Search Results (14)

Gobi solar greenhouses (GSGs) enhance energy, food, and financial security in Gobi Desert regions through passive solar utilization. Thermal mass walls are critical for plant thermal comfort in GSGs but can lead to resource waste if poorly designed. This study pioneers the integration of payback period constrains into thermal mass wall optimization, establishing a new performance–cost trade-off approach for GSG wall design, balancing thermal performance and economic feasibility. We quantified energy-conserving benefits against wall-construction costs to derive the optimal inner-layer thicknesses under <25% GSG lifespan payback criteria. Three GSG thermal mass walls in China’s Hexi Corridor were optimized. For the concrete-layered, stone-layered, and pebble-soil walls, the optimum inner-layer thicknesses were 0.47, 0.65, and 1.24 m, respectively, with extra costs of 620.75, 767.60, and 194.56 RMB yuan; annual energy-conserving benefits of 82.77, 102.35, and 51.88 RMB yuan·yr⁻¹; and payback periods of 7.5, 7.5, and 3.75 years. A dynamic thermal load analysis confirmed that GSGs with optimized walls required no heating during a sunny winter solstice night. Cooling loads of 33.15–35.27 kW further indicated the potential to maintain thermal comfort under colder weather conditions. This approach improves plant thermal comfort cost-effectively, advancing sustainable Gobi agriculture. Full article

This paper demonstrates the benefits of adapting Zero Velocity Update (ZVU) algorithms in foot-mounted pedestrian inertial navigation by finely tuning the algorithm to account for the type of terrain over which the pedestrian travels. Conventional ZVU algorithms for foot-mounted inertial navigation are designed for indoor use and do not account for differences from various terrains. Different terrains affect the natural pedestrian gait and how zero velocity intervals (ZVIs) are identified. By tuning the algorithm to account for accelerometer and gyroscope magnitude and walking cycle duration across four terrains (concrete, grass, pebbles and sand), the accuracy is improved up to 31.04%, dependent on the terrain, and is viable for outdoor use. Full article

Hydraulic engineering projects in high-altitude environments are subject to significant diurnal temperature variations, necessitating concrete with high freeze–thaw resistance. Aggregates play a crucial role in the freeze–thaw durability of concrete. However, the impact of different parent rock types on concrete’s freeze–thaw resistance remains underexplored. This study investigated the effect of five common coarse aggregate types—granite (Gr), tuff (Tu), sandstone (Sa), limestone (Li), and pebble (Pe)—on the freeze–thaw resistance of dam concrete subjected to freeze–thaw cycles. The relationship between the rock type’s properties and the degradation patterns of concrete with different aggregates under freeze–thaw conditions was analyzed. Additionally, the damage mechanisms at the paste–aggregate interface were explored using SEM-EDS, pore structure analysis, and nano-indentation, along with the characteristics of the hydration products in the transition zone. The results showed that the aggregate type significantly influences freeze–thaw resistance, with Gr performing best (Gr > Li > Pe > Tu > Sa), correlating with pore structure and pore spacing. Gr, due to its superior freeze–thaw resistance, was optimal for regions with stringent freeze–thaw conditions. Although the interface zone exhibited a lower elastic modulus and hardness compared to the paste region due to a lower total amount of hydration products, these differences did not substantially affect the freeze–thaw performance of the concrete. This study, contributing to the expansion of the existing knowledge base on the effects of aggregate types on freeze–thaw resistance, provided valuable engineering insights for the selection of coarse aggregates in hydraulic concrete applications in high-altitude regions. Full article

Bolivia has abundant pebbles, while the supply of crushed stone is limited and unstable. Thus, the resource utilization of local pebble as a coarse aggregate and the guarantee of concrete durability are the key scientific issues in the Sucre Highway Project. In this paper, a comparative analysis was conducted of the performance of crushed stone concrete and pebble concrete. Additionally, the impact of fly ash on the water permeability resistance of concrete was investigated. The results indicate that the apparent density, bulk density, and void ratio of pebbles are lower than those of crushed stone, and the aggregate gradation of pebbles is dispersed. The type of aggregate is the primary factor influencing the splitting tensile strength of concrete, with the main failure modes of pebble concrete being slurry cracking, aggregate crushing, and interface debonding. While aggregate and fly ash have a minor effect on compressive strength, they significantly impact flexural tensile strength; however, all concretes meet the requirements for extra-heavy, very heavy, and heavy traffic load levels. In terms of impermeability, fly ash effectively mitigates the negative impact of aggregate type on the impermeability of concrete. These findings support the application of pebble concrete in the highway project. Full article

Obtaining river or sea pebbles from local resources for concrete production is considered an economical and eco-friendly alternative, particularly in marine and island-offshore engineering. However, the resulting changes in the mechanical properties of these concrete have attracted attention. This study investigates the compressive behavior of concretes where river or sea pebbles partially (i.e., 33% and 67%) or fully (i.e., 100%) replace traditional gravel as coarse aggregate, using a noncontact full-field deformation measurement system based on digital image correlation (DIC). Compared to the traditional gravel concrete (GC), compressive strengths of the river pebble concrete (RPC) at constitution rates of 33%, 67%, and 100% decreased by 6.5%, 29.8%, and 38.9% while those values of the sea pebble concrete (SPC) decreased by 13.1%, 32.7%, and 44.3%, respectively. Meanwhile, SPC exhibited slightly lower compressive strength than RPC. The peak strains of both SPC and RPC decreased at lower substitution rates, although their stress-strain curves resembled those of GC. In contrast, RPC and SPC at higher substitution rates exhibited a noticeable stage of load hardening. Full-field deformation data and interfacial characteristics indicated that the compressive failure modes of both RPC and SPC showed significant interfacial slipping between pebbles and mortar with increasing coarse aggregate substitution rates. In comparison, fractures in coarse aggregate and mortar were observed in damaged GC. The study demonstrated that the spatio-temporal compressive deformation response and failure modes of SPC and RPC were distinct due to the introduction of pebbles, providing insights for engineering applications of river/sea pebble concrete in practical offshore or island construction projects. Full article

In the past fifteen years, the contamination of the Italian marine coastal environments by asbestos cement materials (ACMs) represents a known crux mostly reported or denounced by mass media and environmental associations. A recent research reporting compositional and textural data related to ACMs found in the beach deposits of a protected natural reserve (Cape Peloro, Messina, Italy) induced the author to perform new petrographic and textural analyses on the Cape Peloro beach sands, pebbles, cobbles (BSPC), and technofossils (bricks, tails, slab, concrete), associated with the previously studied ACMs, in order to compare the data with those of the ACMs previously reported in the literature. The petrographic investigations allowed the author to determine that beach sands and weakly gravelly sands were characterized by a quartzo–lithic signature, being mainly composed of metamorphic grains of quartz (50–60%) and metamorphic lithics (40–50%, mainly composed of polymineral quartz + microcline, quartz + plagioclase, quartz + biotite, quartz + muscovite grains, and monomineral opaque minerals, plagioclase, k-feldspar, and almandine garnet grains), whereas the pebbles and cobbles were made of acid intrusive (granitoids) and metamorphic rocks (gneiss, augen gneiss prevailing). Pebbles and cobbles made up of porphyroids could derive from the cannibalization of the underlying lower to middle Pleistocene siliciclastic deposits of the Messina Formation. Differently, the gneiss, augen gneiss, and granitoids forming the beach pebbles and cobbles, being present both in the crystalline rocks of the Aspromonte Unit and in the clasts of the SGMF, could originate from both of them. Textural investigations allowed the author to characterize grain size, shape parameters, and roundness in the beach deposits. These were mostly composed of sands and weakly gravelly sands with medium grains. Parameters, such as elongation and flatness, showed higher values in the BSPC than in the technofossils. The shapes of the BSPC were mostly from oblate to equant, whereas the shapes of the technofossils were mostly from bladed to oblate. The main differences depended on the original shape of the technofossils, being mostly platy, and their softer composition. The roundness was from angular to sub-rounded. In the Ionian coast of the Cape Peloro peninsula, the source areas for the well-rounded ACM found on the beach and in the beach deposits could have at least four different origins: (i) Possible landfills widespread since the 1970s in the intensively urbanized coastal areas. (ii) Direct abandonment in the coastal area. (iii) Direct abandonment in the streams. (iv) Activities to counteract the erosion/lack of sediment using non-conforming materials. Considering the diffused damage caused by the coastal erosion affecting most of the Italian coast and the obvious increasing dispersion of the asbestos fibers from the ACMs over time, effectual counter actions to prevent further contamination and guidelines for clean-up efforts are necessary. Full article

During the concrete mixing process, the transition of aggregates from a dry to a moist state introduces a crucial dynamic that significantly influences particle interaction, consequently impacting mixing homogeneity. In this paper, based on the discrete element method, the effect of aggregate moisture on the mixing process of sand and stone was investigated. The interaction between dry particles was described by the Hertz–Mindlin model, while the interaction between wet particles was calculated by the linear cohesion model considering the liquid bridge force. Additionally, a functional relationship between the moisture content and the parameters of the linear cohesive contact model was established. The results show that the numerical method can be employed to simulate the mixing process. Notably, when the moisture content of pebbles ranges from 0% to 0.75% and that of sand ranges from 0% to 10.9%, the linear cohesion model is deemed suitable. The standard deviation of the mixing homogeneity of wet particles is lower than that of dry particles for short mixing time, indicating that a small amount of liquid enhances mixing homogeneity. However, moisture has no obvious effect on mixing homogeneity for a long mixing time. This nuanced understanding of the interplay between moisture, particle interactions, and mixing duration contributes valuable insights to optimize concrete mixing processes. Full article

Significant gravel mines, representative of four regions of Hungary (northeast, central, northwest, and southwest) were systematically sampled to characterize their sand and pebbles as potential constituents of nuclear-grade concrete. The samples were analysed for their elemental compositions as a function of the mining locality and grain size, using two complementary neutron-based analytical techniques, prompt gamma activation analysis (PGAA) and neutron activation analysis (NAA). The combined analysis resulted in reliable mass fractions for over thirty elements that could be used to assess the radiation shielding and activation properties of the resulting concrete, essential in nuclear applications, by means of computer simulations. The studied aggregates are proven to be appropriate constituents for biological shielding at radiological centres, NPPs, and at nuclear research installations, even in mixed neutron/gamma radiation fields. The elemental compositions also revealed geochemical differences between the sedimentologically different regions. Full article

Easy detachment is as important as reliable an attachment to climbing robots in achieving stable climbing on vertical surfaces. To deal with the difficulty of detachment occurring in wheeled and track-type climbing robots using bio-inspired spines, a novel climbing robot utilizing spiny track and dual-rail mechanism is proposed in this paper. The spiny track consists of dozens of spiny feet, and the movement of each spiny foot is guided by the specially designed dual-rail mechanism to achieve reliable attachment and easy detachment. First, the design of the climbing robot and the dual-rail mechanism are presented. Then, the dual-rail model is constructed to analyze the attaching and detaching movements of the spiny feet, and a mechanical model is established to analyze the force distribution on the spiny track. Finally, a robot prototype is developed, and the analysis results are verified by the experiment results. Experiments on the prototype demonstrated that it could climb on various rough vertical surfaces at a speed of 36 mm/s, including sandpaper, brick surfaces, concrete walls with pebbles, and coarse stucco walls. Full article

Disposing of waste tires is a major environmental and economic issue. Different recycling methods have been studied to account for its re-usage. This project aims to evaluate the possible usage of shredded waste tires in thermal energy storage (TES) applications, whether they are sensible or latent materials. An experimental setup has been developed with seven compartments. Each compartment contains different TES materials, including tire crumbs, paraffin wax, paraffin wax with shredded tires, pebbles, pebbles with shredded tires, concrete, and concrete with shredded tires. In all cases of the mixture, the base materials are 60%vol, and the tire crumbs are 40%vol. The experimental included three locations for temperature measurements in each compartment, solar irradiation, and ambient temperature. The tests were carried out from 9:00 a.m. till 7:00 p.m. and repeated for five days to account for the weather’s daily change. Results revealed that mixed 60%vol pebbles and 40%vol shredded tires have the highest recorded temperature, at 112.5 °C, with a 39.5% increment compared to pure pebbles. The interesting finding is that the added tire crumbs reduced the storage capacity of the paraffin wax, which is latent TES material. At the same time, it increased the storage capacity of the concrete and pebbles, which are sensible TES materials. Adding 40%vol of tire crumbs to the paraffin wax has a negative effect, where the thermal storage capacity is reduced by 43%, and the discharge capacity is reduced by 57%. In contrast, the concrete and the pebbles show enhanced storage capacity. Adding 40%vol of crumbs to the concrete increased the charging capacity by 54% and discharging capacity by 33.7%. The 40%vol added tire crumbs to the pebbles increased its charging capacity by 25% and the discharging capacity by 33%. The rudimentary assessment encourages further investigations on using the wasted tires crumbs for TES. The results reveal the probability of a circular economy using wasted tires with sensible TES for solar-to-thermal energy conversion. Full article

The classical continuum mechanics theory cannot sufficiently describe the effect of pebbles on projectile, which leads to a large calculation error. In this paper, an orthogonal curvilinear coordinate system is constructed, which effectively describes and perfects the normal cavity expansion theory. A couple stress theory based on the normal cavity expansion is proposed in which not only the tangential movements but also the rotations of the concrete medium are considered. According to the high-speed impact of pebble concrete, combined with dynamic equations and the FE simulation, the theoretical and simulation results of pebble particles scale on warhead resistance are compared. It is shown that, the larger the scale of pebble particles, the stronger the effect of rotation on the resistant force applied on the warhead. Full article

Crushing is one of the most energy-consuming technological processes. The purpose of grinding is to achieve the desired grain size of mineral raw materials. The process of grinding consists of many factors, for example, the size and form of crushed grains, as well as their mutual arrangement inside the crushing machine chamber, the technological parameters of the crusher, the material properties, and the speed of the moving grains. One of the key parameters of the aggregate is its resistance to grinding. Resistance to grinding is related to the strength of the products made from aggregates subjected to grinding, which affects the overall quality of these products. Therefore, the aim of this study is to analyze the impact of the crushing of natural aggregate on the LA crumbling strength index. Two types of aggregates were analyzed—natural gravel and natural pebbles crushed in a crusher. Aggregates were acquired from two mines belonging to the plant Kruszgeo S.A. in Rzeszów, i.e., ZEK (Zakład Eksploatacji Kruszywa) Ostrów and ZEK Strzegocice II. The aggregate crushing process was carried out for 4–8 mm and 10–14 mm fractions using cone crushers of the 1044 type. Aggregate crushing was carried out in a Los Angeles drum, in accordance with the requirements of EN 1097-2:2020. The analysis showed that for grits of the 10–14 mm fraction, the lower values of the LA indices were obtained, which allows for obtaining a bigger index of crushing strength than in the case of crushing using the 4–8 mm fraction. This analysis showed how important the process of grinding aggregates is and, thus, the appropriate selection of fractions for the grit crushing process for the aggregate strength on grinding. Subjecting the aggregate to the grinding process results in an improvement in the crushing strength indicator, thus obtaining better strength parameters of the products manufactured from the aggregates subjected to the process of crushing (for example, concrete). The originality of the study is an analysis of key Polish aggregates and the crushing strength index. Full article

Most hydrotechnical buildings under construction demand the concrete mixture to be set directly under water. The main reason for such a procedure is to limit the washing away of the the concrete binding mixture and to increase the efficiency of organisation of work so as to ensure continuity in concreting. The impact on the aquatic environment of recent developments in concrete technology and the use of new components has not yet been established. Natural pebble aggregate containing portland cement and fugacious siliceous ash as a binder was used to prepare BP concrete samples, while concrete marked LB was composed with lightweight aggregate and portland cement as a binder. The aim of this paper was to answer to the question whether hydrotechnical concrete of different compositions (BP and LB) and the technology of setting in a water habitat have any influence on the life condition of commonly occurring Dreissena polymorpha (Mollusca, Bivalvia). The lethal effect of two types of freshly hardening concrete was observed. In the case of LB concrete the lethal outcome for D. polymorpha could be the effect of a considerable increase of electrolytic conduction in the test cultivation. In the case of BP the parameters of electrolytic conductivity and pH did not exceed the values appearing in lakes. The possibility of the occurrence of toxic compounds of D. polymorpha, arising from the reaction of the aquatic/lake environment or the elution of some components should be taken into account. D. polymorpha serves as an indicator of toxicity in the aquatic environment and therefore can be used as a model organism in the analysis of the influence concrete on the natural environment. The results obtained in this study indicate the significant impact of modern chemical composition of concrete on the aquatic environment and the living organisms that cover it. They underline the need for research based on the hydrobiont reaction to the substances used in the natural environment. Full article

To evaluate the effects of water velocity and artificial substratum characteristics on the growth rate and biomass accumulation of periphyton, an artificial stream mesocosm experiment was conducted using alternative water sources collected from the Mangwall Stream (MW), the Han River (HR), and bank filtration water (BFW) from the Han River in the Republic of Korea. The measured concentrations of organic matter and inorganic nutrients in the MW were higher than in the HR and BFW. The surface of tile is relatively smooth and nonporous, whereas the surfaces of concrete and pebble are rough with numerous isolated pores in which filamentous periphyton become immobilized against hydrodynamic shear stress and mat tensile strength. Compared with the periphyton biomass of the HR and BFW, the peak biomass in the MW was significantly higher due to higher nutrient concentrations in the MW. Reasonable linear relationships (R² ≥ 0.69) between water velocity and total periphyton biomass/growth rate were obtained, indicating that water velocities above critical values can cause a reduction in biomass accrual. In addition, reasonable relationships (R² ≥ 0.58) between specific surface area and total periphyton biomass were obtained for the HR and BFW, indicating that an increase in the specific surface area of the substratum can lead to an increase in periphyton biomass in a nutrient-poor water body. Principal components analysis (PCA) results indicate that nutrient concentrations were the first dominant limiting factor for the growth and accumulation of periphyton, and water velocity and the specific surface area of the substratum were determined to be potential limiting factors. Consequently, the growth rate and biomass accumulation of periphyton were considered to be a complex function of nutrient concentrations, water velocities, and substratum characteristics. Full article