Environmental Engineering Reference
In-Depth Information
inefficiency when the cGa layer is spread on the
existing pavement is related to the reduced bearing-
capacity of the latter due to the ageing.
as a result, the importance of achieving ade-
quate stiffness of every down-up compacted gran-
ular course has been reflected in this study. When
a granular layer is built on an existing pavement,
previous testing (plate load test, FWD) should be
performed in order to assure sufficient stiffness of
its support. Figure 9 summarizes the empirical cor-
relation between effective stiffness of the support
(from FWD) and relative compaction of the granu-
lar base, found in this field experimental research.
Experimental test section: CGA on existing aged asphalt
pavement.
40 kN applied load
100
90
80
85th Pe rcentile = 79
70
Mean value = 71
60
50
40
30
20
10
0
Station
Experimental test section: CGA on new subgrade of lapilli.
40 kN applied load
180
4
conclUsions
160
85th Pe rcentile = 144
140
Mean value = 130
120
Variability of geotechnical properties of granu-
lar aggregates resulting from volcanic rocks is
generally more significant than with non-volcanic
materials, thus manufacturing and reception con-
trol should be more intensive. however, laboratory
test results have revealed that it is possible to attain
with them satisfactory adjustment to grading and
allowable tolerances of different specifications in
europe, provided that an optimum regularity of
the product can be assured with the production
and stockpiling control. in this way, they can be
employed in road structural courses even with
heavy traffic conditions.
Moreover, field experiences have confirmed that,
in general, a good densification can be achieved
with them if a continuous grading curve is obtained
(Maximum dry unit weight: 21.6 to 23.0 kn/m
3
;
optimum moisture content: 6 to 11%). Grading
modification caused by field compaction has not
produced increasing of fine aggregate fraction
upper to 1.5%, with improvement in flakiness and
elongation indexes of coarse aggregate.
Despite of some previous experiences in relation
to their greater insensitivity to water content vari-
ation during compaction, laboratory test results
and data compiling of similar materials from sev-
eral atlantic volcanic regions have confirmed that
conventional compaction tests and criteria can be
also applied to volcanic materials. it is interesting
to note, however, that moisture directly measured
on the compacted lift underestimates the effec-
tively participant water content in the compaction
process owing to their high permeability.
Plate loading tests can contribute to a better
control of the in-situ performance as they allow
verifying the stiffness of the compacted layer. expe-
rience with volcanic materials from canary islands
indicates that, generally, the spanish specification
related to the allowable limit of the plate load test
k-coefficient (k = e
V2
/e
V1
) results achievable with
100
80
60
40
20
0
Station
Figure 8. effective Moduli of the cGa base course
foundation, backcalculated from FWD tests (40 kn
applied load).
Relative compaction vs. CGA base course
foundation stiffness
100,0
99,0
98,0
97,0
ER (50th percentile). 20 kN applied load.
ER (85th percentile). 20 kN applied load.
ER (50th percentile). 40 kN applied load.
ER (85th percentile). 40 kN applied load.
96,0
95,0
94,0
60
80
100
120
140
160
Effective Modulus of the support, ER
(MPa)
Figure 9. empirical relationship of effective Modulus
(of the foundation, obtained from FWD) versus granular
base relative compaction.
aged asphalt pavement has resulted significantly
reduced compared with that on a new roadbed
structure (including native ground excavation,
fills and subgrade construction with lapilli), with
reductions up to 45%. The interpretation for this
could probably be the advanced distress of the
existing pavement structure, causing dissipation
of the compaction energy without increasing the
rate of densification of the new granular base
course. consequently, the observed compaction
