Evaluation of Sand-Bitumen Mix and Rubber Membrane Joint Sealants for Ongoing Rigid Pavements in Ethiopia: Case of Ditchoto Galafi Concrete Road Project
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Date
2022-06
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Addis Ababa University
Abstract
As a part of its Road Sector Development Program (RSDP), the government of Ethiopia has been
investing a significant amount of money in constructing different surface type roads. And, due to its
higher life span, low maintenance and operation cost, rigid pavements (cement concrete surface types)
have been emerging as the preferred pavement type to be constructed in high-temperature areas like
the eastern part of Ethiopia, where there are 195.5km long ongoing rigid road projects including the
case study project. In rigid pavement construction, space (joint) provided for the concrete pavement
slabs was a solution given to the slabs so that they could be able to expand and contract during hot
and cold temperatures until incompressible materials intrude between slabs and water infiltrating the
subgrade was proved problems. Hence, to mitigate the detrimental effects of such intrusions on the
performance and service life of the pavement, sealing the slab joints with sealants has become
imperative. In connection with rigid pavement joint sealing practices in Ethiopia, the case study
project, unlike the other three similar ongoing road projects in Ethiopia and the trends followed
worldwide, has utilized a sand-bitumen mix in place of the renowned silicone joint sealants. Hence, in
this research, comparative assessments on different joint sealant types (sand-bitumen mix and rubber)
to replace silicone joint sealant were done. Accordingly, starting from the mix design of sand-bitumen
mix with varied proportions (20/80, 25/75 and 30/70) and rubber membrane in Horizon Addis Tire
laboratory, physical-mechanical properties of both sealants were evaluated in the laboratory as per
ASTM standard test method. In addition, field observation was made on the case study project. As the
result, unlike the sand-bitumen mix sealant which has failed all the envisaged physical and mechanical
tests, the rubber membrane has exhibited incredible resistance to oil, UV, heat and abrasion.
Furthermore, the rubber membrane attained an elongation, tensile, adhesion and cohesion strength,
22.2%, 7.4%, 140% and 229.2% higher than the requirement in the respective order whilst the
measured hardness and compression sets were within the permissible range. Additionally, during the
field observation of the case study project, different types of joint sealant failures at different severity
levels (medium =75%) and (low =25%) were detected. Also, initial and maintenance cost comparisons
made between the three sealants revealed that application of silicone sealant to seal the joints costs
almost 200% and 1572% more than rubber membrane and Sand-Bitumen joint sealant in their
respective order. Therefore, this research concluded that, from the alternative sealants, rubber
membrane has endowed potential to replace the renowned silicon sealant. In addition, in this research,
based on the scope and limitations of this research, recommendations were made.
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Keywords
Rigid Pavement, Joint Sealant, Sand-Bitumen Mix, Rubber Membrane, Silicone Sealant