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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 [...]

The discharge of untreated oily wastewater into the environment has serious impacts on human health, living nature, and ecosystems and leads to significant economic losses. Many engineering techniques have been proposed and applied to treat oily wastewater, but limited studies have investigated low-cost and effective techniques using by-products and waste/scrap materials from the construction industry. Materials to treat oily wastewater are needed not only to mitigate environmental pollution but also to promote the reuse and recycling of industrial by-products, especially in developing countries. This study, therefore, examined the sorption capacity of dispersed oil in wastewater (dispersed soybean oil in water; initial oil concentrations, Ci = 10–1000 mg/L; oil droplet size in water <2 μm) onto the hydrophobized/oleophilized autoclaved porous aerated concrete (AAC) grains made from waste scrap in Vietnam by using batch sorption tests in the laboratory. The AAC grains (sizes 0.106–0.25, 0.25–0.85, and 0.85–2.00 mm) were hydrophobized/oleophilized using oleic and stearic acids (coating concentrations of 1.0, 5.0, and 10 g/kg), and two sands (0.18–2.00 and 0.30–2.00 mm) were used as control samples. The results showed that the hydrophobized/oleophilized AAC grains had high sorption capacity for dispersed oil (i.e., high oil removal efficiency) compared to the control sands. Especially, the removal of AAC grains coated with stearic acid was >80% in high oil concentration solutions (Ci = 100 and 1000 mg/L), indicating that the hydrophobized/oleophilized AAC grains have high potential as useful adsorbents to trap dispersed oil in oily wastewater. Moreover, adsorption isotherms were drawn to examine the sorption characteristics of dispersed oil onto AAC grains. For all tested samples, the sorption of dispersed oil increased linearly with increasing equilibrium concentration. The commonly used Langmuir model, on the other hand, did not capture the measured isotherms. [ABSTRACT FROM AUTHOR]

Separation of oil and water is an effective technique to treat oily wastewater. For examining the applicability of porous grains coated with hydrophobic agents (HA) as low-cost and easily available filtration and adsorbent materials in the separation of oil and water, this study assessed the hydrophobicity/oleophilicity of porous grains made from autoclaved aerated concrete scrap coated with low-cost and harmless hydrophobic agents such as oleic and stearic acids. Tests using a sessile droplet method showed unique relationships between the contact angles (CA) of water droplets in air (CAwa), oil droplets in water (CAow) and coated HA concentrations. The CAwa increased linearly with increasing HA concentration and then became almost constant and/or gently increased after a specific point, indicating that a minimum coating amount gives the maximum hydrophobicity to HA-coated porous grains exists. The CAow gradually decreased exponentially with increasing HA concentration. In particular, the CAow of porous grains coated with stearic acid decreased with increasing of HA concentration in a two-step process. Furthermore, analyses of the Pearson correlation showed that both CAwa and CAow correlated well with the specific surface area (SSA), implying that the SSA is a good indicator as a quick assessment of hydrophobicity/oleophilicity of HA-coated porous grains. [ABSTRACT FROM AUTHOR]

Along with economic development, urbanization will generate a large amount of solid waste and put pressure on the waste management systems in developing countries. Face-to-face interview methods were used to investigate the current status of construction and demolition waste (CDW) management (collection, transportation, treatment, and storage) as well as reveal attitudes of governmental agencies and enterprises towards CDW recycling and recycled material products in Hai Phong City, Vietnam. Waste generation rates (WGRs) of the works were also determined by site surveys and as-built drawings method of typical old buildings to be demolished and two licensed new construction works. WGRs of 34.5 kg/m2 and 758 kg/m2 were identified during the construction and demolition of small private houses, respectively, while WGRs at public house demolition sites were 1053 kg/m2. To effectively manage the CDW, the gross floor area of new construction work was estimated by a multiple regression equation with the population and gross region domestic product growth. Based on this model combining the investigation results, the amount of CDW increase in 5–30 years is also predicted. This data set will help management agencies plan storage yards as well as select the appropriate CDW treatment and recycling methods, contributing to building a sustainable and effective CDW management model for Hai Phong City as well as Vietnam in the future. [ABSTRACT FROM AUTHOR]

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]

The soil gas diffusion coefficient ([D.sub.p]) and its dependency on soil air content, [epsilon], and tortuosity--connectivity of the air-filled pore networks control the transport and fate of gaseous-phase contaminants in variably saturated soil. The bimodality in pore size distribution of structured soil often yields a variation of [D.sub.p] with [epsilon] in the intraaggregate pore region that is distinctly different from that in the interaggregate region. Data imply a highly nonlinear behavior of soil gas diffusion [D.sub.p]([epsilon])/[D.sub.o] (where [D.sub.o] is the gas diffusion coefficient in free air), in the interaggregate region of aggregated soils similar to that of structureless soils with a unimodal pore size distribution, probably due to diffusion-limiting effects by connected water films at low [epsilon]. In contrast, for the intraaggregate region, we show that the impedance factor [F.sup.*] (= [D.sub.p]/[epsilon][D.sub.o]) and tortuosity factor T [=[(1/[F.sup.*]).sup.1/2]] are approximately constant for most soil media. We suggest a typically well-defined separation between the two pore regions at the minimum for the pore connectivity factor [X.sup.*] [= log([D.sub.p]/[D.sub.o])/log([epsilon])], at which point the interaggregate pores are devoid of water while the intraaggregate pore region is water saturated. Based on this, a hierarchical two independent region (TIR) [D.sub.p]/[D.sub.o] model was developed by applying a cumulative series of Buckingham--Currie power-law functions, F[[epsilon].sup.X]. A nonlinear, water-content-dependent expression for F best described the measured [D.sub.p]/[D.sub.o] in the interaggregate region, while constant F (around 0.5) and X (around 1) generally sufficed for the intraaggregate region. The TIR model better predicted gas diffusivities for both aggregate fractions and highly structured soils across the entire range of moisture conditions with RMSE reduced by two to five times compared with traditional predictive [D.sub.p]([epsilon])/[D.sub.o] models. Abbreviations: AIC, Akaikc Information Criterion; TIR, two independent region; WLR, water-induced linear reduction. doi:10.2136/sssaj2009.0055

The transport of gaseous compounds in soil takes place by gas diffusion, advection, and dispersion. Gas transport processes are influenced by the soil-gas diffusion coefficient ([D.sub.p]), air permeability ([k.sub.a]) and soil-gas dispersion coefficient ([D.sub.H]), respectively. Of three gas transport parameters, [D.sub.H] is the least understood, especially how it is correlated to soil type, moisture conditions, and other transport parameters (i.e., [D.sub.p] and [k.sub.a]). In this study, a unified measurement system (UMS) that enables sequential measurement of [D.sub.p], [k.sub.a], and [D.sub.H] on the same soil core was developed. The experimental sequence is based on a two-chamber measurement of [D.sub.H] and [k.sub.a], followed by a one-chamber measurement of [D.sub.p]. Gaseous oxygen concentration and air pressure sensors are located in inlet and outlet chambers as well as at multiple points along the soil column. Using different particle-size fractions of non-aggregated (Toyoura sand) and aggregated (Nishi-Tokyo loam) soils, the effects of soil structure, particle (aggregate) size, and column scale (5-cm i.d. and 30-cm or 60-cm length) on the three gas transport parameters were investigated. For both soils, [D.sub.H] linearly increased with increasing pore-air velocity. For Toyoura sand, gas dispersivity ([lambda] = [D.sub.H]/[u.sub.O]) decreased with increasing soil-air content, while for NishiTokyo loam, gas dispersivity decreased with increasing soil-air content to a minimum value when inter-aggregate pores were drained and increased again when the pores inside the soil aggregates started to act as tortuous air-filled pathways. In the arterial pore region (corresponding to the total pore volume for Narita sand and the inter-aggregate pore volume for Nishi-Tokyo loam), a linear relation between tortuosity of the air-filled pore network (T, calculated from [D.sub.p]) and the gas dispersivity ([lambda]) was observed. Abbreviations: APR, Arterial Pore Region; UMS, Unified Measurement System; WLR, Water-induced Linear Reduction. doi: 10.2136/sssaj2009.0012

Natural granular materials widely used in building and infrastructure development consume a considerable number of natural resources. To avoid depleting natural granular materials, recycled concrete aggregates (RCA) from construction and demolition waste are now commonly used as an alternative. The mechanical behavior of RCA used in road construction is highly influenced by field conditions such as traffic load and moisture variation. The particle breakage of RCA influences long-term pavement performance because it changes the RCA grading over time. However, the effect of moisture content (m.c.) on mechanical behavior and particle breakage during compaction and cyclic loading is often neglected. The aims of the study were to investigate the mechanism of permanent deformation development due to moisture change, the breakage response of RCA in this process, and the assessment of existing permanent deformation prediction model. The results showed that initial m.c. effectively controlled the deformation of RCA; the permanent axial strain (εpa) was enhanced, and the breakage of coarse fraction (19~9.5 mm) under cyclic loading was reduced at higher levels of m.c. Based on the experimental results, a modified model for predicting εpa was proposed, incorporating a deviation factor induced by m.c. The model fitted the experimental data well, suggesting that it is useful to have a quantitative estimation of εpa of RCA with different m.c. under cyclic loading. [ABSTRACT FROM AUTHOR]

The construction industry is one of the key industries with high potential for the circular economy; the promotion of reuse and recycling of construction and demolition waste (CDW) is essential for sustainable urban development. In this study, a series of compaction, California bearing ratio, saturated hydraulic conductivity, and particle breakage tests of well– and poor–graded mixtures of recycled clay brick aggregates (RCBs) and recycled concrete aggregates (RCAs) with maximum aggregate diameters of 19, 25, and 37.5 mm were carried out to examine the practical application of those mixtures to unbound roadbed materials in Vietnam. The experimental results suggest that the maximum amount of RCBs added to RCAs should be less than 30% when applied to unbound roadbed materials. In addition, it was found that the mixing proportions of RCBs and RCAs and the maximum aggregate diameter, gradation of aggregates, and initial moisture condition control the saturated hydraulic conductivity. Further, the particle breakage characteristics under compaction were carefully examined, and it was found that the percentage increment/decrement, as well as a newly introduced method of estimating the mixing proportions of RCAs and RCBs in the fine fraction (<2.36 mm), is effective in understanding the mechanism of particle breakage of RCA and RCB mixtures. [ABSTRACT FROM AUTHOR]

Due to the rapid increase in population and urbanization, municipal solid waste (MSW) generation is increasing. Sri Lanka, in particular, faces serious difficulties in finding new sites for MSW disposal, due to the lack of available space; therefore, the rehabilitation of existing MSW dumping sites and the extension of their services are required to achieve sustainable urban development. To examine suitable rehabilitation techniques, it is essential to identify the physicochemical and mechanical properties of dumped MSW, fully considering climatic conditions, waste composition, and the time since the waste was dumped. In this study, therefore, the physicochemical and mechanical properties of dumped MSW were investigated; the dumped MSW was taken from existing MSW dumping sites in three climate zones in Sri Lanka, namely the Karadiyana site in the wet zone, Udapalatha in the intermediate zone, and Hambantota in the dry zone, and it was taken at different times after being dumped. The results showed that the waste composition and biodegradation of organic materials affected the physicochemical and mechanical properties of the dumped waste. The measured compaction parameters of the "old" sites at Udapalatha and Hambantota were higher compared to the "new" sites. Compaction parameters at the Karadiyana site, on the other hand, were low, at even >20 years since being dumped, probably due to the high amount of scarcely compacted materials. In direct shear tests, both strain hardening and softening of the waste samples were observed, depending on the difference in vertical stress. Based on the Pearson correlations among measured physicochemical and mechanical parameters, it was found that the loss on ignition (LOI) would be a good indicator to quickly assess the mechanical parameters of "new" and "old" waste materials, due to the small sensitivities to waste age and climate conditions in Sri Lanka. In particular, LOI correlated well to measured specific gravity and compaction properties, and the r2 values of correlations exceeded |0.80|. [ABSTRACT FROM AUTHOR]

Water repellency (WR) of soils can induce hydrological problems such as reduced water infiltration, enhanced surface runoff and erosion, and the forming of preferential flow patterns in soil. Although soil organic matter (SOM) may cause both soil aggregation and a hydrophobic-material-coating of aggregates, little is known about WR in aggregated soils. We investigated the degree of WR as functions of volumetric water content (0) and pF [= log ([psi]; soil-water potential)] for sieved fractions of a volcanic ash soil samples from different depths with varying soil organic carbon (SOC) contents of between 1.1 and 12.3%. Water repellency was determined by the molarity of ethanol droplet (MED) test. Water repellency was observed in the samples with SOC [greater than or equal to] 4.6%, and the effects of sample pretreatments (pressure chamber desorption, air-drying at 20[degrees]C, and oven-drying at 60[degrees]C) on the degree of WR were small. The degree of WR varied greatly with both SOC content, [theta], and pE Peaks of WR were observed when the water retained in intra-aggregate pores was drained to a moderate extent with the corresponding pF values located in a relatively narrow range from 3.2 to 3.6. This indicates that the hydrophobicity of high-SOC aggregate surfaces might be enhanced the most at a specific soil-water potential. Examining relations between water repellency parameters, the integrated areas below the WR-[theta] and WR-pF curves were useful indexes for characterizing WR, and linear relationships between the integrated areas and both SOC and water contents at maximum repellency were found. Abbreviations: MED, molarity of ethanol droplet; SOC, soil organic carbon; SOM, soil organic matter; WR, water repellency; VG, van Genuchten.