09-10-2012, 11:08 AM
STUDY OF COMPOSITE CONCRETE
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INTRODUCTION
CONCRETE: -
1) Versatile material, recycle able and environmental-friendly material.
2) Its per capita consumption, least energy consumption, ability to absorb vast proportions of waste products.
HARDENED CONCRETE: -
1) Chemical action between cement and water.
2) A compact mass like an artificial stone.
3) Strength depends on properties of ingredients and level of controls on site.
CHARACTERISTICS OF GOOD CONCRETE: -
Performance in green and plastic state.
Compressive strength: Index of overall quality.
Grades of concrete and their strength.
Strong, durable, impermeable concrete with minimum
dimensional changes.
COMPOSITE CONCRETE:
Large compressive strength and low tensile strength.
Less resistance to tensile stresses, causes lack of ductility, poor
fracture, toughness and propagation of cracks.
Composite concrete: Addition of steel fibers.
Different tests on concrete in the experiment.
MATERIALS AND THEIR TESTING
CEMENT:
Physical properties of cement: -
FINENESS TEST: -
By sieving
By blain air permeability apparatus
Sieve test: - 1) IS sieve no. 9
2) Weight of residue left after sieving decides fineness.
3) Wt. shouldn’t exceed 10% for ordinary cement.
Standard consistency: - A Vicat plunger having 10mm diameter and 50mm length to penetrate at the depth of 33-35mm from the top of the mould.
Moisture content: -
The surface moisture expressed as a percentage of the weight of the saturated surface dry aggregate is termed as moisture content.
The determination of moisture content of an aggregate is necessary in order to determine the net water cement ratio for a batch of concrete.
High moisture content will increase the effective water cement ratio to an appreciable extent and may make concrete weak unless a suitable allowance is made.
Aggregate Crushing Value: -
The aggregate crushing value gives a relative measure of the resistance of an aggregate to crushing under a gradually applied compressive load.
This test is made on single size aggregate passing 12.5 mm and retained on 10 mm sieve.
The crushing value of aggregate is restricted to 30 % for concrete used for roads and pavements and 45 % may be permitted to other structure.
Aggregate Impact Value
The aggregate impact value gives relative measure of the resistance of an aggregate to sudden shock or impact.
The ratio of the weight of fines formed, to the weight of the total sample taken is expressed as percentage. This is known as aggregate impact value.
IS 283 -1970 specifies that aggregate impact value shall not exceed 45 % by weight for aggregate used for concrete other than wearing surface and 30 % by weight , for concrete wearing surfaces.
Fibers
To improve the tensile strength of concrete in some amount, fibers are added to the concrete.
The aspect ratio of the fiber is the ratio of its length to its diameter. Typical aspect ratio ranges from 30 to 150.
Some of the fibers that could be used are steel fibers, polypropylene, nylons, asbestos, coir, glass and carbon.
Steel fiber is the most commonly used fibers.
Uses of steel fibers make significant improvements in flexural, impact and fatigue strength of concrete.
Superplasticizers
uses of superplasticizers permit the reduction of water to the extent up to 30 % without reducing workability in contrast to the possible reduction up to 15 % in case of plasticizers.
The use of superplasticizers is practiced for production of flowing, self leveling, self compacting and for the production of high strength and high performance concrete.
The superplasticizers are more powerful as dispersing agents and they are high range water reducers.
superplasticizers also produce a homogeneous, cohesive concrete generally without any tendency for segregation and bleeding.