Chapter IV Design

Chapter IV

Design

4.1 General

Various formulae are developed in different countries to calculate the rate of application for binder & chipping. Two methods are discussed in this chapter for a general guide to surface dressing work. One method is referred from “surface dressing” by G.P Jackson (Published by bitumen division shell international petroleum Co. Ltd. London.) & another from special provision by N.D.Lea. &  Associates Ltd. Canada for this project. In surface dressing work, however much depends on the local condition. Therefore the engineer in-charge of the project should make the suitable adjustment in view of his local knowledge. At the construction stage the actual material to be used should be available for the tests required by the design method. After the test the engineer can calculate the final design value & the exact proportioning of the materials involved. The method of design here is based on the following principles.

a)       When a single size particle is dropped from a spreader to a binder on the road, the particles lie in an unarranged position & the voids between them will be approximately 50 percent ( See Fig) 

b)       After rolling the particles are reoriented & the voids between them will be reduced to 30%.

c)       Finally after appreciable compaction by the traffic, the aggregates are packed to their densest position. The voids at the stage can be as low as 20% (See Fig)

Since the aggregate particles lie on their flattest side, the average thickness mat is average of their least dimension.  This is known as "AVERAGE LEAST DIMENSION" (A.L.D) of the cover aggregate measured in inches or in millimeter. Hence it is A.L.D. one is interested to calculate the rate of application both for binder & chipping.

4.2 Determination of A.L.D. (Average least dimension) of Chipping for surface dressing (Samples are collected in H.N.H.P.)

a)       Sieve Analysis: Sieve analysis are conducted from the stock of materials of H.N.H.P. (Approx. 7 Nos.) for 500 meter of road & the average grading curve is plotted on the chart of surface Dressing grading curve (see the chart for sieve analysis & surface dressing grading curve in Appendix Page 2 and 3.)

b)       Median Size: The medium size of chipping is that the theoretical size through which 50% of the material will pass (See surface dressing grading curve in Appendix Page 17)

c)       Flakiness Index: The flakiness indexes is the total weight of material passing in the appropriate gauges express as a percentage of the combined weight of fractions tested.

FLAKINESS INDEX TEST.

Sieve Size	Slot Size	Wt Retained Gram	Wt Passing Gram	Total Gram	Flakiness Index
¾" - 1/2"	0.375	1002	198	1200	16.5%
3/8" - ¼"	0.188	1241	219	1460	17%

 

SIZES OF SLOTS FOR EACH FRACTION

Size of Material	Slot Width	Slot Length
Passing 1 in retained ¾	0.525 in	2.5 in
Passing ¾ in retained ½	0.375 in	2 in
Passing ½ in retained 3/8	0.263 in	1.5 in
Passing 3/8 in retained ¼	0.188 in	1 in

Finally by use of chart (See A.L.D. Chart) the A.L.D. for ¾ inch (20mm) & 3/8 inch (10mm) aggregates are determined. The median size 0.59 inch on line A is joined to the flakiness index 16.50 % on line C & the A.L.D. read off on line B= 0.432 inch (10.97mm). Similarly the median size 0.295 inch of 3/8 inch aggregate on line A is Joined to the flakiness index 17% on line c, & the A.L.D. read off on line B = 0.225 inch (5.72mm)

4.3 First Method of Design

Once the A.L.D. of the aggregate is determined, Mr. G.P. Jackson in his book “Surface dressing” has considered the different constants for different conditions to know the binder application rate in the following tables.

TRAFFIC	VEHICLES/DAY		CONSTANT
Very Light	0-100		+3
Light	100-500		+1
Median	500-1000		0
Median heavy	1000-3000		-1
Heavy	3000-6000		-3
Very heavy	6000+		-5
EXISTING SURFACE
Untreated / Primed base		+6
Very lean Bituminous		+4
Lean Bituminous		0
Average Bituminous		-1
Very  Rich Bituminous		-3

TYPES OF CHIPPING	CONSTANT
Round / Dusty	+2
Cubical	0
Flaky	-2
Pre-coated	-2

CLIMATE CONDITION	CONSTANT
Wet & Cold	+2
Wet & hot (Tropical)	+1
Temperate	0
Semi-arid (dry & hot)	-1
Arid (Very dry & very hot)	-2

The various constants can be obtained according to the suitable conditions for this project. These consideration are considered arithmetically form which is determined an over hall factor figure indicating the particular factor line on the chart to be used. This is illustrated in the following example.

A.L.D. of Chipping: - 0.432 inch (10.97) for ¾ inch aggregate (Bottom layer) & A.L.D. for top layer 3/8 inch aggregate =0.225 inch (5.72)

CONDITION	CONSTANT
Traffic -light (100-500 veh/day)	+1
Existing surface untreated/ Primed base	+6
Type of chipping - Cubical	0
climatic condition - Tropical	+1
Total over hall factor	+8

Note: The rate of application of chippings at the top horizontal scale in kg/m2 with 10% whip off is based on the loose density of chippings of 1.62. Alternatively the rate of application of chippings can be calculated by tightly packing the chippings on the tray of known area which is then weighed with at least ten repetitions and addition of 10% for whip off.

Aggregate Application Rate:

Reference should now be made to the chart (See fig. for "surface dressing chart") to determine the rate of application for chipping read across from the appropriate A.L.D. in this case 10.97 mm (For bottom layer of surface treatment) on the vertical scale to where it interest the single diagonal line A.B. & then read up to the top horizontal scale which gives the application rate 17.77 kg. Per m². Similarly for A.L.D. of 5.72 mm (For top layer of surface treatment can be determined i.e. 9.27 Kg/ m²

Binder Application Rate:

For binder application rate read across again from the A.L.D. of 10.97mm (For bottom layer) to where it intersects the appropriate factor line, in this case +8, & from there read down the bottom scale which gives the rate required i.e. 1.32 Lit/ m². Similarly for A.L.D. of 5.72 mm (For top layer) can be determined i.e. 1.08 lit/ m².

Total Chipping Rate:

a) For bottom layer (3/4 inch aggregate)                        =              17.77 Kg/m²

b) For top layer (3/8 inch aggregate)                               =              9.27 Kg/m²

                                                Total Kg/ m²          =              27.04 kg/m²

Total Binder Application Rate:

a) For bottom layer              =              1.32 Lit/ m²

b) For top layer                    =              1.08 Lit/ m²

Total Kg/ m²                          =              2.40 Lit/ m²

It should be noted that these scales refer to the case of a medium cutback i.e. Mc/Rc.4, Mc./Rc.5. If a lighter cutback Rc.2 or an emulsion is to be used then the quantity of binder is to be increase slightly by 0.10 Kg/ m²& on the other hand the quantity required should be reduced by about 0.10 Kg/ m², if a penetration bitumen is to be used.

4.4 Second Method of Design Application rate

The design application rate for D.B.S.T. (Double Bitumen Surface Treatment) in H.N.H.P. is based on the formulae in the. Special provision prepared by ND Lea & Associated ltd. For this project is as follows.

a)       Aggregate application rate: - A preliminary value of aggregate quantity to provide for a thickness equal to the average least size dimension with 20% voids is as follows.

A (Kg/ m²=08F.G.H

        Where F = wastage factor  + 1.02 for ¾ inch aggregate & 1.07 for 3/8 inches aggregate.

G = Bulk Specific gravity (A.S.T.M. test method c127-68)

H= Average least size dimension in mm.

The above equation assumes voids in the loose aggregate to be 50%. Control tests shall be carried to determine the loose density according to A.S.T.M. C29-69 & Loose voids content is determined as follow: -

V= 1 – J /G

     

Where: -

V is loose voids content

J is loose unit weight (T/M³)              = 1.62 Ton /m³

G is Bulk specific gravity                    = 2.62

 : V =  1-1.62/2.62                                =0.382. %

Then the final design aggregate quantity is calculated as follow: -

A (Kg./m²) = (1-0.4V) F.G.H.

Or A = (1-0.4x0.382) 1.02x2.62x10.97 = 24.83 kg/M² for bottom layer.

In the same way the quantity for 3/8 inch (top layer) can be calculate as follow: -

A (Kg/ m²) = (1-0.4v) F.G.H. or A = (1-0.4x0.382) 1.07 x 2.62 x 5.72 = 13.628Kg/m².

Total for both layer = 24.83 +13.28 = 38.11 kg/ m²

B) Bitumen application rate: - The theoretical bitumen application rates for each layer to embed the aggregate to about 70% of its average least size dimension can be determined from the following formulae.

B (Lit/ m²) = 0.4 H.T.V.      + S 

                             R

B = Theoretical (cold 60 Degree F) Bitumen application rate for each layer.

Where: -

T is traffic factor = 0.75 (See table of traffic factor for different volume of traffic)

R is residual value of bitumen: - 0.85 as per the test (See the table of test result of bitumen in chart II)

S             = Surface texture correction for first layer only.

                = -0.1 to -0.3 Lit/ m²for black flushing surface.

                = Nil for smooth surface, good priming.

                = +0.1 to +0.3 lit/ m²for hungry & rough surface.

Bitumen for first layer "B”                    = 0.4 H.T.V.     +S

                                                                        R

0.4x10.97x0.75x0.382  +  0               =1.48 Lit/ m²

                     0.85

Bitumen for second layer "B"             = 0.4 H.T.V.    +S

                                                                         R

= 0.4x5.72x0.75x0.382 +0                 =0.77 Lit/ m²

                   0.85

Total for both layer = 1.48 +0.77      = 2.25 Lit /m²

It should be noted that traffic factor of different volume of vehicles per day for different type of aggregate to fill the percentage of theoretical voids is as follows (Surface condition smooth)

Traffic flow Veh/ day	Type of Aggregate
	Good Type	Rounded
<50	90	95
50-150	85	90
150-250	80	85
250-500	75	80
500-1000	70	80
1000-2000	65	75
>2000	60	75

4.5 Comparison of above two Methods

Aggregate application rate for -3/4 inch.:

1)       From the first method                          = 17.77 kg/ m²

2)       From the second method                   = 24.83 kg/ m²

Diff          = 7.04kg/ m²

For 3/8 inch aggregate:

1)       From the first Method                          = 9.27 Kg/m²

2)       From t1he second method                                = 13.28 Kg/m²

    Diff              = 4.01 Kg/m²

b.) For Bitumen application rate for 3/4 inch

1)       From the first method                          = 1.32 Lit/ m²

2)       From the second method                   = 1.48 Lit/ m²

Diff          = 0.16 Lit/M2

For the Second Layer:

From the first method                                          = 1.08Lit/ m²

From the second method                                  = 0.77Lit/ m²

Diff          = 0.31Lit/M2

Total Combined Rate for Both the Layers:

a)                   For Aggregate :-

1.                   From the first method          =              27.04 kg/ m²

2.                   From second method         =              38.11 kg/ m²

                                                        Diff          =              11.07 kg/ m²

b)                   For Bitumen :-

1.                   From the first method          =              2.40Lit/ m²

2.                   From second method         =              2.25Lit/ m²

                                                        Diff          =              0.15 Lit/ m²

Rate of application fixed for H.N.H.P. is as follows

For Aggregate in kg/m2:

1)    For the first layer      =         20.40 kg/ m²including 2% wastage

2)    For second layer       =        10.20 kg/ m²including 7% wastage

                             Total         =    30.6 kg/ m²

For Binder Mc 4:

1.) For the first layer            =            1.00 Lit/ m²

2.) For second layer           =             1.25 Lit/ m²

                        Total       =             2.25 Lit/ m²

The special provisions prepared by N.D. Lea. & Associates for this project are as follows.

For Aggregate

This design quantity shall be checked by tightly packing the aggregate one stone thick on a sample tray & by field trial.

                                                                                                                     

For Binder Application Rate

For double surface treatment, the theoretical bitumen quantities for each layer shall be added together & converted to hot rates at the spraying temperature (See table for the volume correction factor) 

For warm season construction 60% of the combined rate shall be applied for the first layer & 40% for the second layer and for cool season construction 50% of the combined rate shall be applied for the first layer & 50% for the second layer.

If we fix the rate for binder from the above method, the binder application rate will be as follow:

Theoretical combined rate: - 2.25 Lit/m²

The rate of application for warm season will be 1.35 lit/m² for the first layer & 0.90 Lit/m2 for second layer & for cool season, the application rate shall be 1.125 Lit/m² for each layer.

Field Trail

a)          For aggregate: - Several tests are conducted in the laboratory of this project by tightly packing one stone thick aggregate on a sample tray (0.5 m x0.5m) for ¾ inch & 3/8 inch aggregate separately. It has been observed from the test in an average of 20-kg/ m²& 9.35 kg/m² for 3/4 inch & 3/8 inch aggregate respectively. In this way the rate for both layer were fixed as follows.

1)    For 3/4 inch aggregate including 2% wastage  =20.4 kg/ m²

2)    For 3/8 inch aggregate including 7% wastage =10.2 kg/ m²

Spread ratio "S" for aggregate in m²/m³ or m³/m² can be calculated from the following equation applied for this project only: -

S (m²/m³) = 869 or s (m³/m²) =A.L.D.

                                       ALD                 869

(B) For Bitumen

According to the asphalt surface treatment and Asphalt Penetration Macadam Manual, the asphalt institute manual series no 13 (MS 13) in Pg. no 21, the first application of asphalt usually amounts to 40% of the total asphalt and the second application of asphalt usually amounts to 60% of the total amount.

According to the above method some trials were conducted in the Tintapke camp in different speed of distributor (Bitumen) to get the different rate of application & these rates were checked by laying a metal tray of      0.30m x 0.30m size & by passing the distributor over it. Then the tray was lifted carefully & it was weighted properly to find out the spread rate in a certain speed of distributor. The speed of distributor & height of the spray bar from the ground (The height from the ground to the center of spray bar is 0.38m) was noted for the different rates applied. These application rates were checked by dipstick also.

About five trials were conducted on the road in different rates. The present rates fixed for the binder was found most suitable for this project (1 Lit/m2 for the bottom layer & 1.25 Lit/m2 for the top layer.)