Improvement of marginal materials by fly ash road works

Abstract

The national road network continues to play a fundamental and catalytic role in the promotion of social and economic development of Botswana. However, a combination of adverse climatic and geological factors, such as scarcity of conventional road building materials, near absence of a non saline surface water, and climatic extremes have dictated the need for innovative engineering approaches to highway design, construction and maintenance. In recent years application of fly ash has been considered in road construction with great interest. Fly ash is a pozzolanic material, which in the presence of water combines with lime to produce a cementetious material with excellent structural properties. Attempts have, therefore, been made at Botswana Roads Department in collaboration with University of Botswana to explore the feasibility of utilizing fly ash alone to improve the physical and strength characteristics of locally available non-standard marginal materials. The results indicate that with the addition of fly ash plasticity dereases while California Bearing Ration (CBR) increases for calcrete and other locally available marginal materials for road construction. With appropriate amount of fly ash and an adequate curing the material can be improved to meet the requirement of base and sub-base coarse.