Parameters Controlling Strength of Coal Fly Ash—Lime Improved Soil

Unconfined compressive tests and suction measurements were carried out on sandy specimens with distinct Class F fly ash amounts (6.25%, 12.5% and 25%), lime contents (3% to 9%), porosities and 28 days as the curing period to assess key parameters controlling strength of fly ash-lime amended soil. A special effort has been allocated in order to develop a dosage methodology for fly ash-lime improved soils based in a rational criterion, as it exists in concrete technology where the water/cement ratio plays a fundamental role in the assessment of the target strength. The results show that the unconfined compressive strength (q_u) increased linearly with the amount of lime for soil-fly ash-lime mixtures at all curing time periods studied. A power function fits better the relation q_u — porosity for soil-fly ash-lime mixtures. The bigger the amount of fly ash and the curing time, the larger the q_u for any given porosity and lime content. Finally, the porosity/volumetric lime content ratio shows to be a good parameter in the evaluation of the unconfined compressive strength of the soil studied.