Concrete Mix Design & Concrete Calculator – A useful app for civil engineers

Concrete Calculator is a free calculator that can be used for the following purposes :-

1. Measure cement, sand and aggregate quantity in concrete.
2. Measure the number of premix bags necessary for your project.

3. There is option to settle your own size and rate of premix bags.
4. Measure the volume of concrete necessary for slabs, walls, footings and columns.
5. Work out the weight of materials essential for making the calculated volume of concrete.

The purpose of concrete mix design method is to make proportion of the materials of concrete (cement, sand, and aggregate) inexpensively to attain superior strength and stability on the basis of the materials obtainable at a construction site.

The nominal concrete mix proportions adhering to the code may contain a greater amount of cement with regard to the actual amount necessary when it is designed on the basis of actual design parameters, consequently the cement requirement may be low for the equivalent grade of concrete for a specified site.

The proportions originating from concrete mix design are examined for their strength through compressive strength test on concrete cubes and cylinders.

This concrete calculator is specifically designed for professional Civil Engineers, Concrete Technologists, Civil Engineering Students and DIY(Do It Yourself) enthusiasts similarly.

The user interface is very simple and results are provided specifying the amount of ingredients necessary in kilograms. The design steps are also provided in order that s the user will be able to simply validate the calculations.

To download, click on the following link play.google.com

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Published By
Rajib Dey
www.constructioncost.co
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Specifications of cement concrete in detail

Cement, fine aggregates, coarse aggregates and water are mainly used to form cement concrete. While writing detailed specifications, explain The specifications of every single component should be narrated briefly at the time of formulating detail specifications.

CEMENT: Cement belongs to the elementary and most vital component of cement concrete. The quality of cement should be fresh while utilizing it for construction work and it should satisfy the standard specifications.

FINE AGGREGATE: Sand is utilized as fine aggregate in cement concrete. Sand particles should comprise of coarse, sharp and angular edges. Size of sand particles should be maintained in such a manner that it can move through 4.75mm sieve. Sand should be clean and does not contain dust and organic matters. Sea sand should not be applied for construction work due to extreme salt contents.

Stone dust is also applied as fine aggregate in cement concrete, but prior to application, check that it adheres to specifications.

COARSE AGGREGATE: Normally, pieces of feverous rocks are applied as coarse aggregates. These stones should be solid, strong, long-lasting and clean. The shapes of aggregates should be cubic or closed to cubic shape. The shape of coarse aggregates should not be laminated and elongated. It should be clean and does not contain from any irrelevant organic matters.

The size of coarse aggregates should satisfy the approved construction work requirements. It should not move through the sieve size of 5mm and coarse aggregates should be graded. Voids should not go beyond 42%.

PROPORTIONING: Based on their fixed ratios, cement, sand and coarse aggregates should be calculated. Prepare a standard measuring box as per the volume of one cement bag. Volume of one cement bag is 1.25 cubic foot.

When, it is required to calculate the ratio of sand, bulking of sand should be taken into consideration. Choose dry sand at the time of making calculation of proportioning. Work out the moisture content in sand and include extra volume of sand. Constantly work out moisture content throughout construction work and include extra volume of sand based on the amount of moisture. It is suggested not to compact coarse aggregates at the time of proportioning.

CONCRETE MIXING: Mixing machine is suitable for large scale construction works whereas hand mixing is chosen since it is cost-effective for smaller concrete works.

CONCRETE CONSISTENCY: Concrete consistency is based on water to cement ratio. Surplus amount of water reduces the strength of concrete and also concrete constituents can be easily detached. The quantity of water given below should be applied against 50kg cement bag.

Concrete Ratio - Amount of Water
1:3:6 - 34 liters
1:2:4 - 30 liters
1:2:3 - 27 liters
1:1:2 - 25 liters

If vibrator is utilized for concrete compaction, then the amount of water should be reduced as per suggestion of engineer in charge.

 
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Some useful guidelines for the calculation of concrete costs

Besides, considering the price of concrete per yard (or meter), cost calculation of new concrete includes other items like surface prep, formwork, reinforcing materials, and finish work, as well as the cost of the ready-mix concrete, that will be included to the total price of the concrete work. The Costs for specific items differ location wise or from site to site, but an approximate estimate can be prepared with some average amounts.

Cost Per Yard of Ready-Mix Concrete

The most vital item refers to the price of concrete, whether ready-mix concrete or other concrete material are utilized. Local ready-mix concrete suppliers can provide you the quotes based on the project specifications and the job location. Concrete pricing is generally stated per cubic yard or cubic meter (metre). For an average estimating purpose, utilize $77 per cubic yard.

Cost of Concrete Sub-Grade Work

When the concrete is set over soil, it is required to grade or make the surface ready for the concrete. Pricing for this includes the expenses associated with grading, compacting soil, excavating, trenching, and other components. As a good average, it is recommended to utilize $65 per hour of work required to set up the surface, supposing that the surface is leveled over 75 percent and no special work is necessary to make the site ready.

Costs for Extra Sub-Grade or Site Work

If the surface is unleveled, it is required to incur expenses for additional site work like excavating and filling with proper material or eliminating a soft spot on the terrain to prepare it for resisting structural loads. Based on the distance from where the sand will be arranged or any other proper fill material, it could put in over $10 per cubic yard or meter to your estimate. Another cost may incur for polyurethane plastic or vapor barrier essential to be set up prior to concrete placement.

Cost of Concrete Formwork

Developing concrete forms generally indicate a vital part of the total cost of concrete work, since it is one of the most time-consuming tasks of the job. It is required to recognize the type of formwork to be utilized as well as how it will be set up, and whether the form materials will be purchased or rented. Other related costs may contain a crane or other equipments which are applied to shift the form materials, form release product, re-processing form materials, and the cost to repair forms after various applications.

On average, formwork costs at $1.10 per square foot of the concrete area. It is calculated for a square or rectangular area. The cost is increased for concrete, if the formwork is rounded or contoured.

Cost to Finish Concrete

Concrete prices change considerably based on the type of finishing stated in the design. Concrete is finished several ways like smooth surface, exposed aggregate surface, or stamped concrete finish. Some surfaces may need only a strike-off and screed to perfect contour and elevation, whereas for others surfaces, a broomed, floated, or troweled finish should be specified. To calculate the finishing in your concrete pricing analysis, add $0.75 per square foot or perhaps more, based on the intricacy of the specified finish. The cost of any curing compound or testing services required should also be considered.

Cost of Concrete Reinforcement

Most concrete comprises of some type of reinforcement, like rebar, wire mesh, plastic mesh, or fiber which are included to the concrete mix to make the strength and crack-resistance better. Standard reinforcing materials can include roughly $0.18 cents per square foot. This number is greater for large-diameter rebar or other special reinforcement.



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How to design rectangular and T shape beam

Beams are defined as members which are exposed to flexure. So, it is important to give attention to the analysis of bending moment, shear and deflection.

When the bending moment operates on the beam, bending strain is created. The resisting moment is formed with internal stresses. Under positive moment, compressive strains are developed in the top of the beam and tensile strains in the bottom.

Concrete is weak against tensile strength and it is not perfect for flexure member by itself. The tension side of the beam will collapse prior to failure of compression side when beam is exposed to a bending moment devoid of the reinforcement. To resolve this issue, steel reinforcement is provided on the tension side. The steel reinforcement withstands all tensile bending stress as tensile strength of concrete is zero when cracks are formed.

Rectangular beam

Accept the depth of beam with the ACI code reference, least thickness until the deflection is considered.
Accept the beam width (ratio of width and depth is approx 1:2).

Calculate self-weight of beam & design load.
Work out factored load (1.4 DL + 1.7 LL).
Calculate design moment (Mu)
Work out maximum possible nominal moment for singly reinforced beam (φM n ).

Determine reinforcement type by making comparison between the design moment (M u ) and the maximum possible moment for the singly reinforced beam (φM n ). If φM n remains under Mu, the beam should be designed as a doubly reinforced beam otherwise the beam should be designed with tension steel only.

Find out the moment strength of the singly reinforced section (concrete-steel couple).

Calculate the necessary steel area for the singly reinforced section.
Determine an essential residual moment, deducting the total design moment and the moment capacity of the singly reinforced section.
Calculate the extra steel area from the required residual moment.
Calculate the total tension and compressive steel area.
Design the reinforcement with the selection of the steel.
Verify the actual beam depth and assumed beam depth.

T-shape Beam

Calculate the design moment (Mu ).
Presume the effective depth.
Choose the effective flange width (b) depending on ACI criteria.

Workout the practical moment strength (φM n ) anticipating the total effective flange is supporting the compression.

When the practical moment strength (φM n ) is greater than the design moment (Mu ), the beam is measured as a rectangular T-beam with the effective flange width b. If the practical moment strength (φM n ) is not more than the design moment (Mu ), the beam will operate as a true T-shape beam.

Determine the approximate lever arm distance for the internal couple.
Work out the approximate required steel area.

Design the reinforcement
Verify the beam width
Calculate the actual effective depth and analyze the beam



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Published By

Rajib Dey

www.constructioncost.co

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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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Stress Control by Deflecting & Debonding Tendons in PSC Design

If precast beams contain straight, fully bonded tendons, they can be easily detailed and manufactured. The main benefit of pre-stressing is that it can apply the dead toad of the unit to minimize the transmission of the tensile stresses in the concrete.

But dead load is lost in such members since this tension remains most critical at the ends of the beams, where the alleviating effect owing to dead load is zero. The methods of deflecting and debonding tendons are frequently applied in pre-tensioned beams to obtain a pre-stress distribution much like that is obtained by the draped profiles of post-tensioned systems. It maintains some of the dead-load benefits, which lead to fewer tendons in the beams or a slightly smaller depth of beam than would be feasible with straight, fully bonded tendons.

Stress Control by Deflecting Tendons: The method of deflecting some of the tendons upwards towards the ends of a beam at a proper position along the span transfers the important section at transfer to this position, where vital relieving stresses as beam dead-load bending moment is accessible. Based on the stress computations for the end regions of the beam, the design engineer set the number of tendons to be deflected and the position of the deflection point.

The deflection point normally remains in the neighborhood of the quarter-span position, where three-quarters of the mid-span value of dead-load moment is accessible to neutralize the tensile stress (top fibre) because of pre-stress at transfer.

The angle of deflection of these tendons are placed in such a manner that the effective eccentricity and the pre-stressing force of the tendons do not generate a tensile stress of more than N/mm2 at transfer at the important sections, a limit set in the Code.

This method of deflecting tendons is specifically effective where continuity for live loads should be set in the finished structure since by deflecting some of the tendons upwards towards the ends of a beam, some compressive stresses are produced in the top fibre at the ends. This is useful for withstanding tensile stresses occurred because of the hogging moments caused by the passage of live loads on the superstructure. It also minimizes the formation of compressive stress in the bottom fibre because of prestress and live loads or any other loads at the ends of the beam.

Another benefit of deflected tendons is that the Code allows the vertical component of the tendon force to be applied in withstanding the imposed shear force on the beams in areas which stay flexurally uncracked at the ultimate limit state. This component is also suitable for the flexurally cracked regions and for examining the maximum shear stress condition in the member. Due to some limited test evidence, however, the Code does not allow relief against shear in these later conditions. Actually, the shear resistance of any section is decided in both flexurally cracked and uncracked modes and the lower value is selected. The shear links are then designed to bear the rest of the enforced shear force. Because only the tendons which are situated within the web width are deflected, the strand pattern for the whole unit should be cautiously chosen so that sufficient strands are available for deflecting upwards towards the ends to meet the stress conditions during the length of the beam.

To get more details, go through the following link engineeringcivil.org



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www.constructioncost.co
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RCC Column Design – An exclusive mobile based app for civil and structural engineers

RCC Column Design is an exclusive app for civil and structural engineers. This app is available in google play store. It can only work in windows platform.

The app is very user-friendly. There are several fields in the app which range from Factored Axial Load (kN), Length (mm), Width (mm), Concrete Strength (M15, M20 and M25), Steel Strength (HYSD 415, HYSD 500).

Just enter the values in these fields and click on calculate button to get the desired values.

This app is designed on the basis of the Limit State Method with adherence to Indian standard code IS 456:2000. This app takes into account the axial load on a column to recommend a secure design depending on input of column size, concrete strength and steel strength. The app is also very useful for Uniaxial and biaxial bendings.

This app can design a rectangular slender RCC column that contains standard height. It works out necessary reinforcement for a specified axial load for the assumed inputs.

This app is developed for educational purposes only. The answers should be double checked manually.

To download the app, click on the following link play.google.com

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Published By

Rajib Dey

www.constructioncost.co

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Benefits and uses of Light Weight Concrete

Usually, the traditional concrete is made of a heavy material containing density about 2400kg/m3 and strong thermal conductivity. If, the ordinary concrete is used for building up the structure, it can increate the dead weight of the structure and as a result the structure turns out to be heavy. The cost of the structure is also increased significantly.

The light weight concrete is defined as the concrete whose density differs from 300 to 1800 kg/m3.The following methods are applied to build up light weight concrete:

1) By cellular construction.
2) By generating huge quantities of air
3) With the use of no fines concrete
4) With the use of light weight aggregates like expanded clay, shale and slate , fly ash, blast furnace slag etc.

Advantage: The light weight concrete is beneficial for the following reasons :-

a) Because of its low density , it can minimize dead load, enhances the advancement of building and reduces the handling cost.
b) The light weight concrete contains low thermal conductivity. Therefore, in severe atmospheric condition, the type of concrete is mostly recommended.
c) When light weight concrete is used, it provides an opening for industrial wastes like fly ash , slag etc, to get rid of the issue for disposal.
d) It has good resistance capacity against fire.
e) The process for slicing , cutting, drilling or nailing becomes easier for light weight product. It can simplify the construction and repair work.

Uses: Given below, various applications of light weight concrete :-

a) It is extensively utilized as insulator to exterior walls of different types of buildings.
b) It is suitable for erecting load bearing walls, filler wall and partition wall.
c) It is effective for producing pre-cast floor and roof panels and composite walls.
d)It can also be applied for building up in situ composite roof and floor slabs.



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Tips to compute the quantity of cement, sand and aggregate in concrete & water cement ratio

In this construction video tutorial you will learn how to work out the quantity of cement, sand and aggregate in concrete and water cement ratio.

To do it, you should have clear conceptions on the following items :-

Grades of concrete Mix Ratio

M10 - 1:8:6
M15 - 1:2:4
M20 - 1:1.5:3
M25 - 1:1:2

Here, M means Mix and number means the compressive characteristics strength of concrete in 28 days.

Water Cement Ratio :- Grade of cement Water per bag (50 kg) cement (weight of 1 bag cement is 50 kg)

M5 - 60 litre
M7.5 - 45 litre
M10 - 34 litre
M15 - 32 litre
M20 - 30 litre

For calculation purpose, wet volume of concrete = 1 m3

Dry volume = 54% increase by weight volume
Wet volume = 100% + 54% = 154%
In order to covert it to numbers, just divide by 100
154/100 = 1.54

So, dry volume is 1.54 x wet volume
Now, you have to provide the density of cement, fine aggregates and course aggregates as follow :-
Cement = 1440 Kg
Fine Aggregate = 1450 to 1600 Kg/m3
Course Aggregate = 1450 to 1500 Kg/m3

Now, on the basis of the above dimensions, you can start calculation for the different grades of concrete. To know the detailed calculation process, watch the following video tutorial.

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www.constructioncost.co
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How to estimate cement bags in 1 cubic meter

Suppose the proportion of nominal mix is 1:2:4 (one part cement, 2 part sand and 4 part aggregate)

Wastage of cement is taken as 2%
Output of mix is provided as 67%.

For 1 cum output, the requirement of dry mix is 1/0.67 = 1.49 say 1.50 cum.
After including the wastage (2%), the output will be (1.50 + 0.02) = 1.52 cum.
Volume of cement = (cement/cement+sand+aggregate) × Total material

= (1/1+2+4) × 1.52
=0.2171 cum
The density of cement is 1440 kg/cum and
Weight of 1 bag cement = 50 kg.

So, volume of 1 bag cement = 50/1440
=0.0347 cum.
No. of cement bags essential in 1 cubic meter = 0.2171/0.0347
= 6.25 bags.
The above formula can be utilized for measuring cement for other nominal mixes.

To get more details, watch the following video tutorial.



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Comparison between OPC and PPC (fly ash based cement)

OPC 53 Grade Cement:OPC (Ordinary Portland Cement) belongs to the basic form of cement and it is formed with 95% cement clinkers and 5% gypsum.

Gypsum stands for an additive and it’s objective is to enhance the setting time of the cement to a executable 30 minutes or more.

OPC Cement provides high compressive strength at initial phases and at 28 days. A 53 Grade cement provides equal to 70 MPa strength across a minimum 53 MPa stated by BIS. Therefore, fly ash can also be blended (minimum 20% by weight of cement) in concrete as part replacement of cement at jobsite.

Due to this the material cost of concrete is saved significantly as well as durable properties can be maintained because of pore refinement (Less porous concrete).

If the concrete is formed in this way, the adaptability of concrete is enhanced greatly and it leads to higher strength in due course.

Recommended use for OPC 53 Grade Cement:

OPC 53 Grade cement is normally mostly suitable for Structural Concrete or Reinforced Concrete Works (like Columns, Beams, Slab etc.,).

PPC (Fly Ash Based) Cement: Alternatively, PPC (Portland Pozzolana Cement) is formed with 75 – 77% cement clinker, 20% flyash and 3-5% gypsum.

Recommended use for PPC: Flyash based cement (PPC) will be effective for brick masonry, plastering, tiling and waterproofing works. In these works, strength is not a vital factor. PPC is more beneficial as compared to OPC because PPC contains slower rate of heat of hydration.

Thus PPC is likely to less cracks & shrinkage), superior workability and finishing (because fly ash based cement are circular in shape and thinner in size).

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Definition of M20 grade of concrete

In construction, there should be individual strength for each building element.

To maintain the strength of concrete for different elements, various types of concrete grades are required. The strength needed for foundation, beam, slab etc. will be different.

IS 456-2000 has specified the concrete mixes into a number of grades as M10, M15, M20, M25, M30, M35 and M40. In the following construction video tutorial, brief explanation is given on M20 grade of concrete.

In M20, M denotes Mix and 20 refers to the characteristic strength (fck) of that mix i.e. 20mpa. Cement, sand and aggregates are used for mixing in the ratio of 1 : 1.5 : 3. M20 signifies mixture of cement, sand and aggregate which are prepared in such a manner that a cement concrete cube of size 15 cm x 15 cm x 15 cm is formed with characteristic strength (fck) of 20mpa while examining it after being cured for 28 days.

The characteristic strength (fck) signifies the strength under which not over 5% of test results are predictable to fail.

Cement is always calculated with weight. Commonly it is applied in terms of bags. The weight of one bag of cement is 50 kg and it contains a volume of 35 litres (or, 0.035m3). A gauge box is employed for batching of fine and coarse aggregate by volume.

To get more brief information, watch the following video tutorial.

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Some useful construction tips to provide clear cover for reinforced concrete structure

This construction video tutorial will provide detailed guidelines on how to provide perfect clear cover in reinforcement concrete structure.

With the intension of safeguarding the reinforcement from corrosion as well as arranging fire resistance to bars implanted in concrete, clear cover is set for Reinforced Concrete Structures.

Clear cover stands for the distance among C.G of reinforcement bars and bottom most point of concrete.

The thickness of cover is dependent on ecological conditions and nature of structural member.

The depth of concrete cover is calculated by applying a cover meter.

The clear cover that should be provided is determined by Indian Standards. IS 456:2000.

Watch following youtube video to learn the complete process :-

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