surface

3.8.4 Gelatinous exudations and whitish amorphous deposits both on the surface and within the surface and within the mass of concrete, especially in the voids and adjacent to some affected pieces of aggregates.

3.8.5 Peripheral zones of reactivity, alternations or in-filtration in the aggregate particles opal and certain types of acid and intermediates volcanic rocks.

3.8.6 Lifeless chalky appreances of the freshly concrete.

Durability of concrete depends on its resistance to deterioration and environment in which it is placed. The resistance of concrete to weathering chemical attacks, abrasion, fire, frost and depends largely upon the quality and constituent materials. Susceptibility of corrosion of the steel is governed by the COVER provided and the permeability of concrete. The cube crushing strength alone is not a reliable guide to the quality and durability of concrete. It must also have adequate cement content and low water cement ratio. One of the main characteristic influencing the durability of any concrete is its permeability.

To achieve suitably low permeability of concrete following factors are required to be taken high care.

a) strong dense aggregates

b) Low water cement ratio

c) Ensure thorough compaction of the concrete

d) Ensuring sufficient hydration of cement through proper curing methods

e) Adequate workability.

c) Resistance to erosion

The principal causes of erosion of concrete are

i) Movement of abrasive materials by flowing water ( Example: Dams, Bridges Piers & Abutment)ii) attrition friction (Traffic on concrete surface, Industrial floor , Bridge Deck)iii) Impact of traffic

iv) Wind blasting

v) Impact of floating ice and cavitations

Cavitations is one of the most destructive of these causes and use to which concrete offers very little resistance regardless of its quality

High velocity flow on obstruction abrupt change in surface alignment.

Zone of sever sub atmospheric pressure shall be formed against the surface

This zone is promptly filled with turbulent water.

Cavitations may occur in clear water flowing at high velocities when divulgence between the natural path and the surface of the channel or conduit is too abrupt or when there is an abrupt projections or depression on the surface if the channel may occur due to poor formwork or inferior finishing at the concrete cavitations may occur on horizontal or sloping surfaces over which water flows or on vertical surface part which water flows.

Here critical areas are sometime protected by facing with metal or other appropriate materials which have better resistance to cavitations than concrete.

Use of concrete of increased strength and wear resistance offers some relief against the forces of erosion brought by movement of abrasive materials by flowing water, attrition and impact of traffic, sandblasting and impact of floating ice.

Example IPS with Ionite, steel linging where velocity of water and head is very high, proper design, construction and operation of the concrete structure.

Recommendations for Durability of concrete

Durability should be considered as a part of structural design and construction rather than as a separate parameter. The former is generally known as holistic approach, and is increasingly adopted. The later is termed reductionistic (system) approach and does not appear to be as effective as the former.

The following recommendation may be adopted to ensure safe and durable structures with trouble free long service life.

1. Concrete protects steel from corrosion only under controlled conditions. Good quality concrete mix with lowest water to cement ratio compatible with practical placement and finishing techniques should be used. Concrete should be properly placed, consolidated and CURED. Overstressing of structures should be avoided.

2. Application of flexible coating to concrete surfaces which can effectively control the ingredients of chlorides, sulphates, carbon dioxide, oxygen and moisture can be considered as an effective corrosion control measure. However, the coating should be applied before structural deterioration occurs, and not afterwards, to be effective.

3. Corrosion of rebars can be effectively controlled by exercising adequate care at every stage of planning, analysis, design and construction for the exposure conditions. (i) Corrosion reluctant steel (ii) Coating for concrete and cathodic protections enhance durability of structures , However, there is no substitute for well designed and well compacted Concrete cover of adequate thickness to ensure durable structures.

4. The performance of structures should be monitored regularly from the stage of commissioning. Assessment of damage is the first step in a structural repair project. A successful programme of damage assessment is often the key to cost effective repair system.

5. The response of the structural system to the changes due to the repair must be understood for successful rehabilitation programme. It is not possible to generalize rehabilitation schemes. Each system has merits and demerits.

6. Trained Supervision, workable specification, speedy decision and enough working area should be made available for satisfactory, timely, and efficient repair.

7. For structures in non-corrosive environment, grouting is usually adequate for rehabilitations. Surface coating may be necessary to protect concrete in corrosive environment.

8. There is no reference to polymer modified concrete, mortars or other construction chemicals in Indian codes of practice.

9. A holistic approach should be adopted for structural system, wherein structural design and durability are considered together rather than as separate entities.

3.9 Water tightness

Hardened concrete might be completely watertight if it were composed entirely of solid matter. However, it is not practicable to produce concrete in which all spaces between the aggregate particles are filled with solid cementing materials. To obtain workable mixes, non water is used than is required for hydration of the cement. This excess water creates voids or cavities which may be interconnected and form continuous passages.

As hydration of cement proceeds) assuming that water is supplied as necessary, gel development reduces the size of the voids and thereby greatly increases the water tightness of the concrete.

For this reason prolonged thorough curing is a significant factor in securing impermeable water tight concrete.

3.10. Strength of ConcreteThe strength of concrete increases with age. Although the increase in concrete strength may continue for wall over a year the basis of design is taken as the strength at 28 days after placing.

Approximate percentages of strength of ordinary Portland Cement Concrete t different ages in comparison with the strength at 28 days are

Age

Strength %

1 day

16

3 days

40

7 days

67

28 days

100

3 months

122

6 months

146

1 year

155

3.11. Construction JointsConcreting shall be carried out continuously up to construction joints. The position and arrangement of which shall be indicated by designer.

1.When the concrete has to be resumed on a surface which has hardened, such surface shall be roughened. It shall then be swept clean and thoroughly wetted. For vertical joints neat cement slurry shall be applied on the surface before it is dry. For horizontal joints the surface shall be covered with a layer of horizontal joints the surface shall be covered with a layere of mortar about 10 mm to 15 mm thick composed of cement and sand and in the same ratio as the cement and sand in concrete mix. This layer of cement slurry or cement mortar shall be freshly mixed and applied immediately before placing of concrete.

2.Where the concrete has not fully hardened all laitance shall be removed by scrubbing the wet surface with wire. Care being taken to avoid dislodgement of particles of aggregate. The surface shall be thoroughly wetted. The surface shall than be coated with neat cement slurry and subsequently a layer of concrete not exceeding 150 mm in thickness shall first be placed & rammed; thoroughly the work shall proceed in the normal way.Summary for making Good Concrete

The following points pertaining to materials and workmanship are important.1.Cement: - a. Use cement of approved quality as per specification and ensure that it is fresh and not older than 90 days.

b. Cement shall be stored in go-down free from moisture content.

c. Stack of cement bags shall not be rested directly on floor. Wooden planks resting on wooden sizes (sections) to be provided.

d. Issue of cement should be on 1st come & 1st go basis.

e. In case if cement is required to be stacked in open, then the member of bags must be just sufficient for days consumptions.

f. Ensure that entire stack is covered by Tarpolins or Polythene sheet with an adequate overlap, when stacked in raining season.

2.Aggregate: - use well graded aggregates, free from silt, organic matter and other undesirable impurities

3.Batching : - Batching materials on weight basis is preferable rather than volume batching.

4.Mixing : - use a mixer machine / ready mix concrete. Avoid hand mixing. Where it is unavoidable it should be done on an impervious platform and add 10 % extra cement.

5.Quality of mixing water: Use the minimum quantity of water consistent with the degree of workability required to enable easy placing and compaction of concrete

6Transportation: - Avoid dry out, segregation and setting on water

7. Placing : - Place concrete in its position before setting start, avoid segregation of material and disturbance of the form avoid segregation of material and disturbance of the form. Lay concrete in layers without any break of continuity.

8.Compaction: - Use proper hand tools or vibrant, avoid over vibrations.

9.Finishing : - Finish after little stiffening.

10.Curing : - Keep concrete moist for minimum of 10 days

11.Formwork: - use formwork which is rigid and closely fitted having sufficient strength to support the wet concrete.

12.Reinforcement: Make sure that reinforcement used is free from rust, oil, paint, mud etc Important Tips for Good Construction Practices at Site

1. Check the reinforcement, electrical layouts etc. before concreting.

2. Ensure that shuttering and scaffolding is firm and proper so that it can withstand pumping load and load of man and material movement on slab.

3. Seal all joints in formwork with tape or aluminum foil or putty of used grease and cement