Effects of geogrid on reduction of reflection cracking in asphalt overlays

Abstract

During this experimental study, a biaxial geogrid material, Hatelit C40/17, having a tensile strength of 50 kN/m2 in both directions and having dimensions of 3 m (width) X 100 m (length) was used as asphalt reinforcement during an overlay construction in Addis Ababa. Three sites, designated in this research as National Theatre 1, National Theatre 2 and Gandhi Hospital were selected for conducting the research. The geogrid material was laid at the bottom of the overlay sandwiched between two layers of tack coats on 07/04/2015 at the National Theatre sites and on 08/05/2015 at Gandhi Hospital site. Longitudinal and transverse directions of reinforcement were carried out to study the effect of direction of installation. A control section was left unreinforced to observe the difference in performance between reinforced and unreinforced sections of the pavement. The National Theatre 1 and 2 sites were characterized by the wide reflection cracks and high traffic volume they accommodate. However the Gandhi Hospital site was mainly a demonstration site on how to install the Geogrid material during an overlay construction. A manual traffic volume count was also conducted to estimate the number of Equivalent Single Axle Loads (ESALs) the road sections were subjected to during the 8 months of study period. The information collected from the traffic volume count reveals that the National Theatre 1 site was subjected to 4.1 Million ESALs and the National Theater 2 site was subjected to 3.1 Million ESALs during the study period. As the main purpose of this experiment was to study how effective geogrid materials are in mitigating reflection cracks in Asphalt Overlays in Ethiopia, the difference in performance between the reinforced and control sections of the sample roads was evaluated. After duration of 8 months marked difference was observed at the National Theatre 1 site. The width of a major crack was compared with the original width of cracks (prior to geogrid reinforcement) and with the control section. At the National Theatre 1 site, 33.3% of the original crack width was reflected to the surface at the control section whereas 0% of the original crack width appeared to the surface at the reinforced section during the study period of 8 months. The National Theatre 2 site was used to experiment the effect of direction of installation. A transverse direction of installation resulted in 41.2% of the original crack width to appear on both the control and reinforced parts of the road. At the end of the study period, it was found that the longitudinal direction of installation could efficiently mitigate reflection cracking from appearing to the surface whereas the transverse direction of installation did not contribute in arresting reflection cracks. As the other purpose of the research is to introduce the use of geogrid material in asphalt overlay works, a presentation on Geogrids and their applications in the construction industry was held at Gihon Hotel, Addis Ababa. A demonstration on how to install Geogrid material during an overlay construction was also conducted at Gandhi Hospital site as part of the workshop organized by The Construction Project Management Institute of Ethiopia and Ministry of Science and Technology.