Mixture Specimens Research Articles

An Investigation of the Usability of Alkali-Activated Blast Furnace Slag-Additive Construction Demolition Waste as Filling Material

In this study, the usability of construction and demolition waste (CDW) aggregates as filling when stabilized with alkaline activator solution (AAS) and blast furnace slag (BFS) was investigated. The initial stage of this study involved determining the engineering properties of CDW by laboratory experiments. In the next stage, modified Proctor tests were performed to investigate the compaction behavior of CDW, to which 5% to 30% BFS was added with water or AAS. In the following stage, California bearing ratio experiments were performed to determine the mixture specimen with the highest strength. In the final stage, a weak soil layer was created in a test tank, and fillings of different thicknesses were built on it using CDW with and without additives in the determined optimum mixing ratio. Then, plate-loading tests were conducted using a model foundation to evaluate the load–deformation behavior of the fillings. The study’s results indicated that adding BFS with water or AAS to CDW increased strength. Furthermore, the addition of 20% BFS yielded the highest strength value, and the CDW aggregates with the added BFS increased the ultimate bearing capacity by up to 4.72 times compared to those without the additive.

Release of PAHs from reclaimed asphalt mixtures into the water environment after passivation by cold in-place recycling technology.

The paper deals with an analysis of the amount of 16 polycyclic aromatic hydrocarbons (PAHs (Polycyclic aromatic hydrocarbons-16 defined by US EPA.)) released from reclaimed asphalt mixtures used in base layers of road surfaces and in binder layers in road construction using cold in-place recycling. For the ten samples tested, the sum of 16 PAHs was determined directly for the crushed asphalt mixture and for its 24-h leachate. The crushed asphalt samples were used to make cylindrical asphalt specimens of the cold recycling mixture. The asphalt specimens were prepared to simulate as realistically as possible the use of the mixtures in road reconstructions implementing the cold in-place recycling technology, which should ensure the passivation of PAHs. The asphalt specimens were subjected to a dynamic leaching test under laboratory conditions with regular replacement of the leaching liquid. The results showed that the concentration of PAHs released into the water environment from the test specimens (passivated material) was approximately 40-50% lower than the amount of PAHs released from the asphalt mixtures in the 24-h leaching test. When compared to the input PAH concentrations in the asphalt mixtures (36-1323mg.kg-1), on average, only 0.15% of PAHs is released from the passivated material. Dynamic leaching test has shown that the wrapping of the original asphalt mixture with a new binder and its subsequent compaction leads to the preservation of PAHs in the original material at such a level that their total concentrations are reduced by two orders of magnitude.

Long-term rutting prediction of gussasphalt steel bridge deck pavement based on comprehensive finite element modelling

ABSTRACT Gussasphalt is widely used for steel bridge deck pavements, but it is prone to rutting during the operational stage. This paper proposes a finite element-based method for predicting rutting in gussasphalt steel bridge deck pavements. Based on the Nanjing Yangtze River Fourth Bridge project, asphalt mixture specimens were prepared and tested in the laboratory. The viscoelastic-plastic constitutive model was fitted via dynamic modulus test and uniaxial repeated loading creep test results. Wheel track tests were conducted to validate the numerical model. The temperature gradient was obtained using actual environmental data and validated using actual data from buried thermocouples. Based on the equivalent conversion and simplification of traffic loads, the permanent deformation of the pavement layer was calculated using both the viscoelastic-plastic constitutive model and the time-hardening creep constitutive model. The viscoelastic-plastic constitutive model yields an average relative error of 25% and an absolute error of 0.57 mm, while the time-hardening creep constitutive model shows an average relative error of 40% and an absolute error of 1 mm. The results indicate that the viscoelastic-plastic constitutive model can more accurately predict the long-term rutting of the steel bridge deck pavement.

Real-time monitoring of asphalt pavement structure fatigue response based on tri-axis accelerometer

ABSTRACT Fatigue damage is a notable distress of asphalt pavements. However, monitoring the development process of such distresses in real-time remained challenges for researchers. In this paper, the self-developed sensing facility has been utilized to obtain aggregate kinematic response of semi-circular specimen during the fatigue loading process in the upper-middle (H/2), lower-middle (L/2) and lower-right (L/3) positions of the specimen. Angle and acceleration variation in the X, Y, and Z directions were analysed independently at three positions. The correlation between the kinematic characteristic of the aggregate and the vertical deformation of the asphalt mixture specimen is established. The results illustrated that the asphalt mixture viscoelasticity attenuation during fatigue test caused the angle accumulation and acceleration response change of the specimen. The angle accumulation in the X-axis direction and acceleration variation in Y-axis direction of the aggregate at the H/2 position exhibited a significant three-stage change. Angle-Accumulation Rate (AAR) of change is suggested as a long-term monitoring index for the fatigue development of the asphalt mixture. The proposal of AAR index creatively combines the long-term kinematic behaviour and mechanical behaviour of asphalt mixture, making long-term and real-time monitoring of the asphalt pavement health from the perspective of kinematics become possible.

Materials design and strength development of a novel cold recycled mixture with asphalt emulsion and geopolymer

ABSTRACT Cold recycling of asphalt pavement with asphalt emulsion is an important approach for achieving low-carbon and sustainable development in road engineering. Enhancing the performance of cold recycled mixtures has become a key research focus. The objective of this paper is to develop a novel cold-recycled asphalt mixture stabilised with asphalt emulsion and geopolymer (CRM-GE). Firstly, the effects of mixing sequence, geopolymer content, asphalt emulsion content and curing conditions on the strength of the mixture and its time-dependent law are studied. Then, the microstructure and composition of the mixture are analysed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The results show that the optimum amount of asphalt emulsion is different under different geopolymer contents. The indirect tensile strength of the mixture specimen increases with the increase in the curing time and curing temperature. The microstructure analysis indicates that geopolymer reaction and asphalt emulsion demulsification in CRM-GE with 7-day curing are relatively limited, while asphalt film and the geopolymer reaction products are intertwined to achieve a denser microstructure in CRM-GE with 28-day curing. In addition, the element analysis further verifies the result of materials design and micromorphology analysis.

Particle tracking-aided digital volume correlation for clay–sand soil mixtures

In this study, a novel, interdisciplinary method is introduced that merges fundamental geomechanics with computer vision to develop an advanced hybrid feature-aided digital volume correlation (DVC) technique. This technique is specifically engineered to measure and compute the full-field strain distribution in fine-grained soil mixtures. A clay–sand mixture specimen composed of quartz sand particles and kaolinite was created. Its mechanical properties and deformation behaviour were then tested using a mini-triaxial apparatus, combined with micro-focus X-ray computed tomography (μCT). The CT slices underwent image processing for denoising, segmentation of distinct phases, reconstruction of sand particles and feature extraction within the soil specimen. The proposed approach incorporated a two-step particle tracking method, which initially uses particle volume and surface area features to establish a preliminary matching list for a reference particle and then use the iterative closest point method for precise target particle matching. The soil specimen's initial displacement field was then mapped onto the DVC method's grid, and further refined through sub-voxel registration by way of a three-dimensional inverse compositional Gauss–Newton algorithm. The proposed method's effectiveness and efficiency were validated by accurately calculating the displacement and strain fields of the soil mixture sample, and comparing the results with those from a traditional DVC method. Given the soil's compositional and microstructural characteristics, these image-matching techniques can be integrated to create a versatile, efficient, and robust DVC system, suitable for a variety of soil mixture types.

Composite Sand–Clay Infrastructural Soil Fills: Characteristic Consolidation and Hydraulic Properties

In the design construction of infrastructural projects comprised of geotechnical applications, including composite soil fill layers, compacted sand-clay soil fills are widely preferred as barrier layers, particularly in solid waste landfills, to minimize leakage, to prevent leachate from entering into groundwater. When bentonite clay with high water absorption capacity and low hydraulic conductivity is mixed with sand possessing relatively enhanced frictional properties, greater shear strength capacity, an effective fill material exhibiting low sensitivity to frost, and low volume change in case of wetting, drying can be obtained. On the other hand, when montmorillonite clay is loaded, due to highly critical volumetric contraction or dilation characteristics (high compressibility nature of clay), the soil fill composed of sand-clay will significantly consolidate. This situation may cause differential settlement problems of infrastructural fills employed in geotechnical applications. In this regard, the load conditions (mechanical effects) and the environmental conditions (physicochemical effects) in the field control compressibility characteristics and consolidation properties of sand-bentonite clay mixtures. This will ultimately impact the desired stability conditions of sand-clay soil layers built for constructed infrastructural fill, resulting in a deviation from anticipated performance conditions. To this end, in this study, the specimens of sand-bentonite clay mixtures prepared with different contents of sand-bentonite clay were subjected to one-dimensional consolidation tests to investigate the effect of bentonite content used in the mixture on consolidation behavior, hydraulic properties, and effect of sand amount on rate of consolidation and on resulting compressive strength behavior.

Effect of Smart Aggregate Size on Mesostructure and Mechanical Properties of Asphalt Mixtures

In recent years, smart aggregates have emerged as a promising tool for monitoring the movement of and changes in particles inside asphalt mixtures. However, there remain significant differences between smart aggregates and real rock aggregates, particularly the lack of an asphalt coating on the surface of smart aggregates. Currently, the research on the impact of smart aggregates themselves on the structure and properties of asphalt mixtures is lacking. Therefore, this study focuses on the influence of smart aggregate size on the mesostructure and mechanical properties of asphalt mixtures. Firstly, based on laboratory tests and the discrete element method (DEM), discrete element models of asphalt mixture specimens containing smart aggregates of various sizes were constructed, followed by simulated compaction tests. The effects of smart aggregate size on the mesostructure of asphalt mixture voids were then analyzed. Lastly, in this study, the changes in the dynamic modulus of asphalt mixtures were explored with increasing smart aggregate size and the underlying mechanisms. The results indicate that as the size of smart aggregates increases, the average void ratio of the asphalt mixture specimens decreases, but the heterogeneity of the void distribution increases. Additionally, with the increase in smart aggregate size, the dynamic modulus of the mixture specimens decreases. Further strain analysis of the specimens suggests that the increase in cross-sectional deformation is the primary cause of the reduction in modulus.

Salt weathering resilience in masonry: An accelerated laboratory study involving wind-induced variations

Salt weathering resistance is a critical parameter governing the durability of coastal masonry units and mortars. Accelerated weathering cycles are employed at the laboratory to investigate the responses of substrates and mortars upon exposure to salt, moisture, temperature fluctuations and humidity. In this paper, the individual and synergistic performances of bricks and mortar formulations when exposed to accelerated salt weathering cycles are investigated, incorporating the influence of wind on their resilience. The study examines the behaviour of brick-mortar sandwich specimens and separate specimens of bricks and mortar mixtures comprising cement, dry hydrated lime, fly ash, and limestone. These specimens are exposed to repeated weathering cycles in a 5 % sodium sulphate solution. Along with the mass variations during each weathering cycle, physicomechanical, microstructural, mineralogical and morphological characterization of the specimens are used to compare their salt weathering resistance. The results highlight that the responses of individual masonry components might not collectively translate to the overall performance of the combined system due to hygric resistance, which is minimal when the components have comparable pore size distribution. Higher microporosity (pores of diameter between 0.1 μm and 10 μm) and mechanical strength enough to resist the crystallization stresses together provide better resistance to salt weathering to the individual mortars. However, pore structure compatibility and pore fraction similarity between the components govern the behaviour of the combined system and, therefore, reflect the better performance of sandwich specimens with brick and lime mortars. The study demonstrated that wind accelerates material degradation during salt weathering through progressive erosion, accelerated evaporation and subsequent formation of isolated thenardite.

Microwave self-healing characteristics of the internal voids in steel slag asphalt mixture subjected to salt-freeze-thaw cycles

Microwave heating technology can be used to repair freeze-thaw (F-T) cycle damage and cracks caused by the use of snow melting salts and de-icers in winter. This study utilized three different gradations of asphalt mixtures: AC-13, SMA-13, and OGFC-13, and enhanced their microwave absorption performance with steel slag (SS). The heating uniformity was evaluated through surface and internal temperature tests. Additionally, the mechanisms of damage and healing of the asphalt mixtures under salt freeze-thaw (S-F-T) damage conditions were explored using S-F-T cycles test and X-ray computed tomography scans (CT). The results showed that OGFC-13 exhibits a significantly higher rate of temperature increase compared to the other two types due to its stronger wave absorption capacity. The thermal hysteresis caused by steel slag leads to uneven spatial temperature distribution. The study recommends an optimal microwave heating time of 40 s for SS asphalt mixtures, which has minimal impact on the mixture structure, by defining an evaluation method for the uniformity index and local overheat ratio. After undergoing S-F-T cycles, the porosity of all three asphalt mixtures increased, particularly at the top and bottom of the specimens. Among them, OGFC-13 exhibited the poorest durability under S-F-T conditions, with the S-F-T cycles having a significant impact on medium-sized voids (0.15–0.6 mm). After microwave heating, AC-13 and SMA-13 showed good repair effects, with porosity levels returning to their initial states. For large voids (>2.36 mm) in OGFC, microwave heating may not effectively reduce the number of voids. Additionally, the healing rate of mixture specimens at certain mid-height ranges is higher due to elevated surface temperatures in these areas, making it especially effective in repairing F-T damage. This study shows that microwave heating of SS asphalt mixtures can improve the durability of pavement in cold regions. However, implementation challenges include the need for specialized equipment and potential uneven heating. Future research should explore optimizing microwave heating techniques to minimize local overheating and investigate the long-term performance of microwave-repaired asphalt pavements under various environmental conditions.

Research on the migration law of aggregate particles in the compaction process of asphalt mixture based on discrete element method

Asphalt mixture compaction is among the key technologies in asphalt pavement construction, but the effect of asphalt mixture mixing quality on mixture compaction performance is still unclear. This research aimed to develop an asphalt mixture compaction model by discrete element simulation and verify it by compaction degree. Asphalt mixture compaction process was simulated and the effect of asphalt mixture workability on the stress, migration law and void distribution properties of aggregate particles during compaction process was investigated. The obtained results showed that the developed asphalt mixture compaction model was reasonable and correct. The more uniform the asphalt mixture is mixed, the smaller the average force on the aggregates, the aggregate particle migration velocity, and the aggregate particle displacement during the compaction of the asphalt mixture. Under the same conditions, increasing the mixing temperature from 140℃ to 180℃ increased the average velocity of the aggregates in the asphalt mixture by 92 %. It also decreased the voids in the compacted mixture specimens. At the same time, under the action of edge effect, void distribution at the center of compacted specimen was small, void distribution around the specimen was high, and void distribution along specimen compaction force direction was also high.

Investigating intrinsic factors in pavement skid resistance deterioration using an integrated tribology model

To investigate the effect of different texture wavelength deterioration on pavement skid resistance, a tire-pavement tribology model was developed through theoretical derivation and numerical simulation, and five asphalt mixture specimens were used for full life-cycle performance analysis. The results show that simulation model can efficiently calculate stress contribution of each asperity on 3D texture, resulting in simulation outcomes closely matched those of the laboratory tests. Two-dimensional (2D) pavement profile and 2D-PSD show apparent consistency in initial and subsequent stages, it correlates with the asphalt film shedding and aggregate crushing during polishing. Intrinsic factors mainly determine skid resistance durability, which is closely related to the percentage of different particle size aggregates and skeletal structure of the asphalt mixture.

Simulation method of asphalt mixture based on fracturable digital aggregate model

This study proposed an approach to construct a fracturable aggregate model to make the fracture patterns consistent with the real situation. Firstly, this study utilized three-dimensional structured light technology to obtain the geometric shell of aggregate and divide them into four categories of spherical, angular, elongated and flaky aggregates according to the minimum bounding box algorithm. Secondly, this study proposed a discrete-spheres filling algorithm based on the Bubble Pack Filling algorithm to fill the shell accurately. Thirdly, this study established the conversion equations between the macro and micro parameters of aggregate by using the linear parallel bonding model, and used it to establish the fracturable aggregate model. Through the indoor and virtual static fracture tests, this study found that the fracture patterns of the fracturable aggregate models are similar to the real situation and characterized the fracture patterns of four types of aggregates. Further analyzing the virtual static fracture tests, this study found that the bearing capacity of aggregates is determined by the compressive strength of host rocks and the shape of aggregate. Through the indoor and virtual uniaxial compression creep tests, this study investigated the behavior of the mixture specimens consisted by the fracturable aggregate model. The stress-strain curves of the fracturable and unfracturable aggregate model in this test were plotted in this study, and the results showed that the relative error between the results obtained by the fracturable model and those of the indoor test is much smaller than that of the unfracturable model. Considering that existing simulation tests on asphalt mixture often ignore aggregate deformation and fracture, so this study used the method mentioned above to obtain the fracturable aggregate model, which can improve the confidence of asphalt mixture simulation results.

Evaluating and correlating asphalt binder and mixture fatigue properties considering aging conditions

Asphalt fatigue cracking is a critical distress type for flexible pavement. This study utilized the state of practice binder and mixture cracking tests and parameters to investigate how asphalt binders’ and mixtures’ fatigue performance vary between the different mix designs and evaluate their changes with aging. The potential relationships between the measured binder properties and mixture performance were also explored. Five asphalt mixtures with disparate mix designs were evaluated and three different aging conditioning levels were conducted. The binder tests include the traditional time and frequency sweep and linear amplitude sweep test, while the mixture evaluations include the semi-circular bending and cyclic fatigue test. The results indicate that the different fatigue parameters from the tests can evaluate and rank the mixes differently. The correlation analysis using the Spearman correlation coefficient shows that the mixture cracking parameters that are more predominant by asphalt mixture’s flexibility/brittleness show strong correlations (Spearman coefficient larger than 0.8) with binder cracking indices. The LAS fatigue life-related parameters generally do not correlate well with mixture fatigue indices (Spearman coefficient smaller than 0.6). Furthermore, a prediction model to estimate asphalt mixture’s fatigue performance was developed based on linear regression and Artificial Neural Network (ANN) approach, which only requires the mix design info. and binder fatigue property as the inputs, significantly reducing the time and eliminating the effort in preparing and testing the asphalt mixture specimen for mixture fatigue performance measurement.

Preparation method and applicability evaluation of 3D printing alumina ceramic artificial coarse aggregate

Abstract The particle size and morphology of crushed stones impact their macroscopic mechanical and physical properties, which has become a hot topic in the study of road and geotechnical engineering. However, some reported studies fail to control the particle morphology as the only independent variable. This paper presented a new method to print artificial aggregates based on 3D printing technology of particles. The applicability of the new method was verified with uniaxial compression and dynamic modulus tests of asphalt mixtures formed by the printing aggregates. Results showed that the printing aggregates earned similar physical properties to real coarse when sintered at 1400℃ with alumina ceramic powder and CuO: TiO2 a 1:2 additive in mass. Besides, the gross volume density, compressive strength, and shrinkage of the printing aggregates show a similar trend of increasing and then decreasing with the increase of additives. The optimal mass percentage of additives was obtained to be 5%. Mechanical tests indicated that the mechanical indexes of the asphalt mixtures formed with the two types of coarse aggregates were similar, while the results of the specimens formed with artificial coarse aggregates showed less dispersion. The stability of test results was significantly improved for different asphalt mixture specimens prepared with 3D printed coarse aggregate. This provides a basic method for further research on the multi-scale properties of particle material.

Numerical generation and verification of a two-dimensional virtual asphalt mixture

This paper aims at finding a robust method to generate a two-dimensional virtual asphalt mixture and to verify the suitability of the generated virtual mixture. First, three methods namely stereological method, Walraven formula and phase separation method are adopted to convert the actual three-dimensional gradation curves into two-dimensional ones. Then, an approach called semi whole scale cross section (SWSCS) method is developed to verify the results obtained and to determine the most robust procedure to follow. Third, the numerical two-dimensional geometry shape data library (GSDL) of different aggregates and voids and a robust method to assemble representative volume elements (RVEs) are developed using Matlab. Finally, a gradation curve from the literature is considered to generate a virtual asphalt mixture specimen, which is then imported in the finite element (FE) software Abaqus to simulate the dynamic modulus test. The virtual test results are further verified using available literature and another homogenization numerical prediction method based on the Mori-Tanaka's approach. The results show that the phase separation method is effective to convert the three-dimensional gradation curve to a two-dimensional one. The simulation results of the virtual asphalt mixture developed in this study turn out to be in good agreement with both previously presented literature data and Mori-Tanaka's theory.

Evaluation of aggregate segregation in gyratory specimens of porous asphalt mixture (PAM) by image-based analysis

Evaluation of aggregate segregation in gyratory specimens of porous asphalt mixture (PAM) by image-based analysis

Healing response of cold recycled asphalt mixtures with electric arc furnace slag under microwave heating and re-compaction

The objective of the present paper is the assessment of the healing efficiency of a thermomechanical treatment (microwave heating and re-compaction) on cold recycled asphalt mixtures. The asphalt mixture specimens were fabricated with different electric arc furnace slag (EAFS) contents to improve the mixtures' microwave susceptibility. The healing response was then assessed in terms of recovery of their initial indirect tensile strength. Furthermore, statistical analysis was conducted by means of a three-way analysis of variance to determine the influence of temperature, re-compaction energy, and EAFS content on the healing capability of the mixtures. Although re-compaction and heating in the ranges studied do not themselves cause healing, the combination of both produced excellent healing performance. The optimal content of EAFS was established at 5% of EAFS over the weight of the asphalt mixture.

Verification of Sustainable Asphalt Concrete through the Energy Dissipation

The kinetic energy created in the asphalt concrete due to practicing dynamic loading is absorbed and consumed to retain the properties of the asphalt mixture through its flexibility; however, part of the energy is dissipated in the initiation of microcracking and other types of distresses. In this work, the influence of additives (fly ash and silica fumes) on controlling the energy dissipation of asphalt concrete mixtures was assessed. Beam specimens of asphalt mixture were obtained from the roller compacted slab samples and tested for fatigue under three constant strain levels by implementation of the four points bending beam. It was noticed that for fly ash treated mixture, the consumed time for energy dissipation decline by (75, and 97.5) % while the dissipated energy declines by (84.8, and 99.5) % when the constant strain level increases from (250 to 400 and 750) micro strain respectively. However, for silica fumes treated mixture, the energy dissipation declines by (3.3, and 95) % when the constant strain level rises from (250 to 400, and 750) micro strain respectively. It was noticed that the damage resistance as indicated by the increment in dissipated energy increases by (60, and 140) % when fly ash and silica fumes were implicated respectively. However, the silica fumes additive consumes the energy at lower time of 60 seconds than the case of control mixture. The fly ash additive exhibits no significant variation in consuming the energy when compared with the control mixture.

The Influence of Immertion on Marshall Parameters and Residual Strength Index of Rubber Asphalt Mixture

The bad drainage system in the road pavement area also causes the road body to be submerged in water for quite a long time, causing the bond between the asphalt and aggregate to loosen, resulting in decreased service life. Developments in the field of road construction have now implemented many innovative ideas, one of which is namely the use of rubber asphalt with asphalt containing natural rubber which has 1.5 to 2 times the strength compared to conventional asphalt. In evaluating the performance of an asphalt mixture, especially the AC-WC Wear layer mixture, it can be analyzed using the Marshall test method by taking into account the conditions being tested, namely the test object being immersion in water or continuously flooded with water. The method used in this research is an experiment with treatment conditions for AC-WC rubber asphalt mixture specimens which are continuously immersion in water for 1 day, 2 days and 3 days. The research results showed that there was an increase in the VMA, VIM, and flow parameters, while the VFB, stability, and Residual Strength Index parameters decreased with increasing soaking time. Based on the research results, it can be concluded that although there is an influence on the performance of the asphalt mixture with the use of rubber asphalt, the decrease that occurs is not too large and is still within the required specifications.