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