Mapping Temperature Zone of Ethiopia for Binder Performance Grading System
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Date
2018-03
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
AAU
Abstract
Ethiopia is located near to the equator and climatic condition varies from hot-dry-arid regions to
tropical rain forest. Seasonal temperature fluctuation is very high in some parts of the country.
Hence, temperature and loading time susceptible construction material such as asphalt binder
should assign by considering environmental temperature range and traffic condition.
The first challenge, concerning binder-assigning process in Ethiopia, is prediction of pavement
temperature. In developed countries, pavement temperature is obtained from air temperature using
SHRP temperature conversion algorithm that accounts all heat-flow-balance in both fluids and
solid material. In Ethiopia, it is subjected to the engineer detailed knowledge of project location
and the parameters to be considered with. The second challenge is the test and specifications used
by highway agencies. The current conventional method is empirical and failed to predict how the
binder perform under a wide range of temperature. Therefore, the aim of this study was to provide
a temperature zone map based on predicted pavement temperature and evaluate currently utilized
asphalt binder by rheological test methods.
20 years’ air temperature data for 27 locations are obtained from Ethiopian National
Meteorological Agency to develop the temperature zone map while primary data of pen-grade
40/50, 60/70 and 80/100 binders are collected using conventional and rheological taste methods.
The samples are obtained from ECWC, CCCC and AACRA ongoing road project. Dynamic Shear
Rheometer and Elcometer-2300 rotational viscometer is available in Addis Ababa University. The
first was used to conduct Amplitude and Frequency sweep test at intermediate temperature and
Performance grade determination and Multiple Stress Creep and Recovery test at highest pavement
temperature; and the later was used to determine viscosity at 60
o
C, 135
o
C and 165
o
C.
The performance Grade temperature zone map is developed by converting 20 years’ air
temperature data to pavement temperature using SHRP temperature conversion model at 20mm
depth of the pavement with 98% reliability. The map divided Ethiopian temperature zone into five
main PG-grade counties and most of the areas are dominated by PG58-YY and PG64-YY. On the
other hand, the result from rheological tests indicate that PG determination parameter G*/sinδ is
failed to provide clear distinction between penetration graded binders and categorize both 40/50
and 60/70 as PG 64-YY. Hence, Multiple Stress Creep and Recovery test parameter, Nonrecoverable
Compliance
(J
nr
), are used to provide better ranking on the performance of the binders. Based on J
nr
iv
values, the samples are graded with traffic load designation beside, indicating the
Equivalent Standard Axle Load it can support. Pen-grade 40/50 is designated as PG 52E-YY at
52
o
C, PG 58V-YY at 58
o
C and PG 64S-YY at 64
o
C.
Even though, penetration grade 40/50 have better stiffness and J
nr
value , low-land areas such as
Afar, Gambela and Benshanguil-Gumuz PG category indicate that road projects at these locations
require modified binder; even for standard traffic load. Penetration grade 80/100 and 60/70 are
graded as PG 58S-YY and PG 64S-YY respectively. However, pen-grade 60/70 J
nr
value at 64
o
C
is close to the margin 4kPa
-1
, indicating the risk of using the binder for potentially developing
cities and trade corridors such as Metehara and Metema.
Description
Keywords
Superpave, Temperature zoning, Performance Grade