This study collected basic information and conducted waste composition surveys to identify the present management condition of construction and demolition waste (CDW) landfills in Hanoi of Vietnam and to characterize waste composition and grain size distribution of CDW dumped at landfills. Basic information on seven CDW landfills under operation or closed/abandoned was collected, and the waste composition and the grain size distributions of dumped CDW at two landfills were investigated. Results showed that only one landfill site is currently under operation in Hanoi. Sanitary conditions of investigated landfills were relatively good without dumping of hazardous waste. Illegal dumping of domestic waste from residents, however, could be observed more or less at all sites due to an unclear boundary between dumping and surrounding areas. To improve current management of CDW landfills, a suitable recording system of accepted/dumped CDW and technical support for site managers are required as well as the implementation plan for developing and renovating landfills. Based on the results of the waste composition survey, the major components of dumped CDW were “Concrete”, “Clay bricks”, and “Soil-like”, and the sum of these materials reached >80% of the total. Grain size distributions of “Concrete” ranged from 10–600 mm and of “Clay bricks” ranged from 10–300 mm. Technical recommendations to examine a potential availability of dumped “Concrete” and “Clay bricks” as a base material in road construction are summarized from the viewpoints of segregation from “Soil-like” and impurities, grading of “Concrete” and “Clay bricks”, mechanical properties and environmental safety, and economic feasibility. The findings in this study raise challenges and perspectives to establish sound CDW management and to promote sustainable development of CDW recycling in Vietnam.

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.

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, C_i = 10–1000 mg/L; oil droplet size in water 80% in high oil concentration solutions (C_i = 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.

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 (CA_wa), oil droplets in water (CA_ow) and coated HA concentrations. The CA_wa 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 CA_ow gradually decreased exponentially with increasing HA concentration. In particular, the CA_ow 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 CA_wa and CA_ow 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.

Bentonite is often considered as one of the key components of the Engineered Barrier System (EBS) for the radioactive waste disposal; mechanical, thermal, and hydraulic behaviors of bentonite should be thoroughly studied to ensure the emplaced the quality and to control the performance of EBS. This study examined the effects of dry density and relative humidity (RH) on microstructure and mass transport characteristics of Granulated Bentonite Mixtures (GBM). The tested GBM samples were prepared by sieving and grading Japanese bentonite (trade name: OK Bentonite, Kunimine Industries, Japan). For dry density-controlled conditions, air-dried GBM samples (RH 60%, water content of 6.38% by weight) were packed at six different dry densities ranging from 1.25 to 1.75 g/cm3. The samples for humidity-controlled conditions were prepared at the dry density of 1.45 g/cm3 and stored at RH 90% (0 to 12 weeks). A microfocus X-ray computerized tomography (MFXCT) scanning apparatus was used to visualize the microstructures of packed tested samples. For each tested sample, the mass transport parameters of gas diffusivity (Dp/Do), air permeability (ka), thermal conductivity (λ), and volumetric heat capacity (C) were measured. The results indicated that dry density greatly affected the CT brightness values of GBM; the histogram of CT brightness well captured the internal distribution of density and the CT brightness homogenized more with increasing in dry density. The measured Dp/Do and ka. were mainly controlled by the dry density. On the other hand, the thermal properties such as λ and C were governed both dry density and RH.