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Mass transport in soil occurs through the soil pore network, which is highly influenced by pore structural parameters such as pore-size distribution, porosity, pore tortuosity, and coordination number. In this study, we visualised the networks of meso- and macro-pores (typical pore radius r [greater than or equal to] 10 [micro]m) using micro-focus X-ray computed tomography (MFXCT) and evaluated pore structural parameters of two loamy soils from Japan and New Zealand packed at different degrees of compaction. The effect of compaction on pore structural parameters and relationships between pore structural parameters and measured mass transport parameters were examined. Results showed a clear influence of compaction on pore structural parameters, with the MFXCT-derived mean pore radii and pore tortuosities decreasing and the mean pore coordination number increasing with increasing dry bulk density. Especially, pores with r > 80 [micro]m became finer or were not well formed due to compaction. The MFXCT-derived pore structural parameters were not well correlated with the equivalent pore radii from measured water retention curves. However, volumetric surface areas and pore-network connectivity-tortuosity factors derived from MFXCT allowed a fair prediction of several important mass transport parameters such as saturated hydraulic conductivities, soil-gas diffusion coefficients, and soil-air permeabilities. Further studies are needed to link micro-pores with radii smaller than the X-ray CT resolution to meso- and macro-pores visualised by X-ray CT to improve the prediction of mass transport parameters in soil. Additional keywords: air permeability, hydraulic conductivity, microfocus X-ray computed tomography (MFXCT), pore network, soil gas diffusion coefficient., Introduction A better understanding of gas transport in soil is important to elucidate the emission of greenhouse gases (Kruse et al. 1996; Smith 2003; Kawamoto et al. 2006; Wickramarachchi et [...]

Heavy metal contamination of water sources is an alarming issue across the globe. It may cause several health problems in humans in addition to its damage to aquatic organisms and its adverse effects on the environment. Among the wastewater treatment techniques of heavy metals, adsorption is much favored due to its cost-effectiveness and easy availability, especially in developing countries in tropical and semi-tropical climate regions. Moreover, natural geo-adsorbents like laterite and its crushed grains can be adopted as an attractive alternative adsorbent in floatation and filtration water treatment systems. In this review, the application of natural and pre-treated laterite grains as a low-cost adsorbent was examined based on selected journal articles published during 1990–2020. This paper summarizes basic physical and chemical properties including surface charge and element compositions of tested samples, batch adsorption results including initial conditions, isotherm and kinetic models, and adsorption and thermodynamic parameters such as the maximum adsorption capacity, removal percentage, and Gibbs free energy that categorize the natural and pre-treated laterite grains. In addition, the results of some previous studies of column experiments and desorption/regeneration of adsorbed heavy metals are described together with prospects for future studies and the applicability of laterite in wastewater treatment for heavy metal remediation. [ABSTRACT FROM AUTHOR]

Reuse and recycling of non-hazardous construction and demolition waste and industrial byproducts in the construction industry is vital to promote environmentally sound waste management. In particular, the effective utilization of sludge and waste clay bricks is greatly required in developing countries. This paper studied compaction characteristics and the California bearing ratio (CBR) of water treatment sludge (WTS) blended with clay brick aggregates for the road subgrade application. Raw and waste clay bricks from Vietnam were used for preparing clay brick (CB) and recycled clay brick (RCB) aggregates of three different particle sizes, Coarse 10- 30 mm, Graded 2-30 mm, and Fine 2-10 mm. In addition, fine residues of clay bricks with a size of < 2 mm were tested. WTS sieved under 2.0 mm blended with CB/RCB aggregates with different mixing proportions (f) were used for compaction and CBR tests in the laboratory. Results showed that the measured maximum dry densities (MDD) were dependent solely on mixing proportion f and increased linearly with f irrespective of blended fractions of CB/RCB aggregates. Unlike MDD, the measured CBR was dependent on both f and blended fractions. Especially, the WTS blended with coarse and graded fractions with a range of 60 ≤ f ≤ 80% showed a significant improvement in CBR (>100%). Due to its limited particle breakage and high CBR, the WTS blended with graded CB/RCB aggregates was preferable for the road subgrade application. [ABSTRACT FROM AUTHOR]

It is well known that the resistance to liquefaction of a saturated sand decreases sharply when it has been presheared, either cyclically or quasi statically, beyond a threshold value. The possible mechanism is discussed in light of recent findings on the microstructural anisotropy developed in preshearing (induced anisotropy). A columnlike structure, through which applied stress is mainly transmitted, grows parallel to the major principal stress direction in the strain hardening process. Voids, randomly distributed at first, are also connected in series between the columnlike structures. The anisotropic structure can carry the increasing stress as long as the major stress is applied parallel to the elongation direction of the structure. However, it becomes extremely unstable when the major stress is rotated. The excess pore-water pressure increases markedly under undrained cyclic loading, particularly when the connected voids are stressed perpendicular to their elongation direction. This is the reason why once liquefied sand sharply loses liquefaction resistance in a subsequent reliquefaction test.

Removal of heavy metals from wastewater is of special concern due to the persistence of heavy metals in the environment. The industrial discharge of heavy metals adversely affects soil and water resources, aquatic organisms, and ecosystem integrity. In addition, high concentrations of heavy metals are detected in solid waste landfill leachate in many developing countries due to non-segregated waste dumping. At present, various kinds of adsorbents such as activated carbon, biomass resources, geomaterials, and industrial waste products are used to treat heavy metal-contaminated water. However, the use of construction and demolition waste (CDW) and its recycled materials to treat heavy metal-contaminated water has not been fully examined. Because the generation of CDW is increasing due to rapid urbanization and a high demand for construction, the wise use of CDW and its recycled materials is necessary. This paper reviews journal articles published from 2004 to 2016 that studied the applicability of low-cost CDW adsorbents to remove heavy metals from wastewater. In particular, it summarizes results on using CDW and recycled materials such as cement, concrete, and brick compared to those from various other adsorbents such as biosorbents, geomaterials, and their industrial products. The potential applicability of CDW and its recycled materials as heavy-metal adsorbents was examined based on a comparison table listing material properties, test conditions, and measured adsorption properties. [ABSTRACT FROM AUTHOR]