Efficient use of marginal road materials for low volume roads in Tanzania

Poor performance of marginal materials in low volume roads (LVRs) and the traditional material specifications for LVRs in Tanzania have been challenged due to the prevailing problems of mobility, sustainability and environmental degradation. In order to address this, improved techniques of material testing, design and construction have been used to explore the potentials of marginal materials for construction of LVRs in Tanzania. Environmentally Optimised Design (EOD) method was adopted for design of research programme on the case study roads of Bago - Talawanda in Bagamoyo District and Lawate - Kibong'oto in Siha District. Monitoring was done for 44 months from 2011 to 2015. Insitu strength, gravel loss, texture depth and binder aging were monitored. Procedures for determining refusal density and DN parameter for selection of marginal material have been established. Based on the performance trends, compaction to refusal has reduced gravel loss (GL) from 60 mm to 16 mm per year, maintained the insitu strength, DN, at average value of 7 mm/blow and increased CBR from 35 - 50 % for the tested material. The obtained DN and GL comply with the specified maximum DN of 9 mm/blow and GL of 10-20 mm/yr for a good to satisfactory performing gravel layer. Further, the use of pumice in marginal material has increased strength (CBR). Therefore the study shows that with improved testing methods, construction and appropriate specifications, marginal materials can be used better in Tanzania. It is recommended that appropriate manual be developed for design and construction of LVRs in Tanzania.