Transport Research International Documentation (TRID)

Cement-phosphogypsum stabilized aggregate interlocking road base material: preparation, application and environmental impact

Fri, 28 Aug 2026 08:35:08 GMT

For the extensive and cost-effective utilization of phosphogypsum in highway engineering, a cement-phosphogypsum stabilized coarse aggregate interlocking road base material is developed in this study. The influence of aggregate gradation and phosphogypsum replacement for fine aggregate on the maximum dry density, optimum water content, unconfined compressive strength, water stability and drying shrinkage of the cement-phosphogypsum stabilized aggregate is investigated. Appropriate coarse aggregate content improves maximum dry density, and the formation of an aggregate interlocking framework is beneficial to unconfined compressive strength. The incorporation of phosphogypsum further enhances the strength development, water stability and volume stability of cement-PG stabilized aggregate thanks to its filling and hydration effects. By incorporating phosphogypsum, the required cement dosage can be reduced by at least 20% (e.g., from 5.0% to 4.0% by weight of aggregate) while maintaining an unconfined compressive strength comparable to that of traditional cement-stabilized aggregate. Cement-phosphogypsum stabilized aggregate interlocking road base material is produced and successfully applied in highway construction. The road base exhibits qualified compactness, planeness, thickness and profile elevation, and its core sample presents a denser structure than that of the traditional cement stabilized aggregate road base. Compared with the traditional cement stabilized road base, the raw material cost of cement-phosphogypsum stabilized aggregate interlocking road base can be reduced by 14.4%, while achieving comprehensive utilization of a large amount of phosphogypsum and posing no significant environmental pollution risk. The cement-phosphogypsum-stabilized aggregate interlocking road base material has wide application prospects in highway engineering.

Stepwise filling method for predicting the dynamic modulus and creep behavior of asphalt mixtures

Thu, 20 Mar 2025 09:49:13 GMT

Due to the high volume fraction of inclusions and the wide range of aggregate particle sizes in asphalt mixtures, traditional micromechanical models exhibit certain deviations in predicting the performance of asphalt mixtures. To address this issue, this study establishes a predictive equation for the effective modulus of asphalt mixtures based on the Mori-Tanaka method using a stepwise filling approach. This predictive equation separates the effects of each aggregate size on the modulus during the stepwise filling process through an enhancement factor, effectively distinguishing the sources of prediction errors for different particle sizes. Based on percolation theory, the enhancement factor for the first filling was corrected. The correction of the volume fraction using percolation theory improved the accuracy of the effective modulus prediction. Additionally, an interlocking coefficient was proposed to correct the stepwise enhancement factor, and the corrected enhancement factor effectively eliminated the differences in relative prediction deviations caused by the interlocking effect of aggregates during the stepwise filling process. Further analysis of the applicability of the stepwise filling algorithm in predicting the creep behavior of asphalt mixtures showed that the algorithm is also suitable for predicting the creep behavior of the mixtures.

An Investigation on Load Transfer Behaviour for Whitetopping Pavements

Fri, 21 Feb 2025 17:08:05 GMT

The present work investigates the influence of overlay thickness, bituminous layer thickness, its elastic modulus and bonding condition on flexural stress and load transfer efficiency (LTE) of aggregate interlocked joints in Whitetopping. Analysis has been carried out by developing a three-dimensional finite element model of Whitetopping. The results indicate that overlay thickness has a significant influence on flexural stress and LTE of joints. The flexural stress decreases by 67% and LTE increases by 7% when the overlay thickness is increased from 100 to 200 mm. The influence of bonding condition on flexural stress and LTE is however, found to be more pronounced for lower overlay thickness. The stiffness of bituminous layer influences the flexural stress and load transfer, which is more prominent for thinner concrete overlay than a thicker one. For 100 mm overlay thickness, the flexural stress increases by 27%, when the elastic modulus of bituminous layer decreases from 2500 to 750 MPa for bonded interface whereas, it is 11% for unbonded condition. For 100 mm overlay thickness, the LTE varies from 83% to 87% for similar variation of bituminous modulus, whereas for 200 mm overlay thickness, the LTE remains almost the same for all bituminous modulus values.

Small-scale laboratory tests for quantifying aggregate interlocking in short-panelled concrete pavements

Fri, 15 Nov 2024 09:47:52 GMT

In the present study, a simple and reliabe small-scale laboratory test to assess the performance of aggregate interlocked joints in short-panelled concrete pavements in terms of LTE is proposed. In the proposed test method, conventional standard flexural strength test beam specimens (100×100× 500mm) are used for understanding the performance of aggregate interlocking of PQC mix specimens prepared using coarse aggregates of different NMAS and with addition of both micro and macro fibers. The test setup is also modelled in ANSYS FE software. The experimentally obtained LTE is compared with the LTE obtained from the FE model. The field FWD test is conducted for validation. The relative movement is determined from FWD test, and corresponding LTE is determined using the LTE and RM relationship obtained from experimental results using the proposed test apparatus. There exists good linear fit between the LTE determined using proposed test and field FWD test results.

Effect of Particle Shape on Cyclic Shear Behavior of Granular Mixtures–Geogrid Interface

Mon, 11 Nov 2024 10:48:11 GMT

The cyclic shear stiffness and damping ratio of angular and round particle geogrid interfaces is of much concern in reinforcement structure seismic analysis. In this study, various component percentages of crushed limestone and spherical granular medium mixtures were used to investigate the role of particle regularity in static and cyclic direct shear tests. The test results revealed that an increase in the proportion of round particles decreased cyclic shear strength and volume change. The phenomenon of shear softening was observed with a high amplitude of shear displacement when the proportion of round particles was increased in the mixture. As the percentage of round particles increased, the maximum interface shear stiffness decreased significantly from, 39.69 to 28.28?MPa/m, but a reverse trend in the maximum damping ratio was observed, from 0.308 to 0.37. The effect of cyclic shear history and proportion of round particles on interface strength parameters was also analyzed. A linear regression model was fitted to the data for quantifying the relationship between the proportion of round particles and friction angle. The results suggest that different percentages of round and angular particles can produce varying degrees of particle interlock between aggregate and geogrid, influencing the macro-mechanical behavior of the reinforced soil interface.

Strong interlocking skeleton gradation design and performance evaluation of cement-stabilised crushed gravel via vertical vibration test method

Tue, 23 Apr 2024 16:02:01 GMT

To control the cement-stabilised crushed gravel (CSCG) shrinkage crack and improve the road performance, analysing the composition of CSCG structure on performance influence law and cut-off of coarse and fine aggregate, the strong interlocking skeleton gradation (SISG) of CSCG based on vertical vibration test method (VVTM) was proposed and its performance was verified. The mechanical strength prediction equation of CSCG was established. The results demonstrate that 4.75 mm was the demarcation point of coarse and fine aggregates. When the coarse aggregate forms a stable framework and cement stone is completely filled in the framework, it can form SISG and reduce the shrinkage deformation. In particular, SISG includes coarse aggregates having sizes of 19–31.5, 9.5–19, and 4.75–9.5 mm in a mass ratio of 50:30:20, a fine aggregate grading I value of 0.65, and a coarse-to-fine-aggregate ratio of 65:35. The maximum dry density, CBR value, unconfined compressive strength, and splitting strength of SISG increased by ~1.3%, 9%–17%, 4%–12%, and 4%–8%, respectively, compared with the gradation median values obtained based on the Chinese standard. Furthermore, the error between the simulated CBR values and the measured values was <7%. The proposed mechanical strength prediction equations exhibit high reliability.

A comprehensive particle packing-based design of bituminous mixtures and its mechanical characterisation

Sat, 23 Mar 2024 18:19:01 GMT

The one-to-one contact of coarse aggregate is considered to be the main source for the resistance to permanent deformation and to an extent to fatigue damage. Therefore, it is imperative that the mixture is placed with an interlocked coarse-aggregate skeleton. The conventional mix design approaches generally follow dense graded aggregate gradations, which target for maximum density without accounting the one-to-one contact of coarse aggregates. The current study describes an approach for analysing particle packing in bituminous mixtures based on the compressible packing model (CPM), which provides an analytical expression for the estimation of aggregate packing density. Three mixtures with chosen particle packing indicators and a conventional dense graded mixture are subjected to repeated load haversine compression at temperatures between 25$^{\circ }$° and 55$^{\circ }$° for a frequency range of 0.01–25?Hz. Selection of binder content is carried out based on equivalent compactability criteria. The link between the packing density of aggregate gradation, dynamic modulus, phase angle, master curve parameters, and relaxation spectrum is evaluated in this study. It is observed that dynamic modulus at high temperature, and low frequency, the phase angle, master curve parameters and the relaxation spectrum exhibit sensitivity to the variation in aggregate gradation.

Aggregate packing and interlock evaluation utilizing 2-dimensional synthetic asphalt concrete sections

Mon, 18 Mar 2024 17:19:35 GMT

Under heavy traffic loads, the aggregate skeleton characteristics of asphalt mixtures play a critical role. During asphalt mixture design, the maximum density line is conventionally used as a reference for selecting gradation. The selection of aggregate gradation is critical for asphalt mixtures to ensure good durability and mechanical performance. In this study, a 2-dimensional synthetic asphalt concrete section generation algorithm was developed to evaluate aggregate packing and interlock. During the synthetic section generation phase, an aggregate database consisting of real aggregate images was used. It was validated that synthetic sections with the desired gradation and area fraction (AF) could be generated using the developed method. Aggregate packing and interlock evaluation were conducted on synthetic sections generated for 10 different gradations using Bailey ratios and aggregate contact parameters. The results indicated that the developed methodology can be useful to assess the impacts of gradation changes on aggregate packing and interlock. The relationship between aggregate contact parameters and Bailey ratios was investigated, revealing a strong correlation between contact parameters and Fine Aggregate Coarse Ratio (FAc). The findings indicated that aggregates within the size ranges of the primary control sieve (PCS) and the secondary control sieve (SCS) had a significant impact on the aggregate interlock.

Formulation and Evaluation of the Ballast Shear Interlocking Coefficient based on Analytical, Experimental, and numerical Analyses

Fri, 03 Nov 2023 09:24:01 GMT

The interaction among ballast particles, known as ballast shear interlocking (BSI), significantly influences the dynamic responses of railway track. This research presents a meticulously derived mathematical formulation for calculating BSI stiffness, which is then validated through experimental data obtained from a novel laboratory test procedure. The accuracy of the BSI formulation is demonstrated by its successful prediction of BSI properties in laboratory tests. Additionally, a numerical layered model is introduced to evaluate the sensitivity of the proposed formula to the mechanical and dynamic attributes of the ballasted track. This model highlights the resilience of tracks and emphasizes the critical role of BSI effects in railway track design, offering insights into parameters affecting track behavior. The study comprehensively explores ballast behavior, emphasizing the importance of BSI in track resiliency and advocating for its precise consideration in railway track design, modeling, and maintenance to ensure operational safety and efficiency. The developed methodology not only enhances the modeling of ballasted railway tracks as multi-layer systems but also advances the assessment of shear interlocking effects through laboratory testing.

Enhancing the Performance of Roller-Compacted Concrete Pavement by Synergetic Improvement of Packing Density, Lubrication, and Moisture State of Recycled Concrete Aggregate

Tue, 14 Feb 2023 17:48:46 GMT

Roller-compacted concrete pavement (RCCP) is considered superior to other pavement types with reference to cost, ease of construction, and performance. However, the aggregate demand is significantly higher in RCCP than in the conventional concrete pavement. It is predicted that natural minable limestone sources would be exhausted in India in the next 30 to 40 years. One way to reduce the natural aggregates (NA) requirements in RCCP is through the integration of recycled concrete aggregates (RCA). However, the physical property of RCA is significantly inferior to that of NA owing to the presence of adhered mortar (AM), which increases the water demand by 2.3 to 4.6 times and affects the compactness and hardened-state behavior of RCCP. This study has tried to enhance the compactness and improve the performance of RCCP containing RCA (coarse, fine, and total RCAs) through different synergetic approaches. This, in turn, enhances the interlocking capacity using the particle packing approach, followed by mitigating the negative effects of AM by altering the moisture states, then improving the compactability and lubricating the matrix with superplasticizers. The results depict that altering the moisture states alone could adversely affect the RCCP performance because of the moisture transfer mechanism from the hydraulic gradient. Moreover, the inclusion of superplasticizers in different moisture states could manifest better aggregate rearrangement and compactability. Further, it could improve the tensile behavior of the RCCP compared with the concrete containing NA. These findings favor the complete replacement of NA by RCA for low-volume rural road construction.

Response of instrumented concrete pavement slabs to vehicular loads

Mon, 12 Dec 2022 18:45:58 GMT

Jointed plain concrete pavements are designed on the basis of edge stresses developed at the bottom of the slab, under environmental and vehicular loads. Various parameters related to material, traffic, environment and surrounding conditions of the pavement slab influence these stresses. This paper presents the effect of tie bars, aggregate interlocking, interface friction and lateral placement of wheel load on edge load stresses. An instrumented concrete pavement section with a dry lean concrete base layer was constructed and load tests were conducted. The test results indicated a significant reduction in edge load strains due to tie bars and aggregate interlocking at saw-cut longitudinal joints. An average load transfer efficiency of 60% was achieved at tied saw cut joints. The friction at the interface of concrete slab and underlying dry lean concrete base layer also considerably reduced the bottom tensile strains. Extra-widening of the slab by a minimum of 250 mm or providing a tied concrete shoulder showed an equivalent effect in reducing the bottom edge strains.

Influence of NMAS and groove depths on the static and fatigue shear performance of aggregate interlocking in PQC mixes

Mon, 12 Dec 2022 18:45:57 GMT

In the present study, a new test methodology is proposed to characterise the shear transfer ability of aggregate interlocking in pavement quality concrete (PQC) cylindrical specimens by conducting the direct shear test in the laboratory. The influence of the nominal maximum aggregate size (NMAS) and groove depth (GD) on shear strength (τ), joint shear stiffness (K) and fracture energy mode – II (GIIF) of aggregate interlocking in PQC are studied under static loading. A relationship between GIIF and K is determined. Also, shear fatigue test is conducted at higher stress levels to evaluate the effect of NMAS and GD on the performance of aggregate interlocking in PQC specimens at the grooved cross-section. From the Anderson–Darling statistic test, it is found that obtained fatigue results follow three-parameter Weibull distribution. The shape parameter (β) of the distribution is between one and two, which indicates that failure is due to wearing action. It is concluded that the proposed method in this research can be effectively used to evaluate τ, K and GIIF of aggregate interlocking in PQC specimens. Also, the use of larger NMAS in the PQC mix significantly improves the performance of aggregate interlocking under shear fatigue loading.

Quantification of Asphalt Mixture Interlocking Utilizing 2D and 3D Image Processing

Thu, 17 Nov 2022 10:15:15 GMT

The internal structure of the asphalt mixture plays a vital role in performance because it addresses gradation, air void distribution, and mixture packing. Although the quantification of the effect of the internal structure on the mechanical behavior of hot mix asphalt cannot be achieved through experimental work, the internal structure can be characterized through image-based analysis. Recent studies used imaging techniques to understand how the internal structure influences the performance of a mixture. This study attempted to quantify the interlocking properties of hot mix asphalt using three-dimensional (3D) and two-dimensional (2D) image analyzing processes and correlate the result to the locking point concept. Two types of aggregates (limestone and gravel), one type of bitumen PG64-22, and two types of asphalt mixtures—surface and base (binder)—were utilized in this study. Two software packages were used to process and analyze the captured images: iPas2 for the 2D analysis and Avizo Fire version 9.7 for the 3D analysis. Three parameters were utilized to quantify the interlocking properties, such as the number of contacts between aggregates per volume and area, ratio of interlocked particles to total number of particles, and contact area and length. This study’s results show that 3D and 2D image processing represent promising nondestructive methods to quantify asphalt mixtures’ interlocking properties. The parameters evaluated in this research indicated that the locking point definitions LP3/2-2-3 are the most appropriate to quantify the interlocking of the asphalt mixture.

Gradation optimization and evaluation of AC-20 mixtures based on interlock-dense theory

Mon, 26 Sep 2022 09:13:56 GMT

Aggregate gradation is fundamental to the performance of asphalt mixtures, particularly to ensure high-temperature rutting resistance. Most studies have focused on gradation optimisation indices; however, these indices do not directly reflect the influence law of gradation on the interlock force of aggregate skeleton structures. The objective of the present study is to obtain the interlock-coarse gradation of AC-20 mixtures using the discrete element method. The effects of the rational ranges of key sieve pores on the performance of the mixtures were studied. Then, based on their optimal performance, the interlock-dense gradation of AC-20 mixtures was determined. The simulation results of the interlock force of the coarse aggregates represent the indoor test results of the shear strength and optimal composition of these aggregates. Based on the interlock force numerical tests, the composition of aggregates with size ranges 16–19, 13.2–16, 9.5–13.2, and 4.75–9.5 mm is 37:16:23:24. The recommended fine aggregate gradation is that with a gradation-decreasing coefficient of 0.75. Optimum mechanical properties are achieved when the AC-20 mixture contains 38–47 % fine aggregates, 4–8% 2.36–4.75-mm aggregates, and 4–6% mineral powder. The Marshall stability, dynamic stability, shear strength, and splitting strength of the AC-20 mixture with interlock-dense gradation improved by 25 %, 23 %, 15 %, and 7 %, respectively, compared with those of the mixtures with specific gradation.

Meso-structural evaluation of asphalt mixture based on pore cellular structure model

Tue, 05 Jul 2022 12:02:26 GMT

To provide a reference for the gradation-refined design of asphalt mixtures, pore cellular structure model was developed to evaluate the meso-structure of asphalt mixture, and corresponding meso-structural evaluation indices of the coarse aggregate main skeleton and asphalt mortar interference were obtained. Then three different asphalt mixtures were selected to study the influence of gradation and asphalt mortar performance on the meso-structure of pore cellular structures. The gradual behaviour characteristics of the meso-evaluation indices subjected to load, as well as the correlation between the main skeleton meso-evaluation indices and macro deformation were studied. The results indicated that gradation is a key determinant of the contact point, number of pore cells, and area of pore cell distribution. Under the action of loads, the number of contact points and pore cells within the asphalt mixture increase, interference coefficient decreases, and skeleton rate increases gradually; coarse aggregates with contact that are not involved in the pore cellular structure are the main factor affecting skeleton rate. Meso-structural evaluation indices including interference coefficient and skeleton rate can effectively evaluate the meso-structure of the asphalt mixture and ensure that the coarse aggregates are interlocked with each other to form a stable main skeleton.