Environmental Engineering Reference
In-Depth Information
construction experiences with volcanic unbound aggregates
in road pavements
M.a. Franesqui
Department of Civil Engineeing, University of Las Palmas de Gran Canaria, Las Palmas, Spain
F. castelo Branco
Department of Earth Sciences, University of Coimbra, Coimbra, Portugal
M.c. azevedo
Civil Engineering Faculty, Catholic University of Portugal, Lisbon, Portugal
P. Moita
Marques SA, Ribeira Grande, Azores, Portugal
aBsTRacT: This experimental research discusses the performance of crushed granular materials
resulting from volcanic rocks employed in the construction of subgrades and continuous grading unbound
aggregate road base courses. some frequent doubts related to their suitability for the aforementioned use,
to their observance of the technical specifications of different countries, and to the methodology and cri-
teria to control field compaction and bearing capacity are intended to be clarified. For this purpose some
experiences of several atlantic islands (azores, canary islands, cape Verde, iceland) are compiled and
additional recommendations are contributed for volcanic aggregates as those of canaries or azores. The
experimental results reveal that it is possible to reach a good load-carrying capacity with these granular
materials, and also that conventional tests can be used. The in-situ study has allowed us to obtain the rate
of compaction as a function of the effective Modulus of the base course foundation.
1
inTRoDUcTion
pyroclastic materials, and finally spreading the
unbound crushed aggregate as base course for
the bituminous pavement.
- Directly on an existing pavement (after scarii-
cation and re-compaction) composed of half-
penetration macadam (an obsolete traditional
technique) on a subgrade formed of lapilli.
initially, 12 trial road sections were built with
the same type and origin of crushed all-in aggre-
gate, varying the densification procedure (number
of roller passes, layer thickness, base course foun-
dation conditions and compaction equipment) in
order to establish the most suitable construction
procedure.
The regional road administration had ques-
tioned the observance of Portuguese and spanish
road standard specifications for the local basaltic
crushed materials, related to particle size distribu-
tion and to the utilization of the Modified Proctor
test as the reference test to control field compaction,
due to the possibility of not being strictly applied
to volcanic aggregates such as basalts because of
their greater insensitivity to moisture content vari-
ations. in addition, during the construction of the
Continuous grading aggregates (CGA)
, from vol-
canic pyroclastic deposits or from mechanically or
natural crushed volcanic rocks such as basalts or
phonolites, are typically applied to the construc-
tion of road subgrades and unbound granular
subbase and base courses in volcanic regions. This
work focuses on an experimental study carried out
in a local road in azores (Portugal) related to the
construction of an unbound base course with a
basaltic crushed all-in aggregate.
The construction project planned to build the
untreated aggregate base on two different founda-
tions along the road alignment:
- on a new subgrade constructed with
lapilli
(nat-
ural granular material from low density basaltic
pyroclasts). This is also a characteristic porous
granular material used in these volcanic regions,
composed of a particle-size range from 2 mm to
64 mm. according to the project in these road
sections, it was planned to construct a new road-
bed structure including native ground excava-
tion, fills and subgrade construction with these
