Search Results (8)

This article presents the results of laboratory tests conducted to identify the granulometric stabilization and chemical improvement techniques used in an experimental segment of the unpaved BR-030 highway in the Maraú Peninsula, Bahia. The segment was designed to evaluate the performance of primary coating sections stabilized with sand, clayey gravel, reclaimed asphalt pavement (RAP), and simple graded crushed stone (GCS), as well as chemically improved with Portland cement and hydrated lime. The laboratory campaign focused on mechanical resistance, resilient modulus, and permanent deformation tests. In this research, chemical improvement with the addition of 2% Portland cement presented the most promising results for potential application in the section of the BR-030 highway intended to remain unpaved. Additionally, a life cycle assessment (LCA) revealed that mechanical stabilization of the primary coating has the lowest environmental impacts, making it a suitable and sustainable option among stabilization methods. Full article

In cold mountainous regions of China, the construction of highways is challenging, owing to frost damage of weak subgrade soils and the difficulties posed from dealing with waste materials derived from tunnel excavation. In order to address these issues, Wu et al. proposed a new approach of using coarse gravel reclaimed from tunnel excavation as an antifrost structural fill replacing the top layer of frost-susceptible subgrade soils. This approach was validated against the results of field investigations on the highway between Tanchang county and Diebu county (the TDH) in south Gansu Province, northwest China, but only studied the results of the first year. As an environmentally friendly and sustainable ground-treatment method, this strategy merits extensive research and widespread implementation. In this study, the frost-heave deformation of a two-year monitoring period is investigated through a field trial, and a frost-heave model is applied to explore the growth of the ice lens and accomplish the quantitative prediction of frost heave based on experimental measurements. The fine particles of reclaimed gravel sediments from the Lazikou tunnel are found to be resistant to frost. The measured values of the maximum frost heave are significantly lower than the permissible limit of 50 mm specified in the Chinese standards. The reclaimed gravel could significantly reduce frost heave. With a 2 m thick gravel fill, frost heave could be reduced by more than 70% when the groundwater table is located at a depth greater than 3 m. An empirical relationship to predict the frost heave in terms of the gravel fill thickness is proposed. This study presents a safe and sustainable approach focusing on the construction of highways in cold mountainous regions. Full article

The use of reclaimed asphalt pavement (RAP) is necessary for sustainable and cost-effective road infrastructure construction. This research investigates the effect of the area of weak zones (WZ) on the resilient modulus (M_RT) of mixtures of fresh asphalt with 20% RAP. Experimentation on fresh asphalt–RAP mixtures comprising Superpave (SP-A, SP-B) and Asphalt Institute (MS-2) gradations with 20/30, 40/50, 60/70 and 80/100 penetration grade binders was carried out. WZ were determined based on the analysis of magnified digital images of asphalt specimens obtained using optical microscopy. This study demonstrates that the 20/30 grade binder caused an increase in the M_RT at 25 °C up to 1.8, 2.9 and 9.2 times for a 0.1 s load duration, and 2.4, 3.0 and 9.7 times for a 0.3 s load duration. In contrast, improvement at 40 °C was observed to be up to 1.9, 3.1 and 9.7 times for a 0.1 s load duration, and 1.9, 3.0 and 12.4 times for a 0.3 s load duration in comparison with 40/50, 60/70 and 80/100 grade binders, respectively. Experimental data were validated by factorial analysis. Power trendline equations were also developed between M_RT and WZ to explain the effect of gravel particle orientation on the sustainable resilience of surface course mixtures. Full article

In large projects such as dams, embankments, and seawalls, it is sometimes important to determine the compressive properties of a mixture containing soil and gravel with particle sizes exceeding 75 mm. The Saemangeum Renewable Energy Vision Proclamation Ceremony, held in October 2018 in Korea, confirmed and promulgated the plan to build a total of 4.0 GW of renewable energy power generation complex in the Saemangeum area. The project will be carried out on an area of 31.95 km², and a 1.0 GW offshore wind power development plan is in progress. Since most of the Saemangeum area has a soft ground layer that has been reclaimed, a key research institute is absolutely necessary to lead in the stabilization of the supporting structures for power generation facilities and to achieve the renewable energy 3020 policy in extreme environments. Hence, it is meaningful to investigate the effect of gravel content (P) on the ground strength characteristics. However, such investigation cannot be routinely performed due to the limited size of the equipment available. Several equations have been proposed in the literature to modify the compaction properties of gravel-mixed soils containing coarse aggregates. Among these is the proposed equation by Walker and Holtz, which has widely been used. However, the use of this equation in the case of high gravel content is not appropriate because the physical meaning of this equation is not clear and does not apply to materials with gravel content exceeding 40%. Therefore, a better quantitative evaluation method in determining material characteristics according to gravel content must be established through laboratory tests on samples of acceptable particle size for the experimental equipment. To obtain the compressive properties of decomposed granite soil (D-G-S), in this study, the results from large-scale one-dimensional compression tests on samples compacted at various gravel concentrations, constant compaction energy, and constant water content were analyzed. To quantitatively evaluate the properties of D-G-S according to the gravel content, a modified formula based on the two-phase mixing theory was utilized. It was shown that the degree of mixing between the gravel and sand for the conditions of D-G-S used in the experiments was high, at 0.85. To estimate the compression curves of D-G-S at various gravel content, the compression curves of purely sand (P = 0%) and purely gravel (P = 100%) materials, and the value of R_m = 0.85 were utilized, and it was shown that the compression index and swelling index curves estimated using the method presented in this study were in good agreement with the experimental results. To confirm the engineering applicability of the presented method, finite element analysis was performed, and as a result, it was revealed that it can be sufficiently applied in the simulation of embankment settlement. In order to obtain more reliable results in the future, verification using various samples is required. Full article

Thirty years ago, Mongolia’s Gobi Desert was intact, roadless and had low traffic, and it was a refuge for many endangered and rare species. A large mining boom and significant livestock grazing are currently putting pressure on the desert. Mining products were transported by trucks on dirt (gravel) roads between 2000 and 2012. Emphasizing its importance in the Mongolian economy, a paved road was constructed in 2012 along the dirt road. Unfortunately, vegetation along the paved road was removed without restoration. In the desert, locals continue to use, create and extend dirt roads. The impact of these roads on the vegetation has yet to be studied. We estimated the spatial extent of the dirt-road corridors in three time intervals (the years 2010, 2015 and 2020) and evaluated the vegetation along both paved and dirt roads at three distances (100, 500, and 900 m) from the road. Within ten years, the length of paved roads and soil dirt roads nearly doubled, although the majority of them were developed and created between 2015 and 2020. A single track makes up around 42 percent of the soil road, whereas the remaining 58 percent are roads consisting of three to four tracks with an average width of 26.5 m. The vegetation along the paved road was lower in terms of species richness, canopy cover, and the basal gap between perennial plants and biomass, compared to the soil road. Although the effects of soil roads on the vegetation along the roads is less negative than the effects of the paved road, the corridors formed along the soil roads span a non-negligible area of pastureland in the region. The vegetation along the already-constructed paved road in the desert should be artificially reclaimed with the aim of expediting natural revegetation. Moreover, a “new legislation” is required to prevent continued degradation due to the ongoing creation and extension of soil road corridors by local populations in the desert. Full article

To study the shrinkage and freeze-thaw durability of cement-fly-ash-stabilized brick and concrete reclaimed gravel mixture (CFRBCA), recycled gravel was used to replace 100% of the natural gravel in cement-and-fly-ash-stabilized gravel (CFRCA). Five different mixture ratios of recycled brick and recycled concrete were designed. Dry shrinkage tests, temperature shrinkage tests, freeze-thaw cycle tests, ultrasonic tests, and microscopic analyses were then conducted. The test results showed that the water loss rate, dry shrinkage strain, and dry shrinkage coefficient of CFRBCA increased as the age and brick content increased and tended to be stable by approximately the 40th day of age. The reclaimed gravel content had a great influence on the temperature shrinkage of CFRBCA: the temperature shrinkage coefficient first increased and then decreased as the temperature decreased and reached a peak at −10 to 0 °C. The microstructure analysis showed that as the number of freeze-thaw cycles increases, cracks appear and extend in the CFRBCA, hydration products gradually change from dense to loose, and the Ca/Si ratio increases. Through these experiments, the logarithmic relationship model between ultrasonic wave velocity and CFRBCA strength damage, which can better predict the strength loss caused by CFRBCA variation with freeze-thaw cycles, was established. The brick content is the key parameter affecting the durability of the freeze-thawed CFRBCA, and thus the brick slag content should be properly controlled in engineering applications. Full article

Hydrogeochemical analyses were carried out to identify geochemical processes occurring in the low-lying coastal aquifer of Ravenna, North Adriatic Sea (Italy). The area is characterized by a complex coexistence of several environments: coastal dunes, paleodunes, pine forests, freshwater wetlands, rivers, brackish lagoons, gravel pit lakes, reclaimed lands, agricultural fields and industrial areas. Water quality is of primary importance for the sustainability of these, areas and a full understanding of geochemical processing is fundamental for their management. A total of 104 water samples was collected from groundwater wells and surface water bodies, and analyzed for the major and trace elements (TEs). Field measurements of chemical-physical parameters were carried out by a multiparameter device XS PCD650; major elements were analyzed following the Italian National Environmental Agency standards (APAT-IRSA 2003), while TEs were analyzed by ICP-AES/ICP-MS. The major findings include: organic matter degradation in salinized and anoxic conditions; TEs concentrations related to water–sediment interactions, i.e., adsorption, ion exchange, redox reactions, mineral dissolution and precipitation; anthropogenic contamination from pesticides and fertilizers use; pollution from industrial district; TEs enrichments and depletion due to groundwater salinization and water management practices; comparison of TEs concentrations with respect to national and international thresholds. The findings can provide water managers and local authorities with a comprehensive framework of the coastal water hydrochemistry, allowing a better understanding of the effects of current management practices and the design of mitigation measures to reduce water resource deterioration in the studied coastal area. Full article

A pilot study using natural treatment methods such as a horizontal subsurface flow in constructed wetlands to treat the reverse osmosis concentrate (ROC) was conducted to manage nutrient and metals to reclaim the product water for the coastal wetlands and agriculture use. ROC had a significantly greater concentration of constituents than concentrations typically found in effluent of secondary treated wastewater. During the six-month wetland pilot study, the removal of nutrients from the ROC was monitored. Bulrush (Schoenoplectus californicus), a common wetland plant, tolerated high total dissolved solids (11,000–12,700 mg/L) and provided significant mass removal of nutrients in the concentrate (61% removal of nitrogen and 21% removal of phosphorus) under two hydraulic residence times (HRT1 = 2.5 days and HRT2 = 5 days). Concentration-based reductions of oxidized nitrogen, ammonia-nitrogen, orthophosphate were 63%, 23%, and 23% during HRT1 and 55%, 24%, and 11% during HRT2, respectively. Nutrient mass balance estimates of this microbially dominated wetland system and analysis of mass transformation pathways were also performed. Because of evaporative water loss, mass removal efficiencies were significant. Key processes included denitrification for nitrogen removal, possibly supplemented with Annamox reduction of NO₃-N; labile carbon assimilation supporting oxidized nitrogen reduction; and phosphate-P uptake and precipitation within the gravel substrate. The results indicated that engineered wetland treatment offers useful benefits to the management of ROC produced from secondary treated effluent of wastewater through reduction in volume through evapotranspiration and reduction in concentration through biological transformations for beneficial reuse. Full article