CT 375 Backscatter

Question 1

What is the Title of CT 375?

Answer 1

Determining the In-place Density and Relative Compaction of Hot Mix Asphalt Pavement using Nuclear Gages

Question 2

Backscatter can be used on HMA thickness of at least how much?

Answer 2

At least 0.10 ft.

Question 3

What must be done for each nuke gage to correlate to core densities?

Answer 3

A conversion factor must be developed for each gage for each project.

Question 4

What must be done daily with your nuke gage before you can take any readings?

Answer 4

Standardize the gage

Question 5

When must you establish a new conversion factor? 5 criteria.

Answer 5

Change in lift thickness of 1/2” or more, underlying material, material source, mix design, or recalibration of the nuclear gage.

Question 6

A test strip must have the same what criteria in order to be considered?

Answer 6

Same HMA binder type, binder content, aggregate source, agg type, and grading.

Question 7

How thick must the test strip be in order to be considered?

Answer 7

Must be within +- 0.03 feet of thickness that will be tested on the job.

Question 8

In no case will the lift thickness be less than ______ ft.

Answer 8

0.10 feet

Question 9

Each test strip must be at least __________ ft long?

Answer 9

At least 600 feet long

Question 10

How wide must a test strip be?

Answer 10

One traffic lane wide

Question 11

What must be done if a contiguous 600’ can’t be placed?

Answer 11

Test strip length may be reduced or combine broken segments to achieve as close to 600 feet as possible.

Question 12

How many test locations must be used for the test strip?

Answer 12

A minimum of 10 test sites.

Question 13

How are the test locations determined?

Answer 13

Test locations are random.

Question 14

How many cores do you get?

Answer 14

A set of two cores.

Question 15

What size of cores are required?

Answer 15

4” to 6” in diameter.

Question 16

What must be done if any of your cores are damaged during coring?

Answer 16

Damaged cores must be discarded and replaced by additional cores from the same site.

Question 17

What test method is used to determine the core density?

Answer 17

CT 308 - Method A

Question 18

What must the 2 core densities be within in order to be averaged?

Answer 18

0.05 g/cc

Question 19

What must be done with the 2 core densities that are within 0.05 g/cc?

Answer 19

Average the 2 densities.

Question 20

How is the correlation value determined?

Answer 20

Subtract the average nuclear density from the average core density for the site.

Question 21

Test a minimum of 10 sites for each ________ tons of HMA placed.

Answer 21

500 tons

Question 22

For areas containing less than 500 tons, test at the rate of one test site for each _______ tons.

Answer 22

50 tons

Question 23

No test site shall be represented by fewer than _____ test sites.

Answer 23

Five test sites

Question 24

Which table should be used for ten test sites? What table for less than 10 test sites?

Answer 24

TABLE 1, TABLE 2

Question 25

The numbers for transverse location will always be in what order?

Answer 25

Random

Question 26

At what thickness can you use conventional nuke gages?

Answer 26

Thickness of 0.20 ft. or more

Question 27

For combinations gages, what mode should be used for thickness of 0.20 ft. or more?

Answer 27

Asphalt Mode

Question 28

For lift thickness between 0.10-0.20 ft., what nuke gages should be used?

Answer 28

Thin lift gages that don't use nomographs and combination gages placed in thin lift mode.

Question 29

What sieve size should be used for filling voids?

Answer 29

No. 30 sieve

Question 30

Can conventional gages and thin lift gages be used if the combined thickness of a previously tested layer and a newly placed layer is greater than 0.20 ft.?

Answer 30

Yes, but layers must be added together

Question 31

Where must the sand come from to be used for filling voids?

Answer 31

Sand comes from aggregate mix.

Question 32

If alternate test site must be selected due to surface issues, how do you select the new location?

Answer 32

New test site is 10 ft. forward in longitudinal direction, while keeping transverse location.

Question 33

What must be done after sand is No. 30 sieved over test area?

Answer 33

Straight edge the surface to smooth out voids and scrape away excess sand.

Question 34

What location must the source rod be placed at on the gage?

Answer 34

Place in backscatter mode.

Question 35

What must you do when you have setup your gage before or after your 1 minute count?

Answer 35

Mark the base of the nuke gage on the pavement.

Question 36

After your first reading is complete, what is done? And base is marked.

Answer 36

Flip gage 180 degrees and place over precise location of initial test.

Question 37

How is the count ratio determined?

Answer 37

Dividing nuclear reading by standard count.

Question 38

What decimal must the count ratio be calc'd to?

Answer 38

0.001, nearest thousandth

Question 39

How is the density determined?

Answer 39

Count ratio-density table is referenced to find density.

Question 40

Density is rounded to what?

Answer 40

Nearest 0.01 g/cc

Question 41

What must the 2 density measurements per test site be within what tolerance?

Answer 41

Within 0.05 g/cc

Question 42

What must be done if densities are not within 0.05 g/cc?

Answer 42

Perform tests until densities are within 0.05 g/cc.

Question 43

What must be done if densities do not come within 0.05 g/cc after 3 retests?

Answer 43

Pick different location 10 ft. forward of current test.

Question 44

What is done with the 2 density readings per test site?

Answer 44

Average densities and round to nearest 0.01 g/cc

Question 45

What is done with test site readings that have been averaged per site?

Answer 45

Average densities and round to nearest 0.01 g/cc

Question 46

How is the corrected in-place density calculated?

Answer 46

By adding the conversion factor to the avg in place density.

Question 47

What is TMD?

Answer 47

Test Maximum Density

Question 48

What are the two ways to find TMD?

Answer 48

LTMD and FTMD

Question 49

What does LTMD stand for?

Answer 49

Laboratory Test Max Density

Question 50

What does FTMD?

Answer 50

Field Test Max Density

Question 51

When daily production exceeds ______ tons, take additional representative samples from each ______ tons or portion thereof.

Answer 51

5,000 tons, 5,000 tons

Question 52

Determine LTMD at least once for the following occurances:

Answer 52

Project start-up, Every 5 days or every 25,000 tons placed, whichever first, Change in the HMA or JMF.

Question 53

How often should the LTMD or FTMD be determined?

Answer 53

For each daily sample.

Question 54

Testing LTMD or FTMD may be waived for selected daily samples provided all of the following conditions:

Answer 54

Five consecutive days of LTMD/FTMD do not differ by more than 1% from their average, at least one LTMD/FTMD is tested every 5 paving days and the results does not differ by more than 1% from the average from the previous 5 days. Untested samples are retained for testing if needed.

Question 55

What Test method is used for getting density of LTMD?

Answer 55

CT 308 method A

Question 56

CT 308 Method A rounds to what value for density?

Answer 56

Nearest 0.01 g/cc

Question 57

Determine LTMD of the sample by averaging the density values of the ____ individual specimens.

Answer 57

5 individual specimens

Question 58

Correlation Factor for FTMD must be determined when?

Answer 58

Beginning of a project.

Question 59

What must be done with the sample when determine correlation factor of LTMD and FTMD?

Answer 59

Split sample into two representative portions, submit one for LTMD and other for FTMD.

Question 60

How many test specimens of each LTMD and FTMD must be made?

Answer 60

5 test specimens of each.

Question 61

How is the Correlation Factor calculated?

Answer 61

Divide the average of the LTMD values by the average of the FTMD.

Question 62

How do you calc the relative compaction?

Answer 62

RC=(Corrected In-Place Density/TMD) x100

Question 63

Round relative compaction to what?

Answer 63

Nearest 0.1%