Properties of Ironstone Lateritic Gravels in Relation to Gravel Road Pavement Construction

A laboratory investigation was conducted to determine properties of five samples of ‘oolitic ironstone’ lateritic gravel aggregates which are relevant to their use as road construction materials. Measured values of physico-chemical, physico-mechanical as well as index properties and compaction characteristics are similar to those of other lateritic, gravels occurring in West Africa which are used in road pavement applications. These lateritic clayey gravels have good workability as engineering construction materials and are rated fair to good as road aggregates in terms of probable in-situ behaviour based on water absorption values. Relationships between maximum dry unit weight and optimum moisture content as well as those between California bearing ratio and some derived soil parameters such as grading modulus, plasticity product or plasticity modulus can be described using a third-order polynomial function. The maximum dry unit weight has a bimodal frequency distribution and can be predicted from logarithm to base 10 of compaction energy with fairly good accuracy.     

Compositions and sources of extractable organic matter in Mesopotamian marshland surface sediments of Iraq. I: aliphatic lipids

Shallow surface sediment samples from the Mesopotamian marshlands of Iraq were collected and analyzed to determine the distribution, concentrations and sources of aliphatic lipid compounds (n-alkanes, n-alkanols, n-alkanoic acids, and methyl n-alkanoates) and molecular markers of petroleum in these wetlands. The sediments were collected using a stainless steel sediment corer, dried, extracted with a dichloromethane/methanol mixture and then analyzed by gas chromatography-mass spectrometry (GC–MS). The aliphatic lipid compounds included n-alkanes, n-alkanoic acids, n-alkanols and methyl n-alkanoates with concentrations ranged from 6.8 to 31.1 μg/g, 4.1 to 5.0 μg/g, 5.9 to 7.7 μg/g and from 0.3 to 5.9 μg/g, respectively. The major sources of aliphatic lipids were natural from waxes of higher plants (24–30%) and microbial residues (42–30%), with a significant contribution from anthropogenic sources (27–30%, petroleum), based on the organic geochemical parameters and indices. Further studies are needed to characterize the rate, accumulation and transformation of various organic matter sources before and after re-flooding of these wetlands.     

Time-dependent sorption of Cd on CaX zeolite: Experimental observations and model predictions

Sorption, fixation and desorption kinetics of Cd²⁺ on calcium-exchanged zeolite-X were studied using an isotopic dilution technique utilizing ¹⁰⁹Cd. The technique provided reliable measurements of time-dependent fixation of Cd and was validated using chabazite, which demonstrated wholly reversible Cd²⁺ ion exchange. A first-order kinetic model was developed to describe the progressive transfer of Cd²⁺ to a less reactive form in X-zeolite, following initial sorption, and subsequent desorption of Cd subject to different initial contact times. The kinetic model differentiates between two ‘pools’ of sorbed Cd²⁺ on zeolite-X, designated labile and non-labile sorbed Cd in which the labile sorbed Cd is in immediate equilibrium with the free Cd²⁺ ion activity in solution. Additionally, an intra-particle diffusion model was developed and compared with the kinetic model to determine whether time-dependent Cd sorption is controlled by reaction kinetics or diffusion within zeolite particles. The kinetic model provided a much better fit to the experimental data (R² = 0.987) than the diffusion model. The rate constants describing Cd dynamics in CaX zeolite gave a half-time for Cd desorption of ∼77 d, for release to a ‘zero-sink’.     

Compressibility of porous rocks: Part I. Measurements of Hungarian reservoir rock samples

Pore volume compressibility is one of the physical properties of a reservoir that must be specified in many reservoir-engineering calculations. In the presented research, the effect of compact pressure, temperature and porosity on compressibility was investigated. A total of twenty-two different cores were tested: five limestone, one friable sandstone, fourteen medium to hard sandstone, and two very dense sandstone. Core samples were placed in the test cell and subject to compacting pressure up to 10,000 psi. Runs were made at room temperature and at 52°C for limestone samples. Although there were some publications concerning measurement and study of the effect of pressure and temperature on pore volume compressibility of reservoir rocks, nothing has been published about compressibility of Hungarian reservoir rocks, except of the work of Tóth and Bauer (1988). The present study showed pore volume compressibility data for different Hungarian fields. The result of the study at high temperature (52°C) shows that pore compressibility increases with increasing temperature.     

Groundwater Deterioration of Shallow Groundwater Aquifers Due to Overexploitation in Northeast Jordan

Groundwater is the major water resource in Jordan and most of the groundwater basins are already exploited beyond their estimated safe yield. Azraq basin is one of the most important groundwater basins in Jordan, which supplies Amman with drinking water. However, due to overpumping from the shallow groundwater aquifers, the water level dropped dramatically and signs of salinization and depletion are starting to occur. The severe drawdown in the Azraq well‐field caused a reverse in the hydraulic gradient and consequently, the saltwater in the center of the basin (Qa‐Azraq) started to move in the direction of the well‐field. The salinization in the shallow aquifer (basalt/B5/B4) is believed to result from one of the following scenarios: (i) a reverse flow from Sabkha to the AWSA well field, (ii) an upward leakage from the middle aquifer system (B2/A7) and the combined B3 Aquitard‐B2/A7 aquifer, (iii) a dissolution process between the water and rock matrix due to lowering of the dynamic water levels during pumping which reached the mineralized formations underlying the Basalt. The salinization trend of some AWSA wells represented by the gradual increase of major ions is associated with rather constant stable isotopic contents. This indicates that these constituents originate from the main minerals existing in the matrix of the aquifers and thus this scenario is the most likely to occur.     

Wave equation analyses of tapered FRP–concrete piles in dense sand

Fiber-reinforced polymers (FRP)–concrete composites provide an attractive alternative to conventional pile materials such as steel, concrete and wood by improving the durability of deep foundations. In the current study, FRP tubes with different taper angles are filled with self-consolidating concrete (SCC) and driven into dense sand that is enclosed in a large pressurized soil chamber. Driving tests are conducted on FRP–SCC composite piles to determine how the pile material and geometric configuration affect its driving performance. Dynamic data is employed to determine the soil parameters in the TNO model (i.e., soil quake and damping constant) using the DLTWAVE signal-matching program. The driveability of FRP–SCC and traditional pile materials is compared using the wave equation analysis program PDPWAVE. The experimental data and the wave equation analyses indicate that the taper shape has a favourable effect on the driveability and static resistance of piles. It is also found that the driveability of FRP–SCC composite piles is similar to that of conventional prestressed concrete and steel piles. However, empty FRP tubes required a much higher driving energy. Their low flexural resistance along with risk of buckling can hinder their driveability in different soil conditions.     

Equatorial spread-F initiation: Post-sunset vortex, thermospheric winds, gravity waves

We present experimental evidence and modeling results which indicate that eastward thermospheric wind is the primary controlling factor of equatorial spread-F initiation in the post-sunset ionosphere. Eastward wind-driven Pedersen currents are able to polarize F-region density perturbations with westward tilting wavefronts into rapidly growing modes to trigger the formation of spread-F bubbles. The described process is so rapid that seeding requirements of spread-F initiation by external factors such as gravity waves are effectively eliminated.     

Comparison of the experimental and theoretical production of biogas by monosaccharides,disaccharides, and amino acids

The estimation of biogas production from organic monomers is very important for the optimal design, configuration, and efficient evaluation of the anaerobic digestion processes in a digester. The theoretical estimation of the biogas potential that is most used is that of Buswell and Boyle. In this work, we found that this estimate was much exaggerated compared to the real biogas potential determined in practice. For monosaccharides, we noted that the biogas potential of glucose was very low compared to that of fructose, even though the two substrates have the same chemical composition and molecular mass. The same result was observed for the disaccharides lactose and maltose. The amino acid valine produced more biogas than the amino acid cysteine did. The experimental potential remained lower than the calculated potential. An important difference existed between the experimental biogas potential of the six monomers investigated and the theoretical biogas potential. This indicated that the calculation of the biogas potential by the stereochemical equation of Buswell and Boyle was overstated and did not take into consideration the isometric form, spatial configuration, and intermediate metabolite produced by the monosaccharides in the four steps of anaerobic digestion. For the disaccharides, the theoretical calculations did not take into account the nature of the molecular components in carbohydrate, type of glycosidic bond, and intermediate metabolites of substrates for anaerobic digestion. Finally, for the amino acids, it does not take into account the ramification of the atomic components and the chemical nature of atoms in amino acids.