The appropriate material specifications and manual are key for effective gravel roads design, construction and maintenance practice

Abstract

It is a matter of fact that the gravel road network dominates as the mode of transport infrastructure in most of sub-Sahara Africa. These roads comprise a huge national asset that requires adherence to appropriate locally formulated Pavements and Materials Design Manual (PMDM) and Standard Specification for Road Works (SSRWs) in order for them to give satisfactory performance during their design life. As the length of the engineered gravel road network is steadily growing in Tanzania and elsewhere in sub-Sahara Africa, appropriate PMDM and SSRWs to be employed during design, construction and upkeep of this investment becomes increasingly important for optimal use of locally available gravel materials. In response to the above call, a number of sub-Sahara Africa countries, Tanzania included, has in place PMDM and SSRWs, which are being used during the design and construction of new gravel roads and also during maintenance and rehabilitation of existing gravel roads. These PMDM and SSRWs are used in order not only to standardize design practices and quality control during the design, construction and maintenance period, but also to be able to predict the performance of gravel roads. For these PMDM and SSRWs to be effective and dynamic they have to address local condition and after a certain period of time are to be revised so as to capture changes which are constantly occurring in the gravel road construction industry. The intention is that eventually it should be obligatory to observe the PMDM and SSRWs during design, construction, and maintenance of gravel roads, as they will carry with them the practical experience of over extensive period of time to be questionable. Although it’s always mentioned that engineering practice and judgment have to be observed during the use of any PMDM and SSRWs and under no circumstances shall the PMDM and SSRWs waive professional judgment in applied engineering, it has to be acknowledged that PMDM and SSRWs carry with them some authority in arriving at a final decision during the initial stage of design, preparation of tender documents and whenever an inexperienced engineer is supervising part of the project or a new challenge emerges during the execution of road works. This paper focuses on what is specified in Tanzania PMDM and SSRWs, in particular on gravel roads materials, design, construction and maintenance in one part and what is practiced in the country in another part as it influences the performance of gravel wearing course. It also compares these PMDM and SSRWs with those of developed countries and South Africa. It is expected that by addressing those areas the PMDM and SSRWs have fallen short will make them effective tools in gravel roads design, construction and maintenance works.