Top 9 Experiments on Concrete Technology

Here is a compilation of experiments on ‘Concrete Technology’ especially written for school and college students.

Experiments on Concrete Technology

Contents:

Experiment on the Bulk Density of Aggregates
Experiment on the Surface Moisture in Aggregate
Experiment on the Moisture Content in Fine Aggregate
Experiment on the Bulking of Fine Aggregate
Experiment on the Particle Size Distribution of Aggregate
Experiment on the Fineness Modulus of Aggregate
Experiment on the Flakiness and Elongation Index of Coarse Aggregate
Experiment on the Workability of Concrete Mix
Experiment on the Workability of Concrete

Experiment # 1. Bulk Density of Aggregates:

ADVERTISEMENTS:

To determine the bulk density and voids of aggregates of the given type of aggregates as per I.S. 2316-Part-IH-1963.

(a) 20 mm graded and angular type aggregate.

(b) 20 mm single size and angular type aggregate.

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(d) Fine aggregate.

Theory

Bulk Density:

It can be defined as the weight of material required to fill a container of unit volume. This unit volume consists of solid material plus the volume of voids and usually is expressed as kg/lit. The value of bulk density of aggregate depends upon the amount of effort made to fill the container as densely as possible, its shape, specific gravity and grading of aggregate etc. More graded the aggregate, greater the bulk density. Angular and flaky shape of the aggregate reduces the bulk density. Thus the bulk density of rodded and loose material will differ.

ADVERTISEMENTS:

The knowledge of bulk density helps in the conversion of the aggregate quantity by weight to quantity by volume, which is helpful in weigh batching and volume batching of the material.

For batching purposes, if materials are measured, the bulk density of the loose material should be calculated. On the other hand if the bulk density test is carried out to detect change in grading and shape of the aggregate, then rodded bulk density test should be carried out to compare the results.

If bulk density test is carried out frequently on the site, the appreciable change in the volume of the bulk density helps in detecting change in the grading or shape or the aggregate and enables to maintain better quality control at site.

Apparatus:

ADVERTISEMENTS:

1. A balance having a sensitively of 0.5% of the weight to be weighed.

2. Cylindrical metal measures of 3, 15 and 30 litres capacity according to maximum size of coarsest particle of the aggregate as follows:

3. Tamping rod 16 mm dia and 60 cm long with one end rounded.

ADVERTISEMENTS:

4. Container, trough, steel rule and measuring cylinder 250 ml capacity.

Procedure:

(a) For Todded weight:

Condition of the Specimen:

1. For determining the bulk density, aggregate with the given percentage of moisture may be used.

2. For determining voids, the material should be dry, while noting observations, condition of material should be mentioned.

3. Select the cylindrical metal measure according to the size of aggregate.

4. Fill the measure up to about 1/3rd full with the thoroughly mixed aggregate.

5. Tamp the aggregate with 25 strokes of the rounded end of the tamping rod.

6. Now fill the measure upto 2/3rd of its height with the remaining aggregate and tamp the aggregate with 25 strokes with the tamping rod as before.

7. Now fill the cylinder measure to over flowing and tamp it 25 times as before.

8. Struck off the surplus aggregate by using the tamping rod as straight edge.

9. Weigh the measure with aggregate. The net weight of the aggregate in the measure will give the bulk density in kg/lit.

(b) Loose Weight:

1. Select the cylindrical metal measure according to size of the aggregate.

2. Fill the measure to its capacity i.e. to it’s over flowing condition by a scoop or shovel.

3. The surface of the aggregate is levelled using the tamping rod as a straight edge.

4. Weigh the measure with aggregate and find out the net weight of aggregate.

5. The bulk density is calculated in kg/lit.

Observation:

Condition of aggregate – Air dry/surface dry/moist

Precautions:

1. Weighing should be done very carefully.

2. While filling measure, the aggregate should be discharged from a height not exceeding 5 cm above the top of the measure to avoid any segregation of the aggregate particles.

Experiment # 2. Surface Moisture in Aggregate:

To determine the surface moisture in a given sample of fine aggregate by displacement method.

Theory:

If all the pores in the aggregate are filled with water, but its surface is dry and contains no free moisture, then it is called as saturated and surface dry aggregate. In this condition the aggregate neither absorbs water nor does it give out water.

Surface moisture is expressed in terms of height of saturated surface dry aggregate as well as in terms of wet aggregate.

Fine aggregate when exposed to rain, collects large amount of moisture on the surface and retains this moisture for a long period, fine aggregate received fresh from river bed also contains considerable amount of moisture. Further if fine aggregate is required to be washed before use it retains moisture.

This moisture always adds to the water to be used in concrete mix and increases water/cement ratio resulting in reduced compressive strength of concrete. Thus it is essential to know the surface moisture content of fine aggregate to fix the correct water/cement ratio. Thus actual water to be added in the mix shall be the water calculated from water/cement ratio minus the free moisture content of the fine aggregate.

Apparatus:

1. A balance having capacity of 2 kg or more and sensitive to 0.5 g.

2. Flask of glass graduated upto 0.5 ml or less. The capacity of flask should be 2 to 3 times the loose volume of the sample.

Procedure:

1. Take the representative sample of the fine aggregate and weigh it. Let the weight be W₁ gram. The weight of sample should not be less than 200 gram. Larger sample gives more accurate results.

2. Fill the container upto the mark with water and again weigh it. Let this weight be W₂ grams.

3. Empty the container and add some water sufficient to cover the sample.

4. Put the sample in the container and remove the entrained air, by giving rapid clock wise and anti-clockwise rotation to the container.

5. Fill the container with water upto the original mark and weigh again. Let this weight be W.

Observations:

Precautions:

1. The weight of the sample should not be less than 200 grams.

2. Weighing should be done accurately.

3. Air entertained if any, should be removed carefully.

Experiment # 3. Moisture Content in Fine Aggregate:

To determine the moisture content in fine aggregate by frying pan method.

Theory:

Surface moisture is expressed in terms of height of saturated surface dry aggregate as well as in terms of wet aggregate.

Apparatus:

1. A balance of 2 kg. capacity.

2. Thermostatically controlled heater.

3. A tray 60 cms x 30 cms in size.

Procedure:

1. Take about one kg of representative sample of fine aggregate and weigh it. Let the weight be W₁ grams.

2. Put the aggregate in the tray and dry the aggregate over a source of heat. While heating, care should be taken not to over dry the aggregate.

3. Weigh the dry aggregate. Let the weight be W₂ grams.

Precautions:

1. Weighing should be done very carefully and accurate.

2. Sample should not be over dried. It should be heated to the free flowing condition i.e. if the sand is put into a pile by means of a conical mould, on removing the mould, sand should slump freely.

3. The brownish tinge acquired by the sand is an indication of overheating of sand.

Experiment # 4. Bulking of Fine Aggregate:

To determine the bulking of fine aggregate.

Theory:

Bulking is defined as the increase in volume of a given volume of sand due to the presence of surface moisture. The increase is caused by the film of surface water covering each particle of sand and pushing them apart due to surface tension. Bulking of sand varies with the fineness of sand. Fine sand bulks about 40%, medium sand to 25% to 29% and coarse sand to about 18%.

With the moisture content of 5 to 6%, the increase in the volume of sand varies from 20 to 40% depending upon the fineness of sand. Beyond this percentage of moisture content, bulking tends to decrease with further addition of water. The volume of fully saturated sand is approximately the same as that of dry sand measured in loose condition.

When the batching of aggregate is done by volume, bulking results in smaller weight of sand occupying the fixed volume of measuring box.

The concrete mix thus becomes deficient in sand which causes following defects in the concrete:

1. Sand deficient mix causes segregation of concrete.

2. Sand deficient mix results in honeycombed concrete. The strength and impermeability of such concrete reduces to a great extent.

3. The yield of such concrete is also reduced.

Thus, while adding fine aggregate to the concrete mix by volume, the bulking of sand should be checked carefully and the required volume of sand should be proportionately increased according to bulking of sand.

Apparatus:

1. A container of suitable size.

2. Steel rule.

3. Steel rod 6 mm in diameter.

4. 250 ml capacity measuring cylinder.

Procedure:

Method I:

1. Take a suitable container, preferably a cylindrical container and fill it about 2/3rd full with the sand in loose state i.e. sand should not be compacted in any way.

2. Smooth and level off the top of the sand with the steel rule and push this steel rule in the centre of the surface to the bottom of the container vertically and note its height. Let this height of sand be h cms.

3. Empty the sand out of the container into another container.

4. Fill the container with water to 1/4th to 1/3rd volume occupied by sand.

5. Put back about half the sand in the container having water and stir with 6 mm steel rod so that its volume reduces to minimum.

6. Add the remaining sand and stir or rod it in the same way as in 5 above.

7. Smooth and level off the surface of the sand and measures its depth by pushing the steel rule at the middle by pushing the rule vertically down to the bottom. Let this height be h₁.

Then bulking of sand % = [(h – h₁)/h₁] x 100

Observations:

Method II:

1. Take the 250 ml capacity measuring cylinder and pour damp sand into it. Consolidate the sand by shaking the cylinder until it reaches 200 ml mark.

2. Take the sand out.

3. Put some water into the measuring cylinder and add the sand taken out in step N. 2 and stir it well.

4. The surface of sand in the cylinder will be at a lower mark than original. Let the surface of sand be at y ml mark.

Then percentage bulking = [(200 – y)/y] x 100

Precautions:

1. The top surfaces of sand should be properly levelled smooth at the time of measuring the height.

2. The height of sand should be measured accurately.

3. No sand should be lost while transferring it from one container to the other container.

Experiment # 5. Particle Size Distribution of Aggregate:

To determine particle size distribution of fine, coarse and al! in aggregate by sieve analysis.

Theory:

Coarse Aggregate:

The aggregate particles retained on 4.75 mm I.S. sieve is called coarse aggregate.

Fine Aggregate:

Aggregate particles passing through 4.75 mm I.S. sieve and retained on 75 micron sieve is called fine aggregate.

All in Aggregate:

The combination of coarse and fine aggregate is known as all in aggregate, single size aggregate. In this type of aggregate, the size of particles belongs to one or two consecutive sieve sizes only.

Graded Aggregate:

Aggregate containing particles of all sizes in suitable proportions are known as graded aggregate. The main advantage of this aggregate is that it has minimum voids and improves workability of concrete mix considerably. Aggregate having one sized particles considerably larger than the other sizes makes the concrete harsh (deficient in fine particles) and does not give good surface finish when worked with trowel.

Thus by sieve analysis, the proportions of different sizes of particles in each aggregate can be determined. The results of sieve analysis of each aggregate are calculated in terms of percentage of total aggregate passing through each size of sieve. To get a visual grasp of the grading, the results of each type of aggregate can be plotted on a graph with percentage passing on y-axis as ordinates and sieve aperture on x-axis as abscissa on logarithmic scale. Though there is no ideal grading, yet limits are placed on grading, upper limit for finer grading and lower limit for coarser grading.

Higher the percentage passing, finer the grading and greater the water requirement for a fixed water/cement ratio, resulting in poor quality concrete, Lower the percentage passing, coarser the grading and greater the tendency to segregate. Thus the most suitable grading is that which gives minimum number of fines, but sufficient to give the necessary cohesiveness to the mix.

Apparatus:

1. A set of I.S. test sieves as given in table 4.17.

2. A balance of 10 kg capacity.

3. Brushes.

Procedure:

1. Take the representative sample and make it air dry either by drying it at room temperature or heating it at a temperature of 100°C to 110°C.

2. Weigh the dried sample.

3. Place the weighed sample on the specified set of sieves with the largest sieve at the top according to the maximum size of the aggregate and sieve it successively on each sieve of the set.

4. Shake each sieve separately over a tray until not more than a trace passes, but in no case less than for 2 minutes.

5. At the end of the sieving, clean the material sticking to 75 micron and 150 micron sieves at their bottoms by light brushing.

6. After the completion of the sieving, weigh the material retained on each sieve together with any material cleaned from the mesh.

7. Find the percentage of each weight retained on different sieves in terms of the total sample.

8. Calculate cumulative percentage retained on each sieve.

9. Calculate cumulative percentage passing on each sieve.

10. Draw a graph for each aggregate and compare the curves.

Precautions:

1. Take the sample in specified quantity according to the maximum size of aggregate.

2. The aggregate sample should be air dried before weighing and sieving as wet sample will clog the sieve.

3. Before sieving, finer sieves should be cleaned gently with brush.

4. Sieves should not be surcharged. For coarse aggregate to be sieved through 40 mm sieve the weight of sample should not be more than 1 kg and for fine aggregate to be sieved through 20 mm sieve the weight of the sample should not be more than 500 grams.

5. Sieving should be done in such a way that each particle gets sufficient chance of passing through the sieve opening.

6. Weighing of material should be done carefully.

(a) Observation ― Sieve Analysis Result for Coarse Aggregate:

(b) Sieve Analysis Resulting for Fine Aggregate:

(c) Sieve Analysis Resulting for all in Aggregate:

Experiment # 6. Fineness Modulus of Aggregate:

To determine the fineness modulus of aggregate.

Theory:

Fineness modulus of aggregate is an index number which gives an idea about the coarseness or fineness of an aggregate. It can be written as F.M.

Fineness modulus of an aggregate is approximately proportional of the average size of particles in the aggregate. In other words, coarser the aggregate, higher the fineness modulus. The maximum value of fineness of coarse aggregate is found to be 8.0 and for coarse sand 3.5. The fineness modulus for fine aggregate varies from 2.0 to 3.5, for coarse aggregate from 5.5 to 8.0 and for all in aggregate 3.5 to 6.5.

Fineness modulus is determined by adding the cumulative percentage of material retained on each sieve and dividing the sum of cumulative percentage of material retained on each sieve by 100.

Apparatus:

1. Set of sieves

2. A balance having a capacity of 10 kg.

3. A tray.

Procedure:

Take a suitable sample of aggregate and put it on the specified sieve as follows:

For coarse aggregate 80 mm, 40 mm, 20 mm, 10 mm, 4.75 mm, 2.36 mm, 1.18 mm, 600 micron, 300 micron, 150 micron.

The aggregate is sieved as for sieve analysis, and the weight retained on each sieve is found. From the value of weights retained, cumulative percentage of weight retained on each sieve is calculated. After the lowest sieve, the percentage retained should be taken as explained by the following example.

Very fine or very coarse sand is objectionable for concrete mix because the very fine sand makes the mix uneconomic as finer the sand, greater the amount of water needed for a definite workability producing low strength concrete. On the other hand coarse sand produces harsh and unworkable mix. Thus the fineness modulus of sand should not be less than 2.5 and more than 3.5 for producing good quality concrete.

Observations:

Fineness modulus for coarse aggregate = 746/100 = 7.46

Fineness modulus for fine aggregate = 291/100 = 2.91

Experiment # 7. Flakiness and Elongation Index of Coarse Aggregate:

To determine the flakiness index and elongation index of coarse aggregate.

Theory Flaky Particles:

A particle of aggregate is said to be flaky if its least dimension is less than 0.6 times of its mean dimension. Flakiness index is the weight of flaky particles measured as percentage of the total weight of the sample. Flakeness index more than 35 to 40% is undesirable.

Elongated Particle:

A particle is said to be elongated if its length is greater than 1.8 times its means dimension. Elongated index is the weight of elongated particles measured as percentage of the total weight of the sample. For this no limit has been laid.

The flaky or elongated particles are not desirable as their large number creates more voids, requiring more fine materials and also more water for the same workability. These particles tend to be oriented in one plane, causing laminations, and affect the durability of concrete adversely. Their combined value should not be more than 40 to 45% of the weight of aggregate.

Procedure (For Flakiness Index):

1. Take sufficient quantity of aggregate to provide at least 200 pieces of any fraction to be tested.

2. Sieve the sample through sieves as shown in observations table.

3. Separate particles retained on the prescribed sieves.

4. Try to pass each aggregate particle through the corresponding slot of thickness gauge Fig. 4. The aggregate piece passing through 50 mm and retained on 40 mm sieve, should only be passed through {(50+40)/2} x 0.6 = 27.0 mm slot. If the aggregate passes through this 27.0 mm slot; then the aggregate piece is flaky.

5. Weigh all the pieces which pass through this slot.

6. Calculate the flakiness index = Wt. of material passing through the thickness gauge/Total weight of sample

For Elongation Index:

1. Sieve the sample through I.S., sieve as specified in observation table.

2. Separate aggregate pieces retained on sieves.

3. Try to pass each aggregate piece through the corresponding slot of length gauge (Fig. 5). If the length of the particle {(50+40)/2} x 1.8 = 81 mm, it is said to have retained on the length gauge.

4. Weigh all such pieces

5. Calculate the elongation index as follows ―

= (weight of material retained on the length gauge/total weight of the sample gauge) x 100

Observations:

Note:

Suppose the aggregate particle passes through 50 mm sieved and retained on 40 mm sieve, then ―

thickness gauge = [(50 + 40)/2] x 0.6 = 27.0 mm

length gauge = [(50 + 40)/2] x 1.8 = 81 mm

Experiment # 8. Workability of Concrete Mix:

To determine the workability of concrete mix.

Theory:

The ease in transportation, placement, compaction, finishing, and resistance to segregation of concrete mix is known as workability. In more scientific terms it can be defined as the property of concrete which determines the amount of useful internal work necessary to produce full compaction. Though the definition is quite easy, but its correct determination is quite difficult. However some tests have been devised to measure workability. Two of them are described below.

Slump Test:

Slump is the measure of subsidence of the concrete pile formed in a mould of the shape of frustum of cone.

The decrease in height of the slumped concrete is called slump, slump can be divided into three categories as follows:

1. True Slump:

If the concrete slumps evenly all-round as shown in Fig. 6 (a) then it is called true slump. Actually this slump is aimed to be determined.

2. Shear Slump:

If instead of slumping evenly all-round, one half of the core slides down as inclined plane, then it is called shear slump. It is difficult to measure. Usually it occurs in harsh mixes. Fig. 6(b).

3. Collapse Slump:

In this case, concrete slides as soon as cone is removed and it is difficult to measure. It occurs in very wet mixes. Concrete giving shear or collapse slump is considered unsatisfactory for placing. Fig. 6 (c) above.

This test being very easy to perform, hence it is very suitable for field work. A particular amount of slump is required for different types of concrete work. Once the slump is decided for a particular work, it is easy to obtain concrete of that workability.

This test is very useful to check the day to day or hour to hour variation in the ingredients of the concrete mix used for a particular job on the site. Increase in slump indicates that either the moisture content in aggregate has changed unexpectedly or grading of aggregate has changed. Low value of slump indicates that mix is unworkable.

Cohesive Mix:

A good cohesive mix subsides without the coarse aggregate tending to fall out of the mix.

Harsh Mix:

A mix deficient in fine aggregate or sand is said to be a harsh mix. It gives honey combed surface and its yield is also less! A harsh mix does not give smooth finish to the surface even with trowelling under pressure, while adequately sanded mix gives smooth finish with normal trowelling.

Over Sanded Mix:

It gives smooth finish with even light trowelling.

Apparatus:

1. A mould in the form of frustum of cone (Fig. 7.2).

2. Tamping rod, 60 cms long and 1.6 in diameters, rounded at one end.

3. Trowel.

4. Trough.

5. G.I. plain sheets.

7. Steel rule.

Procedure:

1. Clean the internal surface of the mould thoroughly by removing set concrete, dust or moisture etc. and apply a light film of oil or grease.

2. Place the mould on a smooth horizontal, rigid and nonabsorbent surface, or on a carefully levelled metal plate or masonry platform.

3. Hold the mould in position firmly.

4. Fill the concrete in the mould upto 1/4th of its height and tamp it with the tamping rod by giving 25 strokes uniformly spread over the full surface of the concrete, while tamping, care should be taken that pointed end is thrashed into the concrete.

5. After compacting first layer, fill concrete by quarter height and again tamp. Similarly other layers are tamped.

6. After tamping the top layer, struck off extra concrete by a trowel or tamping rod and level it with the top of the mould. That is the mould is exactly filled.

7. Raise the mould up vertically carefully. On raising the mould the concrete will subside.

8. Measure the height of the subsided concrete heap by steel rule immediately after removing the mould.

9. The difference between the original height and subsided heap of concrete will give the value of slump. The procedure is repeated for three times and their mean value is taken.

10. Compare the value of slump so obtained with the standard value. If they compare well, then workability of the mix is satisfactory for that particular job otherwise change water content; and repeat the procedure, till desired slump is obtained.

Higher value of slump is desirable when the compaction of the concrete is to be done manually or sections arc small or heavily reinforced or size of the aggregate is greater. Standard values of slumps for different type of works are shown in Table 7.2

Observations:

I. Trial

II. Trial

III. Trial

Note:

From above table the effect of water/cement ratio on slump can also be verified when F.A.C.A., cement and aggregate ratios are kept constant.

Experiment # 9. Workability of Concrete:

To determine the workability of concrete by compacting factor method.

Theory:

In drier mixes, slump test does not give slump and to detect the change in workability a more sensitive method is necessary. The compacting factor test works on the principle of determining the degree of compaction achieved by a standard amount of work by allowing the concrete to fall through a standard height. The compacting factor gives an idea of the degree of compaction.

Thus compacting factor can be defined as the ratio of the density actually achieved in the test to the density of fully compacted concrete. Therefore compacting factor method of determining of workability of concrete is more rational method than slump test method. Compacting factor method is more suitable for dry mixes with low slump. It is more useful in laboratory testing, but if possible it could be used at site also.

Apparatus:

1. Compacting factor apparatus as I.S. 1199-1959 (reference Fig. 7.6).

2. Two trowels.

3. Hand scoop.

4. Tamping rod.

5. Platform weighting machine.

Procedure:

1. Clean the inner surface of the apparatus including cylinder and apply light film of oil or grease.

2. Cover the lower hopper and cylinder with an iron sheet to avoid falling of concrete into them while filling the upper hopper with concrete.

3. Close the trap doors of upper and lower hoppers carefully.

4. Now place the sample of concrete gently in the upper hopper with a hand scoop and fill the upper hopper upto its brim.

5. Remove the covering sheet from the lower hopper and open the trap door of the upper hopper, so that concrete falls into the lower hopper.

6. Remove the covering sheet from cylinder and open the trap door of the lower hopper, so that the concrete falls into the cylinder.

7. If the concrete sticks to the sides of the hopper, it may be pushed gently with the help of rod from the top.

8. Remove the excess concrete remaining above the level of the top of cylinder with the help of two trowels.

9. Clean the outside of the cylinder.

10. Weigh the cylinder along with concrete and find out the weight of concrete.

11. Compact the concrete in the cylinder by vibration and fill it fully with the compacted concrete or empty the cylinder and fill it in layers approximately 5 cms in thickness and vibrate fully to obtain full compaction.

12. Clean the outside of the cylinder and weigh it. Find out the weight of compacted concrete, weight of empty cylinder being known.

13. Then compacting factor = weight of un-compacted concrete of cylinder/weight of fully compacted concrete in the cylinder

Observation: