Compacted Mixtures Research Articles

Understanding the role of particle rotation in asphalt mixture compaction by tracking coarse aggregate movement

Compaction is one of the most critical steps in asphalt pavement construction. Understanding the compaction mechanism is essential to improving field and laboratory compaction. Recent studies have transformed from macro- to meso- scale to characterize the compaction process from the perspective of the internal mixture. It has demonstrated that rotation is a critical motion for particles in a confined particulate structure, whereas how particle rotation influences the compaction process in a particulate media is still unclear. This study employs a particle size microelectromechanical systems (MEMS) sensor, SmartRock, and discrete element modeling to track particle movement of asphalt mixture in Superpave gyratory compaction (SGC) for three typical gradation types (dense-graded AC, gap-graded SMA, and open-graded PFC). Results confirm that the particle’s relative rotation could characterize SGC compaction as a two-stage process divided by transition cycle N. Such stage characteristics could be fundamentally related to the mixture’s packing features at the particle scale. The N value decreases in the order of PFC, SMA, and AC with the increase in the Coarse Aggregate (CA) ratio, which indicates that mixtures with a stronger aggregate structure (such as PFC) will be harder to stabilize under compaction loading. The particle relative rotation transition cycle N could be used as a particle-scale index to characterize the internal structure during compaction. Further, in SGC discrete element model, particle rotation was found to be critical in affecting the particle’s horizontal translation and, ultimately material’s densification, which further explains the compaction mechanism of particulate materials.

Transforming Construction and Demolition Waste into Soft-Soil Treatment for Paving Design

AbstractConstruction and demolition wastes (CDW) are a concern in urban areas, in addition, it is well understood that soft soils are inappropriate for paving designs. Therefore, this paper presents an alternative solution combining CDW and a soft silty soil, aiming to overcome the soft soil drawbacks by repeated loadings. For this purpose, a laboratory study was developed, comprising both resilient modulus (MR) and unconfined compressive strength (UCS) tests over soil and soil-CDW compacted blends, to evaluate the mechanical properties of the proposed stabilization. Also, three compaction efforts (standard, intermediate, and modified) and a curing time of up to 90 days were used. The UCS of blends was also measured with the identical specimens with which the resilience tests were carried out. The results indicated that incorporating CDW (size sand and gravel materials) into the soil improves the qu and MR for all compaction energies, and the Resilient Modulus test affects the UCS of all blends, increasing its effect with the decrease in compaction effort. Repeated loads caused a decrease in the specimen's voids whereby the density increased and, therefore, qu. Finally, the results conclude that the compacted mixtures in the intermediate effort and 40–60% CDW by weight are potentially applicable in pavements compared to the traditional soil–cement base/subbase.

Application of neuro-fuzzy systems technology for control the density of asphalt concrete mixtures in the paving process

The increase in the number of cars and trucks, and the intensity of their use, directly affects the asphalt-concrete road surfaces of roads. This is manifested in the reduction of overhaul terms of operation and large financial costs. Improving the quality and increasing the service life of asphalt concrete pavements of roads is a national economic problem. This problem is solved by improving the regulatory framework, improving the properties of road materials, optimizing and automating technological processes in road construction. Road roller density monitoring and control systems are based on Intelligent Compaction and Continuous Compaction Control technologies. In the Russian Federation, the quality of road surface construction largely depends on the results of the work of pavers, who ensure the acceptance, laying and compaction of mixtures. Many defects in the operation of road surfaces are eliminated by high-quality compaction. Automatic control and control of the sealing process for asphalt pavers have not been developed.The aim of the study is to build a density management system for asphalt pavers based on an intelligent automatic control system with feedback. Real-time prediction of the volume density of the layer, effective manual (operator) and automatic density control is organized to achieve the required quality indicators.The results of the development of a new system for intelligent control of the density asphalt concrete mixtures by pavers is considered. The automatic control system with feedback includes a continuous density control system designed to calculate the seal quality index based on the implementation of the neural network structure algorithm in real time, as well as a neuro-fuzzy PID regulator. The study considers a system with models of control objects of high order – the fourth and sixth orders. The structure of a neuro-fuzzy network of the ANFIS type is proposed. The generation of a fuzzy output system is performed on the basis of the lattice partition method. ANFIS training is performed by a hybrid method on an array of variables obtained as a result of modeling an automatic control system with an analog PID controller. Possible modes of use an intelligent compaction control system: continuous automatic control with manual control of the operating modes of compaction; automatic density control. Automatic measure of density and control compaction modes is aimed at improving the quality of asphalt concrete pavements of roads and improving the quality of asphalt pavements efficiency of technological processes road construction.

Optimization of Soil-Sludge Mixtures by Compaction for Potential Use in Mine Site Reclamation

Studies have indicated the potential of mixtures of silty soil and sludge produced by active treatment of acid mine drainage for use in covers with capillary barrier effects for mine site reclamation. Very high water contents of sludge in the settling pond could negatively affect the required hydrogeotechnical properties of soil sludge mixtures with high sludge contents. The challenge is then to determine the optimum wet sludge content of soil-sludge mixtures with air entry values (AEV) and/or saturated hydraulic conductivity (ksat) required for use in mine site reclamation covers. This paper presents a method to determine the optimum wet sludge content βopt for obtaining the maximum dry density of compacted soil-sludge mixtures. Two types of soil (S1 and S2) and two types of sludge (A and W) were tested. It was observed that βopt can be determined when the initial water content of the soil used in the mixture is lower than the optimum water content determined from the Proctor curve of the soil alone (10 wt% and 6 wt% for soils S1 and S2, respectively) and that βopt does not change with increasing initial soil water content. Optimum wet sludge contents found were low (≈15 wt% and ≈7 wt% for mixtures containing soils S1 and S2, respectively) for the test conditions, indicting a limited quantity of reusable sludge in the mixtures. For all mixtures, the water content corresponding to βopt was close to the optimum water content of the soil alone. Results of soil water retention and saturated hydraulic conductivity (ksat) tests conducted on selected optimized mixtures indicated that the mixtures based on soils S1 and S2 have air entry values higher than 20 kPa and would be suitable for use in the moisture retention layer of covers with capillary barrier effects, while soil S2 and the derived mixtures exhibited ksat < 10−7 cm/s and would be potential materials for the low permeability layer in low saturated hydraulic conductivity covers.

Utilization of waste wind turbine blades in performance improvement of asphalt mixture

Redundant wind turbine blades (WTBs) retired from wind power facilities produce substantial waste annually and induce challenging environmental problems. As the most widely used materials for high-grade pavement construction, asphalt mixtures must have excellent high- and low-temperature performance, as well as water damage resistance, since pavement is subjected to complex loading, temperature, and humidity changes. This study proposed an asphalt mixture with the addition of two types of recycled WTB (rWTB): rWTB powders of granular sizes below 0.075 mm and rWTB fibers in the size range of 0.075–9.5 mm. First, the thermogravimetric analysis results indicated the accepted thermal stability of rWTB material for the requirement of compaction, paving, and service condition of asphalt mixtures. Second, the properties of the asphalt mixtures modified by using (i) rWTB powder (5 wt%, 10 wt%, and 15 wt% in fine filler), (ii) rWTB fiber (0.1 wt%, 0.2 wt% and 0.3 wt% in fine aggregate), and (iii) both rWTB powder and fiber were investigated by wheel tracking tests at 60°C, three-point bending tests at −10°C, and Marshall immersion tests. The experimental results showed that the rWTB asphalt mixtures could improve the overall road performance of asphalt mixtures, and that an optimal pavement performance could be obtained by the synergistic addition of rWTB powder and fiber. In addition, it was indicated that the improving mechanism of the rWTB material on the asphalt mixture was mainly attributed to its good compatibility with the asphalt binder, allowing the rWTB to strengthen asphalt mortar and improve the high- and low-temperature performance of the asphalt mixture.

Evaluation of Compaction Characteristics of Asphalt Mixture under Different Compaction Effects

To investigate the effects of different compaction methods on the water damage resistance, the air void and high-temperature stability of AC-13 asphalt mixture, Marshall compaction, roller wheel compaction, and gyratory compaction specimens were compacted with the same air void as the standard for comparative analysis. Then asphalt cement (AC)-13 (dense-graded), stone matrix asphalt (SMA)-13 (gap-graded), and porous asphalt concrete (PAC)-13 (open-graded) mixtures were compacted by gyratory compaction, and the gradation, compaction cycles, and initial compaction temperature, which affect the gyratory compaction characteristics of asphalt mixtures, were studied. The results show that the comprehensive compaction quality of the gyratory compaction specimen was the best considering the air void uniformity, uniaxial penetration strength (UPS), and residual Marshall stability of the three compaction methods. The slope of compaction degree and gyratory compaction times of gyratory compaction specimens can clearly reflect the ratio of compaction degree at different compaction phases. In this research, a new reasonable evaluation method for the laboratory compaction of an asphalt mixture is proposed, and the feasibility of using the corresponding fitting curves at different initial compaction temperatures to quickly determine the required gyratory compaction cycles to achieve the desired compaction degree is verified, which provides a reference for the evaluation of compaction methods and compaction characteristics of asphalt mixture specimens.

Properties evaluation of cold mix asphalt based on compaction energy and mixture gradation

Mix design for cold mix asphalt as a surface course has several factors to be considered, such as the traffic level and environmental condition. The compaction energy in mix design is related to expected traffic level. The choice of aggregate gradation is affected by the environment condition. Generally, there are two types of cold asphalt mixture, open graded and dense graded. The purpose of this study is to investigate the properties of cold mix asphalt surface course considering the compaction energy and aggregate gradation factors by laboratory experiments. The trial specimens were prepared with five different cationic emulsion bitumen contents for each type of mixture gradation at various compaction energy using Marshall compactor machine. The stability and volumetric properties of these specimens were measured by Marshall Test and then compared to the specified values. If the pavement is designed properly, dense graded cold mix asphalt could be used for surface course for medium and light traffic, while open graded mixture has potential application for heavy traffic. Over compaction could cause a greatly increased stiffness of mixture, which potentially lead to crack. Cold mix asphalt with different type of gradation needs different compaction energy to reach the best properties of mixture.

Impact of the mastic phase and compaction temperature on the sigmoidal gyratory compaction curve of asphalt mixtures

In this study, the compactability and workability of asphalt mixtures are assessed in retrospect to key mix design factors. To better understand how the compactability and workability of asphalt mixtures evolve, asphalt mixtures compacted at different temperatures and asphalt mixtures with various mastic compositions were considered. The gyratory compaction data were further analysed using a sigmoidal curve model. To track changes in the mastic phase, the mastic film thickness and the mastic stiffness indicator (MSI) were considered. The sigmoidal curve parameters revealed that the mastic film thickness had a more pronounced effect on the compaction process compared to the effect of compaction temperature. Finally, two space diagrams are proposed for the assessment of compactability and workability, namely the C0 (initial compacity) versus CCIP (compacity at the inflection point), and the plot of β4/β3 versusβ3, with β4 and β3 being shape parameters of the sigmoidal curve.

THE INFLUENCE OF THE TECHNOLOGICAL MODE OF COMPACTION OF CONCRETE MIXTURE WITH FLY ASH AND MICROSILICA ADDITIVES ON THE STRENGTH OF CONCRETE

The aspects of expanding the scope of application of non-reinforced products, in particular, pipes with sufficient strength indicators, were considered, and the objective necessity of developing appropriate concrete compositions and compaction technology, as well as the nomenclature and parameters of additives, was confirmed. The article outlines the trends of increasing concrete strength characteristics due to the rationalization of methods of concrete compaction with the use of waste. It has been confirmed that for the material of the pipes it is necessary to ensure the increased tensile strength of the product. After compaction, it is necessary to remove the liquid from the concrete, which ensures maximum convergence and unification of the particles of the solid phase. The method of iterations was used to determine the influence of each of the factors of concrete strength research on tension. Considered methods of concrete mixture compaction, according to the features and rheological properties of which two principles are implemented during compaction: removal of excess entrapped air and excess water from low-mobility and rigid mixtures by external influence and removal of air from high-mobility mixtures. Special attention was paid to the technologies of compaction by pressing, vacuuming and vibrovacuuming. Samples of concrete compacted by pressing and vibrovacuum ensured the production of concrete of almost the same structure with compaction of all components. Test results, electron microscopy of cement stone, radiographs obtained with different methods of compaction are presented. An increase in the degree of crystallinity was recorded due to the higher speed of reaching the supersaturation of the liquid phase of the cement test during hydration. When processing the research results, a regression analysis was performed, and analytical models for predicting parameters were obtained. The results were obtained that the fine-grained concrete mixture when compacted by pressing provides an increase in strength under the condition of pressing in layers.

Laboratory investigations of the effects of asphalt mortar and its viscoelasticity on the workability of asphalt mixtures

In order to understand the flow characteristics of asphalt mixture in the composition of materials, the influence of the viscoelastic properties of asphalt mortar on asphalt mixture workability was investigated. In this study, an asphalt mixture workability test device was developed and the corresponding evaluation index was proposed. Analysis of the basic and rheological properties of asphalt mortar for different filler-asphalt ratios and asphalt compositions, and evaluated the corresponding asphalt mixture workability. Finally, the distribution uniformities of asphalt mortar, aggregate and pore structure in compacted asphalt mixture were analyzed according to digital image processing techniques. The obtained experimental results showed that asphalt mixture workability was closely related to asphalt mortar viscoelastic properties. Also, rheological indices such as viscosity, complex shear modulus G*, phase angle δ and rutting factor G*/sinδ of asphalt mortar were to be highly correlated with workability index. As the viscosity of asphalt mortar was increased, workability index was also enhanced. In addition, lower asphalt mixture workability resulted in poorer uniformity of material distribution.

Mathematical Modeling of Pavement Gyratory Compaction: A Perspective on Granular-Fluid Assemblies

The compaction of asphalt mixture is crucial to the performance of the pavement. However, the mix design (i.e., porosity, aggregate size distribution, binder content), which is based on compaction results, remains largely empirical. It is difficult to relate the aggregate size distribution and the asphalt binder properties to the compaction curve in both the field and laboratory compaction of asphalt mixtures. In this paper, the author proposes a simple mathematical model from the perspective of granular physics to predict the compaction of asphalt mixtures. In this model, the compaction process is divided into two mechanisms: (i) viscoplastic deformation of an ordered granular-fluid assembly, and (ii) the transition from an ordered system to a disordered system due to particle rearrangement. This model could take into account both the viscous properties of the asphalt binder and the grain size distributions of the aggregates, where the viscous deformation is calculated with a proposed governing equation and the particle rearrangement effect is solved using simple DEM simulations. This model is calibrated based on the Superpave gyratory compaction tests in the pavement lab, and the R-squares of model predictions are all above 0.95. The model results are compared with experimental data to show that it can provide good predictions for the experiments, suggesting its potential for enhancing the design of asphalt mixtures.

ЗАЛЕЖНІСТЬ ОБ’ЄМНИХ ВЛАСТИВОСТЕЙ АСФАЛЬТОБЕТОНУ ВІД НАЙБІЛЬШОГО НОМІНАЛЬНОГО РОЗМІРУ ЗЕРЕН ЗАПОВНЮВАЧА ТА МЕТОДУ УЩІЛЬНЕННЯ

Introduction. One of the aspects of Ukraine's European integration is the introduction of European approaches to the design of asphalt mixtures. In Ukraine, as in other European countries, when designing the asphalt mixtures, asphalt concrete samples are made by compaction in the laboratory; however, different compaction methods are used for this purpose. Statement of the problem. In Ukraine, the method of compaction of asphalt mixtures in the laboratory at a pressure of (30.0 ± 0.3) MPa is used if the crushed stone content in the mixture is higher than or equal to 35%, or at a pressure of (40.0 ± 0.4) MPa if the crushed stone content in the mixture is up to 35%. In the countries of the European Union, the Marshall impact compaction method of 100 strokes (50 strokes on each side) is mainly used for this purpose. Therefore, it is advisable to determine the effect of the method of compaction of asphalt mixtures on the volumetric properties of asphalt concrete, depending on the largest nominal grain size of the aggregate and the compaction method. Objective. To determine the dependence of the volumetric properties of asphalt concrete on the largest nominal grain size of the aggregate and the compaction method. Materials and methods. Analysis of literature sources and laboratory research. Results. With an increase in the bitumen content, there is a decrease in the maximum density of the asphalt mixture and an increase in the bulk density of asphalt concrete. The increase in the bulk density of asphalt concrete is associated with both improved compaction of the asphalt mixture as a result of an increase in the bitumen content and more filling of air pores, as evidenced by the values of the pore content in the mineral aggregate. The only exception is the AC 16 asphalt mixture, for which the values of the pore content in the mineral aggregate remain unchanged, i.e. in this case, the increase in bulk density is due exclusively to the filling of pores in the mineral aggregate. The largest nominal size of the aggregate in the asphalt mixture affects the total pore content of the mineral aggregate. This suggests that the increase in the required bitumen content in the asphalt mixture with a decrease in the largest nominal size of the aggregate is largely due to the need to fill more pores, rather than to an increase in the total specific surface area of the aggregate.

ОГЛЯД МЕТОДІВ ПІДБИРАННЯ СКЛАДУ АСФАЛЬТОБЕТОННИХ СУМІШЕЙ

Introduction. Asphalt mixtures are the most widely used road construction material for the arrangement of the top layers of road pavement. Asphalt mixtures are also used to arrange airfield runways, bridges deck surfacing, streets, pedestrian and cycle paths, etc. There is a large number of asphalt mixtures types that differ by grading, the largest nominal aggregate size, crushed stone content, crushed and uncrushed sand content, quality of components, and viscosity of the bitumen binder. Problem statement. The national method for asphalt mixture design is very similar to the Marshall method and the Superpave method in terms of determining the optimal bitumen binder content by the bulk properties of asphalt concrete. The only difference is that, according to the Marshall and Superpave methods, the optimal bitumen content is the one with an air pore content of 4.0 %. However, in accordance with the national method, the design air pore content varies depending on the type of asphalt mixture. A significant innovation of the Superpave method is the determination of asphalt performance indicators, such as rutting resistance, crack resistance, and resistance of the material to fatigue cracking. Apparently, these methods should also be implemented in Ukraine over time. Purpose. Analysis of the methods for asphalt mixtures design. Materials and methods. Analysis of literature sources on various methods of asphalt mixtures design. Results. The analysis of literary sources on different methods of asphalt mixtures design was carried out. Conclusions. The use of different methods of asphalt mixtures compaction can lead to the production of asphalt concrete with different volumetric properties, which will affect both the optimal bitumen content and the performance of asphalt concrete, thus further research should be aimed at defining the effect of the compaction method on the volumetric properties of asphalt concrete and their relationship with the production compaction of asphalt mixtures.

High-compactability asphalt mix design framework based on binary aggregate packing

High compactability is desired for asphalt mixtures to ensure adequate field density and, therefore, the overall quality of asphalt pavements. However, compactability is typically not considered in standard mix design procedures, and existing methods for improving compactability are largely empirical. This paper proposes a mix design framework that considers the compactability of mixtures, anchored by a rational method to adjust aggregate gradation. The method is developed based on the binary aggregate packing model. The proposed mix design is applied to modify four traditional Superpave mixtures into high-compactability mixtures, to demonstrate the concept. The proposed method is compared with two empirical methods used to adjust aggregate gradation: the maximum density line (MDL) and the Bailey method. The results show that the proposed method provides a theoretical explanation of the two empirical methods and reveals their limitations. Mechanical properties related to rutting resistance, low-temperature cracking, and structural capacity of the mixtures are checked by laboratory performance tests to validate the high-compactability mix designs. The results show that, due to their denser aggregate packing, the high-compactability mixtures outperform the traditional Superpave mixtures. Therefore, the proposed high-compactability mix design framework provides a rational and practical approach to improve the field density and the overall quality of asphalt pavements.

Formation of intermetallic compounds during reaction between Ti and Al–Mg alloys with various Mg contents

The reactions between Ti and Al–Mg alloys were systematically investigated by heating the Ti/Al–Mg alloy powder mixture compacts with Mg contents ranging from 5.09 to 40.36 wt.% at 660 °C. Mg element in the Al–Mg alloys contributed to the breakage of the oxide films on the surfaces of the Ti and Al–Mg alloy powders, thus, promoting the reactions. In the samples with Mg contents varying from 5.09 wt.% to 25.93 wt.%, the first-formed intermetallic compound was Al18Ti2Mg3, and then Al3Ti generated at the Al18Ti2Mg3/Ti interface. Since the Mg content in the Al–Mg melts decreased during the subsequent heating process, the previously formed Al18Ti2Mg3 in the Ti/Al–5.09Mg sample transformed into Al3Ti accompanied by the reaction of Al with Ti to newly form Al3Ti, generating a single Al3Ti phase. In contrast, the new formation of Al3Ti and its transformation to Al18Ti2Mg3 proceeded continuously in the Ti/Al–13.54Mg and Ti/Al–25.94Mg samples, resulting in a mixture of Al18Ti2Mg3 and a little Al3Ti residue. In the Ti/Al–40.54Mg sample, Al3Ti was the unique reaction product throughout the heating process. The final Al3Ti particles in the Ti/Al–5.09Mg sample were in a blocky shape, while they were in a plate-like form in the Ti/Al–40.54Mg sample, which was caused by the enhanced growth anisotropy due to the decreased interfacial energy between Al3Ti particles and Al–Mg melts with the increase of Mg content. A twin plane re-entrant mechanism was suggested for the growth of Al18Ti2Mg3 particles, weakening the anisotropic growth caused by the directional supply of Ti atoms, and contributing to the blocky morphology of Al18Ti2Mg3 particles. In addition, the volume difference between the formed Al18Ti2Mg3 and consumed Ti was greater than that between the Al3Ti and Ti, and the Al18Ti2Mg3 has worse plasticity than the Al3Ti, resulting in the Al18Ti2Mg3 reaction product fracturing more easily during thickening, thus forming a petal-like structure, but the Al3Ti product being in an almost continuous layer.

Effect of early densification on foaming process of glass–calcium carbonate mixture

The understanding of relationship between densification and foaming for preparation of foam glasses is still lacking. In this study, 128 powder compacts of glass-CaCO3 mixture were foamed isothermally for different time by varying glass particle size, foaming temperature and initial density of green compacts. The results showed that densification tends to take place in the early stage by viscous flow sintering prior to predominant foaming expansion. Therefore, there exists a critical time at which the maximum apparent density is reached, and it is correlated with both the densification rate and kinetics of CaCO3 decomposition. Such a densification has a minor effect on the minimum apparent density, however, it significantly impacts the evolution of pore structure including pore size and homogeneity, depending on glass particle size. Coarse-particle glass and high load applied on the green compacts, leading to higher green density, is favorable for slow development of pore structure with time. In this case, the foam glasses were endowed with small size of pores and homogeneity. This study provides an insight into how to obtain low apparent density and the optimum microstructure by the interplay between densification and foaming.

Effect of compaction parameter on aggregate particle migration and compaction mechanism using 2D image analysis

Pavement performance is not only affected by materials and production but also by compaction quality. This paper investigates the migration and rotation law of coarse aggregate during asphalt mixture compaction using the statistical means based on 2D image analysis. The variation of surface texture during compaction was extracted by laser scanner, and its anti-sliding performance was tested. The compaction mechanism was then discussed in combination with the Stribeck curve. The results show that mixtures with different gradations required different compaction energy during compaction, the AC-13 mixture was easier to compacted than the SMA-13. The aggregate contact developed rapidly in the early compaction stage in the horizontal direction but increased gradually in the vertical direction. With the compaction, the radial angle of the aggregate tended to be consistent in the horizontal direction and the major axis of the aggregate approached to the horizontal axis in the vertical direction. At the same time, the aggregates on the surface of the mixture were embedded with each other with compaction, and the surface structure gradually decreased. Combined with the aggregate contact, asphalt mortar viscosity and the Stribeck curve theory, the compaction process of asphalt mixture could be divided into pre-mixed lubrication dominated by asphalt lubrication and post-mixed lubrication dominated by aggregate contact. The research results offer a reliable basis for studying the compaction mechanism and improving the construction quality control of the asphalt pavement.

Evaluation of rheological and mechanical properties of hot and warm mix asphalt mixtures containing Electric Arc Furnace Slag using gyratory compactor

Workability and compactability are two key rheological properties of asphalt mixtures with direct impacts on pavement construction costs. These properties can be estimated by laboratory testing using the Superpave Gyratory Compactor (SGC). The compaction curves obtained from SGC can offer a general assessment of the workability, compactability, and even mechanical properties of asphalt mixtures. The most widely used workability and compactability indicators derived from these curves are the Workability Index (WI), Compaction Energy Index (CEI), Traffic Densification Index (TDI), and the slope of the semi-logarithmic compaction curve (k). In this study, these indicators were used to examine the workability, compactability, and mechanical properties of hot and warm mix asphalt (HMA and WMA) mixtures containing different amounts of Sasobit (0, 1.5, and 3%) and Electric Arc Furnace Slag or EAFS (0, 25, 50 and 75%) with two aggregate gradations (upper limit and middle range of Iran Highway Asphalt Paving Code No. 234). The results showed a decline in workability and compactability with the increase in EAFS content and also with the introduction of 1.5% Sasobit which was respectively caused by the high surface roughness of EAFS materials and the lack of sufficient workability by 1.5% sasobit at the mixing and compaction temperatures. However, the compactability of HMA mixtures with 3% Sasobit was comparable to that of HMA mixtures. Given the correlation between TDI and rutting resistance, experiential TDI values were used to develop a regression model for Flow Number (FN) estimation. The analysis of the variance of experimental results showed the significance of changes observed in the indicators. The study's findings demonstrated that, due to the high surface roughness of EAFS materials, the amount of additive and mixing and compaction temperatures should be chosen in accordance with the mixture's required workability and compactability. The TDI index can also be used to approximate the mechanical properties of asphalt mixtures during the initial stages of preparing laboratory specimens.

Compaction Quality Inspection and Uniformity Analysis of Soil-Rock Mixed Subgrade

GeoGauge is a portable instrument for rapid determination of the stiffness and modulus of compacted soil, which can quickly, safely, and nondestructively evaluate the quality of each compacted layer. In order to deeply study the effectiveness of the detection instrument and equipment used in the soil-rock mixed subgrade, based on the construction project of Beijing-Qinhuangdao Expressway, the influence of water content and compaction degree on the test results and the correlation between GeoGauge detection stiffness and settlement difference were studied and analyzed by indoor model test and field test. Finally, the subgrade compaction uniformity is evaluated according to the measured data of the test section and the predicted value obtained by the ordinary Kriging interpolation method. The results show that: The GeoGauge detection stiffness value shows a trend of first increasing and then decreasing as the water content increases. When the water content is 8%, the detection stiffness value of the earth rock mixture reaches the maximum value. There is a good exponential relationship between the compactness of soil-rock mixture and the stiffness value of GeoGauge detection, and the correlation coefficient is 0.9231, which indicates that the stability of GeoGauge detection results is high. The GeoGauge detection stiffness value increases with the increase of the number of rolling passes. When the number of rolling passes is greater than five, the increase in the detection stiffness of subgrade soil decreases, indicating that the subgrade filler has approached the compaction standard after five passes of rolling. The regression equation between GeoGauge detection stiffness value and settlement difference is established, and the specific index of subgrade stiffness is calculated according to the regression equation when the compactness meets the design conditions, which provides reference for practical engineering.

Densification behavior of asphalt mixture and its relation with particle dynamic responses during gyratory compaction

Compaction of asphalt mixture is a critical step of the pavement construction, which determines the performance and durability for asphalt pavement. The densification behavior of asphalt mixture is complicated and its workability is prone to be affected by the material composition and construction conditions. Knowing the compaction process is of great significance for improving the pavement construction quality. This study aims to investigate the densification behavior of asphalt mixture in the compaction process and its correlation with dynamic responses of the built-in Smart Aggregate. Through Los Angeles abrasion tests and aggregate imaging measurement system, 40 kinds of coarse aggregates with different morphologies were prepared and employed to carry out gyratory compaction tests for asphalt mixtures. The height decline and density growth of the mixtures were concerned in different compaction stages. Meanwhile, the Smart Aggregate was embedded in the mixture to capture the particle dynamic responses, which were further correlated to the densification behavior of the mixture. The results show that material factors have the significant influence on the compaction process after the mixture has been compacted to the P1 at which the height change is less than 1 mm. The gyratory compaction process can be divided into different stages of 0∼P1, P1∼P0.1, P0.1∼P0 according to the change in mixture height, and every gyration would enable the percentage of maximum theoretical specific gravity (Gmm) increase with 1.46 %, 0.3 %, 0.11 % in the corresponding stage. After the threshold point P0, the increment of compaction degree after per gyration is less than 0.05 %. AC and SMA-13 mixtures would achieve the 95.5 %∼97.4 % of Gmm when they are compacted to locking point of P0. Asphalt mixture height is highly related to the relative rotation of the embedded Smart Aggregate. Change in the mixture height can be characterized by the variation of particle relative rotation, which could be further adopted to determine the locking state of asphalt mixture compaction in real-time.