ct aggregates

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AGGREGATES- FUNCTION IN

CONCRETEA TOPIC FROM CHAPTER CONCRETE MAKING

MATERIAL

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DEFINITION• A COMBINATION OF DIFFERENT SIZES AND SHAPES

NORMALLY OF STONES. • MAXIMUM SIZE IS 75 MM.

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• AS AN UNDERLYING MATERIAL FOR FOUNDATIONS AND PAVEMENTS• AS AN INGREDIENTS IN PORTLAND CEMENT CONCRETE

AND ASPHALT CONCRETE.

USES OF AGGREGATES

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USES OF AGGREGATES

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• AGGREGATES SHALL BE HARD, DURABLE AND CLEAN AND FREE FROM ADHERENT COATINGS AND ORGANIC MATTER AND SHALL NOT CONTAIN APPRECIABLE AMOUNT OF CLAY.

• AGGREGATES SHALL NOT CONTAIN HARMFUL IMPURITIES SUCH AS IRON PYRITES, ALKALIS, SALTS, COAL, MICA, SHALE OR OTHER MATERIALS WHICH WILL AFFECT HARDENING AND ATTACK REINFORCEMENT.

SELECTION OF AGGREGATES

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CLASSIFICATION OF AGGREGATES

BASED ON SIZE:

1.FINE AGGREGATES - THOSE AGGREGATES WHICH PASS THROUGH 4.75 MM SIEVE OR AGGREGATES WITH SIZE LESS THAN 5 MM.

2.COARSE AGGREGATES – THOSE AGGREGATES PASSING THROUGH 75 MM SIEVE AND ENTIRELY RETAINED ON 4.75 MM SIEVE OR THOSE AGGREGATES WITH SIZE GREATER THAN 5 MM.

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BASED ON SOURCE OR METHOD OF MANUFACTURE:1. NATURAL AGGREGATE/UNCRUSHED AGGREGATE-

THOSE FROM THE RIVER BEDS, RIVER SAND AND EX-MINES. NORMALLY ROUNDED IN SHAPE AND HAVE SMOOTH SURFACE TEXTURE.

2. MANUFACTURED AGGREGATE / CRUSHED AGGREGATE –THOSE OBTAINED BY MECHANICALLY CRUSHING ROCKS, BOULDERS, OR COBBLES. NORMALLY ANGULAR IN SHAPE AND HAVE ROUGH SURFACE TEXTURE

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BASED ON BASED ON SPECIFIC GRAVITY OR DENSITY MEASURED IN BULK :

1.LIGHTWEIGHT AGGREGATE

2.NORMAL-WEIGHT AGGREGATE

3.HEAVYWEIGHT AGGREGATE

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1. LIGHTWEIGHT AGGREGATE• FINE AGGREGATE AGGREGATE WITH BULK DENSITY <

1120KG/M3

• COARSE AGGREGATE ATE IS ANY AGGREGATE WITH BULK

DENSITY < 880KG/M3

• 2 TYPES OF LIGHTWEIGHT AGGREGATE:

NATURAL LIGHTWEIGHT AGGREGATES (EG: PALM OIL SHELL, RICE HUSK, ETC)

MANUFACTURED (ALSO CALLED SYNTHETIC) LIGHTWEIGHT AGGREGATES.

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2. NORMAL WEIGHT AGGREGATE

• EXAMPLES : CRUSHED STONE, GRAVEL & ORDINARY SAND

• THEY ARE COMMONLY USED IN MANUFACTURE OF NORMAL WEIGHT CONCRETE, ASPHALT CONCRETE AND ROADWAY SUB-BASE.

• BULK DENSITY OF NORMAL WEIGHT AGGREGATE IS AROUND 1520 TO 1680KG/M3.

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3. HEAVYWEIGHT AGGREGATE• THOSE AGGREGATE WITH HIGH DENSITY AND IS USED

PRIMARILY IN THE MANUFACTURE OF HEAVYWEIGHT CONCRETE, EMPLOYED FOR PROTECTION AGAINST NUCLEAR RADIATION AND AS BOMB SHELTER.

• THE UNIT WEIGHT OF HEAVYWEIGHT CONCRETE VARIES FROM 2400KG/M3 WITH S.G. RANGE FROM 4.0 TO 4.6 ..

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PHYSICAL PROPERTIES OF AGGREGATES

1. STRENGTH2. HARDNESS3. TOUGHNESS4. DURABILITY5. POROSITY6. WATER ABSORPTION

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1. STRENGTH OF AGGREGATES

• IN PRACTICE, MAJORITY OF NORMAL AGGREGATES ARE CONSIDERABLY STRONGER THAN CONCRETE

• A GOOD AVERAGE VALUE OF CRUSHING STRENGTH OF AGGREGATES IS 200N/MM2.

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2. HARDNESS OF AGGREGATES• ABILITY OF THE AGGREGATE TO WITHSTAND LOAD OR APPLIED

PRESSURE.

• THIS HARDNESS IS DEPENDING ON THE TYPE OF PARENT ROCK

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3. TOUGHNESS

• IS THE RESISTANCE OF AGGREGATE TO FAILURE BY IMPACT.

• THIS CAN BE DETERMINED BY AGGREGATE IMPACT TEST.

• THE AGGREGATE IMPACT VALUE SHALL NOT EXCEED 45% BY WEIGHT FOR AGGREGATE USED FOR CONCRETE OTHER THAN THOSE USED FOR WEARING SURFACES AND 30% FOR CONCRETE FOR WEARING SURFACES.

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4. DURABILITY OF AGGREGATES

• ABILITY OF THE AGGREGATE TO WITHSTAND EXTERNAL OR INTERNAL DAMAGING ATTACK OR IN OTHER WORDS THE SOUNDNESS OF AGGREGATE.

• THIS CAN BE OBTAINED BY CARRYING OUT THE SOUNDNESS TEST.

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5. POROSITY • AGGREGATE NORMALLY HAVE PORES OF VARIOUS SIZES.• AGGREGATES WILL ABSORB WATER WHEN IT IS DRY BUT

NORMALLY RELEASE WATER IN THE CONCRETE MIX WHEN IT IS WET.• THE AMOUNT OF WATER AND ITS RATE OF PERMEATION

DEPENDS ON THE SIZE AND VOLUME OF AGGREGATE• SINCE THE AGGREGATE COMPRISES 75% OF THE CONCRETE

VOLUME, IT IS ESSENTIAL TO NOTE THAT POROSITY OF AN AGGREGATE CONTRIBUTE TO THE OVERALL POROSITY OF CONCRETE.

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6. GRADING OF AGGREGATES:• COARSE AND FINE AGGREGATES TO BE USED FOR MAKING CONCRETE

SHOULD BE WELL GRADED. GRADATION MEANS THE PARTICLE SIZE DISTRIBUTION OF AGGREGATES. TEST FOR GRADING OF AGGREGATES IS CARRIED OUT USING THE SIEVE ANALYSIS METHOD.

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#KAUSHALJIGARPrepared by .. .

Kaushal Mehta … .. twitter@kaushalmehta96Jigar Patel … .. twitter@jigarpatel_jp

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