Effects of soil pulverisation level and freeze and thaw cycles on fly-ash- and lime-stabilised high plasticity clay: implications on pavement design and performance

This study investigates the effects of soil pulverisation level and freeze and thaw cycles on mechanical properties of a stabilised high plasticity clay. Class F fly ash and hydrated lime were used as additives. Tested compositions were 3% lime, 20% Class F fly ash, 20% Class F fly and 3% lime and 40% Class F fly ash and 3% lime, respectively. Two different soil pulverisation levels which meet the criteria in relevant specifications were used. Unconfined compression strength tests were conducted on 61 samples. The results revealed that both fly ash and hydrated lime increased the mechanical properties. Lime addition increased the effectiveness of Class F fly ash stabilisation significantly. Soil pulverisation level was found to be as important as the amount of the additive used. The most important effect of soil pulverisation level and freeze and thaw cycles was on initial modulus value, which is a key parameter in pavement performance. Coarse soil pulverisation resulted in much lower modulus values than fine pulverisation. High compression strength was not always accompanied with high modulus for coarse soil pulverisation and therefore designing pavements based solely on strength without giving enough consideration to modulus has been shown to be a misleading approach. KENPAVE analysis revealed that shorter design lives were associated with coarse soil pulverisation. The results of this study show that the amount of achieved improvements and economic benefits due to stabilisation of clayey soils for pavements are strongly dependent on the degree of soil pulverisation achieved in the field. Therefore, better soil pulverisation in the field is crucial in increasing pavement performance and therefore decreasing total life cycle costs.