Friday 31 August 2018

Red Clay bricks and Fly ash | Cement Bricks





The advantages of using fly ash brick are, the brick carries good comprehensive strength, provide better thermal insulation than red clay bricks, cheaper compared to clay bricks and are environment friendly. ... They replace clay which has all nutrients for good agriculture.


Differentiate between Clay Bricks and Fly Ash Bricks

The characteristics that differentiate between these bricks are –
 

  • Fly ash bricks are of cement color while the colour of Clay bricks differs from burnt red to light brown depending on the type of clay used for manufacture of the bricks.

  • Fly Ash bricks are cast in moulds hence are always of uniform shape. Clay bricks are handmade causing slight difference in their shape and size.

  • Fly Ash bricks have a very smooth finish hence plaster is not required on the bricks to create a smooth surface. Clay bricks require plastering.

  • Clay bricks are more porous than Fly ash bricks.

  • Fly ash bricks are lighter in weight and less costly than Clay bricks.

  • Fly ash bricks are made of waste materials which come from the combustion of coal in thermal power plants. Clay bricks are made of clay which is collected from fertile land or the top soil. This is the prime reason that makes Fly ash bricks more preferable than Clay bricks. 



FLYASH BRICK
NORMAL CLAY BRICK
Uniform pleasing colour like cement
Varying colour as per soil
Uniform in shape and smooth in finish
Uneven shape as hand made
Dense composition
Lightly bonded
No plastering required
Plastering required
Lighter in weight
Heavier in weight
Compressive strength is around 100 Kg/cm2
Compressive strength is around 35 Kg/cm2
Less porous
More porous
Thermal conductivity 0.90-1.05 W/m2 ºC
Thermal conductivity 1.25 – 1.35 W/m2 ºC
Water absorption 6-12%

                                                                         

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Wednesday 8 August 2018

Subgrade Preparation for New Pavements |Subgrade details |




Subgrade:

Subgrade is that portion of the earth roadbed which after having been constructed to reasonably close conformance with the lines, grades, and cross-sections indicated on the plans, receives the base or surface material.  In a fill section, the subgrade is the top of the embankment or the fill.  In a cut section the subgrade is the bottom of the cut .
The subgrade supports the subbase and/or the pavement section.  To ensure a stable, long-lasting, and maintenance free roadway, the subgrade is required to be constructed using certain proven procedures that provide satisfactory results.


After the rough grading is completed, the fine grade stakes are set and the final processing of the subgrade may begin.
The rough grade is the top grade of the embankment as built using the information provided on the grade sheets.  The grade is normally within 2 in. at this point.  The finish grading operation consists of trimming the excess material down to the final grade.  Filling any low spots with thin lifts of materials tends to slide these lifts around if not properly worked into the underlying materials.

Subgrade Preparation
1.       Types of Subgrade preparation
2.       Typical equipment used
3.       Purpose of equipment
4.       Grading
5.       Compaction
6.       Soils
7.       Testing

Importance of Quality Subgrade
Provide good support for placement and compaction of pavement
pavement deflections to acceptable limits
Minimize differential movement due to frost and Shrinking/swelling soils
Promote uniformity of support (Key element for good long term pavement performance)

Types of subgrade preparation
·         Modification and Stabilization
·         Removal and Replace

Modification and Stabilization

·         Subgrade treatment that is intended to provide a stable working platform during construction.
·          –Adding chemicals like fly ash or cement
·          –Replacing existing soils with aggregates
·          –Geosynthetic reinforcement with aggregates
·          –Moisture conditioning

Chemical Stabiliztion
This work consists of treating the subgrade by combining chemicals such as fly ash, lime, or cement and water with the pulverized soil material to the specified depth and compaction requirements


Benefits of fly ash
Drying agent
 Reduces the shrink-swell potential
Increases the strength of subgrade

Benefits of lime
Lime dries wet soils
Lime modifies clay soils
Lime permanently stabilizes clay soils
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Benefits of Cement
Reduces swell potential
 Produces a weather resistant working platform for asphalt paving
Gains strength with time
Significantly reduces the freeze thaw movement

Soil Stabilization Benefits
Lower material costs – reduces base and pavement thickness
Lower construction costs – eliminates cost of material removal and replacement. 30% - 50% savings
Increased Strength – a dramatic increase in the CBR can be achieved

Soil Stabilization Benefits
Longer durability – stabilized soil is highly resistant to water and frost, which increases the lifespan of the subgrade
Increased environmental responsibility – stabilizing the existing soil eliminates the need to export the poor undesirable soil and import new fill

Remove and Replace
Simple Procedure that does not require specialized equipment

Removal and Replace
This process will consist of removing the unsuitable soil and replacing it with aggregates such as base or sand
Geosynthetics are often placed on the surface of the excavated subgrade prior to placement of aggregates


Geosynthetics
The primary purpose of using geosynthetics in the pavement design is to reduce reflective cracking in the asphalt and resist moisture intrusion into the underlying pavement structure

Geosynthetic Benefits
Improves structural capability of soil
 Allows the use of poorer quality of soils to be used in construction
Construction time can be reduced
Drastically increases the durability of subgrade

Moisture Conditioning
This work consists of blading, shaping, wetting, and compacting the subgrade with moisture and density control
Moisture Conditioning reduces or increases the soil moisture content to be compacted to the required density
Controls shrinking and swelling of soils


Moisture Conditioning Benefits
Allows contractors to expedite work
 Reduction of construction costs Improved utilization of existing materials
Greater environmental protection
 Increased short-term and long-term savings

Full Depth Reclamation Process
 The total asphalt surface is pulverized plus a predetermined portion of the base
The pulverized base is compacted and graded
The new stabilized base is now ready for paving

FDR Benefits
          Cheaper – At least 50% less expensive than traditional road repair methods
          Faster – Get 2-3 times more repairs done in the same time period
          Easier – No excavating, no loading, no hauling off and dumping old asphalt
          Base is stabilized with pulverized road surface
          No reflective cracking!
         Permanent repair, not a temporary fix
         Environmentally friendly

Types of Equipment Needed
Reclaiming machine
Compactors
Motor Graders
Tanker Trucks (Water and Emulsion)
Water Trucks
Loaders and Excavators

Reclaiming Machine
Pulverization of existing materials
–Asphalt
–Dirt
 –Asphalt with bas


Sizing Material
Controlled by the operator who controls the speed and rear door opening

Mixing Additives
Reactive – Lime
Self cementing
– Portland cement and fly ash
 Water

Compactors
Compact material to desired density
 Typical compaction sequence
–Initial or breakdown
– Pad foot roller
–Intermediate
 – rubber tire rollers and vibratory rollers
 –Finish
– smooth drum and rubber tire rollers

Motor Graders
Placing material at desired grade
 Scarify material
Process material

Tanker Trucks
Deliver water
Deliver emulsion materials to declaimer

Water Trucks
Apply water to subgrade surface directly
 Proof rolls

Loaders and Excavators
Removing existing pavement
 Excavating excess or unsuitable soils
Loading trucks

Fine Grading
 Fine grade is required for the final trimming and checking of the cross section.

Setting grade
Stakes are usually set at variable intervals near each edge of the subgrade and the centerline
When the distance is too far apart from stake to stake, intermediate stakes may be required

How to establish cross slope
Measure distance from edge of road to centerline
Multiply the distance to the desired cross slope –For example: 25’ * 2% (.02) = .5 or 6”
That is the elevation difference from the edge of the road to centerline

Checking grade
A string line can be stretched across adjoining grade stakes
 The subgrade is checked by measuring down to the known offset distance from the string line to the dirt
Straight edge
 – easiest way to check uniformity of subgrade

Importance of uniform subgrade

 Strength – Make sure you have full pavement section.
Yield – Uniform subgrade will optimize yield.
 Cost – Asphalt is for more expensive than base
Smoothness – HMA compacts differentially, thicker areas compact more than thinner areas which will affect pavement smoothness

Compaction
Compaction occurs when a force compresses the soil and pushes air and water out of it so that it becomes more dense. Compaction is achieved easer when the soil is wet and less able to withstand compression

Why Compact?
5 reasons to compact
 - Increases load-bearing capacity
- Prevents soil settlement and frost damage
- Provides stability
- Reduces water seepage, swelling and contraction
- Reduces settling of soil



Types of compaction
There are four types of compaction effort on soil or asphalt:
Vibration
Impact
Kneading
Pressure

Static Force
Static force is the deadweight of the machine, applying downward force on the soil surface, compressing the soil.
 Static compaction is confined to upper soil layers.
 Kneading and pressure are two examples of static compaction.

Vibratory Force
Vibratory force uses a mechanism, usually enginedriven, to create a downward force.

The compactors deliver a rapid sequence of blows (impacts) to the surface, affecting the top layers as well as deeper layers. Vibration moves through the material, setting particles in motion and moving them closer together for the highest density possible.
Based on the materials being compacted, a certain amount of force must be used to overcome the cohesive nature of the soil.

Compaction Equipment
Choosing the right equipment for the job is vital to achieving proper compaction. 
Deciding Factors

Soil type
–Cohesive
 –Granular
 Thickness of Lift and Machine Performance
Compaction Specifications
Cohesive soils
A machine with a high impact force is required to ram the soil and force the air out to achieve compaction. 
Pad Foot or Sheep Foot Roller
Jumping Jack

Granular soils
Require a shaking or vibratory action to move them
Smooth Drum Roller
 Plate Compacter
Wheel Rolling
Thickness of Lift and Machine Performance
The thicker the lift the heavier piece of equipment needs to be.

Materials
Vibrating Sheepsfoot Rammer
Static Sheepsfoot Grid Roller Scraper
Vibrating Plate Compactor Vibrating Roller Vibrating Sheepsfoot
Scraper Rubber-tired Roller Loader Grid Roller
Lift Thickness Impact Pressure (with kneading)
Vibration Kneading (with pressure)
Gravel 12+ Poor No Good Very Good
Sand 10+/- Poor No Excellent Good
Silt 6+/- Good Good Poor Excellent
Clay 6+/- Excellent Very Good No Good

Compaction Specifications
Method Specification –Detailed instructions specify machine type, lift thickness, number of passes, machine speed and moisture content.
End-result Specification – Engineers indicate final compaction requirements, allowing the contractor to choose what is the best method to achieve compaction.

Types of Equipment
Rollers
Smooth drum
Padded drum Sheep Foot
Rubber-tired
 Static and vibratory sub-categories
 Walk-behind and ride-on
Smooth Drum Roller

Smooth Drum
Smooth-drum machines are ideal for both soil and asphalt
Sheep Foot Roller
Padded Drum / Sheep Foot
Appropriate for cohesive soils.  The drum pads provide a kneading action on soil.

Rubber Tire Roller
 7 to 11 tires that have an overlapping pattern
Typically a static roller
 Compaction effort is pressure and kneading
Wheel Rolling
Jumping Jack

Rammers / Jumping Jack
 Deliver a high impact force ( high amplitude) making them an excellent choice for cohesive and semi-cohesive soils

 Three types of compaction:
impact, vibration and kneading.
Plate Compacter
Vibratory Plates
 Low amplitude and high frequency, designed to compact granular soils and asphalt.  Type of compaction: vibration

Walk Behind
Appropriate for cohesive soils
Ideal for small areas

Soil types
Soil types are classified by grain size, determined by passing the soil through sieves to screen or separate the different grain sizes.
A well - graded soil consists of a wide range of particle sizes with the smaller particles filling voids between larger particles.
 The are three basic soil groups:
Three Soil Groups
Cohesive
 Granular
Organic (this soil is not suitable for compaction)

Cohesive
• Cohesive soils have the smallest particles. Clays range from .00004" to .002".
• Cohesive soils are dense and tightly bound together. They are plastic when wet and can be molded, but become very hard when dry.
• Proper water is essential for proper compaction.
• Cohesive soils usually require a force such as impact or pressure.
• Silt has a noticeably lower cohesion than clay. However, silt is still heavily reliant on water content.
Granular
• Granular soils range from .003" to .08" (sand) and .08" to 1.0" (fine to medium gravel).
• Granular soils are known for their waterdraining properties.
• Sand and gravel obtain maximum density in either a fully dry or saturated state.
• Testing curves are relatively flat so density can be obtained regardless of water content.

Guide to Soil Types
What to look for Appearance/Feel Water Movement When Moist When Dry
Granular soils, fine sands and silts
Coarse grains can be seen. Feels gritty when rubbed between fingers
When water and soil are shaken in palm of hand, they mix. When shaking is stopped they separate
Very little or no plasticity Little or no cohesive strength when dry. Soil sample will crumble easily.
Cohesive soils, mixes and clays
Grains cannot be seen by naked eye. Feels smooth and greasy when rubbed between fingers
When water and soil are shaken in palm of hand, they will not mix
Plastic and sticky. Can be rolled
Has high strength when dry.
Crumbles with difficulty.
 Slow saturation in water.

Materials
Vibrating Sheepsfoot Rammer
Static Sheepsfoot Grid Roller Scraper
Vibrating Plate Compactor Vibrating Roller Vibrating Sheepsfoot
Scraper Rubber-tired Roller Loader Grid Roller
Lift Thickness Impact Pressure (with kneading)
Vibration Kneading (with pressure)
Gravel 12+ Poor No Good Very Good
Sand 10+/- Poor No Excellent Good
Silt 6+/- Good Good Poor Excellent
Clay 6+/- Excellent Very Good No Good

Fill Materials
Permeability Foundation Support Pavement Sub grade Expansive Compaction Difficulty
Gravel Very High Excellent Excellent No Very Easy
Sand Medium Good Good No Easy
Silt Medium Low Poor Poor Some Some
Clay None+ Moderate Poor Difficult Very Difficult
Organic Low Very Poor Not Acceptable Some Very Difficult

Moisture vs. Soil Density
 Moisture or water content is key to achieving density in compaction.
Water allows the particles of material to move together and decrees voids.
Not enough water particles can not slide past each other. 
Too much water and water voids are created.
 The optimum moisture content is when compaction will be achieved the easiest.
Density Curve

Testing
Why Should We Test?
Measures density of soil for comparing the degree of compaction vs. specs
 Measures the effect of moisture on soil density vs. specs
Provides a moisture density curve identifying optimum moisture
 Save Money

Types of Tests
 Proctor Test
 Modified Proctor Test
Hand Test
Proof Role
 Sand Cone
 Nuclear Density

Proctor Test
Determines the maximum density of a specific soil.
 Tests the effects of moisture on soil density
 Standard Proctor
 Modified Proctor
Standard Proctor
 A small soil sample is taken from the jobsite. A standard weight is dropped several times on the soil. The material weighed and then oven dried for 12 hours in order to evaluate water content

Modified Proctor
This is similar to the Proctor Test except a hammer is used to compact material for greater impact, The test is normally preferred in testing materials for higher shearing strength.

Hand Test
Pick up a handful of soil.
Squeeze it in your hand.
If the soil is powdery and will not retain the shape made by your hand, it is too dry.
 If it shatters when dropped, it is too dry.
If the soil is moldable and breaks into only a couple of pieces when dropped, it has the right amount of moisture for proper compaction.
If the soil is plastic in your hand, leaves traces of moisture on your fingers and stays in one piece when dropped, it has too much moisture for compaction.

Proof Rolling
Sand Cone Test (ASTM D1556-90)
A small hole (6" x 6" deep) is dug in the compacted material to be tested. The soil is removed and weighed, then dried and weighed again to determine its moisture content.
 A soil's moisture is figured as a percentage. The specific volume of the hole is determined by filling it with calibrated dry sand from a jar and cone device. The dry weight of the soil removed is divided by the volume of sand needed to fill the hole. This gives us the density of the compacted soil in lbs per cubic foot. This density is compared to the maximum Proctor density obtained earlier, which gives us the relative density of the soil that was just compacted.

Nuclear Density (ASTM D2292-91)
Nuclear Density meters are a quick and fairly accurate way of determining density and moisture content. The meter uses a radioactive isotope source (Cesium 137) at the soil surface (backscatter) or from a probe placed into the soil (direct transmission).
The isotope source gives off photons (usually Gamma rays) which radiate back to the mater's detectors on the bottom of the unit. Dense soil absorbs more radiation than loose soil and the readings reflect overall density. Water content (ASTM D3017) can also be read, all within a few minutes. A relative Proctor density with the compaction results from the test.