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Pavement subgrades constructed with clay soils can cause significant pavement distress because of moisture-induced volume changes and low subgrade support values. Lime is well known for its ability to stabilize plastic clays; however, portland cement also provides highly effective clay stabilization, usually with the added benefit of higher strength gain. Stabilizing clays with cement or lime can improve subgrade properties at a lower cost than either removing and replacing material or increasing the base thickness to reduce subgrade stress. The clay soil stabilization mechanism for the calcium-based stabilizers portland cement and lime is reviewed. These materials modify soil properties through cation exchange, flocculation and agglomeration, and pozzolanic reaction. Additionally, cement provides hydration products, which increase the strength and support values of the subgrade materials as well as enhance the permanence of the treatment. Comparative laboratory and field performance studies by others, focusing on stabilization of clay soils with portland cement or lime, are critically reviewed. Several factors affecting stabilization are discussed, including stabilizer test procedures, dosage effects to soil properties, mixing, compaction, and gradation and pulverization. Additionally, durability of cement and lime as stabilizers is reviewed, including wetting and drying, freezing and thawing, leaching, and long-term field performance. The research reviewed indicates that, if proportioned and applied properly, both cement and lime can effectively improve the engineering properties of clay soils over the life of a pavement. The results presented provide a guide to the engineer about the property changes to expect when using portland cement and lime with regard to volume stability, strength, and durability.

Self-diffusion of water contained in a porous glass is observed to be strongly enhanced if the pore space is only partially filled. This can be explained by a novel mechanism involving indirect molecular exchange between the liquid and the vapor phase. A theoretical model fits the pulsed-field-gradient NMR diffusion measurements with no adjustable parameters. NMR relaxation measurements were performed to provide a characterization of the homogeneity of the samples.PACS numbers: 66.10. Cb, 05.40,+j, 47.55.Mh, 76.60.Es Relaxation and transport phenomena of fluids in confined structures are presently attracting wide interest l from a number of points of view. Understanding the modifications from bulk liquid behavior introduced by the porous medium provides a tool for their characterization, significant to various technologies such as heterogeneous catalysis and oil recovery from natural reservoirs. However, there may also be cases in which the liquid contained in the porous medium exhibits a completely new phenomenon that cannot be described as a modification of bulk properties. In this paper we report such a discovery in porous glass partially filled with water. We have observed that the self-diffusion of the liquid is markedly enhanced by an indirect process involving exchange with the vapor phase. Crucial to this process is that the liquid should wet the solid surface creating two interpenetrating porous systems, that of the liquid and that of the vapor, each with a different geometry.Nuclear magnetic resonance (NMR) experiments were performed on water imbibed into porous silica glasses. These include longitudinal and transverse relaxation, as well as measurements of the self-diffusion coefficient at various temperatures. Most importantly, experiments were performed for different filling fractions of water in the pore space of the glass samples, as is shown in the accompanying figures. The samples under study were chosen among a set of five porous silica glasses, gelled from mixtures of colloidal silica and potassium silicate, 2 which we identify in the following by their colloidal silica-to-potassium-silicate mixture ratio (for example, 10:90). Each sample was leached 2 in order to remove surface alkali ions, and sealed after impregnation with deionized water, in an NMR tube with a Teflon rod filling the dead volume of the tube in order to prevent water loss from the sample itself. These samples are characterized by very high porosity (85%) and by progressively increasing pore sizes as the fraction of colloidal silica is reduced. 2 The pore-size distributions are relatively narrow, and the peak position ranges between 470 A (for sample 30:70) and 2400 A (for sample 10:90), as determined by the mercury porosimetry technique. 2 We have previously reported NMR relaxation measurements performed on saturated samples. 3 Before we describe the results of diffusion measurements it is appropriate to discuss our characterization of the water-glass system under study. Longitudinal and transverse relaxation measurements ...

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