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Tuesday, January 22, 2019

Difference Between Flexible Pavement and Rigid Pavement

The pavement designing is complicated task in Transportation Engineering. The most recognized methods for pavement design are Rigid pavement and Flexible pavement. The pavement surface has good longevity and it can resist the load operating from the wheel tyres.

Given below, the functional requirement of highway pavements :-

1. Flexible pavement and Rigid pavement contain superior riding quality
2. It should be less slippery
3. It should be rigid
4. It should contain adequate friction keeping the power of the vehicle unchanged.


Variation among Rigid Pavement and Flexible Pavement

1. Flexible Pavement

a. Load is transmitted from grain to grain to the lower layers
b. The design is totally based on the subgrade strength.
c. IRC 37-2012 code is applied for making the design of flexible pavement
d. The strength of flexible pavement is influenced by the aggregate interlock, particle friction and cohesion.
e. Flexible pavement demonstrates the deflection of subgrade at the surface of the pavement.
f. Design life lasts for 15 years.


Rigid Pavement:

1. Rigid pavement contains a strong flexural strength that is considered as the vital factor of design.
2. Rigid pavement contains a concrete layer at the top, the base course and soil subgrade remain underneath.
3. Rigid pavement disperses the load over a broad area due to its high flexural strength.
4. Load is transmitted through slab action.
5. The total thickness of the pavement remains under flexible pavement.

6. IRC: 58-2011 is utilized for making the designing of Rigid pavement.
7. Design life extends for 30 years


Difference Between Flexible Pavement and Rigid Pavement

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Published By
Rajib Dey
www.constructioncost.co
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Monday, January 21, 2019

Variations among Load Bearing Wall and Partition Wall

The wall is categorized as follow: Load Bearing Wall, Partition Wall.

Load Bearing Walls: If beams and columns are not utilized (Frame Structure), load from roof and floors are transmitted to foundation through walls. Such walls are known as bearing walls.

The purpose of these walls is to securely transmit the load. The vital section of the walls is located adjacent to the openings of doors and windows and the positions where concrete beams stand. Minimum wall thickness should be 200 mm. The slenderness ratio of wall called as ratio of effective length or effective height to thickness should not surpass 27.

Effective height of walls with respect to actual height H

a. Lateral as well as rotational restraint 0.75 H
b. Lateral as well as rotational restraint at one end and only lateral 0.85 H restraint at other.
c. Lateral restraint but no rotational restraint at both ends 1.0 H
d. Lateral and rotational restraint at one end and no restraint at other 1.5 H


Effective length of walls of length L

a. Continuous and supported by cross walls 0.8 Length.
b. Continuous at one end and supported by cross walls at 0.9 Length the other end.

c. Wall supported by cross walls at each end 1.0 Length.
d. Free at one end and continuous at other end 1.5 Length.
e. Free at one end and supported by cross wall at other end 2.0 Length.


2. Partition Walls: If the structure belongs to frame structure than partition walls are constructed to separate floor area for different Utilities and it stands on floors. The partition walls are used to bear only self weight. Generally partition walls are thin. According to the requirement, these walls range from clay brick partition, Fly ash bricks partition, glass panel partition, wood panel partition, and aluminium and glass panels partition.

Variations among load bearing wall and partition walls

LOAD BEARING WALL

a. They bear loads from roof, floor, self-weight etc.
b. They are solid and capture more floor area.
c. Since the quantity of material is more, the construction cost is higher.
d. Stones or bricks are the main material for building up the wall.


PARTITION WALL
a. They bear self-weight only.
b. These walls are thin and as a result capture less floor area
c. Since, the quantity of material is less, the construction cost is reduced.
d. Stones are not applied for building up the walls.
Variations among Load Bearing Wall or Partition Wall

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Published By
Rajib Dey
www.constructioncost.co
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Saturday, January 19, 2019

Advantages of microsillica in concrete

Microsilica alias silica fume or condensed silica fume stands for is a mineral admixture that is formed with very fine solid glassy spheres of silicon dioxide. Most microsilica particles remain under 1 micron (0.00004 inch) in diameter, normally 50 to 100 times finer as compared to average cement or fly ash particles. Microsilica belongs to a by-product of the industrial manufacture of ferrosilicon and metallic silicon in high-temperature electric arc furnaces.

Microsilica may be suitable in managing heat formation in mass concrete. It can also be combined with fly ash to provide superior result.

If pozzolanic materials are integrated with concrete, the existent silica in these materials makes a reaction with the calcium hydroxide produced throughout the hydration of cement and develops supplementary calcium silicate hydrate (C – S – H) that enhances the strength and the mechanical properties of concrete.

Types of Microsilica: Microsilica is categorized as follow -

1. Powdered microsilica, 2. Condensed microsilica, 3. Slurry microsilica

Impacts of Microsilica on Concrete

1. Fresh Concrete

a. It decreases the scope of segregation, so it is applied as pumping aid.
b. It almost reduces bleeding, as a result finishing work commences before time.
c. Workability and uniformity of concrete reduces.


2. Hardened Concrete: The inclusion of microsilica enhances the following characteristics of hardened concrete -

a. Improves compressive strength that leads to improve flexural and tensile strength.
b. Bond strength
c. Abrasion resistance
d. Lessens permeability; consequently, it safeguards reinforcement steel against corrosion.
e. Impact and cavitations resistance.
f. Sulphate Resistance
g. Heat Reduction
h. Chemical Resistance


Properties of Microsilica:

1. Microsilica belongs to a grey; almost white to black powder.
2. Spherical particles remain under 1mm in diameter.
3. The mass density of microsilica is dependent on the degree of densification and differs from 130 to 600 kg/m3.
4. The specific gravity of microsilica differs among 2.2 to 2.3


Benefits:

a. Minimizes thermal cracking resulting from the heat of cement hydration.
b. Enhance the strength to resist against sulphate and acidic waters.
c. Minimizes the growth of temperature in preliminary stage.
d. Silica fume is cheap; therefore, it is inexpensive.
e. It minimizes the entire slab weight and cost.
f. Inclusion of microsilica reduces efflorescence caused by the refined pore structure and increased consumption of the calcium hydroxide.


Advantages of microsillica in concrete

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Published By
Rajib Dey
www.constructioncost.co
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Friday, January 18, 2019

Characteristics of polymer-Modified Mortar

Mortar is considered as one of the vital components in masonry construction. It is normally formed by mixing water with portland cement, hydrated lime and sand. If the proportions of each of these ingredients are changed, strength and other characteristics may differ. Mortar with polymeric admixtures is applied extensively and inexpensively in definite situations.

Basics and function: Polymer-modified mortar is developed by interchanging a part of the conventional binders with polymers. Polymers are included with mortar to enhance the characteristics which may contribute to adhesion, toughness, flexural or tensile strength, and resistance to chemicals.

The purpose of the polymers is to make the capacity of work and adhesion of non hardened mortar better and often need fewer quantity of extra water as compared to conventional mortar. It leads to less pores and high capacity cements, consequently the immersion of water & and penetrability to salts are decreased.

Types of Polymers: Polymer-modified mortar is commercially obtainable with all constituents already provided in the mixture. Conversely, polymer additives separated into classes, are included with mortar mix. Redispersible polymer powders like ethylene vinyl acetate are normally included with dry mortar mix.

Water-soluble polymers like polyvinyl alcohol belong to powders but are added to wet mortar mix. Aqueous latex suspensions comprise of latex particles hanged up in water to coat hydrating cement particles. At the end, liquid polymers as epoxy resins or unsaturated polyesters are included throughout mixing to develop a network of cemented polymer hydrate and thus the strength of the mixture is raised significantly.

Application: Polymer-modified mortar is employed in a wide array of mortar and concrete repair and primary construction applications. Low water level and salt infiltrations transform polymer-modified mortar suitable for masonry prone to weathering and other exterior conditions. The main objective of polymer-modified thinset mortar is to bind tile to concrete and cement board substrates devoid of immersing the tiles earlier. Polymer-modified mortars are frequently applied for repairing purposes due to their low shrinkage and capacity to tie with even solid surfaces.

Supplementary Possible Admixtures: Besides, polymers, other types of materials can be included with mortars to attain required characteristics. Color pigments may be included with mortar to change the look of the mortar. If accelerators and retarders are included, these can decrease or raise the length of time necessary for the mortar to be cured, a vital characteristic to control in severely cold or warm, humid weather. Other mortar additives range from mineral additions, like silica fume, aggregates and inert fillers, plasticizing chemical admixtures and fibers to manage shrinkage efficiently.

Characteristics of polymer-Modified Mortar

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Published By
Rajib Dey
www.constructioncost.co
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Thursday, January 17, 2019

Design of Beam

1. Estimation of constants. -For the specified set of stresses, determine KC, JC and RC.
2. Kc= M~cbc/M~cbc+~st
3. Jc= 1-(Kc/3)
4. Rc= 0.5*L*Kc Jc
5. Estimation of bending moment. Suppose appropriate values of overall depth and breadth of beam, and find out the effective span. Work out the self-weight and total U.D.L. and maximum bending moment in the beam.
6. Design of the section. Workout the effective depth of the beam with the following expression:
7. d= [(M)/ (RC*b)] 0.5
8. Reinforcement. Workout the area with the formula.
9. Shear Reinforcement. Workout the maximum shear force in the beam.
10. Verify for Development length at the end.
11. Ld<= (M1/V) +L0.
Design of column:
1. Find out the allowable stresses in concrete, longitudinal bars and ties.
2. Determine the super impose load that should be borne by the column.
3. Find out the area from the following expression - P= ~cc *Ac+~sc*Asc.
4. After getting details about the area, find out the dimensions of column. If it is a square of side b, then b=Ag.
5. For the specified end conditions, find out the effective length of column. Measure lef/b ratio to determine whether the column is short or long.
6. If lef/b ratio<12 it will be designed as short column or else as long column; define the area of steel Asc.
7. Determine the diameters of bars utilized as ties and find out its pitch according to the rules.
DESIGN OF FOOTING: The width B of the footing will obviously be equivalent to [W+W‟]/qo. The thickness is measured based on the bending moment as well as punching shear.
1. Depth for bending moment.
d= [M/B*Rc] 0.5
2. Depth for shear.
3. tv=V/B*d
4. Steel Reinforcement. Ast=M/tjcd
Design of Beam

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Published By
Rajib Dey
www.constructioncost.co
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Monday, January 14, 2019

Building materials is the newest app for civil engineer

Building Materials is an exclusive construction app for the site civil engineer, supervisors available in google play store.

It provides a complete on digital construction and building material for civil engineers. The app comprises of all the crucial notes concerning the material & construction engineering as well as building knowledge.

The app is supported with material for building construction, building materials estimation, building material and construction book.

It is one of the best civil engineering applications that can be used for acquiring knowledge on quick revision & obtaining a complete detail of construction material as well as making estimation of the materials.

Major features of building material notes:

• It is possible to make quick notes with regard to building material items.
• Digitalize your material usage with quick notes.
• Make easy notes with our application.


Generate a material construction checklist with the app.

By using this app, one can take notes of different types of construction materials like bricks, blocks, plaster, cement, sand, gravel, water-base, oil-base, concrete tile. With this app, it is possible to measure steel, brick, concrete, area etc.

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

Building materials is the newest app for civil engineer

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Published By
Rajib Dey
www.constructioncost.co
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Friday, January 11, 2019

Some vital points to make saw cuts in concrete

The purpose of saw cuts is to make control joints in concrete to facilitate managing cracks which may occur because of shrinkage. The cuts should be created at a predetermined spacing and only as soon as the concrete has attained adequate strength but prior to internal cracking starts. So, the timing of saw cuts should be maintained properly. The exact time for creating cuts is based on several factors along with the type of admixtures and aggregate used in the concrete, the air temperature, and the concrete's mix design.

When to Saw-Cut Concrete: Besides, the concrete mix and the weather conditions, it depends on rigidity of the concrete and the type of cutting equipment applied to make the saw cuts. If the cutting is done ahead of time, an effect produced by the saw blade dragging the aggregate out of position, departing a rough, weakened edge along the cut. It also produces undo wear on diamond concrete saw blades. Sawing slowly can lead to uncontrolled cracking since the concrete contracts throughout curing.

In hot weather conditions, saw cutting commences after four hours once the concrete is poured. In cooler weather, sawing should not commence for 12 hours after pouring. The most effective method to find out whether the slab is prepared is to create trial cuts to examine raveling. Saw cutting should be commenced when the raveling stops throughout these trial cuts.

Some contractors defer sawing to defend their equipment and saw blade to minimize blade abrasion. Different types of saw blades are utilized on the basis of the concrete type and how quickly the cuts can be started. The following other factors can produce extreme blade wear and joint raveling:

• Pushing the blade too hard
• Saw cutting is done at high speed
• Applying a saw with a ben spindle
• Application of an improper saw blade


Where to Saw-Cut Concrete: Prior to commence saw cutting concrete, it is crucial to choose where these cuts will be created. It is will be useful to start saw cuts on or at the center of column lines. Joints shall be placed at 24 to 36 times the slab thickness but it should be approved by a structural engineer. Joint spacing generally varies among 10 to 18 feet based on the amount of reinforcement in the slab.

How to Saw-Cut Concrete: Various factors like curing methods, slab thickness, slab length, and base type should be analyzed prior to determine where joints should be cut. As soon as the joints are placed to be cut, mark them with a chalk line.

If water cutting equipment is applied, ensure that the water is running all the way down to the blade. The blade should be allowed to attain the desired depth, then start walking or moving the equipment following the chalk like mark. Here are some recommendations when sawing concrete:

• Never twist the saw blade.
• Do not allow the blade spin in the cut, since it will raise wear on the bond.
• While cutting concrete with heavy rebar, apply blades with soft metal segment bonds.
• It is recommended to utilize use the required PPE (personal protection equipment).


Depth of creating Saw Cuts: A proper rule of thumb is to cut the joints one-quarter to one-third the slab thickness. For a 6-inch-thick slab, it signifies cutting 1.5 to 2 inches deep. Make sure that the saw cut depth is according to the structural engineering specifications. If the joint is adequately deep, aggregate interlocking will not be sufficient to transmit the loads. If the saw cut is too shallow, random cracking may happen.

Some vital points to make saw cuts in concrete

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Published By
Rajib Dey
www.constructioncost.co
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Thursday, January 10, 2019

Some important points for civil site engineer

Civil engineer accomplishes several tasks at construction site. Given below, some points, tips and tricks essential for a civil engineer for doing rapid calculations and providing instant solutions to construction site problems.

Given below, some general points which civil site engineers should focus on to simplify the construction work whereas retaining the quality of construction.

Lapping should not be provided for the bars with diameters in excess of 36 mm.

Highest spacing for chair should be 1.00 m (or) 1 No per 1m2.
For dowels rod, lowest 12 mm diameter should be applied.


For Chairs, bars with minimum diameter of 12 mm should be utilized.
Longitudinal reinforcement should remain not below 0.8% and in excess of 6% of gross C/S.
Least bars for square column is 4 No’s and 6 No’s for circular column.
Main bars in the slabs should not be under 8 mm (HYSD) or 10 mm (Plain bars) and the distributors should not be under 8 mm and not in excess of 1/8 of slab thickness.


Least thickness of slab should be 125 mm.
Dimension tolerance for cubes should be + 2 mm.
Free fall of concrete is permissible maximum to 1.50m.
Lap slices should not be applied for bar greater than 36 mm.
Water absorption of bricks should not be in excess of 15 %.
PH value of the water should not be under 6.


Compressive strength of Bricks should be 3.5 N / mm2.
The binding wire in steel reinforcement should be required 8 kg per MT.
According to IS code for soil filling, 3 samples should be chosen for core cutting test for each 100m2.


Some important points for civil site engineer

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Published By
Rajib Dey
www.constructioncost.co
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Wednesday, January 9, 2019

Benefits of joining & pointing in brick masonry

When bricks are not fully uniform in colour and irregular in shape, the joint finishes should be designed to provide correctness and repose to premier facades with formation of the illusion of perfectness.

JOINTING: The finished profile of the original mortar joint is produced instantly since the bricks are placed later in an individual practice called as pointing. Jointing is associated with bricklaying for finishing the joint faces of the bedding mortar as work continues.

Benefits:

• Combined joint
• Consistency of joint in strength and colour, on condition that mortar is properly measured
• Lower labour costs


Drawbacks:

• Less quality control of joint finish (not all bricklayers joint well)
• Complication in retaining consistent colour all through the wall face.


POINTING: Pointing stands for the method of repairing mortar joints among bricks or other masonry elements to resist penetration of rain water or dampness.

Benefits:

• Greater joint finish
• Consistency of colour and strength
• Better choice of joint finishes
• Clean face work


Drawbacks:

• Higher labor and material costs
• Extra construction time
• When improperly performed the compound joint can’t be joined
• Requirement for expert and experienced pointers.


Structural benefits: The bricks consume moisture from the mortar when perfectly dampened prior to laying or pointing. Together with evaporation, it leads to partial de-hydration of the joint towards the joint face. So the purpose of the jointing tool is to solidify the surface of the joints fixing shrinkage cracks and defending from the ingress of driving rain.

Benefits of joining & pointing in brick masonry

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Published By
Rajib Dey
www.constructioncost.co
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Tuesday, January 8, 2019

How to design a gabion retaining wall with Tekla Tedds

In this construction video tutorial, you will learn how to use Tekla Tedds for making calculations of gabion retaining wall analysis and design with adherence to the Eurocode to verify the strength of a gabion retaining wall from sliding overturning. Besides, it is also possible to find out the maximum and minimum base pressure underneath the wall.

A gabion retaining wall is built up with stacked stone-filled gabions which are attached together with wire. Gabion walls are generally battered (angled back towards the slope), or stepped back with the slope, in spite of stacked vertically. Besides, galvanized steel wire, PVC-coated and stainless steel wire are also utilized. This type of retaining wall is very effective for erosion control applications.

Tekla Tedds is a robust software that can be used to automate your tedious structural calculations. The users can select from one or more of the extensive calculation libraries.

The users will also be able to write their own, and generate professional documentation every time. It is also possible to integrate the structural calculations with 2D frame analysis.

The users can get access to the following extensive library of design modules.

• Loading - Seismic and Wind
• Analysis - Continuous Beams and Rolling Load
• Steel Design - Beams, Torsion, Columns
• Connections - Base Plates and Bolts


Tekla Tedds offer the following benefits :-

a. Get access of an expansive library of structural and civil calculations.
b. Employ a single solution for all common components & materials.
c. Reap benefits from a simple and intuitive interface.
d. Generate apparent calculations which can be simply analyzed.
e. Make comparison among various design options and create modifications instantly.
f. Create consistent documentation.
g. Improve your Quality Assurance processes.
h. Obtain new and improved calculations and code updates regularly.


To get online demonstration of Tekla Tedds, go through the following video tutorial.


Video Source: Tekla Software

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Published By
Rajib Dey
www.constructioncost.co
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Monday, January 7, 2019

Raft foundation construction details

This construction article provides the detail construction methods for raft foundation of a building. The raft foundation is conducted for the multistory buildings or building having heavy loads.

Step 1: Initially, the surveyor should begin exaction and as soon as the survey is completed then exaction is carried out to the desired level on the basis of the validated shop drawings.

Throughout excavation, precaution for safety should be undertaken, the entire area should be guarded and everybody should utilize PPE at site.

Step 2: As soon as the final phase of the exaction is completed then the surface should be consolidated with plate compacter as the area is small and it is not difficult to apply the roller compacter. But 95% compaction should be performed with compaction test.

Step 3: After getting the passable results of compaction test, 75mm or 100 mm blinding concrete is arranged. Blinding concrete should be garde 20/20 SRC (Sulphate Resisting concrete).

The blinding concrete facilitates to arrange a solid and flat surface for the reinforcement of raft foundation.

The curing polythene sheets should be arranged instantly after finishing and when the concrete is set, it should be substituted with hessian cloth and should be retained wet unless the surface becomes fully dry.

Once the blinding surface becomes dry, water proofing of surface should be started according to sanctioned specification.

Step 4: Once water proofing is done, perfect planning should be undertaken for the shuttering work, all material should be retained on a plate form and steel bars should be installed with adherence to sanctioned shop drawings of the surrounding. All working space should maintain neat & clean to get rid of accidents at site.

Upon the completion of the reinforcement work, the contractor should sanction it from the supervision consultants for pouring the concrete.

Raft foundation construction details

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Published By
Arka Roy
www.constructioncost.co
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Saturday, January 5, 2019

Benefits of Parapet Walls

A parapet belongs to a low wall built up over the roofline that normally extents around the boundary of a building. Parapets may be simply aesthetic or largely functional, like hiding mechanical equipment or functioning as a firewall.

The moisture may enter through the top portion of a parapet wall and it creates problems. To get rid of this issue, select a perfect cap.

There are different types of materials like limestone, terra cotta, hard-fired clay, or precast concrete to cap off the wall. These materials contain thermal properties identical to brick and concrete masonry.

Contrarily, metal includes a coefficient of thermal expansion almost three times higher than masonry that produces a considerable amount of differential movement among the parapet cap and the wall underneath. Metal versions should be arranged with firmly sealed slippage joints where the cap section bends.

Caps are available with various shapes, but they should contain pitch, projections (1-in. minimum), and incessant drips. These components safeguard the parapet from pooling water and resist moisture from flowing out of the exterior wall surface.

Most caps are prone to entering of moisture at the head (vertical) joints. In order to reduce penetration at these positions, rake out the mortar head joints, bed joints in the cap to a depth of ½ in., and use elastomeric sealant to fill the joint.

An incessant flashing membrane is to be installed directly underneath the mortar joint under the cap so that the moisture can’t penetrate through the top of the wall. This flashing membrane is built from sheet metal, combination sheet metal/asphaltic, or rubberized asphalt. The flashing has to be arranged entirely through the wall to make a slippage plane among the cap and the wall underneath. The cap should be anchored to the wall underneath.

Different types of stainless steel anchorage systems are applied to fix the coping to the wall. A flexible system should be set up so that the mason can be perfectly arranged with the dowel anchor through the pre-drilled holes in the cap. A considerate amount of mastic should be used to the flashing where anchor punctures may happen.

If the back portion of the parapet is fully uncovered, both exterior wythes should be built up of the same material. Brick situated on the backside of the parapet should be coated with rainproof water repellant.

The bottom flange of the steel beam should be connected with the concrete masonry underneath with a debonded shear anchor. The anchor is mechanically secured to the bottom of the beam at specified spacings that is arranged with the head joints in the concrete masonry wythe. A debonded shear anchor protects out-of-plane (but not in-plane) shear forces and allows structural movement of the steel beam (deflection). The anchor should be completely implanted in mortar, inside the head joint of the concrete masonry unit, for this connection to be effective.

Benefits of Parapet Walls

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Published By
Rajib Dey
www.constructioncost.co
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Friday, January 4, 2019

Some vital tests for checking compressive strength of cement

If water is included in the cement, the compressive strength of the hardened cement is considered as the vital factor. Cement hydrates and exposes cohesion and consistency. It joins all the components like cement, sand, aggregate etc. collectively. The hardiness of cement-based compound like mortar/concrete is based on the type and nature of cement.

Owing to strength, nature of cement, both mortar and concrete contain high strength against compression and less strength against tension. Therefore, testing of cement for compressive strength is very crucial. Cement is examined for compressive strength so that the strength and stability of the structure is retained.

Initial strength gain is affected by high lime or high alumina content. The firmness of cement is also impacted with the degree of burning, the fineness of grinding, and the aeration it obtains once the final grinding is completed.

Under the strength test, cement mortar is applied since neat cement produces shrinkage and cracking and it becomes complicated for testing.

Primarily, cement is recognized with its compressive strength. Cement is designated with its grade like 53 grade, 43 grade, 33 grade of cement. This grade signifies the compressive strength of cement, i.e. 53 grade of cement species that compressive strength of cement cube after 28 days of curing should be 53 N/mm2 (MPa) or 530 kg/cm2.

Compressive Strength Test of Cement according to IS 4031 (Part 6) 1988.

The following equipments are required for conducting the test :

• Compression Testing Machine or Universal Testing Machine.
• Cube Mould: 70.6 mm*70.6 mm*70.6 mm size
• Vibrating Machine
• Weighing Machine
• Gauging Trowel
• Measuring Cylinder
• Tray


Method: Arrangement Of Test Samples

• Testing material is cement, sand and water.
• The necessary material for each cube is as follows:


1. Cement – 200gm,
2. Sand – 600gm,
3. Water quantity (P/4 + 3) % of the total mass of cement and sand. Where P denotes the standard consistency of cement.
• Initially, blend cement and sand in dry condition with a trowel for one minute and then include water and blend unless homogeneous colour is produced.
• The time of mixing should not be under 3 minutes and not in excess of 5 minutes.


Moulding Samples
• Once the blending is completed, mortar is provided in the cube mould. Prior to arrange the mortar, use oil on the inside surface of cube mould.
• To discharge the entrained air and get rid of honeycombing, the mortar should be stimulated 20 times in about 8 s and then consolidated with vibration.
• The vibration period should be 2 minutes at the certain speed of 12 000 ± 400 vibrations per minute.
• Then, the top surface of the cube in the mould should be completed by leveling the surface with the blade of a trowel.


Curing Samples
• Once the vibration is finished, retain the filled moulds in a moist closet or moist room for 24 hours.
• As soon as that period is ended, detach mortar cube from the moulds and instantly immerse in clean, fresh water and put there unless it is removed before testing.
• The cubes should not get dried once they are removed and unless they are tested.


Testing
• The testing is done with compression testing machine or universal testing machine.
• Test 3 cubes for compressive strength for every time period according to detailed specifications. As for instance 3 cubes for 3 days test, 3 cubes for 7 days test and 3 cubes for 28 days test.
• The cubes testing should be performed on their sides. No packing among the cube is allowed and the steel plates of the compression testing machine while testing is going on.
• The load shall be gradually and consistently employed and the rate of loading should remain 35 N/mm2/min.


Points to be considered
• Clean appliances should be applied for the tests.
• Test for temperature and humidity should be carried out at 27 ± 2°C temperature and 65 ± 5 percent of the relative humidity of the laboratory.
• The water in which the cubes are immersed should be changed every 7 days and retained at a temperature of 27 ± 2°C
• While determining the compressive strength, the faulty samples should not be utilized.
• The samples which produce strength differing by above 10 % from the average value of all the test samples.


Some vital tests for checking compressive strength of cement

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Published By
Rajib Dey
www.constructioncost.co
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Thursday, January 3, 2019

Different types of rock drilling tools

Drilling alias boring , is easily performed with specialized equipment known as rock drills. The following types of drills are generally found :

a. The hydraulic drills
b. Electric motor drills
c. Pneumatic rock drills


The above types of tools are utilized in different types of projects like soil nailing, micro-pile, mining and tunneling job sites. The hydraulic drills are mostly recognized due to their light weight and capacity to operate on hard rocks devoid of utilizing a large compressor.

Parts of a Rock Drill: All types of rock drills contain a standard design that is basically a combination of exchangeable attachments. A standard rock drill comprises of the following sections:

1. Drill bit: It refers to the tip of the rock drill that initially touches with the ground throughout a boring operation.
2. Drill stem: It stands for the long frame that enters the ground throughout boring whose end houses the drill bit.
3. Drill rod: It belongs to the empty section of the drill stem that attaches the motor of the rig to the drill bit. The drill rod transmits the cutting force to the drill bit to allow the rock drill to enter into the ground.
4. Carbide bits: These belong to special types of drill bits which are found in rotary and percussive drilling containing carbide tungsten coated onto them at an angle.


How Rock Drills Work: All through soil nailing, micropile, mining or tunneling operations, rock drills enter the earth either by rotating or making incessant impact blows.

Rotary drills are activated by cutting and flushing out rock fragments, whereas percussive drilling splits rocks by making impact blows. Some contractors prefer to join both methods which are suitable for operations on medium to hard rocks.

The method of drilling is based on the type of hole a contractor plans to bore into the ground. The two mostly recognized holes are the cored holes and the open holes. Cored holes contain an opening whose diameter is preset beforehand prior to start of an operation. In this case, cored holes need a stem with exterior tubes to rotate the drill bit.

Alternatively, open holes do not contain predetermined diameter. The drill bit enters straight into the ground throughout an operation. The three main types of drill bits generally exist which are used in boring open holes. These range from rock roller bits, wing bits and down-the-hole hammers.

Rock roller bits alias tricone bits, contain teeth-like steel cones. These cones cut and flush rock fragments outsides via the drill rod. Wing bits alias drag bits, are built with carbide tungsten and effective for soft ground surfaces. Air core hammers contain three protruding blades that cut rock throughout an operation and apply compressed air to flush out fragments on the surface.

Different types of rock drilling tools

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Published By
Rajib Dey
www.constructioncost.co
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