Some important checklists for RCC slab and beams

The following checklists are extensively utilized for RCC slab and Beams.

1. Examine the bottom line, level & width of beam properly.
2. Examine the side line, level & plumb of beam properly.
3. Beam to beam measurements should be examined according to architectural drawings.
4. Individual level & diagonal of each slab bay should be examined properly.

5. The thickness level of slab should be marked with nails on the peripheral beam’s exterior sides.
6. Examine the thickness of slab and depths of beam properly.
7. Support props for slab & beam bottoms should arrange in line & plumb. Bamboo bracing should be accomplished at around 4′ ht from floor level. Support props for double staging terraces should be examined cautiously.
8. Line of external /peripheral beam’s sides should be examined & cross supported to get rid of buldging out of sides.
9. Junctions of columns & beam should be verified to make them water resistant.
10. De-shuttering oil should be provided to beam/slab shuttering.

11. Formwork of stair case should be examined for dimensions of tread and riser, level of treads, plumb of risers.
12. Reinforcement should be examined for beams and slab as per R.C.C drawing
13. Ensure to provide exact cover for bottom /sides of beams.
14. Proper cover should be provided for slab.
15. Electrical points, electrical piping (conduits)/fan hooks should be examined as per drawing.
16. Reduction of column according to drawing should be performed if any.
17. There should be exact numbers of chairs should be arranged for slab.
18. Dowels (if any) should be arranged for elevational feaures / future expansion.
19. Parapet (Pardi) bars should be provided for balconies/staircase etc.

20. Ring (stirrups) should be arranged at the free end of each column reinforcement.
21. Distances among plates /planks should be filled. Taping should be performed at ply joints for the protection of ply shuttering.
22. Before starting pouring work, consent of the architect and R.C.C Consultant should be obtained.
23. Prior to start concreting work, verify the accessibility of necessary labour strength, mixer, lift, vibrators, masons, weigh batcher, diesel/petrol and plastic sheets etc before start of concreting.
24. Hidden beams /inverted beams/cantilever beams should be examined properly.
25. Based on the approved drawings, verify the sunk.
26. Packing underneath support props should not be provided. As an alternative, single wooden plank should be inserted as packing.
27. For large slabs, exact location of concrete joints should be determined beforehand as per approval of RCC consultant.
28. Accessibility of raw material for concrete /RMC per grade of concrete, water , electricity should be examined beforehand prior to start concreting work.

29. Initially, concreting should be performed for the beams & then slabs.
30. Compaction of concrete should be accomplished with vibrators & tamping rods.
31. The top level of the slab should be completed with mason & there should be restrictions to walk on the fresh finished concrete.
32. Carpenter should be provided under the slab shuttering throughout concreting to keep the form work tight.
33. For protection against rains, large plastic sheets should be used to wrap finished concrete.
34. Cast 6 cube moulds for testing.
35. Curing of slab should be accomplished with ponding method by making ponds in cement & sand mortar (1:10) of size around 5′ X 5′. Curing of beams and slabs should be performed for 7 to 10 days or as suggested by the consultant.
36. Deshuttering of the exterior sides of the beam should be accomplished after 24 hours . Deshuttering of the inner sides of beam should be accomplished after 48 hours . Deshuttering of the beam bottoms should be accomplished after 14 days for beam lengths up to 3 M or as per suggestions of the consultant. Deshuttering of the slab should be performed after 7 days for slabs up to 3 M span or as directed by the consultant.
37. Finishing of honeycomb should be accomplished cautiously in front of engineer the next day.
38. Hacking of the beam sides, beam bottoms, slab bottoms should be accomplished within 1 or 2 days from deshuttering.
39. Date of casting and the number of slab should be painted on the front side beam.

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Guidelines to provide concrete cover for reinforcement in slab, footing, beam & column

Concrete cover: Concrete Cover is arranged for the reinforcement in Reinforced Cement Concrete. Cover means the spacing among the exterior surface of the concrete to the inserted reinforcement.

Benefits of arranging Concrete Cover: The purpose of covering is to provide protection against erosion. Reinforcement is susceptible to erosion and fire for atmospheric conditions. In case of improper cover erosion and cracks may occur in hardened RCC.

Covering is arranged for each and every component of the building (Slabs, Beams, footings) where the reinforcement is applied. The covering blocks are utilized to retain the reinforcement in exact position as well as providing a covering for reinforcement.

Several Types of Concrete Cover Block: Depending on the type of materials applied, the following types of covering blocks are commonly found -

1. Wooden concrete cover Block
2. Steel concrete cover block
3. PVC Block
4. Cement Masonry concrete cover block
5. Aluminium Block
6. Stones

Conditions for Concrete Cover: Covering differs based on the dimensions of the components (Slab, beam, column, footings, etc.) The conditions for arranging covering in RCC are provided below -

Condition - Covering

When the length of the item is ≤ 0.3 1 - 1" or 25mm or 0.025mWhen the length of the item remains among 0.4m to 0.5m then - 2" or 50mm or 0.050m
When the length of the item remains ≥ - 0.6m then 4" or 100mm or 0.1m

From above, the maximum concrete cover remains 0.1m or 100cm

1. Concrete Cover in Columns / Beams: The length and width of the column should be 0.5m and 0.45m. The covering for reinforcement in the column should be 0.050m from all sides and similar reinforcement should be designed accordingly. The Dimensions of Reinforcement in the column should be 0.40m and 0.35m.

Suppose the length and width of the column are 0.40 and 0.25. Covering should be equal. Consider the minimum dimension from the two dimensions i.e. 0.25. For 0.25m the covering of 0.025m should be provided. So, the covering of 0.025m is arranged in all the sides. Therefore, dimensions of reinforcement is 0.35m and 0.20m.

Total Length of Stirrup is 2x [0.35+0.20]+ 9D x 2 (hook length)

2. Concrete Cover for Slabs: Suppose, the length and width of the slab are 1.3m and 1.0m. The covering of 0.1m is arranged when the length of the bar is in excess of 0.6m. Use the same condition as mentioned. The covering of 0.1m is arranged from all the sides of the slab.

3. Concrete cover for footings: Suppose, the dimensions of Footing are 0.7m and 0.6m. To length and width of Mesh (reinforcement) utilized in footings are acquired by subtracting the cover. Use the similar principle as above. As per the condition, a concrete cover of 0.1m is subtracted from all the sides. Therefore, the dimensions of reinforcement are 0.5m and 0.4m.

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Guidelines to set up reinforced concrete pipe (RCP)

Reinforced concrete pipes alias RCPs, are suitable for storm sewer systems and water sewer systems. The set up of these pipes is complicated since they are weighty and heavy equipments are required to shift and place them. Given below, the details about RCP handling and installation.

Handling Reinforced Concrete Pipe: Reinforced concrete pipes should be dealt with cautiously so that the bell is not damaged (the wide or flared end of the RCP) and spigot (the narrow end that is inserted into the bell of an adjacent pipe).

RCPs should not be pulled to the site. It is suggested that initially, the pipes should be unloaded with a nylon sling or other certified material to support the weight of the pipe, and make balance properly in the sling.

Excavating Reinforced Concrete Pipe: Prior to start the installation process, make sure to arrange the trench to adapt minimum two pipes so that it becomes possible to check that the installation will retain the necessary slope and the consequent trenching will not affect the pipe being installed as well as endanger the security of workers.

Once each RCP is installed, the line and grade levels should be examined properly. Keep in mind that the trench should be adequately wide to facilitate the workers installing and controlling the pipe securely.

It is recommended not to change the pipe alignment or grade with the pipe in the home position. Keep in mind that all through the installation process the pipes should not be supported on bells since it could damage them. The bedding material should not contain any debris and should retain a consistently level surface.

How to arrange joining surfaces of RCP: Prior to placing the RC pipe, it is required to cleanse all impurities from the joining surfaces of the bell of the pipe cautiously to provide perfect homing of the pipe.

Provide lubricant to the bell portion of the RCP with a brush or gloves. Check with the RCP manufacturer for suggested lubricants that should be used. Lubricant should be sufficient to prevent the gasket from rolling away and damaging the bell end.

Cleanse the spigot or tongue end of the pipe to seal the gasket properly. Lubricate the tongue end of the pipe along with the gasket recess. If the lubricating grease is inadequate, the gasket may twist out of recess. The gasket should be lubricated prior to arrange it on the tongue of the RCP.

How to set up RCP: To set up the RCP, the pipe should be managed with few workers. It is necessary to lubricate pipe bell and gasket not to utilize extra force.

Set up the gasket and apply a round object to level the gasket stretch. Pass the object frequently along the circumference to keep everything in exact location. When the gasket is not expanded, leaks may occur at the joint or the bell may crack. Align bell and spigot, and ensure that the gasket gets in touch with the entry taper.

Ensure the pipe is aligned with surveying or leveling instruments. If the pipe going to be installed contains a small diameter, a wood block should be arranged across the bell end of the pipe and pushed with a wedge bar to shift the pipe gradually into place. Continue pushing unless the pipe is entirely installed. When the pipe diameter remains somewhat bigger and heavier, the pipe pullers should be applied to install the pipe.

Backfilling Reinforced Concrete Pipe: Backfill material should be set cautiously along the pipe and compacted methodically. Backfill material should be arranged consistently in lifts on both sides of the pipe and fill the trench up one foot over the top of the pipe.

The material should not be bulldozed into the trench or provided directly on top of the pipe. The backfill material with large boulders should not be utilized since they will not be consolidated and may damage the pipe.

The material with roots or other organic material should not be used. Backfill should be arranged based on the geotechnical recommendations on particular backfill material.

Lastly, heavy construction equipment should not be operated over the pipe unless sufficient backfill is prepared or the pipe is sufficiently deep in order that it is not damaged.

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Details about Composite Slabs & Columns and their benefits

Composite slabs:

1. It comprises of profiled steel decking with an in-situ reinforced concrete topping.
2. The decking(profiled steel sheeting) perform as permanent formwork to the concrete as well as offers adequate shear bond with the concrete in order that when the concrete has attained strength, the two materials function mutually & compositely.

3. Distance among 3 m and 4.5 m onto supporting beams or walls.
4. When the slab is unpropped throughout construction, the decking single-handedly withstands the self-weight of the wet concrete and construction loads. Subsequent loads are delivered to the composite section.
5. When the slab is propped, all of the loads should be combated by the composite section.
6. These are normally designed as simply supported members in the normal condition.

Profiled steel sheeting:

1. Depths vary from 45 mm to over 200 mm.
2. Yield strengths vary from 235 N/mm2 to minimum 460 N/mm2.
3. The thickness vary from 0.8 mm to 1.5 mm.
4. The different shapes offer Interlock among the steel and concrete.
5. Decking is also applied to make the beams stable against lateral torsional buckling throughout construction.
6. Improve the stability of the building entirely by behaving as a diaphragm to transmits the wind loads to the walls and columns.
7. Temporary construction load normally manages the choice of decking profile.

Composite Columns:

A steel-concrete composite column stands for a compression member that contains either a concrete encased hot-rolled steel section or a concrete filled tubular section of hot-rolled steel. The existence of the concrete is granted for two ways.

1. Safeguard from fire.
2. It may also withstand a small axial load.
3. To minimize the effective slenderness of the steel member, that raises its resistance capacity against axial load.

The bending stiffness of steel columns of H-or I-section is superior in the plane of the web (‘major-axis bending’) as compared to a plane parallel to the flanges (‘minor-axis bending’).

The ductility performance of circular type of columns is considerably superior as compared to rectangular types. There is no need to offer extra reinforcing steel for composite concrete filled tubular sections.

Protection from erosion is arranged by concrete to steel sections in encased columns.

When the local buckling of the steel sections is removed, the reduction in the compression resistance of the composite column caused by overall buckling should definitely be permitted. The plastic compression resistance of a composite cross-section shows the maximum load that can be employed to a short composite column.

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Properties and uses of white cement concrete

White cement concrete has similarity with grey Portland cement but the main difference lies in fineness and color. The white color of this cement is obtained by its manufacture system and its raw materials. There are wide array of color options in this type of cement for developing architectural and structural concrete.

This cement is formed with raw materials with little or no iron or manganese. Normally, china clay is utilized in white cement along with with limestone or chalk.

The cement should be white Portland cement with adherence to the standard specification ASTM C150.

The compressive strength of white cement is less as compared to OPC cement.

A large amount of iron and manganese are added in its manufacturing process to enhance the whiteness of the cement and becomes more expansive. White cement concrete is called as snow Crete. With white cement, a homogenous concrete is produced with exact color for a structure.

To develop white cement, 40% higher energy is necessary as compared to the normal grey cement and it makes the white cement expensive. Light colored sand along with whitest chalk is provided in the production of white cement.

HOW TO CHOOSE PROPER RAW INGREDIENTS:

Cement: The delivery of white cement in both bulks and bagged. The storage of the white cement bagged should not get in touch with the ground. If storing is made in the concrete floor then the cement should be stored up against the exterior walls. White cement bags should be preserved in pallets and it should be safeguarded from weather and maintain them off the ground. Due to the low content of soluble chromium, white cement should be preserved for minimum of 6 months when provided in proper dry condition.

Aggregates: The selection of aggregates for white should comprise of the white marble, white granite, and crushed calcinated flint. The color choice of coarse aggregates is crucial to the final appearance of white concrete. The selection of fine aggregates especially the filler particles should be lower than 0.25mm. Precautions should be taken to make sure that the mix of aggregates remain as constant as possible among batches to avoid in shading of finished products.

Water: Water to be mixed in white concrete should be clean and does not contain organic impurities. The water-cement ratio remains high in white concrete with regards to normal concrete and is critical in finding out the final strength of concrete.

CHARACTERISTICS OF WHITE CEMENT CONCRETE:

1. The initial setting time of white cement should 100 minutes.
2. The fineness of white cement should be 395 kg/m2.
3. The brightness of white cement should remain 87%.
4. The compact density of white density should be 3150 kg/m3.
5. Bulk density of white cement is 110 kg/3.
6. Compressive strength after 1 day 21 Mpa, after 2 days 38 Mpa, 7days 61 Mpa and after 28 days 74 Mpa.

APPLICATIONS OF WHITE CEMENT:

1. White cement is effective for decorative works as well as prestige construction projects.
2. White cement is applied to develop brightly colored concrete and mortars.
3. It is suitable for interior and exterior decoration due to its whiteness.
4. White cement is frequently applied in roads to enhance the visibleness to highway medians.
5. It is useful for huge numbers of manufacturing precast members.

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Some useful terms of construction materials

In civil engineering sectors, there are different types of terms associated with various construction materials. Given below, the details about them.

Aggregate: It belongs to all particles of sand, broken stone or gravel etc. which are applied to form Concrete.

Bulking: It means the surge in volume of sand or aggregate resulting from the absorption of Water.

Concrete: Concrete belongs to a building material that comprises of specified quantities of Cement, Sand, Aggregates and water. At the time of mixing, transmission and placing, the concrete sets and solidifies through the method of hydration as the water reacts with cement and binds other elements finally results in producing a material similar to stone.

Curing: The process of retaining the concrete damp once it is arranged in its position to finish the chemical combination of cement and water.

Final Setting: It happens when the concrete has been properly set but has not been solidified yet.

There should be adequate time for the framework to be detached. Final set happens in about 3 to 4 hours with ordinary cement and should not require in excess of 10 hours.

Hardening: It specifies the increase in strength of a mortar or concrete and occurs at the end of the initial set.

Initial Setting: The period passed between the time when water is added initially to time of cement to develop a paste and the time when that paste is stopped to be fluid and plastic to a certain degree under the specified conditions of test.

Lean mix: It belongs to a concrete mix with a low cement content.

Screeding: It means acquiring a level surface as the exact height with the use of a piece of wood or metal containing a straight edge.

Setting: It stands for the chemical action that starts when water is added to cement and causes the plastic nature of cement to go away gradually. There are initial set and final set of cement.

Segregation: It means the detachment of the particles with various sizes in a concrete mix. The bigger aggregates settle at the bottom. Segregation impacts the strength of the concrete significantly.

Striking: It means dismantling and elimination of form work or centering.

Workability: It is the property of the freshly mixed concrete(or mortar) that ascertains the ease or difficulty with which it can be treated in order to make full compaction.

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Construction Method Of Concrete Slab On Grade

Slab on grade belongs to concrete floor slabs which are poured at grade or ground level to develop a foundation for a home. Prior to start the construction, contractors excavate the soil adjacent to the area where the foundation should be constructed and ensure that the ground has sufficient strength to support the structure.

Normally, the periphery of the slab is very dense as compared to the rest of the surface. This section has similarity with footer that facilitates to circulate the weight of the exterior walls uniformly over the soil underneath the structure. Slab on grade foundations are suitable for the areas where the soil is unusable for crawl spaces or basements.

Grade slabs are provided in areas where the ground is not solidified. This type of slabs may or may not include reinforcement in it. The inclusion of reinforcement depends on the floor loads and local building codes.

The thickness of Grade Slab should be at least 4 inches. If porosity exists in soil, the thickness of the slab should be raised. To maintain safety, a layer of gravel & bitumen should be placed on earth prior to arrange concrete slab to stop the penetration of moisture content into the slab.

Slab on Grade is categorized as follow:

1. Supported Slab on Grade
2. Monolithic Slab on Grade

Supported Slab on Grade / Grade Slab: Supported grade slab or slab on grade foundation should be used when the conventional footings are already set up on site to uplift the columns. Under this system, the wall is laid on a footing and the grade slab stands on a layer of gravel and moisture barrier.

The formwork applied for plinth beams operates as batter boards for slab mould. There is an expansion joint among concrete slab and wall to reduce the stress throughout high-temperature days. Control joints are set in a planned grid with chalk lines to manage occasional cracking on the slab.

Monolithic Slab on grade: There are no footings for monolithic grade slab, the concrete slab itself functions as a footing for the building; and the columns, walls are uplifted from the grade slab. This type of slab is structured with batter boards around the slab based on the plan and the concrete is poured inside batter boards. These batter boards operate as a mould to detect the slab corners.

Grade slabs normally stand on the layers of gravel and moisture barrier. These layers can resist penetration of water into the slab to develop surface cracks.

The periphery of the grade slab is very dense as compared to the rest of surface. This dense section operates as a mini footing and facilitates to circulate top loads more consistently over the adjacent soil.

Construction Method: Prior to cast slab on grade, the excavation of earth is done to the desired depth along with compaction to drive out air voids. Batters are leveled and provided in exact location based on the plan prior to concrete pour. These boards function as a concrete mould to facilitate detecting the slab corners.

After that, soil investigation is performed to design the thickness of the slab. After obtaining the results, the layers of gravel and moisture barriers (bitumen) is again poured on the ground. These layers are used as a sub-base for slab and resist the infiltration of moisture into the slab.

The thick concrete is poured at the edges to form an solid footing and reinforcement rods are placed to increase the strength of the edges.

To reduce random cracking on the surface, the concrete should be cured and dried for long times.

The expansion joint should be arranged among the wall and slab. The control joints on the slab are leveled with chalk lines prior to pouring which can check random cracking.

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Method of concrete compression test with 150mmx150mmx150mm cube samples

In concrete compression test, usually 150mmx150mmx150mm concrete cube samples are arranged for performing test. Can 100mmx100mmx100mm concrete cube samples be applied in the test in place of 150mmx150mmx150mm concrete cube samples?

Fundamentally, the force delivered by a concrete compression machine belongs to a definite value. When normal concrete strength is used i.e. under 50MPa, the stress delivered by a 150mmx150mmx150mm cube is adequate for the machine to crush the concrete sample.

However, when the designed concrete strength is 100MPa, under the equivalent force(about2,000kN) delivered by the machine, the stress under a 150mmx150mmx150mm cube inadequate to crush the concrete cube.

So,100mmx100mmx100mm concrete cubes can be utilized in place of 150mmx150mmx150mm cubes to raise the applied stress to crush the concrete cubes. For normal concrete strength, the cube size of 150mmx150mmx150mm is already adequate for the crushing strength of the machine.

Cube Test:

Tools and Materials: Concrete cube mould with size 150mm or 100mm. It is utilized for aggregate size not surpassing 40mm and 25mm. Cube mould for test should be done from steel or cast iron having smooth inside surface. Every mould should contain steel plate to support and to resist leakage.

Compacting steel rod having 16mm diameter and 600mm length.

Compression test machine:

Methods: Mould and base plate should be properly cleansed and used with oil so that the concrete can’t fix to the side of the cube. Base plate is connected with the mould with bolt and nut.

Fill the cube with concrete in three layers.

Each layer should be consolidated for 25 times. This method is performed systematically and compaction is performed consistently to all the surfaces of the concrete. Compaction can also be performed with machine.

The surface of concrete should be flattened to maintain the identical level with the upper side of the mould. The cubes produced at construction site should be covered with plastic cover for a period of 24 hours prior to disassemble the moulds.

Once remoulded is completed, the concrete cubes are drowned in water for curing.

Compression strength test should be conducted for concrete at age 7, 14, and 28 days with compression test machine.

Result: Record the Strength value of each cube and compare with the targeted strength value. The objective of conducting the concrete test on 7 th day and the 14 th day is to forecast whether the concrete could attain the targeted 28 th day strength. Normally, the concrete would have obtained 70% strength on the 7 th day.

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Types of lime and its applications

Several types of lime are found in construction which range from Quick Lime, Slaked Lime, Fat Lime and Hydraulic Lime. The natural limestone is calcinated at 900 degree celsius temperature to produce lime. Every type lime is different in nature and is utilized in environmental, construction, chemical and metallurgical industries.

The following types of lime is frequently utilized in construction :

1. Quick Lime
2. Slaked Lime
3. Fat Lime
4. Hydraulic Lime

1. Quick Lime: Quick lime is also known as caustic lime ( Calcium Oxide). It is formed by burning clean limestone ( Calcination process). It is the most inexpensive form of lime that which is extremely amorphous and caustic. Quick lime can be easily combined with moisture.

Quick lime is considered as one of the major elements in producing cement. It is also a vital element that can be applied for the treatment of drinking water.

2. Slaked Lime: Slaked lime is formed by the method of slaking under which quick lime is mixed with water. Slaked lime is also called as hydrate of lime. It is found as pure lime in the type of a white powder.

When Slaked lime is uncovered to the atmosphere, it soaks up carbonic acid in the existence of water content. It is also known as calcium hydroxide or calcium hydrate or lime hydrate.

If Slaked lime is produced by adding quick lime and water, a slurry material is made. It is very effective for mortar applications. It is also applied in plastering works and in cement as a binder.

3. Fat Lime: In fat lime, calcium oxide is used in huge amount. It is also known as white lime or rich lime or high calcium lime or pure lime. It slakes intensely while adding water to it. Due to slaking, its volume is raised by two to two and a half times more than that of quick lime.

Fat lime is suitable for pointing in masonry works, foundation, with surkhi to solidify the masonry walls etc.

4. Hydraulic Lime: Hydraulic lime is also known as water lime. It comprises of 30 percent of silica and 5 percent of alumina together with iron oxide. After adding water, this lime sets quickly.

Applications of Lime in Construction.

Major uses of lime are enlisted below:

1. Lime is utilized in the manufacturing of steel to take off the impurities.
2. Make soil stable for construction of roads, airfields and building foundation by mixing lime in huge quantity.
3. Lime slurry is utilized as mortar for masonry work and for plastering.
4. Lime is applied as an additive in asphalt to enhance the property of cohesion. Lime also makes the resistance strength of asphalt better towards stripping and aging.

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Points to be considered prior to concreting ground beams and plinth beams

Prior to start concreting work for ground beams & plinth beams, proper examination should be carried out in the following two phases :-

Initially, test out formwork prior to arrange or bind reinforcement. It is important since specific formwork errors can’t be rectified or it becomes complicated to repair once the reinforcement is arranged in position.

Checking reinforcement.

01. Centering and shuttering / Formwork:

• P.C.C. of proper grade and thickness (least 50 mm and M5 or 1: 4:8 grade) should be provided prior to apply shuttering for ground beam and it should be perfectly leveled and remains in exact line.

• The P.C.C. should be expanded minimum 50 mm exceeding the width of beam on both faces. Verify all the level of ground beams.

It should be minimum 150 mm in natural ground, in order that the earth filled inside walls or a beam doesn’t get out throughout plinth filling. Also check that all ground beams are located on equivalent level.

• Verify that all the soil on which beam is placed is correctly compacted (specifically for freshly excavated foundation pits) so that the ground beam never sags throughout curing or watering due to settlement of loose soil.

• The bricks should not be used since it can’t retain exact level and line.

• Start formwork for ground beams or plinth beams after filling because providing props may lead to delay since time is required for detaching props and filling work can be resumed during that period causing delay of slab.

• Prior to apply mould release agent, the shuttering should be dry and shall be cleansed properly. During shuttering work, the similar type of release agent should be used for same shuttering materials.

• The surface of shuttering should be level and thin coating should be provided with mould release agent.

• The mould release agent should not get in touch with reinforcement or the solidified concrete.

• Shuttering should be set in such a way that the joints are sealed properly to resist leakage of cement slurry.

• Prior to binding or placing reinforcement, the size of beam should be examined properly.

• Make sure that the meeting point of beam & column is tight and no bulging should occur throughout concreting.

• Take out all the debris like dust, paper, leaves, chippings of woods, nails, reinforcement wastage, soil particles etc.

02. Reinforcement:

• Prior to set the concrete, verify the reinforcement details as per bar bending schedule and obtain the approval of structural consultant.
• The reinforcement of beam should remain in exact alignment. If extent of beam exceeds 6 to 9 meter than camber should be arranged according to drawing.
• Examine the laps of beam with detailed drawing. There should not be laps in middle of beams if they contain long span. The lap should be maintained at various positions at few different bars.
• Verify the joints details according to detailed drawing- flexible or rigid.
• Bent up bars should be provided based on detailed drawing.
• Verify whenever the reinforcement of cantilever beam remains in top doubly anchored.
• Also examine the counter balance of cantilever beam.
• Stirrups should be placed at the intersection of beams and columns and in most cases it is generally overlooked.

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Method of silt content test

Sand is considered as one of the vital construction materials for concrete, plastering, brickwork and flooring. Therefore, it is always recommended to use standard quality sand in the construction works.

To check the quality of sand, silt content test should be conducted. Silt content stands for a fine material that is lower than 150 micron. It becomes unstable in the existence of water.

When silty sand is applied for bonding, the strength will be decreased and rework should be required. It is mostly found when the plastering is going on for roof where the plaster continuously peels off at the time of being plastered with the mortar.

Extreme quantity of silt decreases the bonding of cement and fine aggregates as well as hampers the strength and stability of work.

In the job site, it is required to carry out silt test for each 20 Cum of sand although it may differ.

Silt Content Test for Sand

Purpose: Determine the silt content in sand (fine aggregate).

Necessary Tools:

• 250 ml measuring cylinder
• Water
• Sand & Tray

Test Method:

• Initially, the measuring cylinder should be filled with 1% solution of salt and water up to 50 ml.
• Include sand to it unless the level goes to 100 ml. Then fill the solution up to 150 ml level.
• Cover the cylinder and shake it properly.
• Once 3 hours are completed, the silt content settled down over the sand layer.
• Now record the individual volume of silt layer as V1 ml (settled over the sand).

• Then record the sand volume (underneath the silt) as V2 ml.
• Apply the method twice to obtain the average value.
• Silt Content = V1 / V2 x 100

The allowable silt content in sand percentage should be only 6%.

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Basic variations among Shear Stress and Tensile Stress

Stress refers to a quantity that defines how much deforming force is employed per unit area of an object. Shear and tensile stress stands for several types of stress where the forces operate on an object in a various ways.

The major variation among shear stress and tensile stress is that tensile stress is produced when a deforming force is employed at right angles to a surface, while shear stress is produced when a deforming force is employed parallel to a surface.

Definition of Tensile Stress: Tensile stress occurs in a situation when a deforming force, operating perpendicular to the surface of the object pull on the object, trying to elongate it. In this context, tensile stress belongs to a type of normal stress produced by forces perpendicular to the surface of an object.

The other type of normal stress ranges from compressive stress, where a force operates perpendicular to a surface and push in on the surface, trying to curtail it.

Suppose, the force perpendicular to the surface is taken as F and the area of the surface is A, then tensile stress (σ) is measured as follow :-

Tensile strain (ϵ) belongs to the change in length () as a fraction of the original length (x0) :

A quantity known as young modulus (E) defines how comparatively difficult it is to expand a given material. This quantity is given as follow :-

E = stress / strain = σ / ϵ
Shear stress belongs to cases where the deforming force remains parallel to a surface.

The shear stress is again identified as the ratio of the force to the area:

The variation among tensile stress and shear stress occurs in the directions of forces.

The shear strain is provided as follow :

The shear modulus is a quantity that defines how difficult it is for a material to be deformed through a shear stress. The shear modulus for a material is identified as:

Given below, common differences among Shear Stress and Tensile Stress

Direction of Forces: Forces which produce tensile stress remain at right angles to a surface. Forces which produce shear stress function parallel to a surface.

Deformation of the Object: Due to tensile stress, the objects are elongated. Due to shear stress, the one surface of an object is dislocated relating to the surface opposite to it.

Relative Strengths: Solid materials deform quickly under shear stress than under tensile stress. 

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www.constructioncost.co
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Guidelines for making perfect structural design

This civil engineering article focuses on the least standards which should be maintained for the design of various RCC structural elements like the columns, beams, slab and foundation as well as the least safe standards for the reinforcing bars to be applied for making the design of the above mentioned structural elements.

Minimum cross-sectional dimension for a Column should be 9″x 12″ (225 MM x 300 MM). It is the minimum approved size.

It is always recommended to utilize M20 grade concrete for construction as per IS 456:2000. The least steel in a 9″ x 9″ column should be 4 bars of 12 MM with stirrups of 8 MM steel rings at a spacing of 150 MM centre to centre. In a 9″ x 12″ column, more bars (6 bars with 12 mm diameter) should be added to sustain the total efficiently.

Least RCC beam size should not be lower than 9″x 9″ (225MM X 225MM), with an supplementary slab thickness of 125 MM.

Normally, there should be minimum of 4 bars, with 2 bars having 12 MM thickness in the bottom of the beam, and 2 bars having 10 MM at the top of the beam.

A concrete cover of 40 MM should also be provided. It is suggested to utilize M20 grade of concrete (1 part cement : 1.5 parts sand : 3 parts aggregate : 0.5 parts water).

Minimum thickness of RCC slab should be 5″ (125MM) since a slab may comprise of electrical pipes which are implanted into them which could be 0.5″ or more for internal wiring and as a result the depth of slab is decreased at specific places that lead to cracking, weakening and water leakage throughout rains. Therefore, a least thickness of 5″ should be retained.

Minimum size of foundation for a single storey of G+1 building should be 1m x 1m, where safe bearing strength of soil is 30 tonnes per square meter, and the anticipated load on the column does not surpass 30 tonnes.

The depth of footing should be minimum 4′under ground level. It is suggested to get to depths up to had strata.

Minimum Reinforcing bar details:

1. Columns: 4 bars of 12mm steel rods FE 500.
2. Beams: 2 bars of 12 mm in the bottom and 2 bars of 10 mm on the top.
3. Slab

a) One Way Slab: Main Steel 8 MM bars @ 6″ C/C and Distribution Steel of 6 mm bars @ 6″ C/C
b) Two Way Slab: Main Steel 8 MM bars @ 5″ C/C and Distribution Steel of 8 mm bars @ 7″ C/C

4. Foundation: Initially, there should be 6″ of PCC layer. Over it, a tapered or rectangular footing with minimum 12″ thickness should be arranged. Steel mesh of 8 mm bars @ 6″ C/C should be placed. In a 1m X 1m footing, there should be 6 bars of 8 mm on both segments of the steel mesh.

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Common thumb rules for civil engineering works

Thumb Rules is very important for any civil engineer, Site engineer or civil supervisor to obtain instant decisions on the construction site. By applying thumb, the engineers can get the solution with a simple mathematical formula and take proper decisions wherever required. Before applying these thumb rules, it should be kept in mind that the thumb rule can only provide fairly accurate results never the correct results.

The following types of thumb rules for civil engineers are commonly used in construction work :-

Thumb rule for measuring the Concrete Volume relating to the area:
The volume of concrete necessary = 0.038 m3/square feet area.

As for instance, if Plan Area = 40 x 20 = 800 Sq. m., total necessary volume of concrete will be as follow :-
= 800 x 0.038m3 = 30.4m3

Thumb rule for Steel quantity necessary for Slab, Beams, Footings & Columns:
Essential quantity of steel in residential buildings = 4.5 Kgs – 4.75 Kgs / Sq. Ft.
Essential quantity of steel in commercial buildings = 5.0 Kgs-5.50 Kgs/Sq. Ft.

Thumb Rules For Civil Engineers recommended by B N Datta for the Steel quantity that will be applied for several members of the building :-

Proportions of Steel in Structural Members:

1) Slab – 1% of the total volume of concrete
2) Beam – 2% of the total volume of concrete
3) Column – 2.5% of total volume of concrete
4) Footings – 0.8% of the total volume of concrete

As for instance, suppose the length, width and depth of the slab are 5m, 4m and 0.15m. Now, the quantity of steel for the slab will be computed as follow :-

Initially, it is required to work out the concrete volume.
The total volume of concrete for the slab = 5x4x0.15 = 3m3

Secondly, work out the quantity of steel with formula as follow :-
Based on the guidelines provided in B. N. Dutta reference book, the quantity of steel in slab is 1% of the total volume of concrete used.
Thumb rule to work out the quantity of steel in above slab = Volume of concrete x density of steel x % of steel member.

The weight of steel necessary for above slab = 3x7850x0.01 = 235 kgs

To make perfect calculation, use bar bending schedule.

To learn how thumb rules are applied to calculate the shuttering area and the quantity of cement, sand, course aggregate in several grades of concrete, click on the following link civiconcepts.com

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Published By
Rajib Dey
www.constructioncost.co
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