Sampling
What is stratified random sampling?
CDOT Specifications
one random sample selected from each sublot
random number schedule responsibility of tester
What is the temperature needed for testing?
77 +/- 1.8 F or 25 +/-1 C
What is the nuclear gauge used for?
What are the three methods for splitting aggregate and which method is used only for fine aggregate?
A. mechanical splitter
B. Quartering
C Selection by Scoop (fine aggregate only)
What are the 2 methods for determining moisute?
Microwave oven (method A)
Convection Oven (method B)
What are the different aggregate sampling locations?
1. stockpiles (by hand or with power equipment)
2. flowing aggregate stream
3. stopped conveyor belt
4. Processed Windrows
5. Roadway
6. Cover Coat Material Spreader
What is the temperature of the oven if testing cored samples?`
230 +/- 9 F
110 +/- 5 C
Describe standardization procedure, when, where and how.
When: start of the day, when gauge has been off, when readings are in question
Where: Same environment as actual measurement counts, 33 ft away from other nuclear gauges, clear of large masses of water or vertical projections
How: Turn on and warm up (20 min Troxler and Instrotek, 1 min CPN), place on standard block, perform 4 minute standard count, reading must be within 1% of the average if the previous 4 standards
Describe the chutes for both fine and coarse aggregate on a mechanical splitter
Coarse aggregate: minimum of 8 chutes
Fine aggregate: minimum of 12 chutes
openings must be 50% greater than the largest particle
Describe Method A procedure.
Clean glass plan
record sample mass to nearest 0.1 g
550 for S and SX
2000 for SG
5-minute cycles until there is no change
Power equipment: Removed segregated material from the sides, expose a representative face, scoop from bottom to top. Combine and mix to form a separate small pile. Flatten to not thicker than 1 foot. Sample from 3 locations (full depth), combine to form sample.
Hand Sampling: top-third, middle-third, and bottom-third, 2 sets 180 degrees apart. Board upslope of sampling locations. remove top 6 inches of out layer. Sample full depth, combine to form sample.
Fine aggregate: sampling tube 1.25 in diameter by 6ft long, insert horizontally at 5 locations.
What does the bulk specific gravity of a roadway core calculate?
percent air voids
relative compaction
correction factor for nuclear gauge
Describe the procedure for using the nuke gauge to test densities
Long axis parallel to paving direction
6" away from vertical projections
12" away from joints and edge of pavement
1/8" max void space under gauge
backscatter mode
2 one-minute readings, rotate 180 degrees, perform 2 more readings
What are the 5 methods for splitting asphalt?
a. selection by scoop
b. quartering
c. mechanical splitter
d. selection by cross section
e. quartermaster
Describe method B procedure.
500 S and SX
2000 SG
dry at binder compaction temperature for minimum of 3 hours.
check every 30 +/- 5 minutes
constant mass is less than or equal to 0.1g change in mass between 2 measurements
Define nominal maximum particle size.
one sieve size larger than the first sieve that retains more than 10% of the aggregate sample.
what is the formula for calculating bulk specific gravity?
Percent relative compaction?
Percent air voids?
Convert Bulk specific gravity to pcf
Bulk Specific Gravity Gmb= A/(B-C)
(dry/(ssd-wet))
% Relative Compaction= Gmb/RICE x100
% Air voids= 100-%compaction
PCF= Gmbx62.4
How do you calculate percent density?
Have density from nuke gauge, apply correction factor if there is one.
RICE x 62.3 to convert to pcf
your density/RICE converted to pcf x100
What is the timeframe for warming up an asphalt sample?
minimum of 1 hour, not to exceed 4 hours at compaction temperature.
How do you calculate moisture?
a-b/ax100
wet-dry/wet x100
Describe how to sample asphalt from a paver auger.
Paver must be moving
Auger should be operating at lease 80% of the time
Auger area at least 2/3 covered with mixture
Clean square shovel placed in front of the head of the mix
Describe the drying procedure in a forced draft oven.
230 +/-9 F
dry for 3 hours and then determine the mass
put back in oven and check every 2 hours
constant mass= no change of more 0% or 24 hour maximum
cool to room temp and determine the dry mass
Describe the compaction test section procedure.
test strip constructed using first 500 tons
first 300 determines process (rollers, speed, frequency, amplitude, tire pressure, # of passes, surface temp)
last 200 to test for density correction ( 7 nuke gauge tests, 2 cores from each test locations)
Describe procedure for depositing your asphalt sample into the splitting pan and what kind of scoop is used.
method 1: deposit in pan, mix (turn 3 times) flatten to uniform height.
Method 2: flip can upside down, lift 1" and move in circular motion
Use small, flat, square-end scoop with sides
Describe the microwave oven calibration
550 ml of h20
record starting temp
microwave for 5 minutes at 50% power
record ending temo
difference between temperatures should be 75 +/- 10 F
Adjust power settings up or down 10% and run until temp reached in 5-min cycle.