Narrator: This presentation covers methods used for a sampling hot-mix asphalt paving
mixtures immediately behind a paver and prior to rolling in mini stockpile
sampling. It does not, however, claim to address all the safety and health issues
associated with these procedures. One combined sample for behind a paver
consists of a minimum of three increments collected within 10 feet
longitudinally and across the full width of the paving mat. To obtain sample sizes
and the number of samples required, refer to the special provision in the contract.
A composite sample is defined as a sample that includes HMA material from
across the entire pavement width. These sampling procedures may involve
hazardous materials, operations and equipment. It's the technician's
responsibility to be familiar with and follow safety and health practices and
to determine applicability of regulatory limitations prior to sampling. There are
two methods of sampling for behind a paver: sampling with plates and shovel
and sampling with only a shovel. Consult the MTM 3-2-4 when determining
which method should be used. Whichever method is called for, be sure to apply a
light amount of cooking spray to all sampling equipment to prevent HMA
adhesion. First, we'll cover sampling with a plate and shovel. Use this method when
sampling HMA directly over aggregate base, rubberized concrete, crush and shape
HMA base, or a cold-milled surface. Determine the sample locations according
to the special provisions in the contract. First, apply a small amount of
cooking spray to all sampling equipment. Next, the contractor collects some HMA
from the pavers auger system into metal buckets. These must contain enough
material to fill the voids in the pavement caused by removing the sample.
A wire lead is attached to one of the lifting handles for locating the buried
plate in the pavement. Place the plate with the wire lead attached to one of
the handles at the designated location ahead of the paver. Extend the wire lead
beyond the edge of the pavement. Trucks, pavers and door material transfer
devices will be allowed to cross over the plates and wire lead. After the
mixture is placed, use the wire lead to locate the plate. Find and lift the wire
handle out of the pavement. This will locate the four corners of the plate.
Once the plate's edges are defined, use a sampling shovel at the random location.
Dig directly downward into the pavement until the shovel comes into contact with
the plate. Once you make contact, push the shovel forward until the shovel
is two-thirds full of HMA and lift it straight up slowly, being careful not to
lose any HMA. Place the material from the shovel directly into a 3.5-gallon
metal bucket, known as the sampling container. More than one
two-third shovel full of mixture can be removed from individual locations if
additional mix is required to fill the sample container. Make sure that you're
careful to take additional mix only from an undisturbed area. Also be sure to
scrape the leftover HMA material on the inside of the shovel only and equally
into each sample container. Remove the sampling plates from the pavement.
The contractor will fill and level the void left in the pavement with HMA already
obtained from the paver's auger system. The contractor may pack paver up over
sample areas and pave over disturbed sampling areas.
Once the sample has been obtained, be sure to fill out the form titled "Sample
Identification for HMA Mixture Street Samples" and place the form with the
appropriate sample. Next, we will cover sampling with a shovel without plates.
Use this method when sampling over HMA, concrete surfaces, or when utilizing a
windrow pickup machine. Again, determine the sample locations according to the
special provision in the contract. The contractor gathers HMA out of the auger
system into metal buckets. These must contain enough material to fill the
voids in the pavement caused by removing the sample. Use a sampling shovel at the
random location. Dig directly downward into the pavement until the shovel comes
into contact with the existing pavement surface. Once you make contact,
push the shovel forward until the shovel is two-thirds full of HMA and lift it
straight up slowly, being careful not to lose any HMA. Place the material into a
3.5-gallon metal bucket sampling container. More than one shovel-
full of mixture can be removed from the individual location if additional mix is
required to fill the sample container.
Make sure that you are careful to take additional mix only from an undisturbed
area. Be sure to scrape leftover HMA material on the inside of the shovel
only, equally and to each sample container. The contractor will fill and
level the void left in the pavement with HMA already obtained from the paver's
auger system or the contractor may back the paver up over sample areas and pave over
disturbed sampling areas. Once a sample has been obtained, be sure to fill out
the form titled "Sample Identification for HMA Mixture Street Samples" and place
the form with the appropriate sample.
Sampling HMA loose mix from mini stockpile.
Refer to MTM 3-13. Have the contractor form a mini stockpile
approximately 3 to 5 tons.
For one composite sample, take at least four approximately equal increments of
material from around the stockpile, front, back, right, and left, and at different
heights. At each location around the stockpile, obtain an increment of the
sample by taking into the pile approximately 1 foot, forming a
vertical face to remove the segregated material then shovel material out of
undisturbed shelf created to eliminate segregated materials. Increment sampled
from that stockpile to form one composite sample. Be sure to scrape
leftover HMA material on the inside of the shovel only, equally and to each
sample container. Under some special circumstances, the special provision
calls for a splitting device. These circumstances include sampling for a
test strip or an initial production lot. In that case, collect one composite 45,000-gram
sample using one of the previously defined methods for sampling.
The sample will fill two 3.5- gallon metal buckets.
The two 3.5- gallon metal buckets will be combined together in MDOT's approved
splitter be sure to apply a light amount of
cooking spray to the splitter to prevent HMA adhesion. The material in the
splitter will be split into four 3.5-gallon metal buckets.
Two opposite corner buckets shall be combined to achieve two full 3.5-
gallon metal buckets ready for identification and distribution.
That concludes this presentation covering methods used for sampling HMA paving
mixtures immediately behind a paver and prior to rolling. Now, let's spend
some time reviewing.
1) What is the term "composite sample" mean?
A sample that includes HMA material from the entire pavement width.
2) The HMA sampling method using plates and a shovel is called for when...
When sampling over aggregate base, rubblized concrete crush and shape.
HMA base, or a cold milled surface.
3) The best description of a sample container is...
A 3.5-gallon metal bucket.
4) What is the name of the form that should be filled out and placed with
each sample?
Sample identification for HMA mixture street samples.
5) How should the material from the paver's auger system be placed in the
voids left from removing the sample material?
The contractor should scoop enough HMA material into metal buckets to fill the
voids then dump it directly into the voids
once the sample material is taken.
6) The HMA sampling method using a shovel only should be utilized when
sampling over...
HMA and concrete surfaces.
7) To determine the sample locations you should refer to...
The special provision in the contract.
8) Sampling plates have a wire lead that is used for...
Locating the sampling plate once the paver has covered it with HMA material
9) An MDOT-approved splitting device should be used under special
circumstances, which include...
Sampling for a test strip or initial production lot.