Compaction Characteristics Research Articles

Impact of microplastic pollution in terrestrial ecosystem on index and engineering properties of sandy soil: An experimental investigation

Sandy soils cover a major portion of various natural and managed ecosystems. Soil health plays a key role in achieving sustainable development goals 2, 3,11, 12, 13 and 15. The engineering properties of soil are crucial in determining the stability and safety of structures. The increasing microplastic contamination in the soil ecosystem creates a need to study the effect of terrestrial microplastic contamination on the strength and stability of soil and therefore on the index properties and engineering properties of the soil. The present paper investigates, the effects of varying concentrations (2 %,4 %,6 % (w/w)) of Low-density polyethylene (LDPE), Polyvinyl chloride (PVC), and High-density polyethylene (HDPE) microplastics on the index properties and engineering properties of sandy soil for varying observation days. The moisture content, specific gravity, shear strength, compaction characteristics and permeability are found to be significantly altered by changing the concentrations of microplastics but, insignificant changes are observed with respect to observation days. The shear strength value of non-contaminated sandy soil is 1.74 kg/cm2 which reduces after 5th observation days as 0.85 kg/cm2, 0.90 kg/cm2, and 0.91 kg/cm2 for 2 %, 4 %, and 6 % LDPE microplastic contamination respectively. Similar trends are observed for PVC and HDPE microplastic contamination. It is also observed that although the shear strength value decreases, the cohesion value increases for the microplastics-contaminated sandy soil. The coefficient of permeability for non-contaminated sample is 0.0004 m/s which reduces for 2 % LDPE microplastic contamination to 0.000319 m/s, for 4 % to 0.000217 m/s, and 6 % to 0.000208 m/s respectively. Similar trends of are observed for the PVC and HDPE microplastic contamination. The soil strength and structural stability are affected due to alterations in soil index and engineering properties. The paper provides detailed experimental evidence of the impact of microplastic pollution on index properties and engineering properties of sandy soil.

Effect of soil amendments on the compaction characteristics, hydraulic conductivity, and tire sinkage potential of roadside soils

State highway agencies (SHAs) are required to comply with the National Pollution Discharge Elimination Permit (NPDES), which requires that the majority stormwater runoff from highways infiltrate into the roadside and that agencies implement soil based best management practices (BMPs). Per this new permit, SHAs are to install soil based BMPs that can absorb the 85th percentile of a 24-hour stormwater event. The area used for this purpose is typically the road embankments/slopes located adjacent to the roadside, best known as Clear Recovery Zone (CRZ). The CRZ must be traversable and recoverable to meet roadside traffic safety standards. A major concern for SHAs is the uncertainty on how these BMPs will affect the safety of a vehicle should that vehicle leave the roadway and interact with the soft soils. Considering this concern, the study described in this paper has assessed the impact of soil amendments on the compaction characteristics, hydraulic conductivity, and sinkage potential of six native soils of the state of California. These six soils were amended with four of the most used BMPs by the California State of Transportation (Caltrans). The results showed the hydraulic conductivity drops when the percentage of organic matter increases in the soil. They also showed that soils with a soaked surface had much larger sinkage than soils with an intact surface, this sinkage potential increase at the soak condition is proportional to the soil’s clay content.

Evaluation of potential shaft backfill formulations for use in Canada's deep geological repository

The Canadian Nuclear Waste Management Organization (NWMO) is evaluating Sedimentary and Crystalline geosphere media as potential hosts for a Deep Geological Repository (DGR) for permanent isolation of used nuclear fuel and fuel wastes.Bentonite-aggregate mixtures containing from 50 to 90% by dry mass bentonite were tested. The aggregates used were relevant to the NWMO's DGR geological options (granitic sand (GS) and sand-sized crushed limestone (CRL)). Of importance is that the moisture conditioning fluids used are representative of those that will be encountered at the locations considered by NWMO for their aDGR. These materials, if moisture-conditioned with local groundwater will mean that the porewater of the backfill will be close to chemical equilibrium with its surroundings at the time of placement. The effectiveness of Standard and Modified compaction efforts in densifying these mixtures were evaluated, providing guidance regarding what materials and compaction options are likely to achieve the swelling pressure (Ps) and hydraulic conductivity (k) performance goals (>100 kPa and < 10−10 m/s, respectively) set for shaft backfill once it comes to density equilibrium and chemical balance with the surrounding rock mass.When Standard Compaction Effort was used, aggregate type did not affect densification, while aggregate content and compaction composition fluid did. Dry density increased with increasing aggregate content, while effective montmorillonite dry density (EMDD) showed a small increase as bentonite content increased from 50 to 90%.When Modified Compaction Effort was used, aggregate type and composition of the compaction fluid had little effect on the densification achieved. Dry density achieved steadily decreased with increasing bentonite content and EMDD achieved was little affected by bentonite contents >60% by mass.Hydraulic conductivity values measured were consistent with previously reported data for bentonite and bentonite-aggregate mixtures. The hydraulic conductivity of mixtures prepared using crushed limestone were slightly lower than determined for granitic sand.The swelling pressure and hydraulic conductivity requirements set for the SBF were met for all materials examined (50–90% bentonite blended with crushed limestone or granitic sand, using either standard or modified compaction effort at low salinity. Where highly saline conditions existed, the Ps and k requirements for the shaft backfill were not be met for materials compacted using standard compaction effort.

Effects of Air Void Content, Crumb Rubber, and Pozzolanic Fillers on OGFC Laboratory Performance

Open-graded friction course (OGFC) is recognized for its ability for rapid stormwater drainage and effective noise reduction. Yet, several state highway agencies have limited its use because of concerns about its durability. The objective of this study was to investigate the impacts of air void (AV) reduction, crumb rubber (CR), and pozzolanic fillers on OGFC durability. Six mixtures were fabricated in the laboratory and their performance was evaluated. A control mix, 9.5-NMAS mix, two mixes incorporating CR, and two mixes prepared with pozzolanic fillers (i.e., Portland cement and fly ash) were evaluated. The test factorial was designed so that each mix would be evaluated at three different stages (i.e., production, construction, and field performance). A suite of laboratory tests was conducted including draindown, prediction of compaction effort, Cantabro abrasion loss, Hamburg wheel-tracking, Texas overlay tester, modified Lottman test, and boiling test to evaluate production, compaction, and OGFC resistance to raveling, permanent deformation, cracking, and moisture damage. Results showed that the reduction in AV and the use of CR and pozzolanic fillers considerably enhanced OGFC durability while maintaining appropriate functional performance (i.e., permeability).

Applying the Porosity-to-Cement Index for Estimating the Mechanical Strength, Durability, and Microstructure of Artificially Cemented Soil

Fine, expansive, and problematic soils cannot be used in fills or paving layers. Through additions to these soils, they can be converted into technically usable materials in civil construction. One methodology to make them viable for construction is through a stabilization process. Nevertheless, current methodologies regarding dosage based on compaction effort and the volumetric amount of binder used are unclear. Thus, this research describes cement-stabilized sedimentary silt's strength and durability properties from Curitiba (Brazil) for future application in paving. Splitting tensile strength, unconfined compressive strength, and loss of mass against wetting and drying cycles (W-D) were investigated in the laboratory utilizing greenish-gray silt (originating from one of the Guabirotuba Formation layers, Paraná) and high-early strength Portland cement- ARI (CPV). Utilized were cement concentrations (C) of 3, 5, 7, and 9%, molding dry unit weights (d) of 14, 15, and 16 kN/m3, curing periods (t) of 7, 14, and 28 days, and constant moisture content (w) of 23%. With an increase in cement concentration and curing time, the compacted mixes demonstrate an increase in strength, an improvement in microstructure, and a decrease in accumulated mass loss (ALM) and initial porosity (η). Using the porosity/volumetric cement content ratio (η/Civ), the lowest amount of cement required to stabilize the soil in terms of strength and durability was determined. The porosity/cement index provided an appropriate parameter for modeling the mechanical and durability properties, and a unique equation between the strength/accumulated loss of mass and the porosity/binder index was obtained for the curing times studied. Lastly, C = 5% by weight is the minimum acceptable amount for prospective subbase soil application. Doi: 10.28991/CEJ-2023-09-05-02 Full Text: PDF

DISEÑO DE LA COMPOSICIÓN Y PROPIEDADES MECÁNICAS DE ESCORIAS DE MAGNESIO COMPACTADAS PARA BASES DE PAVIMENTOS EN CARRETERAS

Gradation composition is crucial to the performance of pavement bases, and differently structured pavement bases vary greatly in pavement performance. However, the gradation range recommended in the relevant code is large without specific provision for the gradation range of low-strength aggregates, such as magnesium slags, which easily leads to a wide selection range of synthetic gradation and weak guiding significance to practical projects. To solve the optimization problem of magnesium slag aggregate gradation design, skeleton-dense type gradation was constructed using the Bailey and Stone asphalt concrete (SAC) gradation methods with magnesium slag materials as the base aggregate. Then, the design gradation was optimally adjusted through compaction tests in combination with the fragile nature of magnesium slag materials. On this basis, the applicable gradation range of magnesium slag aggregates in engineering was obtained, and the gradation optimization design method for this kind of material was formed. Finally, the compaction characteristics and California bearing ratio (CBR) of magnesium slag aggregates with design gradation and those with local specification recommended gradation were analyzed. The test results show that the compaction process significantly influences the target gradation of magnesium slag aggregates, and the cumulative change rate of aggregate gradation of the median design gradation is 37.12%. The bearing capacity of the design gradation is excellent, and the CBR values of the upper limit and the gradation's lower limit are greater than 60%, meeting the paving requirements of different traffic load grades and structural layers. The CBR value of the design gradation is better than that recommended by the specification, which verifies the reliability of the gradation algorithm proposed in this study. This study can provide a theoretical reference for the gradation calculation of low-strength aggregates applied to roads. Keywords: road engineering, magnesium slag, gradation design, skeleton-dense type gradation, CBR

Feasibility of granite processing waste as a fill material in geotechnical applications

India is the third largest granite producer worldwide, and an increasing trend in its export has been seen year by year. Granite is generally sold in dimensional and finished form. Large quarried granite blocks are processed to get a finished dimensional granite in processing industries. Processing comprises sawing, grinding and polishing operations. In processing operations, about 30 to 35 per cent of the mass of large granite blocks is left as fine Granite Processing Waste (GPW) in the form of slurry. Dumping of GPW is of major concern for the processing industries; it is often unscientifically dumped. Disposal of GPW in an unscientific manner causes adverse effects on humans and the environment. Delightful results are obtained in previous studies addressing its use in concrete, mortar building blocks and stabilization of expansive soils. GPW has the potential to serve as a fill material in geotechnical applications. However, a comprehensive characterization of GPW addressing its use as a fill material is significantly lacking. The current study intends to characterize GPW in light of its application as a non-conventional fill material in place of natural materials. Based on geotechnical and geoenvironmental tests carried out on GPW involving grain size analysis, Atterberg limits, hydraulic conductivity, swelling potential, compaction characteristics, surface morphology, chemical composition, elemental and mineralogical composition, pH and organic content analysis, it can be inferred that GPW is comparable to conventional fill materials.

Geotechnical-Electrical Evaluation of Soil Compaction Parameters, South of Baqubah City

Soil compaction is fundamental for improving the geotechnical properties of a wide range of engineering structures. Evaluation of compaction parameters is crucial for maintaining the long-term performance of these structures. In this study, geotechnical-electrical relationships were adopted to evaluate the compaction parameters of soil south of Baqubah City. Forty-seven soil specimens, collected from eight locations, were prepared and compacted at various conditions that can be found in the geotechnical practice. First, laboratory tests such as sieve analysis, liquid limit, and plastic limit were carried out to characterize and classify the soil based on USCS classification. Second, the specimens were prepared in the lab using different moisture content, dry density, and compaction efforts. Electrical resistivity measurements were then conducted on compacted specimens using Kangda KD2571B2 instrument. All laboratory tests were performed based on ASTM standards. The results revealed that the soil at the site is fine-grained type CL of medium plasticity clay with sand. Optimum Moisture Content OMC and Maximum Dry Density MDD were, respectively, 14.72% and 1.83 g/cm3 for the Standard Proctor compaction test; and 11.08% and 1.90 g/cm3 for the Modified Proctor compaction test. Geotechnical-electrical relationships achieved showed that soil resistivity is strongly influenced by the main compaction parameters; moisture content, dry density, and compaction energy, particularly at low moisture content. A high correlation coefficient (R2 &gt; 0.98) was achieved for the resistivity-degree of saturation and resistivity-volumetric moisture content relationships. These correlations were validated with R2 (0.896-0.934) between the measured and predicted data, which indicates the advantages of adopting the resistivity method as a complementary tool for the preliminary site investigation.

Study on Compaction Characteristics and Compaction Process of an Unsaturated Silt Based on PFC3D

In order to reduce the construction cost of excessively wet silt roadbeds and improve the compaction quality, this paper studies the compaction characteristics and compaction technology of excessively wet silts through theoretical derivation, indoor experiments, numerical simulation, engineering verification, and other research methods. Based on the pendulum-type liquid bridge structure, this paper uses the Hertz–Mindlin theory, particle motion equation of state, and other theories to modify the force between particles of an unsaturated soil. Through the contact angle, which is a medium, the matrix suction is linked to the water content and is used to approximate the water content state of soil samples. Using PFC3D (particle flow code 3D) numerical simulation software, an unsaturated silt model was established based on Hill contact, and the model parameters were calibrated through basic geotechnical tests and triaxial compression tests. The correctness of the theory is verified by comparing the simulated triaxial compression test of wet silts with the indoor test. By simulating subgrade rolling, considering factors such as the distribution of contact force chain and the variation of compaction degree, the effects of rolling times, strong vibration, and weak vibration on the compaction effect were compared and analyzed. Finally, the optimal rolling and compaction process under the optimal water content is obtained through on-site engineering tests. The results show that: (1) The Hill contact model is reasonable for simulating the wet silt. (2) During the simulation of the roadbed compaction process using PFC3D software, it was found that the compaction degree change during the entire compaction process can be roughly divided into the initial compaction stage and the re-compaction stage. The reasonable number of compaction times was determined to be five through discrete element simulation. (3) It is found from the numerical simulation results that compared to static compaction, both strong and weak vibration compaction can effectively improve the compaction effect of subgrade compaction. The larger the vibration amplitude, the more obvious the improvement of the compaction effect. The compaction effect of strong vibration followed by weak vibration is stronger than that of weak vibration followed by strong vibration. (4) The optimal compaction process obtained under the optimal moisture content of 15% is static pressure once + strong vibration twice + weak vibration twice.

Research and modelling of fiber deformation mechanism of 3D four-direction preform under compression loading

In order to investigate further the compaction characteristics of the three-dimensional four-direction preform of carbon/carbon composite, a model of three-dimensional four-direction numerical preform at the micro-scale was established using the programming language in Python based on the ABAQUS simulation platform more realistically to reflect the micro-structure of the preform. A model of three-dimensional fiber numerical growth was built to describe the changes of fiber bundle cross-section under compressive load considering the random distribution, deflection, bending and the physical characteristics of fibers not penetrating each other in three-dimensional space. In addition to exploring the characteristics of the fiber bundle compaction process in the inter-laminar dimension, the interaction between laminated fibers of the preform was analyzed; the method of finite element was employed to construct a compaction model of the three-dimensional four-direction preform; the deformation of inter-laminar fibers under compressive load was studied by the numerical simulation method; the nonlinear mapping relationship between compressive load and compaction height consistent with the preform compaction experiment was obtained. The results demonstrated that the deflection coefficient of the numerical model was 0.32, which was most consistent with the actual result.

Assessment of engineering properties of slag mixtures as a bottom liner in landfills

This work examines the engineering properties and leachate characteristics of ground granulated blast-furnace slag (GGBS) blended with laterite soil–bentonite mixtures as a bottom landfill liner. In this study, laterite soil is considered a non-expansive and non-plastic clay; in contrast, bentonite is a highly expansive and highly plastic clay. Laboratory experiments were performed to quantify the effect of GGBS–laterite soil–bentonite mixtures on the liquid limit (LL), free swell index (FSI), compaction characteristics, unconfined compressive strength (UCS), hydraulic conductivity (k) and leachate characteristics tests. As the GGBS percentage in the mix blend increased, the LL, FSI, optimum moisture content, k determined with deionised water/diesel oil contaminants and leachate concentration decreased, whereas the maximum dry densities and UCS value increased. Furthermore, X-ray diffraction analysis and energy-dispersive X-ray spectroscopy were performed on UCS samples to determine the occurrence of a hydration reaction in mix blends at 0, 14 and 28 days of curing. The test results revealed that an increase in the calcium (Ca)/silicon (Si) ratio and a decrease in the aluminium (Al)/calcium ratio enhanced the UCS during the curing period. Consequently, 20% GGBS combined with laterite soil–bentonite mixes proved to be the ideal material for landfill bottom liners in waste containment systems.

POLYNOMIAL MODELS FOR PREDICTING TIME LIMITS FOR COMPACTION AFTER MIXING OPERATION OF LATERITIC SOIL REINFORCED USING CEMENT OR LIME

The demand for natural aggregates has increased in recent years because of diverse environmental interests. Consequently, its cost has soared astronomically and the utilization of lateritic soil for low-cost roads has been an attractive option. In most cases during road construction, unprecedented conditions may lead to delays in the compaction of the treated soil after the mixing operation and placing had taken place. Thus, this study developed polynomial models for predicting time limits for compaction after mixing operation within 0-180 minutes at 30 minutes intervals for lateritic soil reinforced with cement and lime. The percentage contents by weight of the dry soil for cement or quick lime mixed with the soil were 2, 4, 6, 8 and 10%. Consistency indices tests and particle size analysis were carried out on the untreated lateritic soil for characterization. The tests conducted on the lateritic soil prepared with cement and quick lime were compaction test (Standard Proctor), California Bearing Ratio (CBR) and unconfined compressive strength (UCS) of 7 days curing. The AASHTO soil classification system and Unified Soil Classification system rated the lateritic soil to be A-6(13) and clayey soil (CL), respectively. Ordinarily, the lateritic soil was found to be a poor construction soil and therefore requires treatment to improve its strength in order to make it useful for pavement purposes. At the increase in time limits for compaction after mixing, there were reductions in compaction and strength characteristics of the lateritic soils that were prepared with cement or lime. The polynomial models developed were a good fit for predicting time limits for compaction after mixing using cement/lime contents, compaction and strength characteristics of the strengthened soil. The polynomial models gave coefficients of correlation and determination of 0.988 and 0.976, respectively, when the soil was prepared with cement whereas, in the case of lime-prepared soil, the values were 0.966 and 0.933, respectively. The cement/lime contents, optimum moisture content (OMC), CBR and UCS (7 days curing) were entirely statistically significant in predicting time limits for compaction after mixing at a 95% confidence level.

Mechanism and Engineering Characteristics of Expansive Soil Reinforced by Industrial Solid Waste: A Review

Expansive soils exhibit detrimental swelling and shrinking characteristics in response to variations in water content, posing a threat to engineering safety. Utilizing industrial solid waste for improving the engineering properties of expansive soil presents a promising solution due to its low pollution and high recoverability. This paper reviews the progress of research on various industrial solid wastes in stabilizing expansive soil. The review comprehensively discusses the microscopic characteristics and mechanism of industrial solid waste-stabilized soils, as well as their impact on the compressive strength, shear, compaction characteristics, consistency, swelling and shrinkage properties, and durability of expansive soils. The addition of appropriate curing agents or the combination with other stabilizing materials can enhance the strength of expansive soil, mitigate volume changes, and improve the durability and stability of expansive soils. The mechanisms of stabilization of expansive soils by industrial solid waste involve cation exchange, flocculation-agglomeration, pozzolanic reaction, and carbonation. Additionally, microscopic characterization analysis reveals that the formation of C-S-H and C-A-H is the primary contributor to the improvement of soil geotechnical properties.

Soft Computing Models to Predict the Compaction Characteristics from Physical Soil Properties

In almost every earthwork, it is essential to compact soil so that the densest possible state of the soil can be achieved. The suitability of soil for earthworks relies on the compaction characteristics; Optimum Moisture Content (OMC), and Maximum Dry Density (MDD). The determination of the compaction characteristics in the laboratory, for a vast volume of soil, is time-consuming. Therefore, for the initial assessment of soil, it is crucial to determine the compaction characteristics from physical soil properties. In this work, three different models of the Artificial Neural Network (ANN), M5P-tree, and Multiple Linear Regression (MLR) are used to predict the compaction characteristics of the soil. In the models, particle size and plasticity properties of soil are combined and, seven input parameters of gravel, sand, silt, and clay contents, plastic limit, liquid limit, and plasticity index are comprised. To develop the models, 1038 datasets are compiled and processed. Several statistical analyses, including coefficient of determination (R2), scatter index (SI), root mean squared error (RMSE), mean absolute error (MAE), and Objective (OBJ) value, are used to assess the effectiveness of the proposed models. The findings demonstrated that overall, the ANN model performed better in predicting the OMC, while the MLR model performed better in predicting MDD. Further, from the sensitivity analyses, it was indicated that the plastic limit has more influence on the value of OMC while, to predict the MDD, both sand content and the plasticity index play a foremost role.

Experimental and Numerical Studies on Bending and Failure Behaviour of Inflated Composite Fabric Membranes for Marine Applications

Owing to their excellent physical characteristics of lightweightiness, compactness and rapid deployment, the inflated membrane structures satisfy the demands of maritime salvage and military transportation for long-distance delivery and rapid response. Exploring the failure behaviour of inflated membrane structures can greatly contribute to their widespread applications in ocean engineering. In this research, the main objective is to comprehensively investigate the bending and failure behaviour of inflated membrane structures. Thus, the Surface-Based Fluid Cavity method is employed to set up the finite element model (FEM) which is compared to the experimental results to verify its reliability. In parallel, the effects of internal pressure and wrinkles are discussed. An empirical expression of the ultimate bending loading was fitted by face-centred composite designs of the Response Surface Methodology. The results of experiments and FEM show that the bearing capacity of the inflated membrane structure is positively correlated with the internal pressure but decreased obviously with the occurrence and propagation of wrinkles. The deformation behaviour and the stress distribution are similar to those of the traditional four-point bending beam, and the local instability induced by wrinkles will cause structural failure. In addition, the numerical model and the proposed expression showed deviations below 5% in relation to the experimental measures. Therefore, the FEM and proposed expression are high of reliability and have important engineering guiding significance for the application of inflated membrane structures in ocean engineering.

Corrosion Behaviors of N80 and 1Cr Tubing Steels in CO2 Containing Downhole Environment—A Case Study of Underground Gas Storage in LiaoHe Oil Field

In order to evaluate the effect of chromium content in carbon steel on the corrosion resistance of carbon steel materials, the corrosion behavior of 1Cr and N80 steels was investigated in this study by immersion weight loss method under three different CO2 partial pressure and temperature conditions in formation water for 72, 168 and 336 h. Detailed material surface morphological characterization was performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and confocal laser scanning microscopy (CLSM). The results show that the pitting corrosion of N80 carbon steel is serious at medium temperature and low CO2 partial pressure (50 °C, 0.30 MPa), and the corrosion rate is significantly higher than that of 1Cr steel. However, at high-temperature and high CO2 partial pressure (100 °C/0.63 MPa and 114 °C/0.73 MPa), 1Cr steel is more inclined to the mesa corrosion dominated by local corrosion characteristics, and the corrosion rate is seriously higher than that of N80 steel with uniform corrosion. From the experimental results, we can know the corrosion resistance of carbon steel and 1Cr steel is not only affected by the corrosion environment, but also depends on the formation process of the product film, as well as its compactness and integrity characteristics. At low-temperature and low CO2 partial pressure, 1 wt.% chromium content can provide a certain degree of corrosion resistance, while high temperature and high partial pressure can broaden the application window of carbon steel N80 and weaken the corrosion inhibition effect of chromium.

Control Parameters for the Long-Term Tensile and Compressive Strength of Stabilized Sedimentary Silt

The yellow-layer soils of the Guabirotuba formation in Brazil are problematic due to their expansive nature and low-bearing capacity. There has been little exploration into stabilizing these soils using a calcium-based binder. In addition, existing methods for dosing lime to fine and coarse-grained soils using the porosity-to-lime index (η/Liv) have primarily focused on non-optimal compaction conditions to determine the split tensile and compressive strengths and empirical relationships between both tests while ignoring the study of optimal lime-soil mixes compaction conditions. Therefore, the objective of this research is to examine the unconfined compressive (qu) and split tensile (qt) behavior of a traditional Guabirotuba yellow silt stabilized with dolomitic hydrated lime (L) under standard, intermediate, and modified effort conditions and the correlation between qu and qt. The lime-soil blends were cured for up to 180 days, and 3-9% lime percentages were used under optimum compaction conditions (maximum dry density and optimum water content). The porosity/lime index (η/Liv), a semi-empirical index, was utilized to investigate the evolution of qu and qt over the short and long term. η/Livvaried between 6-25% by volume. Furthermore, the qt/qu index was calculated to be between 0.12-0.20, depending on the curing time, independent of lime addition and compaction effort used. Equations well-suited to a power function dosing qt and qu based on curing time and η/Livindex was proposed. Finally, some dosages of soil-lime mixtures were proposed for possible applications in geotechnical engineering, applying the porosity and volumetric binder index in optimal compaction conditions, which had not been applied before for lime-improved soils. Doi: 10.28991/CEJ-2023-09-04-03 Full Text: PDF

Improved Mechanical Performance of Gravel Reinforced by Polyurethane Polymer Adhesive

This study evaluates the effectiveness of a polyurethane polymer adhesive (PPA) in reinforcing a uniformly graded gravel. A series of laboratory tests were carried out to study the permeability, strength, and deformation of gravels improved with different contents of PPA. The permeability of PPA-reinforced gravels under the same compaction effort was observed to decrease as the content of PPA increased, but was still higher than those of sand. PPA-reinforcement can increase the strength while reduce the contraction capability of gravels. Despite of the strength improvement, the ductility of gravels reduced with the increasing content of PPA. Upon shearing, the secant modulus kept decreasing until approaching a stable value, where the decreasing rate became higher as the content of PPA increased. An optimum content of PPA around 4% can be suggested, where a compromise between the moderate ductility and high strength/stiffness of PPA-reinforced gravels can be reached.

Metasurface Antenna With Cocircularly Polarized Radiation Characteristics for Wideband Monostatic Simultaneous Transmit and Receive Applications

A monostatic simultaneous transmit and receive (STAR) antenna system consisting of a metasurface-based STAR antenna and two elaborately designed microstrip-based feeding networks is proposed to suppress the self-interference (SI) from transmission (TX) to reception (RX), a key challenge in STAR design to realize its potential in doubling system capacity. The metasurface antenna is for the first time used in designing a monostatic STAR antenna system for its compact and wideband characteristics. The proposed STAR antenna system possesses the features of monostatic operation, wide bandwidth, high TX/RX isolation, cocircularly polarized radiation with similar patterns for TX and RX, easy fabrication, and low cost. The metasurface-based STAR antenna is formed by four dual-polarized metasurface antennas, or units, and is used for both TX and RX to achieve monostatic operation. A wide operating bandwidth is obtained for each antenna unit by combining the resonate modes of the unit and a crossed slot, the feeding structure of the unit, using characteristic mode analysis (CMA). To achieve high TX/RX isolation and identical right-handed circular polarization (RHCP), the four TX and RX ports of the STAR antenna, respectively, are excited with equal amplitudes and relative phases of 0°, 90°, 180°, and 270°, by two dedicated-designed wideband feeding networks based on the sensitivity analysis. Accordingly, the proposed STAR antenna system is prototyped. The measurement results show that the STAR antenna system achieves <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$&gt;$ </tex-math></inline-formula> 36 dB TX/RX isolation and <3 dB axial ratio from 4.5 to 6 GHz and maintains similar radiation patterns with the same RHCP for TX and RX.

Utilization of Industrial Waste Phosphogypsum as Geomaterial: A Review

Phosphogypsum (PG) is a waste product of phosphate fertilizer and phosphoric acid industries. Vast quantities of the waste product are generally left stockpiled on the ground or discharged into rivers or ponds, and pose serious environmental concerns. Several countries are facing problems with the handling, storage, and utilization of PG. This article is a comprehensive review of the physicochemical, microstructural, geotechnical, radiation, and leaching characteristics of raw PG. The performance of PG with other admixtures (cement, fly ash, lime, ground granulated blast furnace slag) and soils (clays, loess, sands) has also been reviewed. In addition, the factors, such as pH, calcination, forms of PG, and curing methods, that affect the geotechnical, durability, and leaching characteristics of PG mixtures are also discussed. Based on the review, it has been observed that raw PG has high sulfate content, high water absorption capacity, and high variability in strength, leaching, and radioactivity properties; thus, using raw PG alone as a backfill or embankment material is not suitable. However, the geotechnical, durability, and leaching properties of PG may be enhanced by using it in combination with other admixtures. The excessive usage of PG should also be undertaken with caution, as the higher amount of PG may lead to a decrease in the strength and the formation of cracks. There are studies that have reported the optimum content of PG; however, the range is quite varied and can differ for soil types. Therefore, it is recommended to investigate the optimum content of PG before the start of any road or ground improvement project. The compaction characteristics of PG-admixed soils are highly contrasting and hence need more comprehensive studies. The strength characteristics and resilient modulus are also highly variable and hence need more exhaustive research for actual usage of PG in road construction. Other critical issues that require attention have been highlighted, and associated research gaps that could be explored in future research works have been identified.