Application of Fly ash and Blast Furnace Slag Stabilized Soils in Pavement Design: Case Study Harare – Mutare Road, Zimbabwe

Abstract

This project is based on the incorporation of fly ash and blast furnace slag from industries and mines for the stabilisation of soils for pavement design and construction. The project aimed at the determination of the subgrade characteristics of the project site and to designing a pavement structure using fly ash and blast slag in stabilisation of the soil. Tests were conducted at two sites along the Harare-Mutare Road in Zimbabwe on chainages 30.000 m to 35.000 mm. The research was carried out from November 2012 to July 2013. A series of laboratory tests were done on the stabilized and unstabilised soil samples to Zimbabwe Standards (ZWS/SAZ) 185 Part 1 (1998) and part 2 (2001) and British Standards (BS) 1377 (1990) Part 1standards for the purpose of analyzing the bearing strength of untreated and treated samples when stabilizing materials are added. These results were later used for designing the pavement layers. The study proposes the use of waste products, fly ash and slag, as stabilizing materials in place of/in combination with conventional methods of stabilisation with lime and cement. These waste products can be used in combination with the natural soils and might make roads durable and combat cracking, depressions and pothole build up on roads. They might reduce volume imported primary aggregates since site soil properties will be enhanced thus reducing transport cost. Also it will reduce energy cost compared to conventional road construction such as asphalt construction which requires heating of bitumen. Only water will be used as a solvent in this project. The pavement layers were designed according to South African Pavement Engineering Manual and Transport and Road Research Laboratory (TRRL) Manuals after analysis of laboratory and in-situ test results. The use of fly ash and slag improves the bearing capacity of pavements on low volume roads in urban areas and saves construction costs. The total project cost is $158,500-00 and use of Portland cement as a stabiliser costs 150% more as compared to the use of fly ash and slag.