No abstract

Clayey soils often exhibit undesirable engineering behaviour such as low strength, swelling and shrinkage characteristics etc. To improve these properties, the common method followed is stabilization. An

Highway construction engineers often face the need for more stable, durable and, at the same time, more economic road structures. This is nowadays true because of increased traffic volumes and heavier loads on the roadways. As a consequence, enhanced pavement structures and improved subgrades is a necessity. The international highway "New Egnatia" crosses areas in Thrace, Northern Greece with abundant clayey soils having poor technical properties.The treatment of physical soils with some substances could bring up new materials, which would operate better under the traffic and environmental conditions. This has led to the decision to investigate the possibilities of improving the existing soil materials using chemical additives. Soil samples were collected from the abovementioned area and mixed with lime and fly ash, in various proportions. The modification of the soil properties with special emphasis on their strength has been examined in the laboratory after different curing periods.The experimental results have shown that the unconfined compressive strength increased as a function of both the percentage of additive in the mixture and the time of curing. The improvement depended upon the soil mineralogy and the kind and quantity of exchangeable cations. This holds true when the influence of the kind and quantity of the additive is taken into account. The effects of lime on the swelling clayey soils tested were more beneficial than those of fly ash.The soils after their treatment could be used as a subgrade or even as a subbase layer in roadway pavements.

Increased care about the environment is currently evidenced by governmental, industrial, and consumer concern for ozone depletion, solid and liquid waste disposal, and pollutants. This concern has led to an increase in marketing of the "environmentally friendly" aspects of products. In the past, fly ash was generally released into the atmosphere, but pollution control equipment mandated in recent decades now requires that it is captured prior to release. In order to upgrade expansive soils as construction materials, fly ash, which is a waste material, has been selected and successfully used for stabilizing expansive clays in the Thrace region. The strength characteristics of the stabilized soils were measured. Depending upon the soil type, the effective fly ash content for improving the engineering properties of the soil varied between 8% and 12%. Using fly ash in roadwork projects will help the environment reducing the deposited amounts.

Very often, pavements constructed in an economical manner or matching surface elevations of adjacent lanes cannot be designed for the soil conditions of the existing subgrade. Therefore, there is a need to stabilize the soil with an appropriate chemical substance in order to increase its strength to a satisfactory level. For the enhancement of subgrade soil strength characteristics, lime and cement are the most commonly used stabilizers. An experimental program was directed to the evaluation of a clayey soil and its mixtures with different cement contents performing tests on the index properties, the moisture-density relation, the unconfined compressive strength, and linear shrinkage. There is a definite improvement in strength. The time interval used to cure the prepared specimens affected positively both strength and plasticity features of the mixtures. A comparison with mixtures of the same soil with lime has been made, because of the wide use of lime in clay soil stabilization projects.