Los Angeles Abrasion Test , Why and How To Perform

LOS ANGELES ABRASION TEST:

This is hardness test for aggregates, used in Laboratory  to determine the hardness value or abrasion value 

APPARATUS :

 Los Angeles Abrasion Testing Machine ,

Abrasive Charge – Cast iron or steel balls ,
Test sieve – 1.70 mm IS sieve ,

 Balance of capacity 10 kg , Oven , Tray

The aggregate used in surface course of the highway pavements are subjected to wearing due to movement of traffic. 

When vehicles move on the road, the soil particles present between the pneumatic tyres and road surface cause abrasion of road aggregates. 

The steel reamed wheels of animal driven vehicles also cause considerable abrasion of the road surface. 

Therefore, the road aggregates should be hard enough to resist abrasion. 

The principle of Los Angeles abrasion test is to produce abrasive action by use of standard steel balls which when mixed with aggregates and rotated in a drum for specific number of revolutions also causes impact on aggregates. 

The percentage wear of the aggregates due to rubbing with steel balls is determined and is known as Los Angeles Abrasion Value.

Key point of los angles test:

Rotate the machine at a speed of 30 – 33 revolutions per minute. The number of revolutions is 500 for grading A, B, C & D and 1000 for grading E, F & G. The machine should be

5 kg of sample for grading A, B, C & D and 10 kg for grading E, F & G

THE CALCULATION PART:

Original weight of aggregate sample = W1 g

Weight of aggregate sample retained = W2 g

Weight passing 1.7mm IS sieve = W1 - W2 g

Los Angeles Abrasion Value = (W1 - W2) / W1 X 100

Los angeles abrasion value should lies in below given range for different types of roads

Types of pavement layers                                         Max. Permissible Abrasion Value in %

1:WBM , SUB BASE COURSE                                                      60%

2:WBM BASE COURSE WITH BITUMEN SURFACE               50%

3: BITUMEN BOUND MACADAM                                             50%

4:WBM SURFACING COURSE                                                    40%

5: BITUMINOUS PENETRATION MACADAM                              40%

6:BITUMINOUS SURFACING DRESSING CEMENT
 CONCRETE SURFACING COURSE                                              35%

7:BITUMINOUS CONCRETE SURFACING COURSE                   30%

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Highway Design-Parking Along Highways and Arterial Streets

These paragraphs below deal with parking as it pertains to the mainlanes of a controlled access highway, the frontage roads for such a facility, and parking along urban and suburban arterials. Rest areas as parking facilities are not considered in this article.

Emergency Parking

Parking on and adjacent to the mainlanes of a highway will not be permitted except for emergency situations. It is of paramount importance, however, that provision be made for emergency parking. Shoulders of adequate design provide for this required parking space.

Curb Parking

In general, curb parking on urban/suburban arterial streets and frontage roads
should be discouraged. Where speed is low and the traffic volumes are well below capacity, curb parking may be permitted. However, at higher speeds and during periods of heavy traffic movement, curb parking is incompatible with arterial street service and desirably should not be permitted. Curb parking reduces capacity and interferes with free flow of adjacent traffic.

Elimination of curb parking can increase the capacity of four-to-six lane arterials by 50 to 60 percent. If curb parking is used on urban/suburban arterials or frontage roads under the conditions stated above, the following design requirements should be met:

• provide parking lanes only at locations where needed
• parallel parking preferred
• confine parking lanes to outer side of street or frontage road
• require that parking lane widths be 10 feet [3.0 meters]
• restrict parking a minimum of 20 feet [6 meters] back from the radius of the intersection to allow for sight distance, turning clearance and, if desired, a short right turn lane.

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Modulus of Elasticity vs Modulus of Rigidity |Elastic Modulus vs Shear Modulus

Modulus of Elasticity vs Modulus of Rigidity |Elastic Modulus vs Shear Modulus 

Modulus of elasticity and modulus of rigidity are two properties of matter. These properties are very important in designing and implementing mechanical and structural designs. These concepts are very important in understanding the proper mechanics and statics of solid systems. To have a clear understanding in fields such as engineering and physics, a clear understanding in these concepts is required. In this article, we are going to discuss what modulus of elasticity and modulus of rigidity are, their applications, definitions of modulus of elasticity and modulus of rigidity, their differences and finally the difference between these two.

Modulus of Rigidity (Shear Modulus)

Shear stress is a deformation force. When a force is applied tangential to a solid surface, the solid tends to “twist”. For this to happen, the solid must be fixed, so that it cannot move in the direction of the force. The unit of shear stress is Newton per meter squared or commonly known as Pascal. We know that Pascal is also the unit of pressure. However, the definition of pressure is the force normal to the surface divided by the area, whereas the definition of shear stress is the force parallel to the surface per unit area. Torque acting upon a fixed object can also produce shear stress. By definition, not only solids but also fluids can have a shear stress. Objects have a property called the shear modulus, which tells us how far will the object twist for a given shear stress. This depends on the shape, size, material and temperature of the object. Shear stress of constructions and automobile engineering plays a main role in designing and implementing the design.

Modulus of Elasticity

Elasticity is a very useful property of matter. It is the ability of the materials to return to their original shape after any external forces are removed. It is observed that the force required to keep an elastic rod stretched is proportional to the stretched length of the rod. Modulus of elasticity is the tendency of an object to deform elastically when an external force is applied. The definition of the elastic modulus is the ratio of stress to the strain. The stress is the restoring force caused by the deformation of the molecules. Stress is given as a pressure. Strain is the ratio of the deformed length to the original length of the object. Strain is a dimensionless quantity. Therefore, modulus of elasticity also has the dimensions of stress, which is Newton per square meter or Pascal.

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What is actually poisson's ratio.. Read it u will learn something most important

Poisson's ratio is defined as the negative of the ratio of the lateral strain to the axial strain for a uniaxial stress state. If a tensile load is applied to a material, the material will elongate on the axis of the load ﴾perpendicular to the tensile stress plane﴿,

Tensile deformation is considered positive and compressive deformation is considered negative. The definition of Poisson's ratio contains a minus sign so that normal materials have a positive ratio. Poisson's ratio, also called Poisson ratio or the Poisson coefficient, or coefficient de Poisson, is usually represented as a lower case Greek nu, n. 









Note: Poisson's Ratio has no units

Poisson's ratio is sometimes also reffered to as the ratio of the absolute values of lateral and axial strain. This ratio, like strain, is unit less since both strains are unit less.

For stresses within the elastic range, this ratio is approximately constant. For a perfectly isotropic elastic material, Poisson's Ratio is 0.25, but for most materials the value lies in the range of 0.28 to 0.33.

Generally for steels, Poisson's ratio will have a value of approximately 0.3. This means that if there is one inch per inch of deformation in the direction that stress is applied, there will be 0.3 inches per inch of deformation perpendicular to the direction that force is applied.


In other words poission ratio indicates the fraction by which a material is deformed by the action of compressive  or tensile(elongating) force in one of its perpendicular direction...

the best example to understand its physical effect is when u stretch a rubber band,it increases its length and at the same time,its diameter decreases , amount of decrement is given by poisson's ratio wrt its elongation

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Characteristic strength of concrete

Characteristic strength of concrete is one of the important properties of concrete which indeed unanimously by design engineeror any other person involved in the construction sector.

The compressive strength of concrete is given in terms of the characteristic compressive strength of 150 mm size cubes tested at 28 days (fck)- as per Indian Standards (ACI standards use cylinder of diameter 150 mm and height 300 mm). The characteristic strength is defined as the strength of the concrete below which not more than 5% of the test results are expected to fall.

This concept assumes a normal distribution of the strengths of the samples of concrete.

                               

Normal Distribution curve on test specimens for      determining compressive strength

The above sketch shows an idealized distribution of the values of compressive strength for a certain number of test specimens. The horizontal axis represents the values of compressive strength in MPa. The vertical axis represents the number of test samples for a

particular compressive strength. This is also termed as frequency.

The average of the values of compressive strength (mean strength) from the graph is 40 MPa. The characteristic strength (fck) is the value in the x-axis below which 5% of the total area under the curve falls. From the graph we can clearly say that 30 MPa is the characteristic strength of the given concrete mix. The value of fck is lower than fcm (40 MPa- mean strength) by 1.64σ, where σ is the standard deviation of the normal distribution.

So we can say the given concrete mix has a characteristic strength of 30 MPa or it is a M30 grade mix.

   M- Mix

* Note: For a 95% confidence level k=1.64 , hence k value varies on the confidence level of the experiment

Definition:

Characteristic strength of concrete is the strength of concrete specimens casted and tested as per given code of practice and cured for a period of 28 days; 95% of tested cubes should not have a value less than this value.

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About piles

End Bearing Piles ::-

1:-In end bearing piles, the bottom end of the pile rests on a layer of especially strong soil or rock.

2:- The load of the building is transferred through the pile onto the strong layer.

3:-In a sense, this pile acts like a column.

4:-The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.

Friction Piles ::-

1:-Friction piles work on a different principle.

2:- The pile transfers the load of the building to the soil across the full height of the pile, by friction.

3:-In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil.

NOTE: In practice, however, each pile resists load by a combination of end bearing and friction

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POINTS TO REMEMBER FOR CIVIL SITE ENGINEERS

Following are few general points to remember for civil site engineers to make the construction work easier while maintaining quality of construction.

• Lapping is not allowed for the bars having diameters more than 36 mm.
• Chair spacing maximum spacing is 1.00 m (or) 1 No per 1m2.
• For dowels rod minimum of 12 mm diameter should be used.
• Chairs minimum of 12 mm diameter bars to be used.
• Longitudinal reinforcement not less than 0.8% and more than 6% of gross C/S.
• Minimum bars for square column is 4 No’s and 6 No’s for circular column.
• Main bars in the slabs shall not be less than 8 mm (HYSD) or 10 mm (Plain bars) and the distributors not less than 8 mm and not more than 1/8 of slab thickness.
• Minimum thickness of slab is 125 mm.
• Dimension tolerance for cubes + 2 mm.
• Free fall of concrete is allowed maximum to 1.50m.
• Lap slices not be used for bar larger than 36 mm.
• Water absorption of bricks should not be more than 15 %.
• PH value of the water should not be less than 6.
• Compressive strength of Bricks is 3.5 N / mm2.
• In steel reinforcement binding wire required is 8 kg per MT.
• In soil filling as per IS code, 3 samples should be taken for core cutting test for every 100m2.

Density of Materials:

Material	Density
Bricks	1600 – 1920 kg/m3
Concrete block	1920 kg/ m3
Reinforced concrete	2310 – 2700 kg/ m3

Curing time of RCC Members for different types of cement:

Super Sulphate cement: 7 days

Ordinary Portland cement OPC: 10 days

Minerals & Admixture added cement: 14 days

De-Shuttering time of different RCC Members

RCC Member	De-shuttering time
For columns, walls, vertical form works	16-24 hrs.
Soffit formwork to slabs	3 days (props to be refixed after removal)
Soffit to beams props	7 days (props to refixed after removal)
Beams spanning upto 4.5m	7 days
Beams spanning over 4.5m	14 days
Arches spanning up to 6m	14 days
Arches spanning over 6m	21 days

Cube samples required for different quantity of concrete:

Quantity of Concrete	No. of cubes required
1 – 5 m3	1 No’s
6 0 15 m3	2 No’s
16 – 30 m3	3 No’s
31 – 50 m3	4 No’s
Above 50 m3	4 + 1 No’s of addition of each 50 m3

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BURJ KHALIFA : THE NAME TELLS EVERYTHING== >>

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==>> THEORY OF STRAIN==>>

STRAIN==>> When a body is subjected to some external force, there is some change of dimension of the body. The ratio of the change in dimension of the body to the original dimension is known as strain..
=>Strain is dimension less quantity...

generally STRAIN = change in length / original length 

TYPES OF STRAIN==>>
=> TENSILE STRAIN 
=> COMPRESSIVE STRAIN
=>VOLUMETRIC  STRAIN
=>SHEAR STRAIN

TENSILE STRAIN==>> If there is some increase in length of the body due to external force, then ratio of increase of length to the original length of the body is known as tensile strain.

COMPRESSIVE STRAIN==>> If there is some decrease in length of the body , then the ratio of decrease in length of the body to the original length is known as compressive strain.

VOLUMETRIC STRAIN==>> The ratio of change in the volume of the body to the original volume of the body is known as volumetric strain..

SHEAR STRAIN==>> The strain produce of shear stress is known as shear strain.. 

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