Introduction to grading of aggregates on concrete

Grading Of Aggregates for Concrete

• Aggregate contains nearly 85 % volume of mass concrete
• Concrete includes aggregate equal to a maximum size of 150 mm
• Grading of Aggregates
• Way particles of aggregate are adapted collectively in the mix and depend on the gradation, shape, and surface texture
• The functionality and finishing attribute of fresh concrete are influenced by grading as a result the attributes of hardened concrete is also impacted.
• Standard grading signifies, sample of aggregates which contain all standard fractions of aggregate in necessary proportion in such a way that the sample comprises least voids
• Well graded aggregate that comprises of least voids will necessitate minimum paste to close the voids in the aggregate
• Minimum paste is defined as less quantity of cement and less quantity of water which lead to increased economy, greater strength, lesser-shrinkage and better longevity.

Gap Grading

• Voids formed with greater size filled up by instant next lower size.
• Lower size is not adjusted in the existing gap because of small voids left out to decrease density.
• Voids formed with a specific size can adjust second or third lower size only.
• As for instance voids formed with 40mm can adjust 10mm & 4.75mm but not 20mm, this concept is known as Gap Grading.

Gap-Graded Mix

• Gap-graded mixes comprises of aggregate sustained on a 19mm or 37.5mm sieve
• Fines passing the No. 4 sieve (4.75mm)
• It is suitable to retain homogenous textures for exposed-aggregate concrete
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• Susceptible to Segregation, controlled by FA %
• Rounded used, by 25%
• Air entrainment generally is essential for better functionality

Benefits of Gap-Graded Mix

Enhance strength and curtail creep and shrinkage
Necessity of sand is decreased by 26 to 40%
Particular area of total aggregates are lowered because of less sand
Needs fewer quantity of cement owning to net volume of voids is lowered

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Types of reinforcements applied in the process of prestressing

Prestressed concrete is a process for resolving concrete's natural weakness in tension.
Prestressing tendons (normally made of high tensile steel cable or rods) are employed to arrange a clamping load that forms a compressive stress to equalize the tensile stress occurs because of a bending load.


(i) Spalling reinforcement
Spalling stresses are developed in the areas behind the loaded faces of anchor blocks and it leads to departing of surface concrete. These stresses are produced with strain inconsistency with Poisson’s effects or with the shape of stress trajectories. The spalling stresses are arranged because of the strain compatibility with regard to the effect of Poisson’s ratio. For prestressing concrete bride, the stress in the reinforcement (0.87fy) should have been retained to manage cracking whereas the bars should have been set as closer to the end face as possible and fixed over the concrete edge.

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(ii) Equilibrium reinforcement 
Equilibrium reinforcement is essential when there exist various anchorages wherein prestressing loads are employed successively.  It is found in building construction & bridge.


(iii) Bursting Reinforcement 
Tensile stresses are caused throughout pre-stressing operation and the highest bursting stress happens where the stress trajectories are concave against the line of action of the load. The objective of Reinforcement is to withstand these lateral tensile forces.

Article Source : http://www.engineeringcivil.com

Geotextile - Benefits for improving soil quality

Geotextiles are mostly utilized in the civil construction, particularly in roads and fills to make the quality of the soil better. Geotextiles can transform a poor soil to be stronger and prepare it for developing building. Geotextiles are very effective for varuiys infrastructure works like roads, harbors etc.


Function of Geotextiles

The objective of Geotextiles is to enhance the characteristics of soil so that roads, embankments, pipelines and earth retaining structures can be easily constructed on it.
Based on the uses, there are different types of geotextiles like open mesh type, warp-knitted structure, or with a closed fabric surface (a non-woven). According to uses or projected design, geotextiles are dependent on the various factors like separation, filtration, drainage, reinforcement, sealing and protection.


Geotextile Separation

If the geotextile is to be set up among two diverse soil materials, the separation factor is very important. Here, the geotextile will divide and sustain individual unrelated materials to retain the necessary soil characteristics. This type of geotextile is applied so that the soils are not blended when water enters into the soil strata. It is found in road construction, when it is required to maintain fine subgrade aggregate from coarse aggregates which are arranged as the base course.

It is performed to retain the drainage characteristics perfect by resisting the fine aggregate from filling the voids among the larger aggregate. These types of geotextile contain extra density and permeability characteristics to resist soil contamination and facilitate the water to pass smoothly devoid of damaging the strength and structural integrity of the road.



Geotextile Applications

Geotextiles are utilized for various purposes - To enhance the quality of unpaved and paved roads in airport runways; on landfills and stone base courses; underneath sidewalks and sand drainage layer; below parking lots and curb areas; To enhance green areas and recreational facilities, underneath retaining wall structures; To make the soil quality better, below duct banks and pipe trenches.

Geotextile Filtration

Geotextile Filtration facilitates water to pass in both directions. It can be woven or non-woven to resist fine aggregates to proceed among soil layers. In order to choose perfect one, evaluate and examine the porosity and permeability of the projected geotextile. Keep in mind that geotextiles are employed on both axis, vertical and horizontal. Geotextile with perfect porosity and permeable can facilitate resolving drainage problems over the house and roads and curbs. The geotextile advocates a lateral flow thus dispersing the kinetic energy of the capillary rise of ground water.



Geotextile Reinforcement

When a geotextile is used to improve soil characteristics, it shall consider the following criteria: friction or movement restraint, support of loads and changes in bearing failure plane.

This is comparable to the function of rebar in concrete, that it is used to reinforce concrete. This is why geotextiles are used on embankments and roads being built over very poorly graded soils. It will allow also to have a steeper embankment built, although it is always recommended to have that information provided by the geotechnical engineer.

Geotextile Sealing

When a geotextile is impregnated with asphalt or other mixes it will turn into an impermeable fabric that will restrict the flow of liquids in both directions.it is important to highlight that this will only occur if the geotextile is a non-woven fabric as normally is used in road improvements projects. There are multiple options and types of geotextiles but the remember that always the suggestion needs to come from a soil expert based on the information gather from existing soil strata.

For more information, go through the following article.
https://www.thebalance.com/construction-materials-4073376