The Design, Construction and Maintenance of Otta Seals

Abstract

An Otta Seal surfacing was first constructed in Botswana in 1978 on the Oodi - Modipane road. Since then, this type of bituminous surfacing has been used successfully on more than 1000 km of roads comprising more than 20 per cent of the primary and secondary road network of the country. Experience has shown that, in appropriate circumstances, Otta Seal surfacings can be very cost-effective when compared with more traditional bituminous surfacings such as single or double surface dressings (Chip Seals). Moreover, Otta Seals are particularly well suited for use with local materials which may be non-standard or of marginal quality and have proved to be very durable and cost-effective in the harsh, semi-arid climate that prevails in Botswana. The main objective of the Otta Seal Guideline is to provide a ready, practical reference for engineers and technicians at Roads Department and District Councils as well as for consultants, contractors and other organisations that are involved in the specification, design, construction and maintenance of bituminous surfacings. The Guide-line provides detailed guidance on the materials constituents and selection criteria for the Otta Seal as well as a general approach to its design, construction and maintenance. Consideration is also given to various contractual issues associated with the use of Otta Seals and, for completeness, a model specification is also provided. It is my hope that the Otta Seal Guideline will provide useful guidance to practitioners and promote the continued wide-spread use of this innovative type of bituminous surfacing in situations favouring its adoption.