Tests During Highway Construction for Civil Engineers.

                        

                   Tests During Highway Construction For Civil Engineers

There are several number of tests done on site and in lab during highway construction. The frequently and must to do are

1. Moisture Content or Calcium Carbide Test 

2. Particle Size Distribution Test

3. Sand Replacement Method 

4. California Bearing Ratio Test (CBR)

                               Moisture Content or Calcium Carbide Test 

Apparatus: Calibrated Moisture Meter , Calcium Carbide Powder 

Procedure:
1.Take soil sample in the moisture meter 

2.Put calcium carbide powder 

3.Shake it well until they mix properly

The moisture in the soil sample reacts with the powder and creates pressure on the calibrated needle and gives you the moisture content.

                                       Particle Size Distribution Test

A typical Particle size distribution  test set-up is composed of:

• Drying oven maintained at 110 ± 5°C
• Standard sieves
• Sample splitter
• Mechanical sieve shaker
• Pans

Procedure

1. Obtain a representative oven-dried soil sample
2. Pulverize the soil sample as finely as possible, using a mortar and pestle or a mechanical soil pulverize.
3. Obtain a soil sample of about 500 g and determine its mass W0 (g).
4. Stack the sieves so that those with larger openings (lower numbers) are placed above those with smaller openings (higher numbers). Place a pan under the last sieve (#200) to collect the portion of soil passing through it. The #4 and #200 sieves should always be included in the stack.
5. 
   Make sure the sieves are clean, If soil particles are stuck in the openings, use a brush to poke them out.
6. Weigh the pan and all of the sieves separately
   
7. Pour the soil from above into the stack of sieves and place the cover on it. Put the stack in the sieve shaker, affix the clamps, set a timer for 10 to 15 minutes, and start the shaker.
   
   

Stop the sieve shaker and measure the mass of each sieve and retained soil.

Plot all the obtained masses w.r.t their cumulative masses and plot the graph 

                                             Sand Replacement Method 

This test is also called Soil Density Test. This is an on field test to determine the moisture in terms of soil density or soil compaction. This is done during the making of granular sub base for pavement.

Apparatus:  

1. Sand cone apparatus, filled with uniformly graded sand passing through No. 20 sieve and retained on No. 30 sieve.

2. Density Plate, with a central circular hole of diameter equal to the diameter of pouring cone.

3. Digging tools.

4. Balances sensitive to 1 gm & 0.1 gm.

5. Spoon.

6. Brush. 

Procedure:

Sand Replacement Method Procedure:

1. Calibration of cone apparatus should be done firstly:

2. Weigh the sand cone apparatus full of known density sand.

3. Seat the density plate on leveled clean test ground.

4. Dig out soil 4” to 6″ deep with the same diameter as the density plate hole. Clean all loose soil out of the test hole with brush and spoon.

5. Collect all the excavated soil and weigh it.

6. Invert the sand cone apparatus over the density plate and open the valve to tilt the hole with sand. When the sand stops flowing, close the valve and remove the apparatus from the test hole.

7. Weigh the sand cone apparatus with remaining sand.

8. Collect as much of the sand from the hole as possible.

9. Put a sample of the excavated soil in the weighed moisture container and place it in the oven for water content determination

                                     California Bearing Ratio Test (CBR)

The California Bearing Ratio or CBR test is performed in construction materials laboratories to evaluate the strength of soil subgrades and base course materials. Those who design and engineer highways, airport runways and taxiways, parking lots, and other pavements rely on CBR test values when selecting pavement and base thicknesses.

            

Apparatus:

1. Cylindrical mold with inside dia 150 mm and height 175 mm, provided with a detachable extension collar 50 mm height and a detachable perforated base plate 10 mm thick. 

2. Spacer disc 148 mm in dia and 47.7 mm in height along with handle. 

3. Metal rammers. Weight 2.6 kg with a drop of 310 mm (or) weight 4.89 kg a drop 450 mm. 

4. Weights. One annular metal weight and several slotted weights weighing 2.5 kg each, 147 mm in dia, with a central hole 53 mm in diameter. 

5. Loading machine. With a capacity of atleast 5000 kg and equipped with a movable head or base that travels at an uniform rate of 1.25 mm/min. Complete with load indicating device. 

6. Metal penetration piston 50 mm dia and minimum of 100 mm in length. 

7. Two dial gauges reading to 0.01 mm. 

8. Sieves. 4.75 mm and 20 mm I.S. Sieves.

9. Miscellaneous apparatus, such as a mixing bowl, straight edge, scales soaking tank or pan, drying oven, filter paper and containers. 

 CBR Test Procedure:

---

• Normally 3 specimens each of about 7 kg must be compacted so that their compacted densities range from 95% to 100% generally with 10, 30 and 65 blows.

• Weigh of empty mould

• Add water to the first specimen (compact it in five layer by giving 10 blows per layer)

• After compaction, remove the collar and level the surface.

• Take sample for determination of moisture content.

• Weight of mould + compacted specimen.

• Place the mold in the soaking tank for four days (ignore this step in case of unoaked CBR.

• Take other samples and apply different blows and repeat the whole process.

• After four days, measure the swell reading and find %age swell.

• Remove the mould from the tank and allow water to drain.

• Then place the specimen under the penetration piston and place surcharge load of 10lb.

• Apply the load and note the penetration load values.

• Draw the graphs between the penetration (in) and penetration load (in) and find the value of CBR.

• Draw the graph between the %age CBR and Dry Density, and find CBR at required degree of compaction

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