Test on aggregate
Any Concrete work before must be Test on aggregate because of sure working quality of Concrete. Difference type of test no aggregates. as per below tests point out of aggregate tests
1. Sampling of Aggregate Tests
2. Aggregate Crushing Value
3. Impact Value of Coarse Aggregate
4. Sieve Analysis Test of Coarse Aggregates
5. Flakiness Index of Aggregate
6. Elongation Index of Aggregate
7. Compressive Strength Test for Concrete
Sampling of Aggregate Tests
Samples from stockpiles shall be taken equally from the top third, midpoint and bottom third of the height of stock.
The outer layer of the sampling point shall be removed, and the sample is taken from the material beneath.
The sample thus collected will be the gross sample. The quantity of the total sample depends on the aggregate size.
Reduction of Gross Sample will be made as per quartering method to required sample size for testing as per following;
Take the gross sample on the open platform. For Fine aggregate, use tray so that residual fines can be collected by brushing.
The aggregate shall be mixed and then scooped into a cone shape pile.
After the cone is formed, it shall be flattened by pressing the top.
Then it is divided into four quadrants diagonally.
The bulk of the sample is reduced by rejecting any two diagonally opposite Quarters
This method is repeated until the sample size is approximately achieved forgiven.
Aggregate Crushing Value
Aim:
To calculate aggregate Crushing value by testing aggregate passing 12.5 mm sieve and retained on a 10 mm sieve.
Scope:
This procedure covers all relative activity for the project site.
Apparatus:
15cm dia. steel cylinder with plunger and base plate
Tamping rod 16 mm dia. and 600 mm long with one end rounded
Weighing balance of accuracy 1 g
Sieves 12.5 mm 10mm & 2.36 mm
Drying Oven
CTM
Procedure:
Take a sample of aggregates by sieving through 12.5mm and retained on 10mm.
The aggregate shall be tested in dry surface conditions. If dried by heating, the period of drying shall not exceed 4 hours and temp shall be 100-110 deg C.
A sample shall be cooled down to room temperature before testing. Take approximately 6 kgs of a sample.
The quantity of the sample shall be such that the depth of material in the cylinder after tamping shall be 10cms.
The cylinder shall be filled up in 3 layers, and each layer shall be tamped 25 times with tamping rod and finally leveled off.
The weight of the material comprising the test sample shall be determin.
The plunger shall be placed in position, and the apparatus shall be then placed between the platens of CTM.
The load shall be applied at a uniform rate so that the load of 40T is reached in 10 minutes.
The load shall be removed from the cylinder, and the crushed sample shall be sieved through 2.36 mm sieve. The fraction passing sieve 2.36 mm shall be weighed to nearest 1gm.
Such two tests shall be taken for each lot.
Calculation & Records:
• Aggregate Crushing Value, % = (B / A) x100
• The mean of the two results shall be reported to the nearest whole
Impact Value of Coarse Aggregate
Aim:
To determine the moisture content of coarse aggregate.
IS code for aggregate testing Is CODE: IS 2386 Part 1,
IS code for aggregate testing Is CODE: IS 2386 part 4
Apparatus:
Impact testing machine (metal base)
A cylindrical steel cup of internal dimension: 102mm & depth 50mm
IS sieves of sizes 12.5, 10 & 2.36mm
A straight metal tamping rod of circular cross-section 16mm in dia. And 600mm long rounded at one end.
The weight balance of 01 gm.
A suitable oven thermostatically controlled to maintain a temperature of 100°C to 110°C
Samples:
Coarse Aggregate
Procedure:
The impact machine shall rest without wedging or packing upon the level plate.
The cup shall be fixed firmly in position on the base of the machine and whole of the test sample placed in it subject to fifteen blows of the metal hammer of weight 14 kg falling from a height 38 cm.
The quantity of excellent material passing through 2.36mm resulting from pounding will indicate the toughness of the sample of aggregate. The ratio of the weight of the fines (more beautiful than 2.36mm size) formed to be the weight of the total sample taken is expressed as a percentage. This is known as aggregate impact value test IS 283-1970
Result:
Aggregate impact value shall not exceed 45 % by weight for aggregate used for concrete other than wearing surface and 30 % by weight for concrete for wearing surfaces such as runway, roads, and pavements.
Sieve Analysis Test of Coarse Aggregates
Aim:
To determine the properties of Coarse aggregate/test on coarse aggregate for size and grading
Scope:
This procedure covers all relative activity for the project site.
Apparatus:
Drying Oven
IS Sieves 40 mm, 20 mm, 16 mm, 12.5 mm, 10mm, and pan – for Analysis of 20 mm metal.
Weigh scale to the accuracy of 1gm.
Metal trays etc.
Procedure:
Sample of aggregate shall be collected as given earlier.
Sieves shall be cleaned and arranged in sequence in descending order. Pan shall at the lowermost end and Lid on top.
Take around 5 kg of sample and dry it in an oven at a temp of 100-1100
A dried sample shall be then weighed ( 5 kg preferably) and sieved successively on sieves starting with 40mm and then through 4.75mm (For 20 mm down an aggregate size ) and through 2.36 mm (For 12.5/10 mm down an aggregate size).
Each sieve shall be shaken at least for two minutes on a clean tray until no more trace passes.
The motion shall be varied like back and forth, left to right, circular clockwise and anti-clockwise and with frequent jarring.
Material shall not be forced through the mesh. But for coarser than 20mm particles, placing is permitted (passing particles through sieve opening manually).
Sieves shall be brushed from underneath of mesh and pass on to the next.
On completion of sieving, material retained on each sieve is to weigh Separately.
Check for permissible limits for passing.
Reporting:
The cumulative % by weight of the total sample passing each sieve, to the nearest whole number.
Or
The % by weight of the total sample passing one sieve and retained on the next Smaller sieve to the nearest 1 decimal.
Check for permissible limits for passing.
Flakiness Index of Aggregate
Aim:
To determine the Flakiness of particles of Coarse aggregate / test on coarse aggregate more significant than 6.3 mm in size.
Scope:
This procedure covers all relative activity for the project site.
Apparatus :
Balance with an accuracy of 0.1% of the weight of a sample
Flakiness Index Gauge
All other as per Sieve analysis.
Sample :
It shall be taken from retained material from Sieve analysis preferably and should
have at least 200 pieces of each fraction.
Procedure :
Each sample of 20 mm and 10mm shall be taken from the retained fraction.
Each fraction shall be the gauge in turn for thickness on the metal gauge.
The total amount retained on the gauge shall be weighed.
Calculation & Records:
The flakiness index is the total weight of the material passing the various thickness gauge; expressed as a % of the weight of the total sample gauged.
Elongation Index of Aggregate
Aim:
To determine the Elongated shape of particles of Coarse Aggregate/test on coarse aggregate greater than 6.3 mm in size.
Scope:
This procedure covers all relative activity for the project site.
Apparatus:
Balance with an accuracy of 0.1% of the weight of the sample
Elongation Index Gauge
All other as per Sieve analysis.
Sample:
It shall be taken from retained material from Sieve analysis preferably and should have at least 200 pieces of each fraction.
Procedure:
Each sample of 20mm and 10mm metal shall be taken from the retained fraction
Each fraction shall be gauged in turn for thickness on the metal gauge.
The total amount passing the gauge shall be weighed.
Calculation & Records:
The Elongation Index the total weight of the material passing the various
Thickness gauges; expressed as a % of the weight of total sample gauged…
Compressive Strength Test for Concrete
Aim:
To establish the Compressive strength of concrete sample for acceptance
Apparatus:
A compressive Testing machine had adequate capacity.
Weighing Balance.
Measuring Scale.
Procedure:
Remove the cubes required for testing from curing tank wipe clean of water and air dry them to surface dryness.
Stack cubes in sequence as per mix, dates, locations etc.
Record the actual surface area ( sq cm)of the cube which will be in contact with Platen of CTM ( A in cm2 or mm2 ).
Weigh the cubes and record the weights in the registering.
Place the cube on platen centrally keeping the toweled side in front.
Position the top platen on the cube surface. See that there is no gap left between the cube top and platen.
Load the CTM at the desired speed without any shocks. ( Pointer and needle shall move together)
When crushing takes place in the specimen, a needle will start falling back, but the pointer will remain at maximum reading.
Record the reading shown by pointer viewing perpendicular to the face of the dial. (Load applied in kN or tone- W)
Relieve the load from CTM. Remove the cube. Clean the platens.
Check the features of cube failure. Good failure is that cube mass retained shall have concavity on sides. If failures are occurring consistently by crack developing only on one side, it means cubes are eccentrically loaded. If cracks are always developed centrally means point load is getting applied due to the Convexity of platens. Remedial measures are required to be taken for this.
Calculations:
Compressive Stress ( c ) in N / mm2 or Kg / cm2 as below :
• c = Wx1000 /A in N/mm2 or Kg /cm2
• Average of the set of three or more cubes to be recorded (c’ ).
When three or more cubes from single batch/lot are tested, max variation is allowed +/- 15%. If any cube is showing more variation, a result of that cube is discarded, and an average of two or more is to be taken.
Recording:
Record is generated as per the sample format is given in chronological order.
Format to be Used: To be recorded in Cube Register.
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