Aggregates Impact Value Test

Aggregates Impact Value Test (IS 2386 Part 4)

• Toughness is the property of a material to resist the impact. Due to traffic loads, the road stones are subjected to the pounding action or impact and there is possibility of stones breaking into smaller pieces. The road stones should therefore be tough enough to resist fracture under impact. A test designed to evaluate the toughness of stones i.e., the resistance of the stones to fracture under repeated impacts may be called an impact test for road stones.

Apparatus

 Impact testing machine: The machine consists of a metal base with a plane lower surface supported well on a firm floor, A cylindrical metal measure of 75mm dia. and 50mm depth,  tamping rod of 10mm circular cross section and 230mm length, rounded at one end, Sieves of sizes - 12.5mm, 10mm and 2.36mm, Oven: A thermostatically controlled drying oven capable of maintaining constant temperature between 100° c and 110°c.

Impact Testing Machine

Sampling

1. Take aggregates passing through 12.5mm IS Sieve 100% • Retention on 10mm IS Sieve 100% 
2. The sample should be oven-dried for 4hrs. at a temperature of 100 to 110oC and cooled.
3. The measure should be about one-third full with the prepared aggregates and tamped with 25 strokes of the tamping rod.

Procedure

1. • The cup of the impact testing machine should be fixed firmly in position on the base of the machine.
2. Whole of the test sample is to be placed in it and compacted by 25 strokes of the tamping rod.
3. Weigh the sample with cup to nearest gram.Let it be W1. Also weigh the empty cup, let it be W2.
4.  The hammer should be raised to 380mm above the upper surface of the aggregates in the cup and allowed to fall freely onto the aggregates.
5. The test sample should be subjected to a total of 15 such blows, each being delivered at an interval of not less than one second.
6. Lock thee hammer at the top and remove the cup from the base of the machine.
7. Sieve the crushed sample through the sieve of 2.36 mm. Weigh this fraction and say it is W3

 Calculation 

 Aggregate impact value = W3/(W1-W2) x100

W1=Weight of sample with cylinder
W2=Weight of cylinder
W3= Weight of fraction passing through 2.36 mm sieve.

Impact value vs Strength

Vee Bee Consistometer Test for Workability of concrete

Vee Bee Consistometer Test

 It is based on measuring the time (Called VEE BEE time) needed to change the shape of a concrete mix from a frustum cone to a cylinder (these shapes are standardized by the apparatus of this test), by vibrating and compacting the mix. The more VEE BEE time needed the less workable the mix is. This method is mostly useful for measuring workability of stiff mixes.

 Apparatus

  Cylindrical container with diameter = 240 mm, and height = 200 mm
Mold: the same mold used in the slump test.
Disc : A transparent horizontal disc attached to a rod which slides vertically
Vibrating Table : 380x260 mm, supported by four rubber shock absorbers
Tamping Rod ,Stop watch  for measuringVee Bee Time.

Vee Bee Consistometer

  Procedure

1.  Place the slump cone inside the sheet metal cylindrical pot of the consistometer. Pour the concrete inside the cone and tamp it properly.
2. The glass disc attached to the swivel arm is turned and placed on the top of the concrete in the pot.
3. The electrical vibrator is then switched on and simultaneously a stopwatch started.
4. The vibration is continued till such time as the conical shape of the concrete changes in to the  cylindrical shape.
5. This can be judged by observing the glass disc from the top disappearance of transparency. 
6. Immediately when the concrete fully assume a cylindrical shape, the stopwatch is switched off.
7. The time required for the shape of concrete to change from slump cone shape to cylindrical shape in second is known as Vee Bee time.
8. This method is very suitable for very dry concrete whose slump value cannot be measure by slump test.

  Note

The test fails if Vee Bee Time is less than 5 seconds.For this flow test may be used.

Workability vs Vee Bee time

Flow test for the workability of concrete

 Flow Test for Concrete (IS1159:1959)

The flow table test or flow test is a method to determine the consistence of fresh concrete.This test is giving us the ability of concrete to flow under the gravitational force when poured and compacted  within the cone and suddenly lifted up.

Equipment

Flow table with a grip and a hinge, 70 cm x 70 cm,  Abrams cone, open at the top and at the bottom -  Water,Tamping rod of 16mm diameter, Scale for measurement.

Flow table apparatus

Procedure

1.  The flow table is wetted properly with water.
2. The cone is placed on the flow table at the center and filled with freshly prepared concrete in two layers, each layer is given 25 blows with tamping rod.
3. After waiting for 30 seconds the cone is lifted all at once, allowing the concrete to flow freely.
4.  The flow table is then lifted up up to 12.5 mm and then dropped 15 times within 30 seconds, causing the concrete flow a little bit further. 
5. After this the diameter of the concrete is measured in c.m. in a 6 evenly distributed directions and take the average of these measurements.

Calculations 

 

Flow percentage and Consistency of concrete

Compaction Factor Test for the Workability of Concrete

                  Compaction Factor Test

 Compaction factor test is used to check the workability of concrete in laboratory. The compaction factor may be defined as the ratio of weights of partially compacted concrete to the fully compacted concrete.Its value ranges from 0.8- 0.92. Compaction factor test is used for concretes of lower workability (slump<50mm). It is governed by Is Code 1199:1999.

Apparatus

Compaction factor test Apparatus, scoop, trowel, weighing balance.

Compaction factor test apparatus

 Sampling

 Concrete sample prepared in laboratory as per design mix or prepared in red mix plant.

Procedure

1.   Apply Grease on the inner surface of the apparatus.

2.   Measure the mass as W1 kg by weighing the cylinder accurately and fix the cylinder on the base in such a way that the central points of hoppers and cylinder lie on one vertical line.

3.   Fill the freshly mixed concrete in upper hopper part. Then release the trap door so that the concrete to fall into the lower hopper.

4.   Fall of the concrete into the lower hopper causes standard Compaction immediately.

5.   After the concrete has come to rest, open the trap door of lower hopper and let concrete to fall in to cylinder.

6.   Remove the excess concrete above the top of the cylinder. Clean the cylinder from all sides properly

7.   Weight the partially compacted concrete filled in the cylinder along with it and say it W2 kg.

8.    Refill the cylinder with the same sample of concrete in 3 layers, by tamping each layer 25 times as to expel all the air and  to obtain full compaction of the Concrete.

9.    Struck off level the concrete and weigh cylinder filled with fully compacted concrete. Let the mass be W3 kg.

10.  Calculate the compaction factor as following

Calculation

Compaction factor = (W2-W1)/(W3-W1)

W1=Weight of empty cylinder
W2= Weight of partially compacted concrete with cylinder
W3=Weight of fully compacted concrete with cylinder

Compaction factor and application of concrete