Aggregate impact value test

Aggregate impact value is measure of toughness of aggregate. Toughness is the property of material which indicate its capacity which impact in sudden. Tougher the aggregate more suitable for wearing surface such as road surface. Lower the impact value stronger the aggregate, again the impact these for good quality concrete , aggregate with lower AIV (Aggregate Impact Value) is prepared. AIV should not be exceed 30 % for concrete used for wearing surface such as road work or runways or airport. AIV should not be exceed 45 % for concrete used for any non-wearing concrete work such as beam, slab, column etc.

AIM:

To determine the aggregate impact value of coarse aggregate.

Apparatus:

• Aggregate Impact Value Testing Machine.
• Sieves (12.5mm,10mm)
• Cylindrical metal measure (internal diameter 75 mm and depth 50 mm)
• Tamping Rod (10 mm in diameter and 230 mm long, rounded at one end.)
• Balance.
• Oven(300⁰c)

FIGURE:

Procedure:

(i) Sieve the material through 12.5 mm and 10.0mm IS sieves. The aggregates passing through 12.5mm sieve and retained on 10.0mm sieve comprises the test material.

(ii) Pour the aggregates to fill about just 1/3 rd depth of measuring cylinder.

(iii) Compact the material by giving 25 gentle blows with the rounded end of the tamping rod.

(iv) Add two more layers in similar manner, so that cylinder is full.

(v) Strike off the surplus aggregates.

(vi) Determine the net weight of the aggregates to the nearest gram(W).

(vii) Bring the impact machine to rest without wedging or packing up on the level plate, block or floor, so that it is rigid and the hammer guide columns are vertical.

(viii) Fix the cup firmly in position on the base of machine and place whole of the test sample in it and compact by giving 25 gentle strokes with tamping rod.

(ix) Raise the hammer until its lower face is 380 mm above the surface of aggregate sample in the cup and allow it to fall freely on the aggregate sample. Give 15 such blows at an interval of not less than one second between successive falls.

(x) Remove the crushed aggregate from the cup and sieve it through 2.36 mm IS sieves until no further significant amount passes in one minute. Weigh the fraction passing the sieve to an accuracy of 1 gm. Also, weigh the fraction retained in the sieve.

Compute the aggregate impact value. The mean of two observations, rounded to nearest whole number is reported as the Aggregate Impact Value.

OBSERVATIONS:

Observations	Sample 1	Sample 2
Total weight of dry sample (W1 gm)
Weight of portion passing 2.36 mm sieve (W2 gm)
Aggregate Impact Value (percent) = W2 / W1 X 100

Result of Impact Test

Aggregate Impact Value =

Recommended Aggregate Impact Test Values

Classification of aggregates using Aggregate Impact Value is as given below:

Aggregate Impact Value	Classification
<20%	Exceptionally Strong
10 – 20%	Strong
20-30%	Satisfactory for road surfacing
>35%	Weak for road surfacing

Specified limits of percent aggregate impact value for different types of road construction by Indian Roads Congress is given below.

Sr. No.	Type of pavement	Aggregate impact value not more than
1.	Wearing Course	30
	a) Bituminous surface dressing
	b) Penetration macadam
	c) Bituminous carpet concrete
	d) Cement concrete
2.	Bitumen bound macadam base course	35
3.	WBM base course with bitumen surfacing	40
4	Cement concrete base course	45

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1. Aggregate abrasion value test.

2. Aggregate crushing value test.

3. Determination of Bulk density of Course Aggregates.

4. Determination of Particle Size Distribution of Course Aggregates.

5. Determination of Specific Gravity and Water Absorption of Course Aggregate.

Determination of Bulk density of Course Aggregates

This method is used to determine the bulk density of given specimen during the concrete mix design when the aggregate is to be batched by volume or by weight. Then it is necessary to know the mass of the aggregate that will fill the container of unit volume.

If we know the bulk density of aggregate material than we can easily calculate the mass required to fill a unit volume container.

Bulk Density also indicates the percentage of voids present in the aggregate material.

This percentage of voids effects the grading of the aggregate which is important in higher strength concrete.

AIM:

To determine the bulk density and percentage voids of aggregate.

APPARATUS:

•  Weighing Balance
•  Temping Rod
•  Measuring Cylinder
•  Shovel 

FIGURE:

 

Procedure:

1.   Take the weight of empty measure (W)

2.   Fill the measure with aggregates sample for about one third height and tamp evenly with 25 strokes of the rounded end of the tamping rod.

3.   Add a similar quantity of aggregate as second layer and tamp it evenly with 25 strokes.

4.   Fill the measure with a third layer of aggregate up to over following and tamp it with 25 strokes

5.   Strike off the surplus aggregate using the tamping rod as a straight edge. And take the weight (w1)

6.   Empty the measure and fill it again to over flowing by means of a shovel, the aggregate being discharged from a height not exceeding 5 cm above the top of the measure.

7.   Level the surface of the measure and weight it (w2).

CALCULATIONS:

Diameter of metal measure =

Volume of metal measure (v) = (W1-W)

Bulk density of compacted coarse aggregates = ——————–

V

Bulk density of loosely packed aggregates= (W2-W)/V

Percentage of voids =100x (Gs-r)/ Gs

Where Gs = Specific gravity of aggregate

r = Bulk density of aggregate in kg / liter.

Determination of Particle Size Distribution of Coarse Aggregates

Grading refers to the determination of the particle-size distribution for aggregate. Grading limits and maximum aggregate size are specified because grading and size affect the amount of aggregate used as well as cement and water requirements, workability, pumpability, and durability of concrete. In general, if the water-cement ratio is chosen correctly, a wide range in grading can be used without a major effect on strength. When gap-graded aggregate is specified, certain particle sizes of aggregate are omitted from the size continuum. Gap-graded aggregate are used to obtain uniform textures in exposed aggregate concrete. Close control of mix proportions is necessary to avoid segregation.

AIM:

To determine particle size distribution of coarse aggregates by sieving or screening.

Apparatus:

·         Test Sieves conforming to IS: 460-1962

o   80 mm,

o   40 mm,

o   20 mm,

o   10 mm,

o   4.75 mm,

·         Balance,

·         Stop Watch.

FIGURE:

Procedure:

1.       Take a sample of coarse aggregate in pan and placed it in dry oven at a temperature of 100 – 110^oC.

2.       Take the sample weight to nearest 0.1 gram.

3.     Place the set of sieves, with the largest opening on top, into a pan and pour the aggregate onto the top sieve.

4.       The use a mechanical sieve shaker is the preferred method for separating the materials into the specified sizes. If a mechanical shaker is not available, proceed with hand shaking.

5.       Establish a shaking time for different types of aggregates that will assure proper sieving of the material without degradation.

6.       When the required mechanical shaking time is complete, hand sieve by lateral and vertical motion of the sieves with a “jarring” action that keeps the material moving continuously over the surface of the sieves.

7.       Continue hand sieving until no material passes through the sieve.

8.       Brush particles clinging to each sieve into the next lower sieve with a bristle brush. Ensure no material is lost.

9.       Determine the individual weights to the nearest 0.1 g of aggregate retained on each sieve and record these weights.

10.    Report the percentages to the nearest 0.1% for each size of aggregate retained on each sieve.

OBSERVATION:

IS Sieve	Weight Retained on Sieve (gms)	Percentage of Weight Retained (%)	Percentage of Weight Passing (%)	Cumulative Percentage of Passing (%)	Remark
80 mm
40 mm
20 mm
10 mm
4.75 mm
Total

CALCULATION:

The percent retained (%), Cumulative retained (%) & percent finer (%) is calculated.

Percent retained on each sieve = Weight of retained sample in each sieve / Total weight of sample

The cumulative percent retained is calculated by adding percent retained on each sieve as a cumulative procedure.

The percent finer is calculated by subtracting the cumulative percent retained from 100 percent.

Conclusion / Result:

The result of the sieve analysis is reported graphically on a semi log graph, taking sieve sizes on log scale and % finer in arithmetic scale.