Use of waste limestone dust and steel slag in UK highways type 1 unbound mixtures

This paper reports the results of a research project which evaluated the benefits of modifying UK highways type 1 unbound mixture for sub-base by the addition of a significant proportion of a number of waste products, namely pulverized fuel ash, limestone dust, steel slag and granulated blast-furnace slag. Assessment of the effect of modification was carried out in the triaxial apparatus, which was used to measure the resilient modulus of the modified mixtures and comparing those values with those ascertained from unmodified type 1 unbound mixtures. The modified materials containing up to 20% extra limestone dust presented inadequate resilient modulus values for use in road pavement foundations. However, addition of the other wastes improved the resilient modulus of the material to a level that made the materials suitable for use as sub-base in pavement foundations. The intention is that this research could initiate justification of using limestone dust in sub-base potentially leading to use of this plentiful by-product currently considered to be a waste material depending upon the economics.