CHAPTER 3 Methodology 3
A total of six different samples were collected, four of which were metamorphic rocks and two were igneous rocks. The rocks were collected for laboratory testing from the three quarries which include Lose quarry, Tewane quarry and Maope quarry. The obtained rocks were trimmed to a common size so that the samples show the rock features well. For accuracy, the samples were ensured that they included all minerals of the rock and it shouldn’t have weathered surfaces because the weathering process changes the original mineralogy which also changes the properties of rocks.
3.2 LABORATORY TESTS
Laboratory tests were done to determine the various rock properties and other parameters which define the nature of the rock. The samples collected from the field were properly stored for laboratory tests so that the true nature of the rocks are not altered. The following tests were conducted;
Slake durability test
Aggregate impact value
Los Angeles abrasion resistance test
Point load test
3.2.1 LOS ANGELES ABRASION TEST
This test was done to determine the abrasion value of the given rock aggregate
Los Angeles machine with inside diameter 70cm and inside length of 50cm.
Abrasive charges having diameter 4.8cm and weight 390 to 445 gm
I.S Sieves with 40mm, 25mm and 1.7mm opening.
Weighting Balance of 0.1gm accuracy.
Figure 1. Los Angeles Abrasion machine
The aggregates were dried in the oven at 105 ?C for a period of 24 hours and then cooled to room temperature before they were tested. There are seven aggregate sizes grading to choose from in the ASTM method as presented in table 2 below. Grading A was chosen to be used for this test. The abrasive charge was chosen depending upon the grading of the test specimen from table 3 below.12 steel spheres were placed in a placed in a steel drum along with ~1250+/-50g of aggregate sample and the drum was rotated for 500 revolutions at a rate of 30-33rev/min. After the desired number of revolutions, the machine is stopped and the samples were discharged from the machine taking care to take out entire stone dust. The sample was sieved through the No.12 sieve (1.7mm). The amount of material passing the sieve, expressed as a percentage of the original weight, was the LA abrasion loss or percentage loss
Los Angeles abrasion value (W1-W2)/W1X100
W1-Original weight of samples
W2-retained weight of sample passing the 1.7mm sieve
Two tests were done and the average value to the nearest whole number was reported as the abrasion value.
Weight of g of test sample for grade
80 63 – – – – 2500+/-10 – –
63 50 – – – – 2500+/-10 5000+/-10
50 40 – – – – – 5000+/-10 5000+/-10
40 25 1250+/-50 – – – – – 5000+/-50
25 20 1250+/-50 – – – – – –
20 12.5 1250+/-50 2500+/-10 – – – – –
12.5 10 1250+/-50 2500+/-10 – – – – –
10 6.3 – – 2500+/-10 – – – –
6.3 4.75 – – 2500+/-10 – – – –
4.75 2.36 – – – 5000+/-10 – – –
Table 2. Grading’s for test specimens
Grading Number of spheres Weight of charge (g)
A 12 5000+/-25
B 11 4584+/-25
C 8 3330+/-20
D 6 2500+/-15
E 12 5000+/-25
F 12 5000+/-25
G 12 5000+/-25
Table 3. Abrasive charge per grading
The density of the rocks was found using the wax immersion method. This test method is used to determine the bulk density for any irregular shape in the construction industry, by coating the sample with a thin layer of wax and then conducting a water immersion trial.
Figure 2. Density apparatus
Figure 3. Pot wax and Hot plate
The sample was dried at 110 ?C for a period of 24 hours to remove any trapped moisture from the interior of the sample. This was done to ensure that the true bulk density was achieved. After drying, the samples were allowed to cool down to room temperature prior to testing. The samples were then weighed to determine the dry weight of the sample and this was recorded as weight W. The wax was melted in the pot and the sample was tied using a string to dip the sample into the melted wax.to coat the sample one end of the sample was held and the other half of the sample was dipped into the wax. The sample was slowly removed from the wax and allowed to cool so that it hardens on the sample. If they were any air bubbles that were trapped in the wax, they were carefully pushed out and an extra coat of wax was added to cover the holes in the wax. The sample was then inverted and dipped in the other end, making sure the two wax layers overlap. The sample was weighed again and recorded as the weight P. The water tub was filled with water and it was put on the balance scale making sure the balance was reset to zero. The water level in the tub was ensured that it was deep enough to fully cover the sample. The clamp was placed close to the water tub so that the sample will be hanged over it while it’s being dipped in the water. The sample was placed into the water tub and the weight was recorded as the suspended weight (Swax).
The volume was calculated as the difference between the original Dry weight,W,and the Suspended weight,Swax.
Volume =Dry weight-Suspended weight Equation 1
Bulk density=(Dry weight)/Volume Equation 2
3.2.3 AGGREGATE IMPACT VALUE
The aggregate impact value test was done to determine the aggregate impact value of coarse aggregates as per IS: 2386 (Part IV) – 1963.
The apparatus consists of an Impact testing machine: The machine consists of a metal base. A detachable cylindrical steel cup of internal diameter 10.2 cm and depth 5 cm. A metal hammer of weight between 13.5 to 14 kg, 10 cm in diameter and 5 cm long. An arrangement for raising the hammer and allow it to fall freely between vertical guides from a height of 38 cm on the test sample in the cup.
A cylindrical metal measure having 7.5 cm and depth of 5 cm for measuring aggregates.
A tamping rod of circular cross section, 1cm in diameter and 23 cm long, rounded at one end.
Balance of capacity not less than 500 gm to weigh accurate up to 0.01 gm.
IS Sieves of sizes – 13.2mm, 9.5mm and 2.36mm
A tamping rod of 10mm circular cross section and 230mm length, rounded at one end
Figure 4:IS Sieves
Figure 5. Aggregate Impact test machine
PREPARATION OF SAMPLE
The test sample was conformed to the following grading: – Passing through 13.2mm IS Sieve 100% – Retention on 9.5mm IS Sieve 100% .The sample was then oven-dried for 4hrs at a temperature of 105 ?C to remove moisture from the rocks and then cooled. The measure was about one-third full with the prepared aggregates and tamped with 25 strokes of the tamping rod. A further similar quantity of aggregates was added and a further tamping of 25 strokes was given. The measure was then finally filled to overflow, tamped 25 times and the surplus aggregates were struck off, using a tamping rod as a straight edge. The net weight of the aggregates in the measure were determined to the nearest gram.
The cup of the impact testing machine was fixed firmly in position on the base of the machine and the whole of the test sample was placed in it and compacted by 25 strokes of the tamping rod.
The hammer was raised to 380mm above the upper surface of the aggregates in the cup and allowed to fall freely onto the aggregates. The test sample was then subjected to a total of 15 such blows, each being delivered at an interval of not less than one second. The sample was removed and sieved through a 2.36mm IS Sieve. The fraction that was retained on the sieve was weighed. The ratio of the weight of the fines formed to the total sample weight was expressed as a percentage.
The Aggregate impact value was obtained by the relation;
Equation 3: aggregate impact value
3.2.4 SLAKE DURABILITY TEST
The slake durability test was done to determine the weathering resistance of the sample
Slake Durability device
Oven, capable of maintaining a temperature of 110 ± 5º C ( Thermostatically controlled)
Timing device (stop watch or clock)
Brushes for cleaning
Plastic bags for sample or envelopes
Figure 6.Slake Durability apparatus
Sample should be kept in a manner that preserves the natural moisture content , for example, kept in Ziploc plastic bags or end tied with cable ties in a plastic bag
The sample of the slake durability test shall consist of 10 representative fragments that are intact, roughly equi-dimensional, each sample must weigh between 40g ; 60g
The fragments may be naturally occurring or may be produced by breaking with a pick hammer
Break off any sharp corners, if possible, remove all the dust by brushing the sample prior to weighing
The total sample should weigh 450g to 550g
The sample fragments were placed in the drum and the drum was weighed while the sample fragments were in the drum. After weighing, the drum together with the sample fragments were dried in the oven for 16 hours. The sample and drum were allowed to cool at room temperature for 20 minutes and then weighed again. The natural water content was calculated using the following formula;
W=((A-B))/((A-D))*100 (Equation 4)
w = percentage of water content
A = mass of drum plus sample at natural moisture content (g)
B = mass of drum plus oven-dried sample before the first cycle (g)
C = mass of drum (g)
The drum was mounted in the trough and then coupled to the motor. The trough was then filled with distilled water at room temperature to 20mm below the drum axis. The drum was rotated at 20 rpm for a period of 10 minutes and the water temperature was recorded at the beginning and at the end of the run. After the completion of the rotation, the drum was removed from the trough and they were retained by drying in the oven for 16 hours at 105 ºC .After cooling, the drum and sample were weighed to obtain the oven-dried mass for the second cycle. The steps from recording the temperature at the beginning and end of the run up to cooling and weighing both the drum and sample to obtain the oven-dried mass for the second cycle were repeated. The drum and sample were weighed again to obtain a final mass. At the end, the drum was brushed clean and then weighed again to obtain its mass.
3.2.5 POINT LOAD TEST
The point load test is a geotechnical test which was conducted to determine the rock strength index,
Point load Tester
This machine consists of
Conical end Platens
Digital pressure gage
A ruler on the frame
Figure 7. Point load tester
Specimen and Test type selection
Nature of the sample= sample can be fully water saturated or in the natural water content
Tests on samples are based on their size and shape
Sample size(mm) Shape Ratio Distance L Suitable Test type
50±35 Block or lump 0.3; D/W