Laboratory Manual Concrete and aggregate Content Section 1 Trial Mix

Section 2 Slump

Section 3 Density of Compacted Fresh Concrete

Section 4 Making of Test Cubes, Beams and Cylinders

Section 5 Percentage of fine aggregate passing 600 μm

Section 6 Relative Density and Water Absorption of Coarse Aggregate

Section 7 Water Absorption of Fine Aggregate

Section 8 Compressive Strength of Concrete Cubes

Section 9 Test of Reinforced Concrete Beam

Section 1 Trial Mix Procedure:

1. Design a mix proportion for a concrete of specific characteristic strength.

2. Calculate the total volume of concrete of specimens to be prepared. Add

twenty percent for wastage.

3. Calculate the weight of each constituent

4. Determine/Estimate the moisture content of the aggregate used.

5. Make correction for absorption and moisture content to the weight of

aggregate used.

6. Weight correct amount of aggregates and cement. Mix them in dry

thoroughly.

7. Weight correct amount of water. Withhold about 10% of water and add the

rest into mix and then mix them thoroughly.

8. Add water into the mix slowly while continue mixing until the desired

workability is observed.

9. Determine the slump of the mix. If the workability is within the desired

range, proceed to next step. Otherwise, repeat from step 8.

10. Record the total amount of water added into the mix.

11. Determine the density of fresh concrete of the mix.

12. Make two test cubes.

13. Add about 20 ml superplasticizer into the mix.

14. Determine the slump after thoroughly mixing.

15. Make two test cubes.

Section 2 Slump Test I Apparatus

1. Slump cone and base plate

2. Tamping rod

3. Measuring rule

II Procedure

1. Hold the cone firmly on the base plate, then fill the cone by 3 equal layers

of fresh concrete.

2. Tamp each layer by 25 times with a tamping rod. Be sure to penetrate to

the previous layer when tamping.

3. Clean away concrete spillage with a sawing and rolling motion of the

tamping rod.

4. Lift the cone slowly and steadily in five to ten seconds.

5. If the slumped concrete shear or collapse, the test must be restarted from

the first step. If true slump is achieved, continue to the next step.

6. Invert the cone and stand it beside the slumped concrete.

7. Lay the tamping rod across the cone and above the slumped concrete.

8. Record the height different between the underside of the rod and the top of

the slumped concrete to the nearest 5 mm.

III Form of slump

Slump Apparatus (Source: ELE)

(Source: CS1)

Section 3. Density of Fresh Concrete I Apparatus

Cylindrical container with a Perspex cover

II Procedure 1. Weight the cylinder with the Perspex cover (m1).

2. Fill the cylinder with water and slide the Perspex cover on top of the rim.

Make sure that no air bubble is trapped inside.

3. Wipe the outside of the cylinder with a dry cloth to remove surface water.

4. Weight the cylinder with its content and the Perspex cover (m2).

5. Empty the cylinder and clean it thoroughly.

6. Fill the cylinder with concrete in six approximately equal layers. Each

layer shall be compacted with a compacting bar of not less than 30 strokes.

7. Level the top of the cylinder with a steel float.

8. Clean the outside of the cylinder with a damp cloth.

9. Weight the cylinder with its content and Perspex cover (m3).

III Calculation

Density of the fresh concrete

= 12

13

m - m

m - m x w (report in kg/m3)

Where w = 1000 kg/m3

Section 4 Making of test cubes, beams and cylinders

I Apparatus

1. Cube moulds, cylinder moulds and beam moulds

2. Compacting bar

3. Scoop

II Procedure

1. Clean the mould and properly tighten the bolts.

2. Evenly apply a thin film of mould oil on the inside surface of the mould.

3. Fill the mould with fresh concrete to a thickness of about 50 mm.

4. Use a compacting bar to compact the concrete. Refer to the table below for

the minimum of strokes.

5. Repeat step 3 and step 4 until the mould is full.

6. Level the top with a trowel.

7. Cover the mould with a plastic sheet or Perspex cover.

Type of specimen Minimum number of strokes per each layer 100 mm cube 25 150 mm cube 35 100 mm cylinder 20 150 mm cylinder 30 100 mm beam 100 150 mm beam 150

Concrete Moulds and Test Specimens (Source: ELE)

Section 5 Percentage of fine aggregate passing 600μm Apparatus:

Test sieves of aperture size 2.36 mm and 600μm

Procedure:

1. The sample shall be thoroughly dried in an oven and cooled to room

temperature.

2. Weigh about 200 g specimen to 0.1 g (m1).

3. Sieve the specimen with the 600 μm sieve protected with the 2.36 mm sieve.

4. Weigh the materials passing a 600 μm sieve (m2).

Calculation:

Percentage passing 600μm = 1

2

m

m x 100%

Remark:

The test procedure is modified from BS 812 : Part 103 Dry Sieving Method

Section 6 Relative Densities and Water Absorption of Coarse Aggregate Apparatus:

Pyconometer

Procedure:

1. The sample for test shall be thoroughly washed on 5 mm test sieve to

remove finer particles. Immerse the prepared test sample in water for 24 h.

(The above procedure has been done by laboratory staff.)

2. Fill the pyconometer with the aggregate to about one-half of the

pyconometer. (Careful, don't break the glass pyconometer !)

3. Add water to cover the aggregate, stir gently to remove bubbles of entrapped

air.

4. Screw the cone into place. Top up the pyconometer with water so that no air

is trapped.

5. Dry the outside of the pyconometer and weigh it (B).

6. Gently empty the aggregate from the pyconomter and drain the water away.

7. Refill the pyconomter with water, screw the cone into place, top up with

water, dry the outside and weigh (C).

8. The drained aggregate shall be placed on a dry cloth and gently surface

dried.

9. Spread the aggregate on the second cloth until all visible water has gone, but

the aggregate still has a damp appearance. Weigh the aggregate (A).

10. Place the aggregate in a container and dry it in the oven for 24 hours.

11. Cool the aggregate in the airtight container, then, again weigh the aggregate

(D).

12. Repeat the test on a separate sample to obtain one more result.

Calculation:

Calculate the densities and water absorption of the sample from the following

equations :

Relative density on an oven dried basis

D

A B C( )

Relative density on a saturated and surface dried basis

A

A B C( )

Apparent relative density

D

D B C( )

Water absorption (percent of dry mass) 100( )A D

D

where A = mass of saturated surface dried sample in air (g). B = mass of pyconometer containing sample and filled with water (g). C = mass of pyconometer filled with water only (g). D = mass of oven dry sample in air (g). Remark: This method is modified from BS 812 : Part 2

Section 7 Water Absorption of Fine Aggregate Apparatus:

Means of supplying a current of warm air, e.g. hair dryer

Procedure:

1. The sample for test shall be thoroughly washed on 75μm test sieve to

remove finer particles. Immerse the prepared test sample in water for 24 h.

(It has been done by laboratory staff.)

2. Record the weight of a tray (m1).

3. Carefully drain the water from the sample by decantation and transfer the

sample to the tray.

4. Expose the aggregate to a gentle current of warm air to evaporate surface

moisture.

5. Stir the sample frequently to ensure uniform drying.

6. When the sample attains a ‘free-running’ condition (see figure below),

weigh the tray with its content (m2).

7. Dry the sample in an oven for 24 hours and allowed to cool in an air tight

container.

8. Weight the sample with the tray (m3).

9. Repeat the test on a separate sample to obtain one more result.

Calculation:

Water absorption = 13

32

m - m

m - m x 100%

Source: BS812: Part2

Section 8 Compressive strength of Concrete

I Apparatus

1. Compression machine

2. Cube checking jig.

3. Caliper

4. Balance of capacity 20 kg and readable to 0.1 g.

5. Feller gauges

II Procedure 1. Identify and remove the cube specimen from curing tank.

2. Wipe off excess water from specimen surfaces with a piece of cloth.

3. Record the date of the specimen cast.

4. Record the cube if it is having an edge broken for 20mm or more in any

direction.

5. Place the cube in cube checking jig with the trowelled surface upwards.

6. Check the contract between the cube and the jib with the feeler gauges.

7. Turn the cube through 90° and repeat the check.

8. Measure the length (l1), width (l2) and height (l) between the three pairs of

opposing faces of the cube with a caliper.

9. Weigh the cube.

10. Place the cube on the centre of the lower platen with the trowelled surface

of the cube vertical.

11. Apply the test load steadily so that the stress is increased at a rate within

the range of 0.2 N/mm2 per second to 0.4 N/mm2 per second until no

greater load can be sustained.

12. Record the maximum load applied (F) to the cube specimen.

13. Remove the cube specimen from the test machine. Examine and record

the mode of failure of the specimen.

(Source: CS1)

III Calculation

Compressive strength = 31 l x l

F

(Report in N/mm2)

IV Failure patterns of cubes

l2

l1

l3