May_1967 — Page 33

occurred during construction owing to bad weather. It was, however, decid- ed to construct a working course in stabilized soil under the chosen pave-

ments.

Conventional flexible pavements with crushed stone bases were not adopted on account of the difficulties attached to providing the enormous quantities of stone required for pave- ments up to 28 in, thick and the de- lays in construction which would have occurred in bad weather. A concrete pavement was also considered but was not adopted largely on the grounds of cost. Typical depths of construction adopted for the aircraft pavements and internal roads are shown in Fig. 2.

In adopting a bituminous form of construction for the aircraft pave- ments and in particular for the park- ing aprons it was realized that they would be subject to damage by fuel. and experiments were carried out with epoxy compounds to assess the degree of protection which would be provided by a surface dressing with this form of binder. The results of the tests showed that an adequate form of protection would be given and that the main disadvantage of a bituminous pavement could be over-

come.

In estimating the depth of pave- ment required for an 1.c.n. of 100 on a subgrade CBR of 10%, reference was made to the curves produced by Burmister. The assumptions made for a flexible pavement with a conven- tional granular base gave rise to a total thickness of approximately 27 in. from the Burmister curves, which agreed fairly well with the thickness obtained from the more usual I.c.n.. CBR curves, whereas for the deep bitumen construction it was estimated from the curves that a thickness of approximately 16 in. only would be required for the same 1.c.n. CBR con- ditions.

This form of construction was there-

Sample grouping

Sample description

Sample classification Group index in brackets

(AASHO)

1

Yellow sandy silty clay

2

Yellow sandy silty clay with red mottling

3

Yellow with red mottling or multi- coloured sandy clayey silt

A

Coarse sand

D

Fine sand

A-6 and A-7

(1-19)

A-7

(1-19)

A-7

A-1 and A-3

A-2-4

(L- 19)

(0)

(0)

Particle size distribution

Passing B.S. No. 7 sieve *„

Passing B.S. No. 36 sieve 5,

Passing B.S. No. 200 sieve %

Sili (0-06 nm-0-002 mm) 71.

Clay (<0-002 mm) X

Atterberg tests

70-100

75 100

95. 100

60-100

90-100

40-90

40-90

55.90

5-55

36-90

36.70

36-70

16-70

1-10

10-20

5-30

5-55

35-60

Not tested

Not tested

25-60

10-50

5.20

Not tested

Not tested

Liquid limit *

Plastic limit

Plasticity index

Type of compaction

Maximum dry density ib,ew.fi

Optimum moisture content *%

x 100

silt silt+clay.

35-100

45-105

40.70

25 48

25 48

30 45

10 50

10-62

$ 30

TT

N.P.

-

N.P.

B.S. heavy Proctor B.S. heavy Proctor B.S. heavy Proctor B.S. heavy Proctor B.S. heavy | Proctor

97-114

85-107

H4 26

18 31

100-112 93-99

14-24 20-24

100 103

11 19

96

119-127

20

6-11

8 to 36

14 to 69

70 to 85

Table 1. Summary of general soil properties

fore decided upon, but the construc- tion of a trial area for testing before construction of the main pavements was included in the specification.

Specifications for the bituminous materials were:

(a) Dense rolled asphalt wearing

course (Marshall method) Aggregate: coarse.

For runway and taxiways: granite or crush- ed gravel

For other paved areas: rock or

crushed gravel

fine: rock or sand

Binder Type: straight run bitu- men 80 100 penetration, or straight run bitumen 60 70 penetration

Compacted thickness of wearing

course: 11⁄21⁄2 in.

Design requirements

(i) stability: as determined by test but not less than 1800

113-119

6-14

lb. and preferably of the order of 2500 lb.

(ii)

flow: not more than 0.16 in.

(iii)

voids in total mix: 3% to 5%

(iv)

voids filled with binder: 75% to 85%

or base

(b) Rolled asphalt binder or

course (Marshall method) Aggregate: coarse: rock or crush-

ed gravel

fine: rock or sand

Binder Type: straight run bitu- men 80 100 penetration, or straight run bitumen 60/70 penetration

Compacted thickness of binder or

base course: 21⁄2 in. Design requirements

(i) stability: as determined by test but not less than 1800 lb. and preferably of the order of 2500 lb.

(ii) flow: not more than 0.16 in.

#7p3

Ftrimmed

Perimeter road

Edge

trimmed

Shoulder

Taxiways and parking aprons

Shoulder

-3′0′′

White topping

Runway

Taxiways and parking apron to private hangars

12" x 16",

12" x 8"

Flush kerb

Flush kerb

פר

ठ

Fig. 2. Details of pavement construction

Far East Architect & Builder May, 1967

Wearing course

*

Binder course --

Base course Lime-soil slab

KEY

To schedule I of part IV of specification To schedule il of part IV of specification To schedule III of part IV of specification As part Ill of specification

Concrete as part V of specification

-3'0"

White topping

Internal roads

| 12′′ x 8′′,

Flush kerb

57