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Section 3
Experimental Program
3.1Introduction test lanes, a description of the construction process and the
test variables in the field experiment is presented in the fol-
Based on the results of Task 1, a comprehensive experi- lowing section.
mental plan was designed to identify consistent, reliable, and
practical methods for (1) evalutracating the bonding charac-
teristics of tack coats; (2) selecting the tack coat material type 3.2Tack Coat and Overlay
and residual asphalt binder application rate required for opti- Construction at the Test Site
mum performance in new HMA pavement and HMA overlay Table 4 presents the test matrix simulated in the LTRC PRF
construction, rehabilitation, and reconstruction; (3) calibrat- field experiment, which used conventional paving equipment
ing application equipment; and (4) maintaining field quality and a computerized tack coat distributor truck. Four types of
control and quality assurance. Findings reported in Chapter 2 pavement surfaces and five tack coat materials were evaluated,
also identified a number of factors that were reported to influ- but only one emulsion (SS-1h) was used on the new HMA
ence interface bond strength including tack coat type, tack surface, and two emulsion grades (SS-1h and SS-1) were used
coat application rate, tack coat curing time, surface condi- on the milled surface. Four residual application rates were
tion, and pavement temperature. Responses from the world- selected including zero (no-tack). Effects of wet and dusty
wide survey indicated that the residual application rates of conditions during construction operations were simulated
emulsions typically vary from 0.02 to 0.08 gal/yd2, depending for the different surface types as part of the experimental pro-
on the type of pavement surface. As pavement temperature gram. To evaluate variation in the results, triplicate samples
increases, laboratory bond strength significantly decreases for were tested for each condition; 375 samples were tested as
all tack coat types and application rates. The most common part of the test matrix. Laboratory specimens (cores) were
types of emulsions used for tack coats include slow-setting obtained from the pavement test sections.
and rapid-setting grades of emulsions. In the United States,
most states use slow-setting grades of emulsions. To this end,
the experimental plan investigated the influence of a number 3.2.1 HMA Pavement Surface Preparation
of factors on the interface shear strength: HMA and PCC sur- Figure 11 presents a plan view of the five test lanes con-
face type and properties (e.g., texture, air voids content, and structed at the LTRC PRF. Each lane was a total of 215 ft in
permeability), surface cleanliness, tack coat material type, and length and 12 ft in width. It is noted that each lane contained
application rate and method. test and distributor truck access areas. Each test section had
The majority of the research activities conducted in this a length of 15 ft and a width of 6.5 ft. The lengths of the adja-
project were based on tack coat experiments conducted in cent (access) areas were selected to ensure that the distributor
a field environment. Field experiments were complemented truck could attain the required speed in order to achieve the
with a number of laboratory experiments to assess the influ- correct tack coat application rate. All test lanes selected for
ence of variables such as laboratory compaction, rheological this experiment contained a similar old HMA surface type.
properties of tack coat materials, and test temperature. The Surface texture values for each lane were measured using a
experimental program was divided into experimental test laser type device (DYNATEST 5051 Mark III road surface
matrices, which answered specific objectives of the experi- profiler), according to ASTM E 1845, Standard Practice for
mental program. Since all experiments made use of full-scale Calculating Pavement Macrotexture Mean Profile Depth. The
