Detailed laboratory investigations were conducted on Mae Moh fly ash from northern Thailand for the determination of its grain size distribution, mineralogy, pozzolanic activity, compaction and strength characteristics, and the collapse potential. On the basis of the experimental results, this fly ash is classified as ASTM class C, which is considered to be pozzolanic. It has good potential to be utilized as an effective fill for embankments (roads and dams), airfields, pavements, and building bricks, as well as for the stabilization of compressible or erodible foundations. Because of the fact that Mae Moh fly ash contains only a negligible amount of unburned carbon, its pozzolanic reactivity is accelerated, in comparison with the relatively inert, high-carbon fly ash produced elsewhere in Thailand and many other parts of Asia. It is also demonstrated that Mae Moh fly ash can be easily compacted to produce acceptable dry densities over a wide range of water contents. Curing with an adequate moisture supply in the presence of calcium oxide plays an important role in accelerating the pozzolanic reactions, hence improving the time-dependent-properties. This study further proposes that a curing period of 2–3 weeks is sufficient for this material to approach its maximum strength. Although the behaviour of one specific fly ash cannot generalize the wide array of other ashes, the test results obtained for Mae Moh fly ash may be applied to lignite ashes in the category of ASTM class C. Key words: fly ash, structural fill, compaction, compressive strength, shear strength, collapse potential, pozzolanic activity.

No abstract

An important feature controlling the elastic and plastic constitutive behaviour of a soil is the orientation of the particles. The overall behaviour of a soil on application of a load depends not only on its initial particle orientation, but also on its change during the loading. In this Paper a non-destructive, indirect method of measuring the change in anisotropy of particle orientation is described. The method is based on electrical conductivities measured in different directions. Results obtained on clay and sand specimens during one-dimensional consolidation are presented. The stress—strain behaviour of an assembly of two-dimensional cylindrical roads is simulated numerically, and the change in mechanical anisotropy is computed. The variation of mechanical anisotropy computed from numerical experiments is qualitatively in agreement with the variation of electrical anisotropy measured in the laboratory. L'orientation des particules est un paramétre important du comportement élastique et plastique d'un sol. Le comportement d'un sol sous une charge ne depend pas seulement de l'orientation initiale des particles, mais aussi de l'évolution de cette orientation lors du chargement. L'article décrit une méthode indirecte non destructrice permettant de mesurer les variations d'anisotropie d'orientation des particules. Le principe de cette méthode consiste à mesurer les conductivités électriques dans différentes directions. Les résultats obtenus lors de la consolidation unidimensionnelle d'échantillons d'argile et de sable sont présentés. Le comportement en contrainte-déformation d'un assemblage de baguettes cylindriques bidimensionnel a été modélisé et l'évolution de l'anisotropie mécanique a été calculée. Ces variations d'anisotropie, issues de calculs numériques, sont du point de vue qualitatif en bon accord avec les variations d'anisotropie électrique mesurées au laboratoire.

This paper is concerned with the influence of fly ash (pozzolanic) on the stabilization of a dispersive soil commonly found in northeast Thailand. The effect of various proportions of fly ash on the rate of erosion, dispersiveness, strength and frictional properties and the compaction and consolidation characteristics, are discussed. It is noted that in general the addition of fly ash not only inhibits erosion and dispersiveness but also contributes to a significant improvement in strength and deformation characteristics. Nevertheless, excessive quantities of fly ash (>8%) generate diminishing returns and in fact promote segregation (erosion) of the stabilized soil again due to insufficient cohesion. Mineralogical studies based on X-ray diffraction analysis indicate that the reduction in the rate of erosion of the blended soil is associated with fine particle flocculation. The long term properties, however, are directly linked with the self-hardening nature of fly ash which contributes to timedependent strengthening of the stabilized soil.

No abstract