This present paper proposes new investigations aiming at: (i) studying the effect on oxygen diffusion coefficients of the presence in clean water of some compounds usually encountered in biological media and (ii) quantifying their consequences on liquid-side mass transfer coefficients. The oxygen diffusion coefficients D were firstly measured in various synthetic liquid phases containing either salt (NaCl), sugar (glucose) or surfactant (sodium laurylsulphate). When compared to clean water, noticeable reductions of D were observed; the variation of D with the compound concentration C was modelled and found dependent on the nature of the compound added. In a second time, using the same liquid media, experiments on a train of bubbles rising in a quiescent liquid phase were carried out to determine the associated liquid-side mass transfer coefficients (k L). For all cases, as for diffusion coefficients, a decrease of k L with increasing C was clearly observed whatever the aqueous solutions. These findings firstly showed that, even if the properties of clean water (density, viscosity, surface tension) were not significantly changed by the addition of salts (NaCl), the liquid-side mass transfer coefficients could be, all the same, modified. For the aqueous solutions of glucose, the reduction of k L with diffusion coefficients D was well correlated, and mainly due to the change in viscosity with concentration. For surfactants, the hydrodynamic conditions (i.e. bubble Reynolds number) being almost kept constant for all concentrations, only the change in oxygen diffusion coefficients was thus responsible for the decrease of k L. The present study clearly confirmed the need to complete and/or account for the database related to oxygen diffusion coefficients in complex media, this condition being imperatively required to describe and to model appropriately the gas-liquid mass transfer phenomena.

The objective of this present paper is to propose a new theoretical prediction method of the volumetric mass transfer coefficient (k L a) occurring in a gasliquid contactor based on the dissociation of the liquid-side mass transfer coefficient (k L ) and the interfacial area (a). The calculated results have been compared with those obtained with the experimental process in a small-scale bubble column. Tap water was used as liquid phase and an elastic membrane with a single orifice as gas sparger. Only the dynamic bubble regime was considered in this work (Re OR = 150-1000 and We = 0.002-4).This study has clearly shown that, whatever the operating conditions under test, the generated bubble diameters (d B ), bubble frequency (f B ) and their associated rising velocities (U B ) were the important parameters in order to predict, not only the values of k L a, but also the values of a and of k L . Moreover, these obtained results could provide a better understanding of the parameters which influence the oxygen transfer mechanism in the aeration process. By using the correlations to estimate these bubble hydrodynamics (d B and U B ), it diminishes times for measuring the associated mass transfer parameters and also their experimental complexities and errors.

An improvement of flexural strength of cement stabilized soils using geogrid designated as compacted cement-geogrid-sand (CCGS) is investigated in this research. The studied material performance of the CCGS includes postpeak behavior, toughness, and equivalent flexural strength ratio. The geogrid inclusion significantly improves the postpeak flexural behavior, which is a requirement for bound pavement materials. The first peak flexural strength f1 and stiffness of both compacted-cement-sand (CCS) and CCGS are essentially the same for the same cement content. The tested soils were obtained from Ayutthaya province, Thailand, and is commonly used as a construction material for backfill and pavement applications. The backfill soils were used sand. In this study, Type I Portland cement was used as a cementing agent and geogrid two type were used as a reinforcement material. Properties of the cement and the geogrid, which were obtained from the manufacturers. The specimens were subjected to a flexural performance test according to ASTM C1609/C1609M-10 (2010). The results showed that in the flexural performance of the CCGS includeing postpeak behavior, toughness, and equivalent flexural strength ratio depends on the type and shape of apertures of the geogrid. It was found that the triaxial geogrid with shape of triangular apertures was more effective in reinforcing and provided the high equivalent flexural strength over uniaxial geogrid.