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APPENDIX C
Chip Seal Design Details
INTRODUCTION aggregate gradation, pavement condition, traffic volume, and
type of asphalt. McLeod made it apparent that correction fac-
The very early practitioners of chip seals appear to have tors for the quantity of binder lost by absorption of aggregate
used a purely empirical approach to their designs. Sealing a and texture of existing surface are recommended. McLeod's
pavement was considered then, as it is now in many circles, work also gives guidelines on the appropriate type and grade
an art. The design of a chip seal involves the calculation of of asphalt for the selected aggregate and surface temperature
correct quantities of a bituminous binder and a cover aggre- at time of application. The Asphalt Emulsion Manufacturers
gate to be applied over a unit area of the pavement. Several Association and the Asphalt Institute have gone on to adapt
design approaches outlined in the available literature are this method in the form of recommendations for binder types
briefly described in this appendix. and grades for various aggregate gradations, and correction
factors to the binder application rate based on existing surface
The details of the various design methods in use in the condition (Seal Coat . . . 2003).
United States, Canada, and overseas are reported here. An
effort has been made to report the salient details of each
method without describing the entire method in detail. Repre- KEARBY METHOD
sentative examples of design charts and tables are presented to
illustrate the level of design detail that is involved in each In 1953, J.P. Kearby, an engineer with the Texas Highway
method. The reader should refer to the literature for details. Department, made one of the first efforts at designing chip seal
material application rates in the United States. Kearby was
quick to point out that "computations alone cannot produce
HANSON METHOD satisfactory results and that certain existing field conditions
require visual inspection and the use of judgment in the choice
The first recorded effort at developing a design procedure for of quantities of asphalt and aggregate" (Kearby 1953). Kearby
seal coats appears to have been made by a New Zealander, developed a method to determine the amounts and types of
F.M. Hanson (1934/35). His design method was developed asphalt and aggregate rates for one-course surface treatments
primarily for liquid asphalt, particularly cutback asphalt, and and chip seals. Kearby's work resulted in the development of
it was based on the average least dimension (ALD) of the a nomograph that provided an asphalt cement application
cover aggregate spread on the pavement. Hanson calculated rate in gallons per square yard for the input data of average
ALD by manually calipering a representative aggregate sam- thickness, percent aggregate embedment, and percent voids
ple to obtain the smallest value for ALD that represents the (Kearby 1953). The design methodology requires the knowl-
rolled cover aggregate layer. He observed that when cover edge of some physical characteristics of the aggregate, such as
aggregate is dropped from a chip spreader on to a bituminous unit weight, bulk specific gravity, and quantity of aggregate
binder, the void between aggregate particles is approximately needed to cover 1 yd2 of roadway. The unit weight test, bulk-
50%. He theorized that when the layer is rolled, this value is specific gravity test, is done for calculating unit weight and
reduced to 30% and it is further reduced to 20% when the bulk-specific gravity. Figure C1 is the nomograph developed
cover aggregate is compacted by traffic. Hanson's design by Kearby for use in chip seal design.
method involved the calculation of bituminous binder and
aggregate spread rates to be applied to fill a certain percent- In addition to developing the nomograph, Kearby recom-
age of the voids between aggregate particles. Hanson speci- mended the use of a uniformly graded aggregate by outlining
fied the percentage of the void space to be filled by residual eight grades of aggregate based on gradation and associated
binder to be between 60% and 75%, depending on the type of average spread ratios. Each gradation was based on three sieve
aggregate and traffic level. sizes. He also recommended that combined flat and elongated
particle content not exceed 10% of any aggregate gradation
McLEOD METHOD requirement. Flat particles were defined as those with thick-
ness less than half the average width of the particle, and elon-
Throughout the 1960s, N. McLeod developed a design pro- gated particles were defined as those with length greater than
cedure based partially on Hanson's previous work (McLeod twice that of the other minimum dimension. Kearby suggested
1969). McLeod's design determines the aggregate application that when surface treatments are applied over existing hard-
rate based on gradation, specific gravity, shape, and a wastage paved surfaces or tightly bonded hard base courses, the per-
factor. McLeod provided a correction factor owing to the frac- centage of embedment should be increased for hard aggre-
tion of voids. The binder application rate is determined by the gates and reduced for soft aggregates. He also mentioned that
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FIGURE C1 Nomograph to determine asphalt cement application rate in seal coats and one-
course surface treatments (Kearby 1953).
some allowance should be made for highway traffic. It was · It is better to err on the side of a slight deficiency of
suggested that for highways with high counts of heavy traf- asphalt to avoid a fat, slick surface.
fic, the percent embedment should be reduced, along with the · Considerable excess of aggregate is often more detri-
use of larger-sized aggregates, and for those with low traffic, mental than is a slight shortage.
it should be increased with the use of medium-sized aggre- · Aggregate particles passing the No. 10 sieve act as
gates. However, Kearby did not recommend any numerical filler, thereby raising the level of asphalt appreciably,
corrections. and cannot be relied on as cover material for the riding
surface.
Kearby also elaborated on the following construction · Suitable conditions for applying surface treatments are
aspects of surface treatments and seal coats based on his controlled by factors such as ambient, aggregate, and
experience at the Texas Highway Department: surface temperatures and general weather and surface
conditions.
· Chip seals had been used satisfactorily on both high- · Rolling with both steel-wheeled and pneumatic rollers
volume traffic primary highways and low-volume traffic is virtually essential.
farm roads, with the degree of success largely depending
on the structural strength of the pavement rather than on During the same period, two researchers from the Texas
the surface treatment itself. Highway Department (Hank and Brown 1949) published a
· Thickness of the surface treatment ranges from 1/4 in. to paper about their aggregate retention studies on seal coats.
1 in., with the higher thickness being preferred. How- They conducted tests to determine the aggregate retention
ever, lighter treatments have, in general, proven satisfac- under a variety of conditions, including source of asphalt
tory when the pavement has adequate structural capacity cement, penetration grade of asphalt, number of roller passes,
and drainage. binder type (asphalt cement versus cutback), aggregate
· In general, most specification requirements for aggre- gradation, and binder application temperature.
gate gradation are very broad, resulting in considerable
variations in particle shape and size as well as in percent All of their tests were conducted under the same condi-
voids in the aggregate. tions, with only the test parameter being variable. Those
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TABLE C1 Eq. C1 was used to calculate the asphalt application rate
EFFECT OF AGGREGATE GRADATION AND AGGREGATE (in gallons per square yard), which included two correction
TREATMENT ON RETENTION
factors determined for traffic level and existing surface
Aggregate Loss condition.
Test Condition for Aggregate as a Percentage of
Original
12.6% passing No. 10 sieve
6.7% passing No. 10 sieve
0% passing No. 10 sieve
72.0
57.4
30.5
A = 5.61
E
d {
1-
W
62.5G
T +V} (C1)
12.6% passing No. 10 sieve and rock preheated to 250°F 17.7
12.6% passing No. 10 sieve and rock precoated with MC-1 33.6 The modified Kearby method also recommends a labora-
tory "board test" method to find the quantity of aggregate
Source: Hank and Brown 1949.
needed to cover 1 yd2 of roadway. The board test is performed
by placing an adequate number of rocks on an area of 1 yd2.
The weight of aggregates that cover this area is determined
authors concluded that aggregate retention was not signifi- and converted into a unit of pounds per square yard.
cantly different from that of asphalt cements picked from
five different sources commonly used by the Texas Highway Epps and associates developed correction factors for the
Department at the time. Kearby method, based on what seemed to be working well in
practice (Epps et al. 1980). The binder application rate cor-
In the same study, the effect of aggregate gradation on rection factors corresponded to traffic level and surface con-
the performance of chip seals was investigated. An OA- dition. Epps also suggested that consideration be given to
135 asphalt cement (close to an AC-5) applied at a rate varying the asphalt rate both longitudinally and transversely,
of 0.32 gal/yd2 was used under different aggregate treat- as reflected by the pavement surface condition (Epps et al.
ments. The corresponding aggregate loss values are repro- 1980). Since that time, this design approach has been labeled
duced in Table C1. These results highlight the authors' con- as the modified Kearby method by both practitioners and
tention that increased No. 10-sized aggregate content poses researchers. Since the publication of that design procedure,
aggregate retention problems in seal coats. In addition, the Texas Department of Transportation's Brownwood
those researchers showed that a smaller portion of aggre- District has expanded on the asphalt application correction
gate, less than 1/4 in. in size, results in better performance of factors to include adjustments for truck traffic and existing
the seal coat. surface condition.
Table C2 shows the design output that was used in a
MODIFIED KEARBY METHOD (TEXAS) research study documenting chip seal performance on high-
volume roads in Tulsa, Oklahoma, in 1989 (Shuler 1991). It
In 1974, Epps and associates proposed a further change to the
reveals the differences in design binder and aggregate appli-
design curve developed by Kearby for use in seal coats by
cation rates when using the two different methods with the
using synthetic aggregates (Epps et al. 1974). On the basis of
same design input parameters. One can see that there are con-
high porosity in synthetic aggregates, a curve showing
siderable differences in the resultant rates calculated by each
approximately 30% more embedment than with the Benson
of the two methods. One must remember that both these meth-
Gallaway curve was proposed. The rationale for this increase
ods are being used by agencies that then expect experienced
was that high-friction, lightweight aggregate may overturn
field personnel to adjust the design rates to match the chang-
and subsequently ravel under the action of traffic.
ing surface conditions found in the actual project. It must also
be noted that the project carried an estimated 38,000 average
In a separate research effort, the Epps team (1980) con-
daily traffic (Shuler 1991) and, therefore, these rates will
tinued the work done in Texas by Kearby (1953) and Benson
probably appear higher than expected. However, most expe-
and Gallaway (1953), by undertaking a research program to
rienced chip seal personnel are used to seeing rates for low- to
conduct a field validation of Kearby's design method. Data
moderate-volume roads.
from before and after construction of 80 different projects
were gathered and analyzed for this purpose (Holmgreen
et al. 1985). It was observed that the Kearby design method ROAD NOTE 39
predicts lower asphalt rates than what was used in Texas
practice, and the study proposed two changes to the design The United Kingdom's Transport Research Laboratory has
procedures. The first one is a correction to the asphalt appli- published several editions of a comprehensive design proce-
cation rates based on level of traffic and existing pavement dure for "surface dressing" roads in the United Kingdom
condition. The second is the justification of the shift of the (Design Guide . . . 1996). The technology that makes this
original design curve proposed by the Kearby and Benson design procedure so advanced is the extensive use of a com-
Gallaway methods, as suggested for lightweight aggregates puter design program based on decision trees (Colwill et al.
(Epps et al. 1974). 1995). Known as Road Note 39, this design procedure is
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TABLE C2
COMPARATIVE DESIGN OUTPUT FOR THE MODIFIED KEARBY AND McLEOD
CHIP SEAL DESIGN METHODS
Existing Surface Condition
Design Method Slight Bleeding Normal Slight Raveling
Nominal Aggregate Modified Modified Modified
Size Kearby McLeod Kearby McLeod Kearby McLeod
3/8 in. Emulsion 0.25 0.18 0.29 0.22 0.33 0.27
Natural Rate
Aggregate (gal/yd2)
Aggregate 21.2 17.1 21.2 17.1 21.2 17.1
Rate
(lb/yd2)
5/8 in. Emulsion 0.29 0.30 0.33 0.34 0.37 0.39
Natural Rate
Aggregate (gal/yd2)
Aggregate 24.6 25.6 24.6 25.6 24.6 25.6
Rate
(lb/yd2)
3/8 in. Emulsion 0.54 0.27 0.58 0.32 0.62 0.36
Synthetic Rate
Aggregate (gal/yd2)
Aggregate 17.1 14.0 17.1 14.0 17.1 14.0
Rate
(lb/yd2)
5/8 in. Emulsion 0.51 0.30 0.55 0.35 0.59 0.39
Synthetic Rate
Aggregate (gal/yd2)
Aggregate 14.3 18.3 14.3 18.3 14.3 18.3
Rate
(lb/yd2)
Source: Shuler 1991.
highly advanced and uses a multitude of input parameters. 5. Rate of aggregate spread--The aggregate spread rate is
Traffic level, road hardness, surface conditions, and site geom- determined based on a "tray test" and depends on the
etry are critical input factors. Skid-resistance requirements and size, shape, and relative density of the aggregate.
likely weather conditions are secondary inputs into the pro-
gram (Design Guide . . . 1996). This procedure includes the The basic inputs into the decision trees include selection
following five steps: of the type of treatment and selection of grade and type of
binder based on traffic and construction season. Table C3 is
1. Selection of the type of dressing--The selection of sur- taken from the Road Note 34 design manual and lists the
face dressing (surface treatment) is made from five design inputs used in the chip seal design software.
treatments: single dressing, pad coat plus single dress-
ing, racked-in dressing, double dressing, and sandwich The aggregate type and size are selected based on skid and
dressing. friction requirements, likely weather conditions, and hard-
2. Selection of binder--Binders are selected from either ness of existing surface. The resulting design application rate
emulsion or cutback asphalt, specified based on viscos- of binder is determined by the size and shape of aggregates,
ity. Modified binders such as polymer-modified binders nature of existing road surface, and degree of embedment of
are also recommended if their need and additional cost aggregate by traffic. The resulting design application rate of
can be justified. The grade of binder is selected based on aggregate spread rate depends on the size, shape, and relative
the road traffic category and construction season. density of the aggregate (Design Guide . . . 1996).
3. Selection of aggregate--The nominal size of aggregate is
selected based on traffic and hardness of existing surface.
Specified are 20-, 14-, 10-, 6-, and 3-mm nominal-size AUSTROADS SPRAYED SEAL DESIGN METHOD
aggregates. However, the 20-mm size is not commonly
used, owing to the risk of windshield damage. The 2004 Austroads' Sprayed Seal Design Manual provide a
4. Binder spread rate--The required rate of binder spread performance-based design method that uses an extensive list
depends on the size and shape of aggregates, nature of of input parameters for determining aggregate and binder
existing road surface, and degree of embedment of application rates. Aggregate angularity, traffic volume, road
aggregate by traffic. The rate of binder spread should geometry, ALD of aggregate, aggregate absorption, pavement
not vary by more than 10% from the target figure. absorption, and texture depth are the input variables for this
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TABLE C3
ROAD NOTE 34 OPERATIONS IN DESIGNING SURFACE DRESSING
Operation Task Section* Selection Section*
Concept Decide to surface dress 2.1
Site Type selection and Stage 1 6.2 Latitude 6.2.1
binder-spread category Altitude 6.2.2
parameters Road hardness 6.2.3
Traffic category 6.2.4
Traffic speed 6.2.5
General surface condition 6.2.6
Highway layout 6.2.7
Material selection 6.3 Skid-resistance requirements 6.3.1
Season and weather 6.3.2
conditions
Site Consider existing condition of site 7.1
Divide up site 7.1
Select type of surface dressing 7.3 Single surface dressing 2.2.1
Racked-in surface dressing 2.2.2
Double surface dressing 2.2.3
Inverted double surface 2.2.4
dressing
Sandwich surface dressing 2.2.5
High-friction surface 2.2.6
dressing
Rationalize types of surface 7.4
dressing
Material Select type of chippings 8.1 Uncoated chippings 8.1.2
Selection Lightly coated chippings 8.1.3
Artificial aggregate 8.1.7
chippings
Select size of chippings 8.2 6 mm, 10 mm, 14 mm, or
combinations
Select type of binder 9.1 Unmodified bitumen 9.1.1
emulsion, cutback bitumen
Modified binder 9.1.2
Resin binders 9.1.4
Rate of Unmodified bituminous binders
Spread Stage 1 binder-spread category 9.2.2
of Binder Stage 2 binder-spread category 9.2.4 Chipping shape 6.4.1
(from aggregate properties) Type of chipping 6.4.2
Stage 3 adjustment factors 9.2.5 Surface condition 6.5.1
(from site conditions) Gradient 6.5.2
Shade 6.5.3
Local traffic 6.5.4
Target rate of spread of binder 9.2.5
Modified bituminous binders 9.2.2
Resin binders 9.3
*Refers to paragraph in design manual that governs the specific aspect of chip seal design in that row of the table.
Source: Design Guide for Road Surface Dressings 1996.
method. The main assumption of this design model is that the cater to the texture and absorption of the pavement surface and
aggregate in a seal is orientated approximately one layer thick the aggregate. Some aggregates are susceptible to absorbing
and contains a percentage of air voids. Thus, filling a percent- binder, resulting in the decrease of effective binder and a
age of the voids with binder determines the binder application possible loss of aggregate from the seal under traffic. Adding
rate. The minimum binder application rate is determined by allowances to the basic binder application rate compensates
the percentage of voids to be filled, the total available voids, for this characteristic. The amount of binder required depends
and the thickness of the seal. on the size, shape and orientation of the aggregate particles,
embedment of aggregate into the base, texture of surface onto
The first step in the Austroads procedure is to determine a which the seal is being applied, and absorption of binder into
basic voids factor. Adjustments for aggregate characteristics either the pavement or aggregate. The geometry of the road
and anticipated traffic levels are added to derive a design voids can affect the design of a seal, and it is necessary to make
factor. That factor is then multiplied by the ALD of the aggre- adjustments to the binder application rate. Geometric factors
gate to determine the basic binder application rate. This base include narrow lanes, climbing lanes, and turning locations.
binder application rate is then modified with allowances to Where traffic is channeled into confined wheelpaths, such as
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on single-lane bridges, tight radius curves, or pavements with to stage a delay in the application of the courses, the binder
confined lane widths, a traffic adjustment factor is necessary. application rates for the additional courses are generally set at
The design binder application rate is calculated by adding all a minimum, and aggregate application rates are commonly
the allowances to the basic binder application rate. It should be reduced to 70% of conventional design. Figure C2 illustrates
noted that some of the allowances may be negative, and thus the Austroads Design Procedure for Single/Single (single
the design binder application rate may be lower than the base course) Sprayed Seals.
binder application rate.
For multiple course chip seals, the Austroads design SOUTH AFRICAN METHOD, TRH3
methodology distinguishes between whether the additional
courses are applied immediately or later. When it is planned South Africa has an extensive and well-developed chip seal
that all courses of the chip seal will be placed on the same day, program on routes with up to 50,000 equivalent vehicle units
the design is essentially the same as for a single-course treat- (Beatty et al. 2002). The South African design process for chip
ment, with a reduction in the design voids factor. Adjustments seals is based on a number of input parameters. Traffic vol-
are made for designing as a reseal, but adjustments for surface ume, preferred texture depth, and surface hardness are the pri-
texture and embedment are not performed. When it is planned mary inputs in the design process. Practical adjustments for
FIGURE C2 Austroads sprayed seal design procedure, 2000.
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climate, gradients, existing coarse texture, hot applications, The aggregate spread rate is extrapolated from design charts
preferred aggregate matrix, and use of polymer-modified based on the ALD of the aggregate and the required texture
binders are common. The approach taken by the South African depth. The South Africans have eliminated single seal design
design method, TRH3, is a hybrid of the United Kingdom and without modified binder, because they do not construct any
Australian design methodologies. The selection of surfacing is single-coarse seals without the use of a modified binder.
made between single seal with modified binders, double seals, Another important assumption of this design method is includ-
Cape seals, and sand seals. The decision is primarily based on ing correction factors to adjust binder application rates when
the traffic level and pavement condition. Of particular interest using modified binders. Polymer-modified binder application
is that this method measures and evaluates surface hardness by rates are adjusted, because the South Africans have found that
using a ball penetration test, corrected for temperature. The aggregate orientation is different in comparison with conven-
grade of binder is selected based on traffic level, road surface tional seals. The design charts shown in Figure C3 are exam-
temperature, climatic region, and aggregate condition. The ples of typical TRH3 charts, and Figure C4 is a sample design
required rate of binder spread is determined by using charts spreadsheet illustrating the application of the TRH3 chip seal
that incorporate aggregate spread rate, traffic level, and ALD. design method.
Embedment (mm)
0 0,5 1,0 1,5 2,0
0
5000
Traffic (veh/lane/day)
10000 4
15000
3
2,5
20000
25000
2
30000
35000
40000
Corrected Ball Penetration 0 - 1 mm 1,5
9mm ALD
3
Net Cold Binder (L/m2)
2.5
2
1.5
1,23 max.
1 min.
0.5
0 0.5 1 1.5 2
Embedment (mm)
Minimum Text. 1mm Text. 0.7mm Text. 0.5mm
FIGURE C3 Example of South African chip seal design charts.
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Prepared by/date:
Basic
Checked by/date:
19,0/6,7 mm
Approved by/date:
double seal design
Road / Pad (Street / Straat) : N1
Carriageway / Padbaan : Northbound and Southbound
Lane / Laan : Slow lane
From / Van : Ch. 28 500 to / na : Ch. 62 800
Seal Type / Seëltipe : 19,0/6,7mm double seal Design method / Ontwerpmetode TRH 3 1998
Binder Type / Bindmiddel Tipe : Class S-E1 modified binder (SBR type of modifier) + 30% anionic emulsion diluted 50:50
General / Algemeen
Traffic Counts / Verkeerstellings slow lane fast lane Total / Totaal
Heavy Vehicles per day / Swaarvoertuie per dag 680 170 850
Light Vehicles per day / Ligtevoertuie per dag (LV) 2 720 680 3 400
Equivalent LV per day / Ekwivalente LV per dag 29 920 7 480 37 400
Climatic Zone / Klimaatstreek 2/3 boundary
Ave Ball Penetration / Gem. Balpenetrasie (corrected) (mm) 2,57
Texture Depth / Tekstuur Diepte (Existing) (mm) 0,40
Aggregate / Aggregaat
Particulars of Aggregate / Besonderhede van Aggregaat Dark grey dolorite
Source / Bron Petra quarry, Bloemfontein
Type / Tipe dolorite, precoated @ 14 l/m3 with sacrasote 70 or similar approved
Nominal Size / Nominale Grootte 19,0mm 6,7mm
ALD / GKA (Meas. / Gemeet) (mm) 12,2mm 4,5mm
Flakiness / Platheid (%) 24.0 7,1
AIV / AIW (Dry/Droog // Wet/Nat )* (%)
ACV/AVW (Dry/Droog // Wet/Nat) * ( %) 11,7% dry : 16,8% wet 11,7% dry : 16,8% wet
FIGURE C4 South African TRH3 chip seal design method sample. (Continued on next page.)
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Data
Method used: TRH3 (Incorporating latest amendments) Ball penetration: 1,53mm
Road description: N1 Section 15: Sydenham to Glen Lyon Corrected ball penetration: T0 = 1,53 - 0,04(17-43)
(km 28,5 to 62,8) - Bloemfontein W. Bypass = 2,57mm (TMH6)
Binder: Class S-E1 (SBR modified) Sand patch length: 1,96m
Aggregate (Bottom): Precoated 19,0mm Grade 1 aggregate with Existing texture depth T = 250/(1000x0,3x1,96)
ALD = 12,2mm and Flakiness Index = 24% = 0,40mm
(Top): Precoated 6,7mm Grade 1 aggregate with
ALD = 4,5mm and Flakiness Index = 8,6%
Traffic conditions: 4 250 vehicles per day (of which 20% are heavy vehicles)
i.e. 3 400 light vehicles + 850 heavy vehicles
Assume slow lane 80% traffic, including 80% of heavy vehicles.
On slow lane: (0,8 x 3 400) + (40 x 680) = 29 920 elv/lane/day (Design for slow lane)
Design
Design texture depth: 0,7mm (Desired final texture depth)
ALD of aggregate: ALD of bottom layer + 50% of ALD of top layer
= 12,2mm + 2,25mm = 14,45mm Adjustment for modified binder: 2,03 x 0,035 = 0,07 l/m2(Fig.9,TRH3)
Embedment (from charts): 2,32mm Adjustment for existing texture: 0,14 litre/m2 (Fig.7,TRH3)
Modified embedment: 0,5 x 2,32 = 1,16mm Adjustment for climate: 2,03 x 0,01 = 0,02 l/m2 (Fig.2, TRH3)
Nett cold binder (from charts): 2,03 l/m2
* Adjustment for new asphalt: - 0,10 l/m2 (discresionary)
Adjustment for grade: Nil
2
Nett cold binder (after adjustments): 2,03 + 0,07 + 0,10 + 0,02 - 0.10 = 2,12 l/m
Control check (Alternative design Methods)
PAWC: 0,172 x 13,55 = 2,33 l/m2
F.S. Concept seal 1976 : 2,24 l/m2
Spray rates
Adjustment for hot application: 1,08 x 2,12 = 2,30 l/m2
Tack coat (hot applied): 1,15 l/m2
Penetration/Tack coat (hot applied): 1,00 l/m2
Fog spray (60% anionic, diluted 50:50) 1,00 l/m2 (Effective = 1.0*0.3*50% = 0.15l/m2)
Aggregate spread rate:
19,0mm aggregate: 70 m2/m3 (Fig.F-1, TRH3)
6,7mm aggregate (Applied in two layers): 110 m2/m3
2 3
Layer 1 : 450 m /m as choke layer
Layer 2 : + 155 m2/m3 as top layer on double seal and as single seal on sides
(Fig.F-1, TRH3)
FIGURE C4 (Continued).
