Gradational Changes Research Articles

Impact of initial gradation on compaction characteristics and particle crushing behavior of gravel under dynamic loading

Gravel is a widely used construction material due to its versatility and cost-effectiveness. However, gravel particles are prone to crushing under dynamic loading, causing changes in gradation. The evolution of gradation and its effects on physical properties are not well understood. This study investigates the physical properties of gravel, such as dry density, void ratio, and relative crushing index, under different initial gradations (uniformity coefficient, Cu), using surface vibration compaction tests. A hyperbolic relationship was established between initial Cu and dry density, showing that an increase in Cu can result in a decrease in the void ratio and an increase in the coordination number until stabilization. Particle crushing increases with higher initial Cu, correlating quantitatively with relative crushing indexes. Maximum dry density, minimum void ratio, and fractal dimension also correlate with these relative crushing indexes, suggesting intrinsic relationships among these properties and particle crushing. The size effect can be eliminated by establishing empirical relationships between crushing parameter and particle size.

The felsic volcanism associated BIF-like iron formations: Their origin and implication for BIFs

The Banded Iron Formations (BIFs) have been invaluable archives for the Precambrian eons, providing evidence for the paleoenvironment conditions, including the atmospheric oxygen levels. This study explores the geological origin and depositional mechanism of BIF-like Carboniferous Heiyingshan (HYS) and Mesoproterozoic Pilot Knob hematite (PKH) formations, characterized by hematite-rich (Fe-rich) layer and quartz-rich (Si-rich) jasper layer alternations within felsic volcanic rocks. Through comprehensive mineralogical analyses and geochemical modeling, we present evidence supporting their formation in intra-caldera hot spring lakes, where episodic inputs of Fe(H3SiO4)2-bearing fluids mixed with ambient lake water. Experimental simulations and PHREEQC modeling corroborate a mechanism where ferrihydrite and amorphous silica precursors sequentially precipitate, possibly driven by the oxidation and decomposition rates of Fe(H3SiO4)2 complexes. The sharp or gradational change in the Fe- and Si-rich layering transition can be caused by varying atmospheric oxygen levels. The Carboniferous HYS specimen exhibits a sharp FeSi boundary that is in accordance with modeling under high atmospheric O2 condition. In contrast, the Mesoproterozoic PKH sample contains both sharp and gradual change in the FeSi transition, implying the pO2 lies between 10−3 and 10−5. This chemical precipitation model of BIF-like iron formations could provide insights into the FeSi source and banding mechanism of BIFs, and Precambrian pO2 levels.

Role of particle gradation of clay–sand mixtures on the interfacial adhesion performance of polymer coatings

Abstract The interface performance between clay–sand mixtures and concrete structures is governed by the mixture's composition and its physical properties. Moisture content and particle-size distribution play important roles in deciding the mixture's arrangement of soil particles, porosity, hydraulic conductivity and behaviour under various mechanical loadings. Application of a polymer interfacial coating can improve the bond performance between soils and concrete mainly via interfacial friction/mechanical interlocking. The present work analyses the development of interfacial strength between clay–sand mixtures and a polymer coating with changes in particle gradation. The multi-scale mechanisms at the interface are investigated, giving primary attention to soil porosity. A 50:50 clay–sand mixture exhibited a greater interfacial adhesive performance compared to other soil mixtures. In addition, the moisture-controlled pores and gradation-controlled pores demonstrated differences in macroscale interfacial strength. Both mercury intrusion porosimetry (MIP) and 129Xe nuclear magnetic resonance (NMR) were utilized to detect the pore structure of the mixtures. 129Xe-NMR revealed the pore distribution of the mixtures as ranging from macropores to nanopores, and MIP complemented the pore information by determining the critical pore entry diameter in the macropore regime. Mesopores dominated with increasing fine sand content until a threshold value was reached; thereafter, merging of pores occurred and macropores dominated.

Similarity Model Test on Rainfall Scouring Mechanism of High-Speed Railway Subgrade Slope

The subgrade slope, when exposed to the natural environment for a long time, is easily affected by rainfall scouring, which leads to a large loss of filling materials and soil sliding, affecting the stability of the subgrade slope. In this paper, the model test of a high-speed railway subgrade slope under rainfall scouring was conducted to quantitatively study the occurrence and development process of subgrade slope erosion. Compared with the model test results and the theoretical results, the incipient flow velocity formula of coarse-grained soil was verified. Then, the curve of rainfall intensity varied with the incipient particle size under different rainfall intensities, slope gradients and soil particle grading conditions was analyzed. Results show that during rainfall scouring, the smaller the particle size, the earlier the scouring erosion occurs. In addition, the soil particles on the slope bottom were scoured more severely than those on the slope upper. With the increase in rainfall intensity, slope gradient, and the change in soil particle gradation (removing the minimum particle size), the incipient flow velocity of soil particles on the slope will be reduced. The curve of the rainfall intensity varied with the incipient particle size, which plays an early warning role in the analysis of slope erosion stability and reflects the particle size range of the scouring erosion incipient on the slope surface under different rainfall intensities, providing the basis for the analysis of slope erosion stability and the slope protection design of the high-speed railway subgrade slope.

Permeability of polymer-modified kaolinite and fly ash–kaolinite mixtures

With the goal of promoting the treatment and reuse of fly ash (FA), a series of permeability tests were conducted to investigate the hydraulic conductivity (K) of polymer (chitosan, polyethylene oxide (PEO) and xanthan gum)–FA—kaolinite (KA) systems under different confining pressures and overconsolidation ratios (OCRs). The addition of FA increased the K of KA due to changes in particle size and gradation, and the effect is not significant when the FA content is below 30%. PEO and xanthan gum increased the K of KA, with xanthan gum having a more significant effect, while chitosan reduces it. For FA–KA mixtures, chitosan and xanthan gum had negligible impact on the K, whereas PEO increased it by an order of magnitude. In addition, confining pressure restricts the flow channel while increasing the effective contact area between polymers and soil particles. The Koc/Knc of polymer-modified KA rapidly converges at high OCRs, while that of polymer-modified FA–KA converges at low OCRs. This study provides insight into the effects of polymer modification on the hydraulic conductivity of FA–clay mixtures and provides guidance for the application of polymer modification technology in soil improvement.

Mechanical and Microstructural Response of Iron Ore Tailings under Low and High Pressures Considering a Wide Range of Molding Characteristics

The dry stacking of filtered tailings is an option to deal with safety-related issues involving traditional slurry disposition in impoundments. Filtered tailings can be compacted to pre-define design specifications, which minimizes structural instability problems, such as those related to liquefaction. Yet, comprehending the tailing’s response under various stress states is essential to designing any dry stacking facility properly. Thus, the present research evaluated the mechanical response of cemented and uncemented compacted filtered iron ore tailings, considering different molding characteristics related to compaction degree and molding moisture content. Therefore, a series of one-dimensional compression tests and consolidated isotropically drained triaxial tests (CID), using 300 kPa and 3000 kPa effective confining pressures, were carried out for different specimens compacted at various molding characteristics. In addition, changes in gradation owing to both compression and shearing were evaluated using sedimentation with scanning electron microscope tests. The overall results have indicated that the 3% Portland cement addition enhanced the strength and stiffness of the compacted iron ore tailings, considering the lower confining pressure. Nevertheless, the same was not evidenced for the higher confining stress. Moreover, the dry-side molded specimens were initially stiffer, and significant particle breakage did not occur owing to one-dimensional compression but only due to shearing (triaxial condition).

Structure stability and shear failure behaviors of asphalt mixtures from the perspective of aggregate particle migration

Shear deformation of asphalt mixtures is the macroscale accumulation of aggregate migration, addressing excessive aggregate slip and rotational migrations can reduce shear failure. In this research, the slip failure and torsional failure tests were introduced to achieve targeted investigations using developed instruments. Deformation resistance of the asphalt mixture was analyzed from the granular properties. The results indicate that shear energy is dissipated by structural self-organization induced by aggregate migration. Coarse gradation and complex aggregate morphology enhance the structure stability. The shear failure threshold resulting from aggregate slip exceeds that of rotation over fourfold. The packing coefficient (PC) and the critical moment of inertia (IC) were proposed to evaluate the slip and rotation resistances of asphalt mixtures, the indicators show good parabolic and linear relationships with the peak forces of slip and rotation as gradation changes, which can be illustrated by the interfacial friction and the spatial hindrance provided by the aggregate morphologies of texture and form. Finally, the findings were validated by the discrete element method.

Simulation study on load-bearing capacity and broken characteristics of the loose gangue based on Talbot theory

In order to investigate the axial compression failure characteristics of gangue with varying particle sizes under the Talbot distribution, the Talbot gradation coefficient is constrained within the range of 0.3–0.7, the loading strain rate is set to 1kN / s, and different colors are employed to differentiate the particle sizes within the mixed gangue during the loading process. The test results demonstrate that the selected gangue materials have an elastic modulus of 13.62 GPa and a compressive strength of 73.25 MPa. Furthermore, the changes in gradation between different particle sizes are visually expressed and analyzed using the gangue breakage rate. It is concluded that the ‘large sized particle’ gangue tends to be broken locally, while the ‘small sized particle’ gangue tends to be broken as a whole. The initial porosity distribution of the mixed gangue is calculated to establish the initial model of the gangue sample using the Particle Flow Code program. Numerical simulation experiments related to uniaxial compression were implemented. The strain change characteristics observed in the actual uniaxial compression test are further validated. Analyzing the simulation results, it was observed that the force chain propagates from the top to the bottom, causing cracks to form in the same direction. Moreover, the transmission area of force chain gradually decreases, resulting in the highest compaction degree at the top and the loosest at the bottom of the compressed model.

Asphalt Mixing Performance Evaluation at Province Road Junction Sta 1+700 - 2+300

Asphalt mixture is a very important component that needs to be taken into account in flexible pavement construction to achieve the durability of a highway construction. In order to achieve the durability of road construction, it is necessary to control the quality of the mixture used to determine the quality of the mixture used in road construction. Evaluation of the mixture is carried out in the laboratory to check asphalt content, aggregate gradation and field density which must meet the required tolerances for the working mixture (JMF). Evaluation of the asphalt mixture can be done by the extraction method. The extraction method used in this study is the centrifugal extraction method. With this extraction method, the composition of a mixture can be known so that it can be compared with the mixture required in the Job Mix Formula (JMF). In conclusion, there is a decrease in the extracted asphalt content with the planned asphalt content, that is, with an average asphalt content value of extraction results of 6. 58% while the planned asphalt content value is 7.10% with the required tolerance of ±0.3%. In addition to the value of asphalt content, the field density also decreased from that which was planned in the work mix. It is known that the density value in the work mixture is 2,250 g/mm3 while the average field density value is 2,095g/mm3 so that the Job Standard Density (JSD) value is 93.108% and this value is below the tolerance limit. Then the aggregate gradation of the semi-gap HRS WC mixture at the Intersection section of the Lito province on average underwent a gradation change, namely a decrease in the percentage of passing on each sieve.

Effect of wet – dry cycles on CBR value and grain size distribution particle on compacted residual tuff soil

Uncertain climate change is a natural phenomenon that is common nowadays. Soil is the result of weathering of rocks and climate change is one of the causes of this weathering. Residual soil is soil formed on top of the original rock layer. In addition to the parent rock, climate change also affects the residual soil, both in terms of grain size and shear strength. This climate change modeling was carried out by giving wet-dry treatment on residual tuff soil samples at the Institut Teknologi Sumatera (ITERA) which were compacted with a wet-dry cycle of 2 cycles, 4 cycles, 6 cycles, 8 cycles, and 10 cycles. From this treatment, it will be seen the change in gradation and the magnitude of the CBR value. The change in grain gradation is obtained which is calculated based on the concept of grain breakage, namely the Br value in each cycle of 15.89%; 21.51%; 25.35%; 32.01%; 36.28%. For the CBR values obtained for the initial conditions and each cycle are 50.74%, 40.34%; 29.763%; 25.16%; 22.825%; 20.580%. These results indicate that the longer the cycle occurs in the soil, the greater the change in grain gradation and the CBR value of the residual tuff soil. For this reason, the wet-dry process needs to be considered for the use of residual tuff soil as the subgrade of the road pavement.

An investigation of the electrical conductivity of different stone mastic asphalt mixtures

In recent years, many studies on the prevention of icing on highways and airports through the use of electrically conductive asphalt pavements have been carried out. However, although electrical conductivity in asphalt mixtures has been extensively investigated, the gradation in conductive stone mastic asphalt (SMA) mixtures has not yet been studied in detail. The main purpose of this study was to investigate, for the first time, the effect of aggregate gradation variation on the electrical resistivity and temperature change of electrically conductive SMA. Samples of conductive SMA were produced using three different aggregate gradations (series 1A, 2A and 8S) and 5 mm long carbon fibres (0.2% by weight) as the conductive component. Marshall mix design was performed on series 1A, 2A and 8S. The samples were tested for volume resistivity, temperature change under constant electrical voltage and ultrasonic pulse velocity and the results were compared. The results showed that a change in aggregate gradation had a significant effect on the electrical conductivity properties of the conductive SMA, with a denser gradation of the SMA mixture leading to higher electrical conductivity.

Experimental measurement of particle crushing around model piles jacked in a calibration chamber

During installation of driven or jacked piles in sand, particle crushing occurs in a region below the base of these piles. Quantification of the degree and extent of particle crushing during driving or jacking in sand is necessary to improve current design methods. To study the effects of particle crushing on the capacity of piles jacked in uniform silica sand samples, a model pile was jacked and tested in a half-cylindrical calibration chamber with transparent observation windows in its front wall. Annular samples of crushed sand 3 mm in thickness were recovered after testing from several locations along the shaft and the base of the model piles and used to assess particle gradation changes and to calculate breakage parameters. Relationships between the load mobilized at the base of the model piles and three breakage parameters are proposed. Furthermore, the number of jacking strokes (ranging from 1 to 32 in this research) has a negligible effect on the degree of crushing produced during installation and on the measured stresses at the base of the model pile. Analyses of the digital images captured during pile jacking indicate that the silica sand particles in the path of the model pile crush mainly along irregularities and sharp edges. Different zones are identified below the model pile according to the degree of particle crushing. Digital images taken during static loading of the model pile allowed tracking of the displacement paths of individual sand particles during loading.

Aggregate packing characterisation of cold recycled mixtures

ABSTRACT Despite its significant role in cold recycling mix design and construction process, the effect of reclaimed asphalt pavement aggregates’ gradation and physical properties are relatively less understood. The ambiguities associated with the gradation effect led to challenges in determining the best practices in gradation control and stockpile management and blending in both cold-in-place and central plant recycling operations. Therefore, the main goal of this paper is to quantify the impact of gradation changes and proportioning of reclaimed asphalt pavement aggregates on the packing characteristics and performance of cold recycled mixtures. Binary blends consisting of fine and coarse reclaimed asphalt pavement stockpiles were combined to obtain fourteen gradations using a volumetric aggregate proportioning technique. The compatibility of five of the most prominent binary aggregate packing models was evaluated in cold recycling application. The modified Toufar model was able to accurately predict the blend of fine and coarse aggregates that offers the optimum packing prediction. Complex modulus tests showed linear viscoelastic characteristics of the cold recycled mixtures as well as the sensitivity to the packing states. In essence, this research shows the effectiveness of applying volumetric packing principles and aggregate proportioning techniques to achieve improvements in cold recycled mixtures’ volumetric and mechanical performance.

Study of the sorting pattern of dredger fill under artificial disturbance based on the concealment degree.

This paper focuses on the sorting pattern of silt deposited at estuaries under artificial disturbance based on the concept of bidirectional concealment, which is introduced for such silt with similar particle size, low disturbance exposure angle, and difficult sorting. By establishing the relationship among the absolute concealment (Δi), the drag force coefficient ({C}_{mathrm{D}}), and the lift force coefficient ({C}_{mathrm{L}}) of highly concealed silt particles under disturbance and considering the concepts of disturbance intensity, disturbance direction, and particle concealment degree, the contribution equation for the effective depth (Y) of artificial disturbance in the deposited slurry is introduced, and the mechanical equation for the internal disturbance of silt is established. On this basis, the motion initiation probability for fine particles ({varepsilon }_{{d}_{i}}) is calculated using the Shields parameter (Thetac), and the theoretical model of plastic sandy silt sorting under artificial disturbance is derived from the Markov chain-based three-state transition. The method proposed in this paper can explain the bedload gradation of sandy silt under internal physical disturbance. The calculated data in this paper agrees well with that of the flume test on uniform sandy silt and the related sediment particle theories. Therefore, the clay particle transport pattern model in slurry under artificial disturbance based on the bidirectional concealment degree can explain the gradation changes of flow-plastic sandy silt under artificial disturbance, thus providing a theoretical basis for the research on the sorting of flow-plastic sandy silt under artificial disturbance.

The Effect of Addition RAP as Quality Improved for Hot Paved Mixtures

Reclaimed Asphalt Pavement (RAP) is the residual waste of pavement that has been damaged or has reached the end of the pavement by using a Cold Milling Machine (CMM). The old aggregate undergoes gradation changes due to traffic loads and weather effects so the gradation is not following the ideal gradation plan. The addition of natural aggregates aims to improve the grading envelope to meet the upper and lower limits of the AC-BC layer requirements. This study aims to determine the optimal composition of the RAP material in terms of Marshall characteristics. The use of RAP material variations is 30%, 40%, and 50% of the total composition of the mixture. This study refers to the 2018 Bina Marga specifications and the Marshall method for laboratory testing. The research steps consisted of material extraction testing, aggregate and asphalt properties, sieve analysis tests for mixed grading envelopes, and Marshall tests. The results of this study are the characteristics of the mixture in terms of Marshall stability for the composition of RAP 30%, the stability value is 1433.3 Kg, RAP 40% is 1621.7 Kg, and RAP 50% is 1920.8 Kg. The greater the composition of the RAP, the greater the stability value, which shows the strong mixed nature of holding vehicle traffic loads

Laboratory evaluation of the effect of compaction method and compaction work on the performance of SMA-13 mixture.

The influence of compaction methods such as the Marshall compaction method (MCM), vibration compaction method (VCM) and gyration compaction method (GCM), on the performance of stone mastic asphalt (SMA-13) mixture has yet to be explored. Therefore, to compare the influences of compaction methods and work on the physical and mechanical properties of SMA-13 mixture, the volume parameters, mechanical properties, and gradation changes of SMA-13 mixture specimens prepared under different vibration compaction times, Marshall double-compaction numbers, and gyration compaction numbers were studied. The compaction method for SMA-13 mixture design was also proposed under the principle of optimum properties. Results demonstrate that the asphalt aggregate ratio and compaction work directly affect the volumetric properties (VV, VFA, and VMA) of asphalt mixture specimens while the raw material and mineral aggregate gradation were fixed. The influence of compaction work on physical properties is greater than that of asphalt aggregate ratio. The mechanical strength of VCM and GCM specimens is higher than that of MCM specimens under the same compaction work and the optimum asphalt aggregate ratio. With the increase in compaction work, the mechanical properties of SMA-13 mixture are improved at the same compaction method and the optimum asphalt aggregate ratio. The aggregate gradation of the SMA-13 mixture before and after compacted using VCM and GCM changes minimally compared with that of the SMA-13 mixture compacted by MCM. Thus, the compaction methods of VCM65 and GCM130 were recommended for SMA-13 mixture design.

Potential use of recycled concrete aggregate (RCA) for sustainable asphalt pavements of the future: A state-of-the-art review

With the continuous paving of roads around the world, the huge consumption of natural aggregate (NA) obtained through widespread excavation and extraction is now an inevitable part of highway construction. To alleviate this phenomenon, the use of recycled concrete aggregates (RCA) is considered beneficial to potentially substitute these aggregates in asphalt mixtures while concurrently providing secondary environmental, economic, and societal benefits. Nevertheless, engineering asphalt mixtures containing RCA to meet desired performance properties still poses several challenges and uncertainties for practitioners. Based on this, the present work reviews the previous relevant literature on this topic and summarizes the potential use of RCA for asphalt pavement related applications. An important characteristic of RCA is that it consists of various interfacial transition zones (ITZs) and voids caused by adhered mortar which leads to higher water-absorption and crushing characteristics as compared to NA. The treating methods used such as mechanical processing, calcium carbonate bio-deposition, and pozzolanic materials incorporation have been shown to be effective to improve the quality of RCA. The structural and material durability of RCA-asphalt pavement is closely dependent on its mix design, moisture-induced damage, and high and low temperature properties, which is in direct relation to the overall properties of RCA. Moreover, the shape variability of RCA during mixture preparation leads to the change in design gradation and its influence on the properties of RCA-asphalt mixtures should be carefully considered. The total substitution of coarse NA by RCA in asphalt pavement can be reached as long as the engineering properties, particularly the moisture susceptibility, are satisfactorily addressed. Overall, the potential application of RCA is a promising candidate to replace the excessive use of NA for the construction of high quality and sustainable asphalt pavements of the future.

Mechanical-strength-growth law and predictive model for ultra-large size cement-stabilized macadam based on the vertical vibration compaction method

The mechanical properties of ultra-large particle size cement-stabilized macadam (CTB-50) and traditional cement stabilized macadam (CTB-30) have been tested, and the correlation between the vertical vibration compaction method (VVCM), the static pressure method (PCT), and mechanical strength of field core samples has been confirmed. The mechanical strength growth equation and mechanical strength growth model of cement-stabilized macadam are proposed and tested for dependability. Correlation between the VVCM sample and field core sample is higher, reaching up to 90%, and the gradation change after compaction is less. In addition, the correlation coefficients of the mechanical strength growth equation and mechanical strength growth model of cement stabilized macadam with the indoor test results were 97% and 92%, respectively. And the error between the simulated and test values is <14%. CTB-50 has greater mechanical strength and requires less cement content, which can reduce cement cost, reduce base cracking problems, and extend pavement service life.

Study on the mechanical properties of coral sands with different particle gradations

The properties of coral sands are significantly affected by the gradation changes caused by the particle breakage. In this paper, a series of triaxial consolidated drained (CD) shear tests were carried out to investigate the influence of gradation on the particle breakage and mechanical properties of coral sands. The results showed that the softening and dilatancy during shearing are more significant for coral sands with smaller average particle sizes under low confining pressure. The peak friction angle decreases with the confining pressure and can be fitted by a power function for different gradations. The particle size distribution of the “hyperbolic” or “straight” curve has a trend to transform into a “sigmoidal” type after shearing; and the variation is affected by the confining pressure and the initial gradation. The critical state lines of the coral sands with different gradations are parallel straight lines on the plane. In addition, the relative breakage of coral sand particles increases with the confining pressure and the mean particle size. Based on the triaxial compression test results, the expressions relating relative breakages to the confining pressure and the gradation parameters were proposed.

Mechanism Characterization and Nondestructive Inspection Method of Thermal Degradation Faults in EPDM Cable Termination

There is a significant positive proportional correlation between the condition of ethylene propylene diene monomer (EPDM) insulation and partial discharge(PD) characteristics in electric multiple units (EMU) cable termination. Especially for the cable terminations with long service life, the aging effect of EPDM insulation material is significant due to long-term high-current load. In this paper, electrical deterioration and PD development of EPDM insulation under long-term thermal degradation is conducted. During the test process, the phase-resolved partial discharge (PRPD) analysis, partial discharge inception voltage (PDIV), physicochemical properties, and flashover voltage of EPDM samples with different thermal degradation are measured. The relationship between the thermal degradation extent of EPDM insulation and PD characteristics is also proposed. The results show that electrical deterioration of the aged sample can be divided into four gradations by PD amplitude and pulse repetition rate. In the four gradations, the shape of the PRPD spectrum in every gradation changes significantly with different thermal degradations. Surface morphologies of EPDM insulation show different features such as gully areas and white particles. The results of the Fourier transform infrared spectroscopy(FTIR) test indicate that the increase of oxygen-containing groups and free radicals are the key reasons for the rapid PD development process of cable insulation under different electrical gradations and thermal-oxygen degradations.