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INTRODUCTIONfrc
Concrete made from Portland cement, is relatively strong in compression but weak in tension and tends to be brittle .The weakness in tension can be overcome by the use of conventional steel bars reinforcement and to some extent by the mixing of a sufficient volume of certain fibers.
FIBRE
A fibrE is a small discrete reinforcing material produced from various materials like steel, plastic, glass, carbon and natural materials in various shapes and size
Properties of sfrc
High fatigue strength resistance to impact, blast and shock loads
Shrinkage control of concrete
Tensile strength, very high flexural, shear
Erosion and abrasion resistance to splitting
Temperature resistance, high thermal
Earth quake resistance
The degree of improvement gained in any specific property exhibited by SFRC is dependent on a number of factors that include:-
Concrete mix and its age
Steel fiber content, volume fraction
Fiber geometry, its aspect ratio (length to diameter ratio) and bond characteristics volume fraction
Glass fibre reinforced concrete
Glass fibre–reinforced concrete is (GFRC) basically a concrete composition which is composed of material like cement, sand, water, and admixtures, in which short length discrete glass fibers are dispersed. Inclusion of these fibres in these composite results in improved tensile strength and impact strength of the material
glass fibre reinforced concrete
Problem of gfrc
At the beginning age of the GFRC development, one of the most considerable problems was the durability of the glass fiber, which becomes more brittle with time, due to the alkalinity of the cement mortar. After some research, significant improvement have been made, and presently, the problem is practically solved with the new types of alkali-resistant (AR resistance) glass fibers and with mortar additives that prevent the processes that lead to the embrittlement of GFRC.
polymer fibre reinforced concrete
There are many ways to minimize the failure of the concrete structures made of steel reinforce concrete. The custom approach is to adhesively bond polymer fiber composites onto the structure. This also helps to increase the toughness and tensile strength and improve the cracking and deformation characteristics of the resultant composite. But the method adds another layer, which is prone t degradation. These fiber polymer composites have been shown to suffer from degradation when expose to marine environment due to surface blistering. As a result, the adhesive bond strength is reduced, which results in the de-lamination of the composite.
Polymer fibres
NATURAL FIBER REINFORCED CONCRETE
The first use of fibers in reinforced concrete has been dated to 1870‟s. Since then, researchers around the world have been interested improving the tensile properties of concrete by adding, iron and other wastes. Local interest has been demonstrate through research work performed. In addition to industrial fibers, natural organic and mineral fiber have been also investigated in reinforced concrete Wood, sisal, jute, bamboo, coconut, asbestos and rockwool, are examples that have been used and investigated.
nfrc
Specification for Concrete Aggregates
Water and admixtures
The water to be used for the mix should be clean and of good quality. Admixtures such as accelerating agents may be used in order to decrease the influence of the glucose retardant
Methods of mixing-
The two methods of mixing and placing are:-
Wet mix
Dry-compacted mix.
In the wet mix, a low volume fraction of fibres is used. The water to be added to the mix has to take into account the high natural water content in the natural fibers
Fibres
The length of fibers may vary from 1 to 2 in. (25 to 500 mm). Because natural fibers are naturally available materials, they are not uniform in diameter and length. Typical values of diameter for unprocessed natural fibres vary from 0.004 to 0.03 in. (0.10 to 0.75 mm)
FACTORS AFFECTING THE PROPERTIES OF FRC
Volume of Fibres
Aspect Ratio of the Fibre
Orientation of Fibres
Workability and Compaction of Concrete
Size of Coarse Aggregate
Mixing
ORIENTATION OF FIBRES
The effect of randomness, was tested using mortar specimens reinforced with 0.5% volume of fibres, by orienting them:
parallel to the direction of the load
perpendicular to the direction of the load
in random
MERITS OF FIBRE REINFORCED CONCRETe
Lower the permeability of concrete.
Reduce bleeding of water
It control plastic shrinkage cracking and drying shrinkage
It increase the strength of concrete.
It reduce the flexural creep.
DEMERITS OF FIBREREINFORCED CONCRETE
Not as reliable as steel in high stress/strain concrete members.
Good in crack prevention, but if a crack does form , fibre is not as efficient as controlling the crack
Application of frc in civil infrastructure
Repairs of existing structure
Development of new constructions for long service life including tunnel
Used In many constructions subjected to the combination of mechanical load and impact load
Pile Integrity Testing by Sonic Echo Method
Main Contents
Introduction
Important Terminologies
Working Principle
Detailed Procedure
Apparatus Specifications
Benefits and Limitations
Case Studies
References
Common Names For Test
Low Strain Integrity Test
Pulse Echo Method (PEM)
Sonic Echo Method
Standards and Specifications
ASTM-D 5882 (To be Followed)
IS : 2911
Introduction
Today Piles are being cast in large diameters and depths to carry heavy loads involving large volume of concrete so they are expensive.
Moreover , Deep foundation Construction process is inherently a BLIND process.
Thus it is imperative to have some Quality Control tool to quickly evaluate the structural integrity of these piles.
Keeping in view the above factors the Low strain testing is devised which is Quick , Inexpensive and Fairly Reliable method
Important Terminologies
Pile Integrity:
It is the qualitative evaluation of physical dimensions , continuity of pile and consistency of the pile material.
Pile Impedance: (Z=EA/C)
The young modulus of pile multiplied by cross sectional area of the pile and divided by wave speed.
Pulse Echo Method:
Test in which measurements of velocity are evaluated as as a function of time