Why pouring concrete over present concrete slab is not recommended

It takes huge time and labor to remove a subsisting concrete slab. In this regard, the most suitable process is to pour a new layer over the subsisting slab.

Thus, the requirement for labor will be reduced significantly as well as the money and resources will also be saved greatly. But, once the new layer is poured perfectly, it will only be as secure and durable similar to the older slab under it.

Increases the Level: The level will be increased by several inches while pouring a new layer of concrete over a subsisting walkway, patio or porch. If the slab puts up to a door, there may not be required clearance for the door to open with the lifted surface.

Towards a walkway, increasing the level by several inches can give out its alignment with the driveway, steps or another structure. When a slight ramp is added from the driveway to the increased surface, a trip hazard is reduced and the debris is retained from being collected in the corner.

Fewer Years of Service: A well-poured concrete slab containing a deep, strong foundation can survive for 30 to 40 years. Pouring concrete over old concrete rather than directly over a new gravel foundation restrains the scope to enhance the longevity of the slab.

The longevity of the new concrete is mainly dependent on the condition of the subsisting slab. If the foundation under the slab is not strong, the new concrete may sink or produce deep potholes.

Bonding: If new concrete is attached with the subsisting slab, cracks may occur. Retaining the new concrete from tying to the subsisting slab, new damage can’t develop as well as any damage in the old slab from extending to the new one. It makes both slabs adaptable to shrink and enlarge when temperatures change. To get rid of bonding, plastic/sand or other long-lasting material are arranged among the two layers of the slabs.

Maintenance: Due to its robust strength and low maintenance cost, the concrete is becoming popular. A slab poured over a subsisting slab may experience frost heave damage and cracks. The damages should be repaired immediately as soon as they form so that they can’t be expanded. The new layer must be sealed with deep penetrating sealer to get rid of water damage. If there are long, deep cracks, analyze the damage to find out any structural problem.



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Some useful tips to repair the damage to the brick wall

This article throws light on brick wall damage due to frost & water along with cracking, spalling & white or coloured mineral salt deposits that is called effloresence.

One can get details about the types of damages to structural brick walls as well as how to identify & assess movement and cracks in brick walls together with brick wall bowing or bulging and cracking failures.

Water & Frost Damaged, Broken Bulging Brick Walls: Frost damage to the brick wall happens because of roof spillage that passes through the building wall. Water penetrates the space behind the facing wythe of bricks on the wall and it leads to continuous frost-push and risk of falling of at least the exterior parts of the wall.

Cracked Bricks in Strutural Building Walls

If there are cracked bricks in the exterior walls, leaks occur at the abutment of balcony as well as to the building structure.

Efflorescence: white, yellow, brown deposits on brick walls, chimneys, foundations

Efflorescence is the white mineral deposits on a structural brick wall caused by water.

The task is very difficult to control roof runoff to retain water from flowing over building walls particularly on bigger, taller buildings where entry to sustain the gutter system is not possible.

Spalling Brick Building Walls: The brick spalling occurs owning to roof spillage and rain splash-up against the foundation wall. The frost spalling create damage to the brick wall, particularly around the building windows.

The brick surface gets damaged (surface spalling and loss of the hard glazed finish) because of weathering, water and salt exposure that results in producing more severe frost damage that involve cracking and frost "pop out" of sections of individual bricks or entire brick portions of the structure.

Water & Frost Damaged Brick Foundation Walls, Loose Bricks

There may be rigorous water and frost damage to the corner of a brick building, perhaps from roof spillage at the end of a gutter that was periodically chocked.

To settle these bricks against further movement and probably more serious foundation damage, a mason should be employed to repair the corner with a combination of reconstruction of the most-loose (or missing) bricks, and tuck pointing the leftover open mortar joints.



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Various tests conducted for Rebar

In rebar pieces, the following items are generally found :-
X stands for diameter of rebar in mm as for instance 20.
ABCD stands for brand of rebar ranging from TATA TISCON, SAIL, JSPL etc.

Y stands for yield stress of rebar as for example 500 signifies Fe500 having yield stress similar to 500 Mpa

Chemical composition test
LSA or ladle sample analysis is performed in LD and details are noted.
TPA or test piece analysis is performed at chemical lab.
The chemical composition analysis should be adhered to Amend 1 of Cl. 4.2 of IS 1786-2008

Main physical property tests for a specific rebar are provided below :

1. Tensile test : Numbers of rebar sample =4, length of rebar sample =about 600 mm
2. Bend test : Numbers of rebar sample =4, length of rebar sample =about 500 mm
3. Rebend test : Numbers of rebar sample =4, length of rebar sample =about 500 mm

Individual Sample: In order to work out the nominal mass of an individual sample, ascertain the mass of any individual sample selected arbitrarily as mentioned in 11.1 and divide the same with the actual length of the sample. The length of the sample should not be under 0. 5m

Batch: The nominal mass of a batch is computed from the mass of the test specimens selected as mentioned in 11.1 and divide it with the genuine total length of the specimens. The length of each specimen should not be under 0.5 m

Tensile test
Existing Inputs :
1. Length of sample = L
2. Weight of sample = w
A = w/0.00785L mm2
[According to Cl. 6.3.1 of IS 1786-2008 given at right]

Gauge length for a rebar of dia D mm = 5D mm
The rebar sample is marked at (5D/2) mm locations.

To get more clear information, go through the following article engineeringcivil.com

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Rajib Dey

www.constructioncost.co

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How to repair concrete with Dry Pack Mortar Method

The purpose of dry pack mortar is to repair the concrete surfaces with cracks or holes of depth greater than or equal to the minimum dimension of the repair area. The holes usually discovered on concrete surfaces are cone bolt holes, she bolt holes, holes formed with ties etc.

Dry pack mortar should not be used for shallow cracks, fully extended holes i.e., from one side to other side, space behind reinforcement etc.

Dry pack method involves the following steps for executing repairing work to concrete.

1. Arrangement of Hole Inner Surface
2. Arrangement of Dry Pack Mortar
3. Using Dry Pack Mortar
4. Curing of Dry Pack Repair Area

1. Preparation of Hole Inner Surface

a. Prior to use dry pack mortar, the surface or hole to be repaired should be cleansed, washed and dried perfectly. Also they should not contain any damaged pieces of aggregates.
b. The inside surface of hole should have been rough to create superior bond. If the surface is smooth, it should be roughened with tapered reamer or star drill.
c. Usually, there exist three methods to develop the inside surface area of holes for maintaining superior bond with dry pack mortar.

Method – 1

a. Bonding grout is used to brush the inside surface of hole. Bonding grout is made of cement and fine sand in the proportion 1:1.
b. Now, the dry pack mortar is applied prior to bonding mortar becomes dry to make superior bond among mortar and surface.
c. When bonding grout is used, ensure that no free surface water exists in the hole so that the hole remains fully dry.

Method – 2

a. By applying wet rags or burlap, the hole is pre-soaked all night with and permitted to dry.
b. When the hole is partly dried or comprises of some amount of surface water, then spray dry cement on to the surface with small brush.
c. The cement will consume free water and develops a layer on the surface. Extra cement still in dry form is eliminated with jet of air so that dry pack can be applied on the surface.

Method – 3

a. Under this method, superior bond among dry pack mortar and surface is formed with epoxy bond resins
b. Epoxy resin is blended and used on the surface with brush.
c. Ensure that the concrete temperature should not exceed at the time of using epoxy or else it may burn or dry up the epoxy promptly.
d. As soon as epoxy is used, instantly use the dry pack mortar prior to epoxy gets dried out.
e. Epoxy bond resin can resist the hydration of water to adjacent concrete surface.

To get more details about dry pack mortar, go through the following link theconstructor.org

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Methods to save sun shade for life long

Sun is the source of our energy; in the construction energy this sun plays a vital role as it helps to dry the site, helps to get the moisture far away from the materials etc.

But it is also true that shade is important in construction process as it plays as a protection shield for rest of the things like doors, window and inner sides of building form the scorching hot sun light and rain water. So if the sun shade is not placed and finished successfully, many problem will come one after another; major failure will be seen in the buildings also.

A sunshade is basically a metal shutter which is installed horizontally over a window and/or vertically in front of a window to stop the insertion of solar heat or glare while allowing daylight views.

Originally metal sunshades were known as “eyebrows” and simply added an extra dimension to a relatively flat surface. They were known as more of a building’s aesthetic feature than a functional one and also one of the first things to execute of the building to decrease owner’s cost.

This article is strongly dedicated to know about the right method of placing and finishing a sun shade through some easy steps.

Placing a Sunshade concrete in perfect way:

• Reinforcement placing and leaving correct clear covers are the two most important factors in sun shade. 
• In Sunshade, Main rod should be on top of the concrete to make the balance of the negative bending movement.
• The development length of sun shade should be followed and inserted to lintel beam as without development length of a rod for sunshade may lead to failure.

Finishing a Sunshade concrete in perfect way: A sunshade must be finished with water proofing where Flat tile should be on top and projected for half inch around three sides. Sunshade ceiling should have a water blocking border on its edge; at joint of the wall and sunshade the flat tile would be inserted to plastering to prevent the water.

To get details, go through the following link youtoobuild.blogspot.com



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Reasons for collapsing of foundation

There are several reasons for collapsing of foundation which range from poor soil condition, structural faults etc. Given below, some of the major causes for collapsing of foundation :-

1. Collapsing of Foundation because of surpassing the bearing strength of soil
2. Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden
3. Collapsing of Foundation because of differential or unequal settlement
4. Collapsing of Foundation because of uneven progress and pattern of construction
5. Collapsing of Foundation because of movement of adjacent soil.

Collapsing of Foundation because of surpassing the bearing strength of soil:-

Ultimate bearing strength means ultimate load intensity that a soil can bear devoid of any shear failure of the Soil. The size of the footing with regard to length, breadth and diameter, is primarily based on the bearing strength.

A foundation/ footing of a structure must contain adequate size in order that the intensity of load directing via that footing from the structure to the soil below should not raise the bearing strength of that soil. If the bearing strength of soil is low or load operating is heavy and the size of the footing is relatively small than actual requirement then the load intensity (i.e. load per unit area say KN/sq.m. etc.) conveyed on the soil may be greater as compared to the bearing strength of the soil, for this reason a shear failure of soil will occur.

To provide perfect footing size, the safe bearing strength rather than ultimate bearing strength should be applied to obtain margin of safety against any accidental loading as well as abnormal behavior of the soil due divergence in its bearing strength. Safe bearing strength is nothing but ultimate bearing strength divided by a appropriate factor of safety usually varying from 2 to 4.

Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden :

It is one of the most crucial factors that should not be neglected. Moisture withdrawn occurs in the following ways :-

a) By draining water from the adjacent well through pump
b) By dewatering adjacent Pond
c) Reduction of ground water table close to the ground previously.

Since the soil usually comprises of soil solid, water and air and super structural load on soil is carried by the both soil solid and pore water, as soon as the pore water is withdrawn, it will produce voids inside the soil system around and at the bottom of the foundation soil that leads to subsidence of the soil together with supporting structure. As a result, the collapsing of foundation happens.

To get more details about other reasons for failure, go through the following link www.mycivil.engineer



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www.constructioncost.co
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Why water cement ratio is vital in concrete mix?

In concrete there are different types of materials like cement, sand, Coarse aggregate and water which are combined in exact ratios. This ratio is provided at either as a nominal mix or by design mix.

All the materials contain definite properties and the strength of concrete is mostly dependent on these properties.

Cement is employed as a binding material in concrete because of the best adhesive and cohesive property whereas water is the cheapest and most vital of concrete. Once these two materials are blended, a chemical reaction alias hydration is produced with a sticky and thick gel that contains a binding property to tie all aggregate in form of hard and strong material. So, cement and water both can be used for binding all the materials of concrete jointly.

When cement and water are applied according to their ratio, it is known as water-cement ratio. Water-Cement Ratio means the ratio of the weight of water to the weight of cement.

Water/cement ratio with adherence to IS 10262 (2009) for the concrete mix differs from 0.4 to 0.6. 0.7 w/c ratio is also applicable for pumped concrete. 0.5 w/c ratio signifies that for each 100 kg of cement, 50 lit. of water is added. When w/c ratio is raised, the amount of water is reduced.

In technical terms, the cement should contain 23% of water for the hydration process and 15% for development of pores and volume increment. So, minimum 38% of the water by weight of cement should be maintained.

There should be adequate amount of water in the concrete mix to maintain full hydration of cement paste and eliminate capillary pores there. The minimum quantity of this water should be similar to 0.38 w/c ratio. Accordingly, if water-cement ratio is under 0.38, complete hydration can’t be performed. If the ratio is surpassed, this concrete mass turns out to be porous and penetrable and if it is less, concrete turns out to be dry and harsh and may not bond and attain full strength.

For work-ability purpose, this water-cement ratio should remain as 0.4, but its selection is based on the requirement of work-ability in various exposure conditions and nature of work. At a water-cement ratio of 0.4, the mix contains adequate water for hydration and simplifies the concreting process for mixing, placing, transporting and compacting since water functions as a lubricant in the concrete mix and decreases the internal friction among particles of concrete.

At this water-cement ratio, the ‘gel’ that is produced remains in good physical structure and solid state. At greater water/cement ratio the ‘gel’ that is produced remains in the poor physical structure. It produces voids throughout subsequent evaporation and develops into more porous. As a result, the strength gets lower in due course of time.

Computation of water quantity for concrete

While measuring the quantity of water for concrete mix, initially determine the cement content for the volume and w/c ratio. Suppose, there is 80 kg of cement for concrete mix and w/c ratio is 0.45.

Required amount of water = Cement volume X w/c ratio
So, essential water quantity is 80 kg X 0.45= 36 lit.

To get further information, go through the following link gharpedia.com




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Detail about 3D reinforcement in civil structure drawing

In this useful construction video tutorial, you will get the details of 3D reinforcement in civil structural drawing.

In this regard, you should have clear ideas on the followings :-

Stirrups 8Ø@150 C/C – It means the stirrups or rings should contain 8mm diameter. The distance among two rings in a column should be 150 mm center to center.

Bottom - 12Ø@150 C/C B/w (both way) – It is applicable in footing. The steel bars are placed horizontally and vertically in the footing. The distance among the two bars is 150 mm in both ways i.e. x axis and y axis.

3D reinforcement is provided in footing or foundation. It has the dimension like 12Ø@300 C/C three dimensional R/F.

Suppose the length, breadth and height of a foundation are 2m, 3m and 2m. Initially, the steel bars should be placed vertically at the spacing of 300 mm with 12mm diameter. It means the spacing should be maintained as 300 mm to both x and y axis horizontally & vertically for settling reinforcement. 3D dimensional reinforced is used to make foundation strong to bear heady load.

To get more clear ideas, go through the following video tutorial.

Video Source: Tutorials Tips

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www.constructioncost.co
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Get some easy to follow tips for executing brick masonry from Floor to roof

Brick masonry work is one of the most vital part of building construction. In this informative construction article, you will learn how to accomplish the complete brick masonry work from Earth beam to roof.

The following four major steps are involved in brick masonry work :-

1. up to basement
2. up to sill level
3. up to lintel level
4. up to roof level.

Brick masonry up to Basement:

Prior to erect brick masonry, the most crucial task is to finish all adjoining column up to basement.

It is recommended to execute the column rising work prior to brick masonry otherwise the following problems may occur :-

While erecting brick wall, shedding of mortar should be provided in to the column bottom to make it rigid and not smoothly detachable.

In next day, as soon as the shuttering work is completed, some saw dust from different shuttering materials like plywood, timber also shedding in to the column bottom. They can’t be detached easily after shuttering.

When the column concrete is arranged after the completion of the brick masonry, the water in the concrete is absorbed with dry brick wall and a dry concrete is placed there devoid of adequate water cement ratio and it leads to a weak structure.

Therefore, the exact method is to initially execute the column work and after that accomplish the brick wall.

Initially, cleanse the entire earth beam with water and ready surface. Employ semi solid cement slurry on it. Spatter the brick with water. Chip the column sides by chisel and make the column surface rough so that a perfect binding is formed with brick joint.

Initially, erect the brick masonry as a reference pillar similar to a benchmark in all corners by applying the plump, set square and verify each opposite brick wall corner with level for each 3 courses. Alter the thickness of the mortar to retain the proper level. Abide by the remaining unless it attains the basement.

There will be 2 options just like above. Any one method can be applied at corners and in cross wall extension.

In the 1st method, there should be no weak straight joints. Mortar can be easily provided.

In the 2nd method, there should be weak straight joint. Mortar can't be easily provided for progressing further.

Once the corner reference wall is finished, each course can be formed one by one by attaching a strong thread among the two benchmark and thus the whole basement will be finished easily.

To get more detail information, go through the following link youtoobuild.blogspot.com

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www.constructioncost.co

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How to calculate mason, labor for brick masonry construction with help of thumb rule

In this construction video tutorial, you will learn how to compute the mason as well as labor toward a 1st class brick masonry construction with the help of thumb rule.

A thumb rule refers to a principle having extensive application that is not projected to be exactly perfect or authentic for each situation. This method can be easily applied for making approx calculation or recollecting some value, or for making some determination.

It should be noted that the quantity of required labor will be gradually increased from ground floor to first floor to second floor etc.

Thumb rule is a constant value that is taken from the earlier construction work i.e. how much volume is covered by the labors employed in earlier projects. All the volumes are summed up to find out the average volume.

In ground floor, first floor and second floor, the volume of total area is taken as 150 m3

Ground floor :-

Mason = Volume x thumb rule (for mason) = 150 x 0.71 = 107 numbers
Now, suppose the charge for one mason = 1100 rupees
So, the cost for mason will be 107 x 1100 = 117, 700 rupees

Labor = 150 x 1.18 (thumb rule for labor) = 177 numbers
Suppose, one labor charge 800 rupees
Therefore, cost of labor = 177 x 800 = 141,600 rupees

Similar process should be followed for 1st floor and 2nd floor. Here, the value of thumb rule will be increased as the steps are increase.

To learn the calculation for 1st and 2nd floor, watch the following construction video tutorial.



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Some useful guidelines for constructing parapet wall

Parapet wall stands for a protection wall that can resist the collapsing from terrace to ground. Different types of parapet walls are found which range from brick wall masonry parapet wall, wooden handrail, iron grill etc.

Size of parapet wall:

1. Thickness of parapet wall should be minimum 9''. (full brick parapet wall)
2. Half brick parapet wall is not recommended for use.
3. Height of the parapet should be minimum 3'0''.

Once the centering and shuttering from roof slab bottom is detached, some deflection may happen at mid span of roof slab (positive bending moment). Similar thing will happen at support like negative bending moment.

With a view to prevent negative bending moment at support, huge amount of loads are required as downwards. In case of constructing the parapet wall as half brick wall, the roof can’t be prevented from uplifting. If the parapet wall is constructed as minimum 9'' thickness and minimum 3'0'' height, the roof slab can be prevented from uplifting. Therefore, different types of cracks at bottom of ceiling will be captured. To get rid of uplifting of roof, the centering & shuttering should be eliminated once the entire full brick parapet wall is constructed.

If the first floor is extended in future, the existing parapet wall should not be dismantled in case the wall is constructed as 9'' thick.

Assume, the parapet wall is constructed as half brick wall, now it is required to demolish the current parapet wall up to roof and make it as 9'', therefore, extra money will be incurred up to sill level of first floor.

While erecting half brick parapet wall, brick pillars should be arranged at regular interval ( 5 to 6 feet). Inner surface of parapet wall does not include flat surface since lots of offset will be created. Therefore, some problems will arise in waterline and sanitary plumping works.

Water from pump and discharge from water tank will be influenced with various offset produced with half brick parapet wall.

No tie exists for half brick parapet wall. As a result, wind pressure may provide some effects. Sliding of parapet wall may also happen.

If the column height is terminated for the height of the parapet wall (3 feet), it is required to dismantle for overlapping in future first floor construction. Adjacent Brick parapet wall will also be affected. If the height of parapet wall remains 3 feet, the column height should be increased for extra height for future overlapping. Then the column and parapet wall will be protected from over damaged.

Conclusion:
It is recommended to construct full brick parapet wall for minimum height of 3 feet devoid of half brick parapet wall.
There should be some provision for column for future overlapping.



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Common types of cracks in reinforced concrete column

Usually, Four types of cracks are found in reinforced concrete column which range from diagonal cracks, horizontal cracks, splitting cracks, corrosion cracks. The cracks happen in columns due to improper design, defective construction or overloading, erosion of reinforcement, isolated settlement of foundations, creep and shrinkage.

Cracking in reinforced concrete column may result in loosing of strength, consistency, longevity, and adversely impact aesthetics.

Types of cracks found in concrete columns:

1. Diagonal Cracks: If there are diagonal cracks in reinforced concrete columns, they encircle the whole face of column anywhere along its height. Because of insufficient load bearing strength of the columns, inadequate cross-section and inadequate reinforcement steel.

Diagonal Cracks significantly impact the structural soundness and therefore it should be monitored carefully.

2. Horizontal Cracks: Horizontal crack in reinforced concrete column is generally found at the beam-column joint, and on column face where tensile stress is massive. Columns with insufficient moment resistance strength, inadequate reinforcements, or disposition of installed reinforcement may lead to horizontal cracking owning to the effect of shear force and direct load and uniaxial bending.

Finally, horizontal cracks significantly decrease the shear strength of the column and as a result there is high risk of failure. So, it should be dealt with instantly and carefully.

3. Splitting Cracks: Splitting cracks in reinforced concrete column belong to short parallel vertical cracks having non-uniform width. These types of cracks may occur in columns with insufficient steel reinforcement, and low concrete quality. Splitting cracks in concrete columns originated because of attaining its maximum load bearing strength.

The ultimate Load bearing strength of the column is exceeded when concrete cross section is not enough or reinforcement ratio is inadequate or combination thereof.

4. Corrosion Cracks: Corrosion cracks in concrete columns are formed along the line of reinforcements. These types of cracks are usually homogeneous in width and expand as the column is ageing.

Probable reinforcement erosion and insufficient bond among the concrete and steel bars lead to erosion reinforcement in concrete columns. If these types of cracks are not dealt with properly, the erosion of reinforcement will be increased at a rapid rate.



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Some useful tips for footing excavation measurements

In this informative construction video tutorial, you will learn how to make calculation for earthwork excavation on the basis of elementary thumb rules. Besides, you will also learn how to make cross examination at the time of estimation.

This video is very useful for building engineer or civil site engineer.

Normally, earthwork is necessary for all the civil engineering projects roads, railways, earth dams, canal bunds, buildings etc.

This earthwork may range from either excavation or earth filling or sometimes both will reach out to as per the required shape and level.

Fundamentally, the volume of earthwork is measured from length, breadth and depth of excavation or filling.

The following items are included in earthwork :- Excavation, Backfilling, Disposal of surplus earth

Here, the calculation is done on the basis of IS Code 1200 for BOQ.

The calculation of earthwork billing is done in the following ways :-

1) Mode of measurement of billing – Types of measurement used for billing of excavation. It is done with the formula like Length x Breadth x Height/Depth

2) Different types of billing – a) R.A. Bill (Running Account Bill)
b) Find Bill

To get more details about the calculation of earthwork excavation, go through the following video tutorial.

Video Source: CE&T-Civil Engg & Technology

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Benefits of post-tensioning concrete slabs in building

Post-tensioned concrete slabs in buildings provide various benefits over reinforced concrete slabs & other structural systems toward both single and multi-level structures. Described below, some of the advantages of the slabs :-

Longer Spans: Longer spans are utilized to lessen the number of columns. It leads to bigger, column free floor areas which significantly enhance the adaptability of application for the structure as well as leads to greater rental returns.

Entire structural cost: The complete cost of materials, labor and formwork which are essential to build up a floor is decreased for spans higher than 7 meters and consequently leads to huge cost savings.

Minimized floor to floor height: Thinner slabs are utilized for the similar imposed loads. The decreased section depths facilitate least building height together with consequent savings in facade costs. As a substitute, toward bigger buildings, it facilitates more floors to be developed inside the original building envelope.

Deflection Free Slabs: Unwanted deflections under service loads are virtually removed.

Water-resistant slabs: Post-tensioned slabs are designed to remain free from cracks and as a result water-resistant slabs should be formed with proper design, detailing and construction. The selection of concrete mix and curing method together with standard workmanship are also very important.

Early formwork stripping: The earlier stripping of formwork and curtailed backpropping requirements facilitate rapid construction cycles as well as fast reprocessing of formwork.

Materials Handling: The decreased material quantities in concrete and reinforcement significantly offer benefit to on-site carnage requirements. The stability of post-tensioning strand is roughly 4 times that of traditional reinforcement. So, the whole weight of reinforcing material is considerably minimized.

Column and footing design: The decreased floor dead loads are applied to create cost-effective design of the reinforcement concrete columns and footings. In multi-storied buildings, decreased column sizes may raise the floor net rentable area.



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Some vital points to be remembered before purchasing ready mix concrete

The ready mix concrete is better as compared to the ordinary concrete mix since it needs less labour, time, efforts and cost. It facilitates to retain homogeneous quality during the work and provides the high speed of concrete construction.

With ready mix concrete, various types of issues like inferior workability, segregation, and bleeding, inappropriate water cement ratio, insufficient mixing time can be easily resolved in the construction site.

Prior to order ready mix concrete, the following points should be taken into consideration :-

01. Grade of Concrete or Mix Design

• Types of work where the concrete will be poured i.e. foundation slab, floor slab, pavements, etc.
• Grade of concrete necessary on site, i.e. M15, M20, M25, M30, etc.
• Slump of concrete both at the batching plant and at the job site.
• The quantity of concrete in cubic meter or cubic yard.
• Address or place of concrete pouring.
• Time of requirement of ready mix concrete on site.
• Time of interval among the two consecutive deliveries of RMC (in the case of higher quantity i.e. exceeding 6 cubic meter).

02. Fly Ash should not be used extra: It is essential to get the proper ratio of fly ash in the concrete. Some RMC producer includes extreme amount of fly ash in concrete which aren’t suggested also by the standards.

Generally, the fly ash is added in concrete at levels which vary from 15% to 25% by mass of the cementitious material component. Plant owner accomplishes this so that the cost is decreased and the profit is raised. So, the purchase should be careful for buying RMC at lower rates, and not get deceived with this lower rates.

It is also essential to get the source of every concrete ingredients (cement, aggregates, admixture, and water), the ratio and quantity of the concrete material per cubic meter, and the types of admixtures applied in RMC. So, prior to give order for ready mix concrete, obtain the above information. i.e. details of mix design from dealer.

03. Source of materials: The RMC dealers buy various concrete materials from diverse sources. The quality of materials may not be always good. So, all the sources should be assessed carefully. If their sources are recognized in the local market for the quality, then the ready-mix dealer can be selected, who will purchase the concrete materials from those renowned sources.

04. Time for Transportation: According to IS 4926:2003, it is recommended to pour the ready mix concrete within 2 hours from the time of loading at the central batching plant. However, a higher period is allowed if retarding admixture is utilized. But, determine the type of retarder used and all steps are followed as suggested by retarding manufacture.

05. Application of Admixture: Sometimes the extra dose of admixture is included at the project site to retrieve the workability of concrete. Some admixtures have chlorides, and if so, it is required to get the amount of chloride content in percentage of the total mass of admixture. If the amount of chloride is increased in ready mix concrete, it will lead to corrosion of the reinforcement steel and the service life of the house or building will be significantly affected. Hence, such admixtures should not be used.

06. Test of Concrete: It is indicated in standards that the ready mix concrete dealers should arrange test facilities at its premises to conduct routine tests, i.e. concrete slump test, concrete cube testing, etc. So, it is possible to double check the workability and strength of ordered concrete.

The workability of concrete can also be verified with slump test on site. Slump of concrete is primarily based on the condition of placement and the requirement of degree of workability. According to IS 456:2000, low reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 25 to 75 mm. Heavily reinforced sections like slabs, beams, walls, columns, etc. are casted with the slump of 50 to 100 mm. From slip form work or pumped concrete, the appropriate slump of concrete is 75 to 100mm.

07. Information about Delivery Ticket of Ready Mix Concrete

The information given below, should be providedd in the ready mix concrete delivery ticket for each batch:

• Name and number of the ready-mixed concrete plant.
• Date and serial number of the ticket
• Truck Number
• Name of the purchaser and location of the site
• Grade of concrete
• Mix design details
• Type and size of concrete ingredients and their weight in table format.
• The quantity of concrete in the cubic meter
• Time of loading
• Slump results at the batching plant
• Signature of the concrete plant operator

The information given below, is required to be filled on ready mix concrete ticket on site.

• Time of arrival on site
• The time when discharge was completed
• Any water/admixture added on site
• Location of pouring of concrete
• Slump test result at the site
• Signature of RMC receiver



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Published By
Rajib Dey
www.constructioncost.co
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