Preliminary Development of Slag as a Stabilised Material for Labour Intensive Construction of Roads

Stabilisation of natural pavement materials to make road pavements is widespread in South Africa, using cement and lime as cementitious binders. The rapid speed of the cementing reaction limits these to plant based construction. Some hydraulic binders have the potential to be developed for Labour Intensive Construction stabilisation technology because their slow hydration reaction allows time to work with the material and place it by hand without loss of quality. The mixture of LD slag and GBFS has such a potential, and there has been limited use of it as a road building material elsewhere. However because its properties vary widely, it needs to be investigated individually for each plant. The potential employment benefits of using a mixture of slag as a road basecourse were calculated, assuming that it was hauled from a locally based central mixing plant, spread, shaped, compacted and cured using labour intensive methods. The percentage of the costs that went to labour compared well with other labour intensive technologies such as waterbound macadam. The laboratory investigation covered the reactivity of the mixture, the use of gypsum as an accelerator, the stockpile life of the mixture, and the strength gain upon hydration. The results obtained so far show that the Witwatersrand LD slag activates Vanderbijlpark GBFS. This slag mixture hydrates to become a bound (cemented) material suitable for road pavement use. A suitable mixture including a small amount of Milled GBFS has been shown to provide a material which, although variable, is close to the South African C3/C4 stabilised road material classification.