Method for Increasing the Use of Locally Available Materials for Road Construction in Ethiopia by Allowing for Climatic Variations

Despite evidence that the environment is a major factor in the performance of pavements with natural gravel road bases, this finding is rarely used fully in road design. Conventional design standards and specifications do not allow optimal use of local materials such as weathered basalt, cinder gravels, and laterites in low-volume road construction. Significant regional variations in climate are common in many African countries, including Ethiopia. This variation may provide opportunities, especially in drier areas and on well-drained soils, to relax national specifications, enhance use of local materials, and reduce construction costs. These are important factors that influence the provision of rural roads in Ethiopia. A range of naturally occurring materials was tested to determine their properties, particularly the relationship between strength (California bearing ratio) and moisture content. The samples tested included materials not currently considered suitable for road base and surfacing in Ethiopia. These road sections are being monitored to understand their behavior under local climatic conditions. Sections have been constructed in cut and fill and with sealed and unsealed shoulders. All materials showed higher strengths at lower moisture contents; but the strength–moisture relationships differed significantly for the different materials and for the same material at different compaction densities. The approaches developed for laboratory testing, together with evidence from ongoing and future trials, will enable Ethiopia to modify its national standards and specifications. Ethiopia will then be able to safely utilize the benefits of local variations in climate and pavement environment and increase the use of naturally occurring materials, thereby reducing construction costs by 45% to 60%.