How to calculate bricks and cement quantity for brick work?
For rate analysis and cost estimation purposes. calculation of quantity of nos of bricks and cement is generally required as per size of available bricks, ratio of mortar that will be used and workmanship factors. This video helps you to calculate nos of brick, quantity of mortar, quantity of cement and quantity of sand for one cum of brick work.
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Different types of drawings is used in construction such as architectural drawings, structural, electrical, plumbing and finishing drawings. These drawings provides layout plans and details for construction of each and every part of the building.
Drawings plays an important role in the construction field to convey the ideologies and perspective of the designer to the layman at site. The drawings may be used to indicate the overall appearance, inside or outside the structure, or they may be used to indicate precise measurements and other details for construction.
Types of Construction Drawings
There are different type of drawing used for the construction process. Depending upon the purpose they serve, construction drawings are divided into 5 types,
1. Architectural Drawing
Architectural drawing can be termed as the mother drawing for all the other drawings used for construction. It contains all the details of the project such as location site plan, setting out plan, elevations, sections and other details.
1.1 Site Plan
This is primary drawing used for marking out the plan on the ground. It represents the location, orientation and information about the site’s topography, landscaping utilities ,and site work.
1.2 Working Plan
This drawing gives the information of horizontal dimensions of the building, thickness of walls, clear spaces inside the building and column locations. it also shows the openings required in the building such as doors, windows and ventilators.
1.3 Section Drawings
Section drawings represents the material of construction to be used, heights and measurement of the different components of buildings, type of structural components such as type of slab , etc. Its represents the drawing when the building is cut through a vertical plane.
1.4 Elevation Drawing
Elevation drawing represents the information of openings, size and shape of external surface, height of building and finish of the building after completion. These drawings are made by having a aesthetic view of the building.
2. Structural Drawing
Structural drawings can be termed as the backbone drawing of the building. It consists all the information about the structural intervention that are coming on a building. It contains many type of drawing with very minute details and description.
2.1 General Note
This is more of a codes and by laws of the buildings. No drawing is found in this, but the details of all the structural drawings are mention in this such as concrete mix, lapping length, curing time, abbreviation, codes and other work procedures.
2.2 Excavation Drawing
This drawing represents the footing excavation dimension, column position, footing plan and grid lines of column.
2.3 Column Layout
This drawing represents the position and orientation of columns and column reinforcement details.
2.4 Plinth Beam Layout
This drawing represents the dimensions, position and section of plinth beam and the details of reinforcement in plinth beam.
2.4 Lintel Beam Layout
This drawing represents the dimensions, position and section of lintel beam and the details of reinforcement in lintel beam.
2.5 Roof Beam and Shuttering Layout
This drawing represents the details of reinforcement of roof beam, its section and shuttering details.
2.6 Roof Slab Layout
This drawing represents the details of reinforcement of roof slab, its section and openings in the roof for various purpose such as stairs or skylight.
3. Electrical Drawing
Electrical drawing represent the details of electrical fixtures, location of switches, fan, light and others. It also represents the load calculation, tapping for electricity, wiring path and other interventions such as AC and UPS and its components.
4. Plumbing Drawing
Plumbing drawings give the location of sanitary, piping for water supply system, fixture, and the process to connect every fixture.
5. Finishing Drawings
Finishing drawings represents the finish type of every component of the building such as flooring pattern, painting color, false ceiling shape, plastering texture and elevation design. These details are sometime given in elevation drawings also.
There is no standard rule of drawings required for a project. Depending upon the type of building and requirement, types of drawings are made and issued .
The estimation of building quantities like earth work, foundation concrete, brickwork in plinth and superstructure etc. can be worked out long wall short wall method and centerline method.
Following are the three different methods used for estimating building works:
Long wall – short wall method
Partly centre line and short wall method.
Long Wall – Short Wall Method
In this method, the wall along the length of room is considered to be long wall while the wall perpendicular to long wall is said to be short wall.
To get the length of longwall or shortwall, calculate first the centre line lengths of individual walls. Then the length of long wall, (out to out) may be calculated after adding half breadth at each end to its centre line length.
Thus the length of short wall measured into in and may be found by deducting half breadth from its centre line length at each end.
The length of long wall usually decreases from earth work to brick work in super structure while the short wall increases. These lengths are multiplied by breadth and depth to get quantities.
Centre Line Method
This method is suitable for walls of similar cross sections. Here the total centre line length is multiplied by breadth and depth of respective item to get the total quantity at a time.
When cross walls or partitions or verandah walls join with main wall, the centre line length gets reduced by half of breadth for each junction.
Such junction or joints are studied carefully while calculating total centre line length. The estimates prepared by this method are most accurate and quick.
Partly Centre Line and Partly Cross Wall Method
This method is adopted when external (i.e., around the building) wall is of one thickness and the internal walls having different thicknesses. In such cases, centre line method is applied to external walls and long wall-short wall method is used to internal walls.
This method suits for different thicknesses walls and different level of foundations. Because of this reason, all Engineering departments are practicing this method.
Cracks in concrete are extremely common but often misunderstood. When an owner sees a crack in his slab or wall, especially if the concrete is relatively new, he automatically assumes there’s something wrong. This is not always the case. Some types of cracks are inevitable. The best that a contractor can do is to try to control the cracking. This is done by properly preparing the subbase, assuring that the concrete is not too wet, utilizing reinforcement where needed, and by properly placing and spacing crack control joints and expansion joints. However, sometimes cracks happen in spite of any precautions taken.
The American Concrete Institute addresses this issue in ACI 302.1-04. “Even with the best floor designs and proper construction, it is unrealistic to expect crack-free and curl-free floors. Consequently, every owner should be advised by both the designer and contractor that it is normal to expect some amount of cracking and curling on every project, and that such occurrence does not necessarily reflect adversely on either the adequacy of the floor’s design or the quality of its construction (Ytterberg1987; Campbell et al. 1976)”.
Diagnosing 6 Types of Concrete Cracks
Plastic Shrinkage Cracks
Probably the single most common reason for early cracks in concrete is plastic shrinkage. When the concrete is still in its plastic state (before hardening), it is full of water. This water takes up space and makes the slab a certain size. As the slab loses moisture while curing it gets a bit smaller. Because concrete is a very rigid material, this shrinking creates stress on the concrete slab. As the concrete shrinks, it drags across its granular subbase. This impediment to its free movement creates stress that can literally pull the slab apart. When the stress becomes too great for the now hardened concrete, the slab will crack in order to relieve tension. Especially in hot weather, shrinkage cracks can occur as early as a few hours after the slab has been poured and finished.
Often, plastic shrinkage cracks are only a hairline in width and are barely visible. However, even though a crack is hairline, it extends through the entire thickness of the slab. It’s not just on the surface as one might think.
One factor that contributes significantly to shrinkage is mixing the concrete too wet. If excessive water is introduced into the mix, the slab will shrink more than if the correct amount of mix water were used. This is because the additional water takes up more space, pushing the solid ingredients in the mix further apart from each other. It’s similar to over-diluting a pitcher of Mi-Wadi. By doing so, a weaker solution is created. When the excess water leaves the slab, the solid particles have larger voids between them. These empty spaces make the concrete weaker and more prone to cracking. Unfortunately, wetter concrete is easier to place and finish, especially in hot weather. This is one reason that many concrete finishers add water to concrete mixer trucks: it makes their work easier. A few litres per cubic metre will not significantly affect the mix. However, if an excessive amount of water is added, one can unwittingly reduce the concrete’s strength.
Plastic shrinkage cracks can happen anywhere in a slab or wall, but one place where they almost always happen is at re-entrant corners. Re-entrant corners are corners that point into a slab. For example, if one were to pour concrete around a square column, you would create four re-entrant corners. Because the concrete cannot shrink around a corner, the stress will cause the concrete to crack from the point of that corner (See Figure 1).
Figure 1: Shrinkage cracks originating at re-entrant corners
A rounded object in the middle of a slab creates the same problem as a re-entrant corner. This is commonly evidenced around slab penetrations such as pipes, plumbing fixtures, drains, and manhole castings. The concrete cannot shrink smaller than the object it is poured around, and this causes enough stress to crack the concrete (See Figure 2).
Figure 2: Shrinkage crack at slab penetration
To combat random shrinkage cracks, control joints (often mistakenly referred to as expansion joints) are incorporated into the slab. Control joints are actually contraction joints because they open up as the concrete contracts or gets smaller. They are simply grooves that are tooled into fresh concrete, or sawed into the slab soon after the concrete reaches its initial set. Control joints create a weak place in the slab so that when the concrete shrinks, it will crack in the joint instead of randomly across the slab (See Figure 3).
Figure 3: A successful crack control joint
For a crack control joint to be effective, it should be ¼ as deep as the slab is thick. That is, on a typical 100mm thick slab, the joints should be no less than 25mm deep; a 150mm thick slab would require 38mm deep joints, etc. To minimize the chances of early random cracking, these joints should be placed as soon as possible after the concrete is poured. If the control joint is not deep enough, the concrete can crack near it instead of in it (See Figure 4).
Figure 4: A crack next to a too-shallow joint
Crack control joints should be placed at all re-entrant corners and slab penetrations, and evenly spaced throughout the rest of the slab. A good rule of thumb for 100mm thick residential concrete is to place joints so that they separate the slab into roughly equal square sections, with no joint being further than about 3 metres from the nearest parallel joint. Following these guidelines, a 1.2 metre wide footpath would be cross- jointed at 1.2m intervals. A 4.8 m x 19.2m driveway would have one joint running up the centre length ways, and joints cut across it every 2.4 metres . This pattern would create sixteen 2.4m x 2.4m sections. If a driveway is metre wide or less, the centre joint up its length can usually be safely omitted, and the cross joints spaced the same distance as the driveway is wide (for example, an 3 metre wide driveway would have no centre joint and cross joints every 3 metres). If joints are not placed where they need to be, the concrete will create its own joints by cracking. It’s interesting to note that it often cracks in the same pattern as it should have been jointed (See Figure 5).
Figure 5: Driveway cracks where joints should have been placed
Another reason that concrete cracks is expansion. In very hot weather a concrete slab, like anything else, will expand as it gets hotter. This can cause great stress on a slab. As the concrete expands, it pushes against any object in its path, such as a brick wall or an adjacent slab of concrete. If neither has the ability to flex, the resulting force will cause something to crack.
An expansion joint is a point of separation, or isolation joint, between two static surfaces. Its entire depth is filled with some type of compressible material such as tar-impregnated cellulose fibre, closed-cell poly foam, or even timber (See Figure 6). Whatever the compressible material, it acts as a shock absorbed which can “give” as it is compressed. This relieves stress on the concrete and can prevent cracking.
Figure 6: Foam expansion joint separating driveway and curb.
Expansion joint material can also prevent the slab from grinding against the abutting rigid object during periods of vertical movement. During these times of heaving or settling, expansion joint material prevents the top surface of the slab from binding up against the adjacent surface and flaking off (See Figure 7).
Figure 7: Expansion joint between these slabs would have prevented chipping
Cracks Caused by Heaving
Another factor which contributes to cracking is ground movement brought on by freeze/thaw cycles. During such cycles, the frozen ground can lift as much as several inches, and then settle again when the ground thaws. If the slab is not free to move with the soil, the slab will crack. The presence of large tree roots can also cause concrete to heave. If a tree is located too close to a concrete slab, the growing roots can lift and crack the concrete (See Figure 8).
Figure 8: Tree roots lifted and cracked this sidewalk
Cracks Caused by Settling
Conversely, if a large tree is removed from near a concrete slab the buried roots will decompose. The resulting void can cause the ground to settle and the concrete to crack. Settling is also called subsidence.
Subsidence is very common over trenches where utility lines and plumbing pipes are buried. Often times, the utility trench is not compacted when it is refilled. If concrete is placed atop a poorly compacted trench, the void created by subsidence can cause a crack across the unsupported concrete slab (See Figure 9).
Figure 9: Crack across the unsupported concrete slab.
Another place where concrete commonly subsides is near a house. Whether the home is built on a basement or crawlspace, the over-dig is subsequently back filled. Unless the back fill material is compacted in lifts as the over-dig is filled, it will settle over time. This settling will cause any concrete poured atop it to settle along with it. Many times this settling will cause the concrete to crack and tilt back toward the house, creating negative slope (See Figure 10).
Cracks Caused by Overloading the Slab
Another factor which contributes to cracking is placing excessive weight on top of the slab. Although it is a very strong material, concrete still has load limits. When you hear someone speak of 4,000 psi concrete, they are referring to the fact that it would take 4,000 pounds per square inch of pressure to crush it. Residential concrete, however, is rarely overloaded as far as compressive strength is concerned. That is to say, the weight doesn’t usually pulverise or crush the concrete. What is more common is that the excessive weight is too much for the ground underneath the concrete. This is especially true after periods of heavy rain or snow melt when the ground is saturated and soft.
When groundwater migrates under the concrete it causes the underlying soil to become soft or spongy. Excessive weight on the slab at this point can press the concrete down. Since the flexural strength of concrete is less than its compressive strength, the concrete bends to its breaking point. Homeowners who place large recreational vehicles or dumpsters on their driveways are more likely to see this type of cracking. Driving heavy vehicles off the edge of a slab creates a similar type of crack.
Figure 12: A heavy truck drove over this sidewalk, cracking the edge
Cracks Caused by Premature Drying
Crazing cracks are very fine surface cracks that resemble spider webs or shattered glass. They can happen on any concrete slab when the top loses moisture too quickly. Crazing cracks can be unsightly, but are not a structural problem. They are so fine that there is no way to repair them (See Figure 13).
Crusting cracks often happen during the concrete stamping process. They usually occur on sunny or windy days when the top of the slab dries out sooner than the bottom. The top becomes crusty so when the stamp is embedded, it pulls the surface apart near the stamped joints causing small cracks around the outside edges of the “stones”. Although they are cosmetically unappealing, crusting cracks present no structural problem but may be patched if desired
Figure 14: Crusting cracks caused by premature surface drying
The Importance of Reinforcement
The use of synthetic fibers, reinforcing wire mesh, or rebar can add some extra support to concrete, but none of them will prevent cracking. In fact, too much steel can actually cause a slab to crack by restraining normal concrete shrinkage. However, if cracks happen, reinforcement can hold the different sections together.
The presence of reinforcement can be the difference between a crack remaining hairline in nature or separating and becoming wider and unsightly. Steel reinforcement can also keep the concrete on both sides of a crack on the same horizontal plane. This means that one side doesn’t heave or settle more than the other, which could cause a tripping hazard. It is sometimes impossible to determine exactly what caused a particular crack. However, proper site preparation and good concrete finishing practices can go a long way towards minimizing the appearance of cracks and producing a more aesthetically pleasing project.
Inspection of concreting works is an important step to achieve greater strength and durability of the structure. Although it is easy to remember number of checks during inspection of concrete member, a checklist is always required for record of the placement of concrete and quality control measures taken at site.
Stages of Inspection of Concrete Works
Inspection of concrete is done in 3 stages,
Type of inspection of concrete depends on type of concrete, i.e. PCC or RCC, type of elements to be casted, such as RCC slab, columns, footing, beams, walls etc. It is both beneficial to contractor as well as engineer to maintain the record of checks, so that they can produce it in case of any discrepancy.
It also allows becomes a proof of quantity of concrete work done by the contractor, so that no discrepancy arises during billing.
The checklist also notes the number of cubes taken for the given work and its id is noted in the checklist, so that when cube test results arrive, it becomes easy to identify the structural elements for the given cube test results.
Fig 1: Concrete Placement Inspection Checklist
1. Concrete Pre-Placement Checklist
Table 1: Standard Inspection Checklist for pre-placement of concrete.
As per drawing
Formwork & Staging
As per drawing & in exact plum
Construction joint location*
As per drawing
Steel reinforcement diameter / spacing & coating*
As per drawing
Cover to the reinforcement and overlap*
As per drawing
Aligned as per drawing and in plumb
RLs and reference levels
As per drawing
Embedment part check, i.e. insert plates, nipple etc
As per drawing
Placement of water stoppers, if any*
Location of construction joint
Water tightness of shuttering, if required
No water seepage allowed
Quality of water
Potable and clean
Measuring jar for water pouring
As per water content requirement
Quality of materials
As per specification
2. Inspection during Placement of Concrete
Table 2: Standard Inspection Checklist during placement of concrete
Water cement ratio
As per specification
Surface preparation by mortar bedding
As per requirement
Adequacy of vibration
40mm and 60mm needle required
Segregation of aggregates
Removal of temporary spacers and ties*
To be removed
Check for shuttering prop displacement / settlement
Number of cubes taken for testing with identification No.: ________ Id: __________
3 No’s for RCC > 6m33 No’s for every 5m3
Continuity of operations
No break in between concreting
3. Post placement Concrete Inspection Checklist
Table 3: Standard Inspection Checklist for Post placement of concrete.
Observation for honeycombing
Line and Level
As per drawing
As per drawing
Cracks and air bubbles
Method of curing
Checked for stripping/Removing of formwork support etc. after specified duration of stripping time.
Checked for position of embedment
Repair and finish all surface defects by specification / approved method
Surface of part of structure is alright and allowed for subsequent activity / backfilling
Others, if any
* The above checklist are valid for Reinforced Concrete works only.
All the empty space has to be filled and remarks if any shall be written in remarks column.
Date of inspection of pre-concrete, during placement and post-concrete placement shall be noted as these steps may not be performed on the same day.
Signature by contractor supervisor and engineer is done after each inspection.