Here is a compilation of experiments on ‘Concrete Technology’ especially written for school and college students.
Experiments on Concrete Technology
Contents:
- Experiment on the Purity of Cement
- Experiment on the Quality of Cement
- Experiment on the Fineness of Cement
- Experiment on the Percentage of Water in Cement
- Experiment on the Setting Time of Cement
- Experiment on the Soundness of Cement
- Experiment on the Compressive Strength of Cement
- Experiment on Fine Silt in Aggregate
- Experiment on the Specific Gravity and Water Absorption of Aggregates
- Experiment on the Specific Gravity of Aggregate
Experiment # 1. Purity of Cement:
To verify the purity of cement in the field.
ADVERTISEMENTS:
Theory:
Though cement is manufactured in factories under controlled conditions, but there are possibilities of its adulteration during transportation and storage. The adulteration in cement may be detected by the following test.
Apparatus- Following apparatus is required:
(a) One stove
ADVERTISEMENTS:
(b) One steel plate
(c) Test tube or glass tumbler
Procedure:
Visual Inspection:
ADVERTISEMENTS:
1. The bright grey colour indicates the freshness and purity of cement.
2. Rub the cement between the fore finger and thumb, the gritty touch will indicate the adulteration with sand while greasy touch will indicate pure cement.
3. Take a sample of about 100 grams of cement and put it on a steel plate and heat it on a stove thoroughly for about 20 minutes. The change of colour of the sample is an indication of adulteration. In case of pure or genuine cement there should be no change in the colour.
4. In case, cement is suspected to be adulterated with flyash (coal ash), then take a small quantity of cement and put it in a glass tumbler and add water till the tumbler is half full with water.
ADVERTISEMENTS:
(b) Shake the tumbler or container thoroughly and allow it to settle for a few minutes,
(c) Cement particles being heavier will settle down and ash particles either will float on the surface or held in suspension. The amount of these particles will give an idea about the extent of adulteration.
Experiment # 2. Quality of Cement:
To verify the quality of cement in the field by verifying the following:
(a) Setting and hardening action.
ADVERTISEMENTS:
(b) Soundness of cement
Theory:
Though cement is manufactured in factories under controlled conditions, but there are possibilities of its adulteration during transportation and storage. The adulteration in cement may be detected by the following test.
Apparatus:
1. Stove,
2. Enameled trays, and
3. Measuring steel rule.
A. Setting and Hardening Action:
Procedure:
1. Take a suitable sample of the cement to be tested and put it into the enameled tray and add 28% water of the weight of cement and mix well. Out of this paste prepare three small pats each 75 mm x 75 mm x 25 mm in size.
2. Prepare similar number of pats with good quality cement.
3. Cover all the pats with wet cloth for 24 hours.
4. After 24 hours, try to make thumb nail impression on the pats taken from both sets of pats. Good quality cement pats will not show the nail impression that is it will resist this impression.
5. If the cement does not resist the impression, then continue the curing of the pats upto 48 hours. After 48 hours of curing, try to break the pat with the pressure of the thumb. Bad quality cement pat will break easily under the pressure of the thumb and this cement should be tested in the laboratory.
6. If after 48 hours, pats show improvement in hardening, but do not attain hardness comparable with good quality cement, a third trial should be made after 72 hours of curing.
7. If the only defect in the cement under test is its slow setting quality, then it will become as strong as good quality cement after this period and no further testing is required.
B. Ascertaining Soundness of Cement:
Make a part of cement 15 mm thick and 75 mm in diameter, cure this pat for 24 hours with moist cloth and then boil it in water for 6 hours and observe the surface of this pat. Section of pat is shown in Fig. 1.
If the surface does not develop cracks after boiling, then the cement is sound, Fig. 1 (I).
If the surface develops a crack patterns as shown in Fig. 1 (III) then the cement is unsound.
Contraction cracks as shown in Fig. 1 (II) are few and well defined and start from edge to edge. These cracks do not indicate anything wrong with the cement, hence they should be clearly distinguished from unsound cement cracks.
Experiment # 3. Fineness of Cement:
To determine the fineness of cement by sieving.
Theory:
A certain fineness of cement particles is essential, as the reaction of water with cement always starts at the surface of the particles. Larger the surface area available for reaction, greater is the hydration of cement. Thus rapid development of strength requires greater degree of fineness. However, too much fineness also is undesirable due to the high cost of grinding, quick deterioration when exposed to air and more shrinkage of fine cement etc.
Apparatus:
Usually following apparatus is required:
1. Weighing balance of 200 gram capacity.
2. I.S. test sieve No. 9 (90 microns).
3. Trowel
4. Tray 30 cms x 30 cms
5. One brush with about 25 cms long handle.
Procedure:
1. Weigh 100 grams cement accurately and put it on a standard I.S. sieve No. 9 (90 microns sieve).
2. Break lumps of cement if any in the sample with thumb and fingers. In no case it should be rubbed on the sieve.
3. Holding the sieve in both hands, sieve it continuously for 15 minutes giving a gentle wrist motion or on a mechanical sieve shaker. However care should be taken that no cement spills.
4. After sieving for 15 minutes, weigh the residue left on the sieve. This residue should not be more than 10% of the weight of sample for ordinary port-land cement and 5% for rapid hardening cement.
Precautions:
1. Sieving must be done continuously.
2. Weighing should be done carefully. Weighing machine should be checked before use.
3. After sieving, cement from the bottom surface of the sieve should be removed gently.
4. At the end, sieve should be cleaned carefully with the help of the brush.
Experiment # 4. Percentage of Water in Cement:
To determine the percentage of water for normal consistency for a given sample of cement.
Theory:
The normal consistency of a cement paste can be defined as the percentage of water by weight of cement, which produces a consistency which permits a plunger of 10 mm diameter to penetrate to a depth 5 mm to 7 mm above the bottom of the vicat’s mould.
Apparatus:
Following apparatus is needed for this experiment:
1. Vicat’s apparatus with plunger of 10 mm diameter.
2. Weighing balance of 1 kg capacity with weights
3. Trowel
4. Enamel trough
5. Standard spatula
6. Stop watch
7. Thermometer 50°C range
8. Non porous plate.
Procedure:
1. Weight 400 grams cement accurately and put it in a enameled trough.
2. To start with, add about 25% clean water by weight of cement and mix it carefully by a spatula. The time of gauging should not be less than 3 minute and not more than 5 minute. The gauging time shall be counted from the time of adding water to the dry cement till commencing to fill in the mould.
3. Resting the vicat mould on non-porous plate, fill it with the cement paste.
4. Make the surface of the cement paste level with the top of the mould with a trowel weighing about 250 grams. To expel the entrapped air, mould should be gently shaken or given jerk.
5. Place this mould together with the non-porous plate under the rod, bearing the plunger. Adjust the indicator at zero mark, when the plunger touches the surface of the test block, (cement paste in the mould).
6. Release the plunger quickly and allow it to penetrate into the paste and note its depth of penetration.
7. Prepare other trial pastes with varying percentages of water and test as discussed above until the needle penetrates 5 mm to 7 mm above the bottom of the mould.
8. Express this amount of water as a percentage by weight of the dry cement.
Observations:
Calculation:
P = (W/W1) x 100
Precautions:
1. For gauging of cement clean appliances should be used.
2. Temperature of cement, water and room at the time of test should be 27 ± 2°C.
3. While filling mould no pressure should be exerted.
Experiment # 5. Setting Time of Cement:
To determine the initial and final setting time of cement.
Theory:
When water is mixed with cement to form a paste, a reaction starts. This reaction is known as hydration. Due to this reaction the mixture of cement and waiter starts changing from a fluid state to a solid state and is called setting. It should not be confused with hardening which is the second stage of hydration. In the first few minutes, the setting action is more predominant and after some time hardening action becomes rapid.
Initial Setting Time:
It is defined as the period elapsing between the time water added to the cement and the time when the 1 mm square section needle fails to penetrate into the test block to a depth of about 5 mm from the bottom of the mould.
Final Setting Time:
This can be defined as the period elapsing between the time water added to the cement and when 1 mm square section needle makes an impression on the test block, but 5 mm attachment fails to make any impression on the test block.
Apparatus:
1. Vacat’s apparatus with mould and non-porous plates, needle etc.
2. Weighing balance of 1 kg. capacity with weight box.
3. Trowel.
4. Enamel trough.
5. Standard spatula.
6. Stop watch.
7. Thermometer °C (0-100°C)
8. Measuring cylinder—500cc. capacity.
Procedure:
1. Weigh about 400 grams of neat cement accurately and put it into the enamel trough.
2. Add 0.85 times water required for standard consistency and prepare the cement paste.
3. Start stop watch as soon as water is added to the cement.
4. Resting the vicat’s mould on the non-porous plate, fill it with the neat cement paste prepared. The gauging time should not be less than 3 minutes and not more than 5 minutes.
5. After filling the mould completely, smooth off the surface of the paste and make it level with the top of the mould.
6. Now put the whole assembly (mould with cement paste and plate etc.) on the base plate of the apparatus.
7. Place the needle in the rod and lower it gently till it comes in contact with the surface of the test block and release it quickly, allowing it to penetrate into the block and note the penetration after every two minutes and rotate the mould, so that needle may not penetrate at one place only.
8. Repeat the procedure till the needle fails to penetrate into the test block to about 5 to 7 mm from the bottom of the mould. Stop the stop watch. The reading of the stop watch in seconds is the initial setting time.
Observation:
(f) Time when needle fails to penetrate about 5 mm to 7 mm. from the bottom of the mould (T2)
(g) Time at which water is first added T1
(h) Initial Setting Time (T2 – T1)
Final Setting Time:
Procedure:
Steps from 1 to 8 are same as above:
1. Now replace the 1 mm square needle (c) of the vicat’s apparatus by the needle with an annular attachment (F).
2. Repeat step 7 a number of times till the needle makes an impression on the cement paste block, while the attachment (F) fails to do go.
3. The time between the moment water is added to the cement and the moment needle only makes the impression is called the final setting time for the cement under test.
Observation:
(a) Time when the needle makes an impression, but the attachment fails to do so, T3
(b) Final setting time, (T3 – T1)
Precautions:
1. Needle must be cleaned each time before use.
2. After recording the penetration of the needle, the mould should be shifted (change its position) so that penetration of needle may not take place at the same place.
3. The accuracy of the stop watch should be checked.
4. For gauging cement clean appliances should be used.
5. The test block should be kept in 90% relative humidity at 27 ± 2°C and away from draught.
Experiment # 6. Soundness of Cement:
To verify the soundness of a given sample of cement.
Theory:
The presence of free lime (CaO) and magnesia (MgO) react with water very slowly and increase in volume considerably. If these two substances are present in cement, they may cause large changes in the volume of concrete after it has hardened and may cause its disintegration. Thus the cement is called unsound if the percentage of free lime and magnesia exceeds 3% and 6% respectively as laid down by I.S.I. The unsoundness can be detected by Le Chatelier apparatus.
Apparatus Required:
1. Le Chatelier apparatus.
2. Two number of glass sheets.
3. Trowel.
4. Measuring cylinder.
5. Stove or water bath with electric heating arrangements.
6. Enamel tray.
7. Thermometer.
8. Stop watch.
9. Weighing balance and weight-box.
Procedure:
1. Weigh 100 grams of cement carefully and add 0.78 times the water needed for preparing a paste of standard consistency and make a good paste.
2. Place the mould on a glass plate and fill it with the cement paste formed as in (1) above.
3. Cover the mould with another glass plate.
4. Place a small weight on the cover plate and immediately immerse the whole assembly in water at a temperature of 27°C to 32°C and keep it there for 24 hours.
5. At the end of 24 hours, measure the distance between the indicator points. This distance should be measured to an accuracy of a mm.
6. Submerge the whole assembly again in water at 27°C to 32°C and heat it at such a rate that water may start boiling within 25 minutes to 30 minutes and keep it in boiling water for three hours.
7. After three hours remove the assembly from the water, and allow it to cool and measure the distance between the indicator points.
8. The difference between the two readings of distances between the indicator points is a measure of expansion of cement.
Observations:
1. Weight of cement (C) = gram
2. Water required for normal consistency (P) = gram
3. Water added to cement sample (P x C) = gram
4. Time at which sample is put in water at 27°C to 32°C = T1
5. Time when water brought to boiling point = T2
6. Distance between the pointer ends at 27°C to 32°C before heating = d1
7. Time of heating = (T2 – T1) = T
8. Distance between the pointer ends after heating = d2 mm
Difference = (d2 – d1)
Precautions:
1. All measurements should be done very accurately.
2. While filling the mould, the edges of split mould should be kept together gently. A fine thread may be tied around the mould.
3. Water should be brought to boiling gradually during the specified time.
4. The indicator arms of the apparatus should not be pressed.
Experiment # 7. Compressive Strength of Cement:
To determine the compressive strength of cement.
Theory:
The compressive strength test is the final check on the quality of cement. The compressive strength of cement is measured by determining the strength of 7.06 cm length cubes made of cement and standard-sand mortar of 1:3 proportions by weight.
Apparatus:
1. Cube moulds of 7.06 cm length.
2. Cube vibration machine.
3. Trowel.
4. Enamel trough.
5. Measuring cylinder of 100 c.c.
6. Balance
7. Thermometer.
8. Non-porous plate.
Procedure:
For each cube weigh and mix materials separately.
For each cube material required is as follows:
(a) Cement 185 gram
(b) Standard sand 535 gram
(c) Water, Pn/4 + 3.0% of combined weight of cement and sand.
2. Weigh the cement and standard sand accurately and place them on a non-porous plate.
3. Mix the cement and sand dry with the trowel for one minute and then add water and mix till the colour of the mixture is uniform.
4. Gauging time should not be less than 3 minutes and not more than 4 minutes.
5. Clean the interior surface of the mould and oil or grease lightly.
6. Place the prepared mould on the vibrating machine and firmly hold it in position by means of suitable clamps.
7. Attach a suitable hopper at the top of the mould to facilitate filling the mould. The hopper should not be removed till the vibration is over.
8. After mixing, put the full mass of the mix as prepared above in (3) in the hopper and compact the same fully by vibration for a period of about 2 minute at a frequency of 1200 ± 400 vibration per minutes.
9. Keep the cube at 27°C ± 2°C and at 90% relative humidity for 24 hours after vibration.
10. At the end of the 24 hours, remove the mould and put the specimen immediately in clean and fresh water at 27°C ± 2°C for curing and keep them there till required for testing. The specimen should not be allowed to dry up before testing.
Testing:
1. The cubes as prepared above are tested at the following ages:
(a) At 3 days and 7 days for ordinary port-land cement.
(b) At 1 day and 3 days for rapid hardening port-land cement.
2. Place the specimen in the testing machine centrally on the faces other than cast faces.
3. Apply the load uniformly at a rate of 140 kg/cm2 per minute.
Observations:
Precautions:
1. All appliances used should be clean.
2. The mixing time should not be more than 4 minutes.
3. The mould should be cleaned before use and oiled.
4. The load on the specimen should be applied uniformly and gradually.
5. The specimen should be immediately tested after taking out from the curing water. The excess water should be wiped out by jute or cloth.
Experiment # 8. Fine Silt in Aggregate:
To determine the fine silt in the aggregate.
Theory:
The fine material such as clay and silt are harmful for concrete. These fine materials may form coatings on the surface of coarse aggregate and prevent good bond between aggregate and cement paste. If present in loose form, they require more water to wet their surface as their surface areas is more per unit weight. The increase in water results in increased water- cement ratio, which reduces the strength of concrete.
The size of silt particles varies between 0.002 mm and 0.06 mm while those of clay below 0.002 mm.
Thus tests should be performed to determine the quantity of silt and clay before using the fine aggregate.
The field test to determine the quantity of silt and clay is accurate, if the percentage of silt and clay is limited to 6% by volume. In case this percentage is more than 6%, then more accurate test as per I.S. 2386 part II 1963 should be carried.
Apparatus:
Measuring cylinder of 250 ml (c.c.) capacity.
Procedure:
1. Fill the measuring jar with 1% solution of common salt upto about 50 ml marks.
2. Add sand to be tested in jar, till the level of common salt solution reaches 100 ml mark.
3. Add more solution of above concentration in the jar till the level reaches 150 mi mark.
4. Now cover the jar tightly with palm and shake the mixture of sand and common salt solution by turning upside down repeatedly.
5. Allow the mixture to stand in the jar for 3 hours and note the level of silt and sand. Silt being lighter than sand will form upper layer.
6. Measure the thickness of silt layer and calculate its percentage.
7. Repeat the above procedure and take three readings and obtain their mean value.
Observation:
Precautions:
1. The sample of fine aggregate should be taken carefully.
2. The 1% solution of common salt should be prepared by dissolving 10 gram of common salt in 1 lit. of water.
3. The mixture of sand and 1% solution should be shaken vigorously.
Experiment # 9. Specific Gravity and Water Absorption of Aggregates:
To determine the specific gravity and water absorption of aggregates.
Theory:
As per I.S. 2386-Part-lII-1963, specific gravity of aggregates can be divided into two categories as follows:
1. Specific gravity
2. Apparent specific gravity
1. Specific Gravity:
It can be defined as the ratio of the weight of aggregate dried and maintained at a temperature of 100°C to 110°C for 24 ± ½ hour to the weight of equal volume of water displaced by saturated surface dry aggregate. The volume of water displaced is equal to the volume of solid matter of the aggregate and volume of all pores both permeable and impermeable. Specific gravity calculated on this basis usually is used in the calculation of absolute volumes of concrete and its yield. Majority of aggregates have specific gravity value between 2.6 to 2.9. Values lower than 2.6 necessarily do not mean that the aggregate is of poor quality. Normally lower limit has been laid down for specific gravity.
2. Apparent Specific Gravity:
It can be defined as the ratio of the weight of aggregate dried and maintained at a temperature of 100°C to 110°C for 24 ± ½ hours to the weight of equal volume of water displaced by the dry aggregate. In this case, the volume of water displaced is equal to the water displaced by solid matter and only impermeable pores.
Water Absorption:
It can be defined as the difference in weight between the saturated surface dry aggregate and dry aggregate. It is expressed as the percentage of dry weight of aggregate. Its knowledge is very important. If the aggregate absorbs water which neither wets the surface of aggregate nor it takes part in chemical reaction, the workability of the concrete will be reduced, resulting in lower strength.
Apparatus:
1. Balance or scale of capacity not less than 3 kg and having sensitivity of 0.5 gram.
2. Oven. A well ventilated oven fitted with devices to maintain a temperature at 100°C to 110°C.
3. A wide mouthed glass vessel such as jar of about 1.5 litre capacity with flat ground lip and a plane ground disc of plate glass to cover it air tight.
4. Cloth. Two pieces of soft and absorbent clothes of size 75 cms x 45 cms.
5. Tray. A shallow tray not less than 325 cm2 in surface area.
6. Container. An air tight container having a capacity to take the sample.
7. Wire basket. Basket of not more than 6.3 mm mesh.
Procedure:
1. Take about 2 kg. of aggregate sample and screen it on a 10 mm I.S. sieve.
2. Wash the sample thoroughly to remove fine particles of dust and drain it.
3. Place the sample in wire basket and immerse it in distilled water at a temperature of 22°C to 32°C for 24 ± ½hours.
4. Soon after immersion and at the end of soaking period, rotate the vessel rapidly in clock wise and anti-clock wise direction to remove the entrapped air or bubbles on the surface of the aggregate.
5. Now over fill the vessel by adding more distilled water and slide the plate glass disc cover over the mouth to ensure that no air is trapped in the vessel.
6. Dry the vessel from the outside and weigh it. Let the weight of the vessel be W1.
7. Now empty the vessel and fill it with distilled water and slide the disc in position as above.
8. Again dry the vessel from outside and weigh it let the weight of the vessel be W2.
9. Place the aggregate on a dry cloth and dry its surface gently with the cloth. When the first cloth becomes wet and absorbs no further moisture, transfer the aggregate to the second cloth and spread it in a thin layer in such a way that no stone remains one above the other. Leave the aggregate exposed to atmosphere away from direct sun rays for not less than 10 minutes or until it appears to be completely surface dry. The aggregate is turned over at least once during this drying period. A gentle current of unheated air may be passed after first 10 minutes to accelerate the drying of difficult particles of the sample.
10. Weigh the aggregate again. Let the weight be W3.
11. Now place the aggregate in a shallow tray and put it into the oven at a temperature of 100°C to 110°C for 24 ± ½ hours.
12. After 24 hours, take the aggregate out of the oven and air cool it in an air tight container and weigh again. Let the weight of the aggregate be W4.
13. Repeat the experiment with three different samples.
Precautions:
1. The aggregate should be thoroughly washed to remove dust.
2. For soaking the aggregate distilled water should be used.
3. The glass disc should be slided over the mouth of the vessel in such a way that no air is trapped in the vessel.
4. The difference in temperature of water in the vessel during first and second weighing should not exceed 2°C.
Experiment # 10. Specific Gravity of Aggregate:
To determine the specific gravity and water absorption when the aggregate is smaller than 10 mm. (Pycno-meter method).
Theory:
As per I.S. 2386-Part-lII-1963, specific gravity of aggregates can be divided into two categories as follows:
1. Specific gravity
2. Apparent specific gravity
Apparatus:
1. Balance
2. Oven
3. Vessel Pycno-meter as shown in Fig. 3
4. Air drier
5. A tray not less than 325 cm2 in area.
6. An air tight container large enough to take up the sample.
7. Filter paper and funnel.
Procedure:
1. Take a sample of one kg. if the aggregate is in between 10 mm to 4.75 mm and 500 grams if the aggregate is finer than 4.75 mm and place it in a tray and cover it with distilled water at a temperature of 22°C to 32°C.
2. Remove the entrapped air or bubbles on the surface of the aggregate soon after immersion in the distilled water by agitating the aggregate gently with a rod. Keep the sample immersed in the distilled water for 24 ± hours.
3. Drain off the water from the sample carefully by decantation through a filter paper and any material retained is returned to the sample.
4. To evaporate the surface moisture the aggregate including any solid matter retained on the filter paper is exposed to a gentle current of warm air. To ensure uniform drying it is stirred frequently till no free surface moisture is seen.
5. Weigh the saturated and surface dry sample. Let the weight be W1.
6. The aggregate is placed in Pycno-meter and filled with distilled water.
7. Remove any entrapped air by rotating the Pycnomter on its side. During this operation the hole in the apex of the cone should be covered with finger.
8. Dry the Pycnometer on the outside and weigh it. Let the weight of sample + water be W2.
9. Dry the contents of the Pycnomter in the tray. While transferring the contents, care should be taken that no aggregate particle falls outside.
10. Refill the Pycnometer with distilled water to the same level as before. Dry it from the outside and weigh it. Let the weight be W3.
11. Remove the water from the sample by decantation and dry the sample in the oven at 100°C to 110°C for 24 ± ½ hour. Cool and weigh it. Let the weight be W4.
Observations:
