Indirect Tension Research Articles

Performance evaluation of temperature effect on hot in-place recycling asphalt mixtures

Hot in-place recycling (HIR) is a novel technique to rehabilitate the surface layer of the pavements, in which recycling agents are commonly utilized to restore the binder rheological properties of reclaimed asphalt pavements (RAP). Considering the energy consumption and smoke issue, the heating temperatures for HIR containing 100% RAP mix are usually controlled around 110 °C, which is significantly lower than that for the traditional hot mix asphalt (HMA). . To evaluate the effect of temperature on the performance of 100% recycled asphalt mixtures after the HIR process, the materials obtained from an HIR project were remixed and compacted at different temperatures (110 °C, 120 °C, and 130 °C). The asphalt mixture performance tester, asphalt pavement analyzer test, Superpave indirect tension tests, and moisture susceptibility tests were conducted to evaluate the performances of the HIR mix. The staged extraction tests were used to identify the mobilized RAP binders under different temperatures. It was revealed that mixtures heated with a higher temperature exhibit better cracking and moisture resistance performances. It was also found that a larger proportion of the RAP binders can be activated to coat the aggregates at a higher mixing temperature, which may increase the rutting potential.

Role of Aggregate Gradation in Balancing the Performance of Asphalt Concrete Mixtures

Improving the durability and long-term performance of asphalt concrete (AC) has become a major concern, especially with the increase in the use of recycled materials, warm mix asphalt additives and modified binders. This paper presents an evaluation of different mix design approaches to balance the mechanical properties of AC mixtures. The current volumetric-based design method was enhanced with a performance-based analysis methodology that specifies the parameters from the overlay tester, Hamburg wheel tracking device and indirect tension tests. Two typical Superpave mixes from different plants that exhibited a poor performance, especially in cracking, were selected for this evaluation. The mixtures were first designed following the current volumetric-based design process and characterized under the proposed performance-based analysis. Two alternative approaches that consider the influence of the asphalt content and the aggregate gradation were explored to improve the engineering behavior of the mixtures. From this evaluation, two mixtures that could potentially yield optimal volumetric and balanced mechanical properties were developed. The optimization of the aggregate gradation is a promising approach to formulate a mixture with a balanced stability and durability, as judged by its rutting and cracking potentials.

Unified characterizing fatigue performance of rubberized asphalt mixtures subjected to different loading modes

The most common primary damage form of rubber asphalt pavements is fatigue cracking. At present, the indirect tension, direct tension, bending, and unconfined compression tests are the main considered fatigue parameters to design the structure of rubber asphalt pavement. However, the fatigue test results analyzed by various test methods have a quite significant divergence, which represents a lack of accuracy to access the durability of rubber asphalt mixture objectively. Thus, in the structural resistance design of rubber asphalt pavement, there exists a problem of artificial randomness of fatigue parameters. Hence, the primary objective of this study is to improve the procedure for determining the structural resistance of rubber asphalt pavement. To this end, the direct tensile, unconfined compressive, and indirect tensile strength tests of rubber asphalt mixture were performed under various loading rates to reveal the velocity-dependent of the strength of rubber asphalt mixture. The model of direct tensile strength, unconfined compressive strength, and indirect tensile strength increasing with loading rate are SD = 7.772v0.205, SC = 1.748v0.204, and ST = 1.077v0.207, respectively. The stress ratio related to both the traditional S–N fatigue equation and the loading rate was defined as the standard stress ratio and the velocity-dependent stress ratio, respectively. The fatigue test of rubber asphalt mixture was conducted. The results from those experiments were analyzed. A fatigue equation (Nf = tv−5.129R2 = 0.853) related to the loading rate was established. The results indicated that the viscoelastic characteristics of rubber asphalt mixture are not taken into consideration in the traditional S–N fatigue equation, which contributed to the non-uniqueness and uncertainty of fatigue test results. The viscoelastic characteristics of rubber asphalt mixture are considered by the fatigue equation related to the velocity-dependent stress ratio. Thus, a new method (Kv = Nf0.0958) considering the influence of the loading rate for calculating the strength structure coefficient of the rubber asphalt mixture was proposed. The effectiveness and completeness of the mechanical behavior of pavement structure characterized by material parameters were improved. Thus, the utilization rate of waste rubber for pavement construction can be significantly increased and the life cycle cost of asphalt pavement is reduced.

Demarcation Study on Reclaimed Asphalt Pavement Contents in Recycled Hot Mix Asphalt Mixtures for Wearing Course in Asphalt Pavements

The present study evaluated reclaimed asphalt (RAP) containing hot mix asphalt (HMA) mixtures performance, to assess the effect of 5% RAP alteration on the marginal change in performance between 20%, 25%, and 30%. Then, the results from assessment were used to classify the RAP contents in HMA mixtures as low, moderate, and high by comparing the performance of the mixtures. The HMA specimen’s preparation followed the Marshall mix design procedure with a 12.5 mm nominal maximum aggregate size (NMAS). Rutting and stripping resistance were selected as the primary performance. The wheel tracking (WTT) and indirect tension strength (IDT) tests were done to assess rutting and stripping performance, respectively. The WTT results indicated that a mixture with 30% RAP performed well in rutting resistance, followed by 25% and 20% RAP mixtures. The results of the tensile strength ratio (TSR) from the IDT showed that mixtures with 0% RAP and 20% RAP were susceptible to stripping. On the other hand, mixture with the 25% RAP had good stripping resistance. From the test results, it was observed that RAP contents up to 20 % had similar performance as 0% RAP mixture. Mixtures containing 25% RAP and 30% RAP found better on rutting and stripping resistance. Based on the experiment results, the 5% variation in RAP content affects the performance of the mixtures significantly. The present study concluded that RAP content could be tiered as follows; up to 20 % is low content, above 20% to 30% as moderate, and above 30% is high content.

Experimental study on acoustic emission (AE) characteristics and crack classification during rock fracture in several basic lab tests

A series of rock tests including Brazilian indirect tension test (BITT), three-point bending test (TPBT), modified shear test (MST) and uniaxial compression test (UCT) were conducted to investigate the acoustic emission (AE) characteristics and crack classification during rock fracture. The test results show that the rock fracture process presents an obvious segmented variation feature and has a dramatic increasing period, according to the change trends of AE hits and AE energy characteristic parameters. The AE characteristics are closely related to the types of micro-cracks produced in the rock fracture process. The elastic strain energy released by shear crack is greater than that released by tensile crack. Most of AE signals generated in compression and shear failures that mainly produce shear cracks have low average frequency (AF) values and low peak frequencies (below 100 kHz). On the contrary, most of AE signals generated in bending and tensile failures that mainly produce tensile cracks have low RA (ratio of rise time to amplitude) and high peak frequencies (above 100 kHz). In addition, the dividing lines were defined to distinguish the tensile cracks and shear cracks in the AF-RA scatter plots for different rocks. For instance, the AE signals above dividing line accounted for more than 62%, which indicated that the tensile cracks were dominant in TPBT. However, the AE signals below dividing line accounted for more than 74%, and the shear cracks were dominant in UCT. Therefore, the AE characteristics can be used to determine the fracture modes of rock, then to shed light on the micro-crack properties.

Review and evaluation of intermediate temperature monotonic cracking performance assessment testing standards and indicators for asphalt mixes

The main objective of this study was to review and evaluate the current monotonic cracking performance assessment tests and indicators. The testing requirements of various test standards were compared. Also, key publications, concepts, calculation methods, physical meaning, and advantages and disadvantages of various performance indicators were documented. In addition, a comprehensive laboratory evaluation was conducted to examine indicators sensitivity to mix compositions, variability, and statistical grouping as well as mix performance ranking. The results showed that the indirect tension test provided better cracking assessment as compared to semi-circle bending tests. In addition, the Weibull cracking resistance indicator was recommended over other performance indicators.

Automated wireless monitoring system for cable tension forces using deep learning

As demand for long-span bridges is increasing worldwide, effective maintenance has become a critical issue to maintain their structural integrity and prolong their lifetime. Given that a stay-cable is the principal load-carrying component in cable-stayed bridges, monitoring tension forces in stay-cables provides critical data regarding the structural condition of bridges. Indeed, various methodologies have been proposed to measure cable tension forces, including the magneto-elastic effect-based sensor technique, direct measurement using load cells, and indirect tension estimation based on cable vibration. In particular, vibration-based tension estimation has been widely applied to systems for tension monitoring and is known as a cost-effective approach. However, full automation under different cable tension forces has not been reported in the literature thus far. This study proposes an automated cable tension monitoring system using deep learning and wireless smart sensors that enables tension forces to be estimated. A fully automated peak-picking algorithm tailored to cable vibration is developed using a region-based convolution neural network to apply the vibration-based tension estimation method to automated cable tension monitoring. The developed system features embedded processing on wireless smart sensors, which includes data acquisition, power spectral density calculation, peak-picking, post-processing for peak-selection, and tension estimation. A series of laboratory and field tests are conducted on a cable to validate the performance of the proposed automated monitoring system.

A stable extended/generalized finite element method with Lagrange multipliers and explicit damage update for distributed cracking in cohesive materials

A flexible, general and stable mixed formulation is developed to model distributed cracking in cohesive grain-based materials in the framework of the extended/generalized finite element method. The displacement field is discretized on each grain separately, and the continuity of the displacement and traction fields across the interfaces between grains is enforced by Lagrange multipliers. The design of the discrete Lagrange multiplier space is detailed for bilinear quadrangular elements with the potential presence of multiple interfaces/discontinuities within an element. We give numerical evidence that the designed Lagrange multiplier space is stable and provide examples demonstrating the robustness of the method. Relying on the stable discretization, a cohesive zone formulation equipped with a damage constitutive formulation expressed in terms of the traction is used to model propagation of multiple cracks at the interfaces between grains. The damage formulation makes use of an explicit solution procedure, couples the normal and tangential failure modes, accounts for different tension and compression behaviours and takes into account a compression-dependent fracture energy in mixed mode. The framework is applied to complex 2D problems inspired by indirect tension tests of heterogeneous rock-like materials.

A simplified approach in determining the c and φ for asphalt mixtures

In this study, using the Mohr-Coulomb failure theory, a simplified method was proposed to determine the cohesion (c) and internal friction angle (φ) for asphalt mixtures based on direct tension (DT) strength and indirect tension (IDT) strength or unconfined compressive strength (UCS) and IDT strength. The direct tension (DT) strength, superpave indirect tension (IDT) strength and unconfined compressive strength (UCS) were conducted to verify this method using three asphalt mixtures. It was found that the determination of c and φ values have mean absolute errors of 5.2% and 1.8%, respectively in comparing two methods indicating that the c and φ can be estimated from DT strength and IDT strength or IDT strength and UCS. Further study is recommended to verify using different binder grades and mixture types.

Model Development for the Prediction of the Resilient Modulus of Warm Mix Asphalt

Increasing material prices coupled with the emission of hazardous gases through the production and construction of Hot Mix Asphalt (HMA) has driven a strong movement toward the adoption of sustainable construction technology. Warm Mix Asphalt (WMA) is considered relatively a new technology, which enables the production and compaction of asphalt concrete mixtures at temperatures 15-40 °C lower than that of traditional hot mix asphalt. The Resilient modulus (Mr) which can be defined as the ratio of axial pulsating stress to the corresponding recoverable strain, is used to evaluate the relative quality of materials as well as to generate input for pavement design or pavement evaluation and analysis. Based on the aforementioned preface, it is possible to conclude that there is a real need to develop a predictive model for the resilient modulus of the pavement layer constructed using WMA. Within the experimental part of this study, 162 cylindrical specimens of WMA were prepared with dimensions of 101.6 mm in diameter and 63.5 mm in thickness. The specimens were subjected to the indirect tension test by pneumatic repeated loading system (PRLS) to characterize the resilient modulus. The test conditions (temperature and load duration) as well as mix parameters (asphalt content, filler content and type, and air voids) are considered as variables during the specimen’s preparation. Following experimental part, the statistical part of the study includes a model development to predict the Mr using Minitab vs 17 software. The coefficient of determination (R2) is 0.964 for the predicted model which is referred to a very good relation obtained. The Mr value for the WMA is highly affected by the temperature and moderately by the load duration, whereas the mix parameters have a lower influence on the Mr.

WATER SATURATION INDUCED CHANGES IN THE INDIRECT (BRAZILIAN) TENSILE STRENGTH AND THE FAILURE MODE OF SOME IGNEOUS ROCK MATERIALS

The present study concentrates on water induced strength reduction and variation of the failure mode in indirect (Brazilian) tension tests of several igneous rock materials under three moisture cases of oven-dry, air-dry and fully saturated states. In this respect, two andesite and three tuff materials which contain no visible flaws were subjected to indirect tensile strength tests using the Brazilian disc method. Once the tension tests were carried out, photographs of the broken samples were taken to investigate the changes in the failure mode. As a result, it was found that tensile strengths of the samples were highly reduced with the presence of the water and the natural humidity. Additionally, it has been deduced that the failure mode of the samples mainly shifts to central fracturing with the presence of natural moisture and saturation. Although the central crack is the ideal type for the theory of Brazilian tensile strength determination, indefinite contact properties like contact angle and frictions are some notable issues to make only considering failure shapes for the validity of the test results misleading. Keywords: Failure mode; Igneous Rocks; Strength reduction; Tensile strength DOI 10.35180/gse-2020-0031

Out-of-Plane Compressive Response of Additively Manufactured Cross-Ply Composites

ABSTRACTDigital manufacturing was employed to 3D print continuous Carbon, Glass and Kevlar fibre reinforced composites in Unidirectional (UD) [0°], Off-axis ±45° and Cross-ply [0°/90°] layup sequence. These 3D printed composites were subjected to quasi-static, in-plane tension and out-of-plane (compression and shear) loading. The tensile strength of 3D printed Carbon, Glass and Kevlar UD laminates was significantly lower than that of 3D printing filaments used to manufacture them. The type of fibre (brittle/ductile) reinforcement was found to be governing the shear yield strength of 3D printed composites despite having the same Nylon matrix in all the composites. Out-of-plane compressive strength of the 3D printed Carbon and Glass fibre reinforced composites was independent of specimen size. Contrary to that, Kevlar fibre composites showed a pronounced size effect upon their out-of-plane compressive strength. A combination of X-ray tomography and pressure film measurements revealed that the fibres in 3D printed composites failed by ‘indirect tension’ mechanism which governed their out-of-plane compressive strength. To gain further insights on the experimental observations, Finite Element (FE) simulations were carried out using a pressure-dependent crystal plasticity framework, in conjunction with an analytical model based on shear-lag approach. Both FE and analytical model accurately predicted the out-of-plane compressive strength of all (Carbon, Glass and Kevlar fibre reinforced) 3D printed composites.

A new analytical approach for stiffness loss modelling of asphalt mixtures under cyclic indirect tensile loadings

In this study, the indirect tension mode of loading was used to investigate the fatigue behavior of both modified and unmodified asphalt mixtures. Experimental data were analyzed by studying the evolution of the stiffness modulus with the number of cycles. A new analytical approach was introduced to model the variation of the material stiffness and determine different phases of testing. The material response under the selected mode of loading was then characterized based on a damage parameter that refers to the quasi-stationary stage of testing. Moreover, the damage parameter, normalized by a specific stiffness value, was used to provide a general fatigue law where the fatigue life of materials is determined independently from mixture composition. Results prove that good correlations can be established.

Durability of chemically modified sisal fibre in cement-based composites

The degradation of sisal fibre in a cement-based matrix due to the highly alkaline environment reduces the strength of the composite. In this research, to avert this degradation, alkaline treatment and acetylation were respectively performed with sodium hydroxide (NaOH) and Acetic Acid or Acetic Anhydride to improve the resistance of the fibre to alkaline attack. In addition, single fibre pull-out (SFP) tests were performed to evaluate the influence of chemical treatment on fibre strength, fibre-matrix interaction and also determine the critical fibre length. Specimens were tested in indirect tension (flexure) at 28 days to determine the strength of the composite. Additional ageing tests by extended curing in water at 24 °C, lime saturated hot water at 70 °C, and alternate cycles of wetting and drying were done. Aged samples were further tested at 90 days to evaluate the durability of the fibre. It was found that a combination of alkali treatment and acetylation was the most effective treatment condition, followed by that of alkali treatment at low concentrations of sodium hydroxide. At higher concentrations of sodium hydroxide, a significant reduction in strength was observed. Chemical treatment improves the durability of sisal fibres in concrete, albeit slight degradation still occurs.

Dynamic tensile mechanical properties and failure mode of zirconium diboride‐silicon carbide ceramic composites

AbstractDynamic indirect tension experiments were performed on zirconium diboride‐silicon carbide (ZrB2−20%SiC) ceramic. Flattened Brazilian disc specimens of ZrB2−20%SiC were prepared to conduct dynamic tensile tests using the modified Split Hopkinson pressure bar system. The tensile experiments were completed at the range of loading rates from 7.53 to 74.71 GP s−1. The tensile experimental results revealed that the zirconium diboride‐silicon carbide ceramic composite is rate‐sensitive in terms of the tensile strength and failure mode. The dynamic tensile strength increases linearly with the loading rate and changes from 195 MPa at 7.53 GP s−1 to 654 MPa at 74.71 GP s−1. Moreover, the dynamic tensile strength decreases with the increase in critical fracture time, which conforms to Tuler and Butcher's fracture criterion. In dynamic experiments, a high‐speed camera was used to examine the tensile failure process, and fragments were collected to analyze the dynamic tensile failure mechanism. The tensile fracture mode of ZrB2−20%SiC obviously showed the sensitivity of the loading rate. The fragment size of ZrB2−20%SiC ceramic decreased but the quantity of fragments increased as the loading rate increased.

Effect of bedding angle on tunnel slate failure behavior under indirect tension

In order to provide guidance for Muzhailin tunnel design and construction, in this study, five groups of slate specimens with different bedding angles (β, angle between bedding plane and vertical axis) were taken from site to conduct Brazilian splitting tests. The tensile strength, applied energy, failure behaviour, and acoustic emission (AE) characteristics were analyzed, and the failure mechanism was elucidated. The results show that average tensile strength of specimen with β equal to 90° is ∼1.38 times of that of β equal to 0°. Additionally, the applied energy exhibits nonlinear monotonic increasing relationship with bedding angle. Moreover, if β > 45°, the surface crack is noncentral. After the tensile failure, the relative roughness of failure fracture linearly increases with the increase in bedding angle. Furthermore, with increase in β from 0° to 90°, the AE signals occurred around peak loading changed from low amplitude and high frequency to high amplitude and low frequency, i.e. the scale of microcracks increases gradually. When β = 0° and 90°, the tensile failures occurred along the bedding plane and at the slate substrate, respectively. Moreover, when β = 30°, 45°, and 60°, the specimen performed as the shear and tensile composite failure.

Повышение качества регулирования натяжения полосы агрегата непрерывного горячего цинкования

The paper studies a system of interconnected electric drives in the operational area of the continuous hot dip galvanizing unit located in the coating shop at PJSC Magnitogorsk Iron and Steel Works (PJSC MMK). It particularly focuses on the mechanical part with elastic elements and electric drive control systems. The paper aims at studying the existing operating modes of electric drives of the main mechanisms in the operational and output areas of the galvanizing unit; identifying ways to improve the static and dynamic performance of the interconnected electric drives system; developing an improved control system that provides for the better dynamic performance with indirect strip tension control. The authors propose a new control system for the operational area electric drives with corrective speed feedback. The dynamic characteristics of the traditional and the proposed systems were studied using a mathematical model of electric drives of the analyzed section with account to their interconnection via an elastic strip. The model accounts for eight electric drives, i.e., a hot tension station, tension stations no. 3, 4, 5, 6 and a training stand. Each electric drive is modeled with account for mecha­nical inertia and a (speed or torque) control system. The comparative analysis of tension control quality indicators for these systems proved the advantages of the developed system. The research outcomes can be used for similar units of continuous strip processing, featuring the technological line sections with a significant length of the strip between the adjacent electric drives.

Finite Element (FE) Modeling of Indirect Tension to Cylindrical (IT‐CY) Specimen Test for Damping Asphalt Mixtures (DAMs)

DAMs have recently been developed to be used as the damping layer in the so‐called antivibration pavement to mitigate the effects of traffic‐induced vibration while rare finite element (FE) modeling has been conducted to simulate the indirect tension to cylindrical (IT‐CY) specimen test for DAMs. In the present study, the methods for the viscoelastic characterization of DAMs and the techniques to characterize the viscoelastic behavior of DAMs in FE modeling were proposed. The FE model to simulate the IT‐CY test was constructed, and it was verified through the corresponding laboratory test. Good agreements were noted between the simulation results and testing results demonstrating that the FE model can provide the accurate prediction of the mechanical behavior of DAMs.

Enhancement of permanent deformation resistance of modified asphalt concrete mixtures with nano-high density polyethylene

The present research was carried out to inspect the influence of Nano-High Density Polyethylene (Nano-HDPE) particles and Styrene-Butadiene-Styrene (SBS) on the rheological characteristics of modified asphalt binders and performance of modified asphalt concrete mixtures. In this study, the base asphalt binder of the PG (64-16) grade was modified with Nano-HDPE and SBS polymers at a concentration of 3% and 5% by weight of total asphalt binder content. The Superpave dynamic shear rheometer (DSR), rolling thin film oven (RTFO), rotational viscosity (RV), pressure aging vessel (PAV) and bending beam rheometer (BBR) were conducted to evaluate performance grade of base and modified asphalt binders, also gyratory compactor was used to find optimum asphalt content. Roller compactor and wheel track tests were utilized to assess the rutting performance of modified asphalt mixture with Nano and SBS polymers, and the Indirect Tension Test (IDT) was used to assess the strength of mixtures before and after water conditioning. The results of the study show that Nano-HDPE particles have a considerable influence on improving Performance Grade (PG) of the binder, but at an equal concentration of polymer, it is not as effective as the SBS. However, the HDPE shows a significant advantage in keeping the viscosity of the modified binder at significantly lower levels and thus allowing much lower mixing and compaction temperatures as determined by the equ-viscous standard procedure. Although the PG grades of the binders showed the SBS to be more effective in improving the high-temperature grade than the HDPE, the mixture rutting performance shows that the HDPE modified binders provide better rutting resistance at 3% and 5% than the SBS modified binders. This finding shows that binder testing of G*/sin δ only could give a misleading indication of the true contribution of modified binders to rutting resistance as polymers could improve mixtures in different mechanisms than what is measure with binder PG testing. The IDT testing also shows that the strength of the mixtures produced with the modified binders at 25 °C is superior to the control mixture, with the HDPE providing slightly higher strength values before and after water conditioning. The overall results of the study show that HDPE can be used as a viable modifier requiring lower mixing and compaction temperature and equal or significantly better rutting and strength performance than conventional SBS Modifier. The study also highlights the need to check mixture performance when using specialty modifiers and not depend on only DSR testing as specified in the Superpave PG grading.

Implications of Including Reclaimed Asphalt Pavement Materials to Performance of Balanced Asphalt Concrete Mixes

Understanding the effect of reclaimed asphalt pavement (RAP) on the mechanical performance of asphalt concrete (AC) mixtures may lead to improved mix design aiming to maximize the use of recycled materials while yielding optimal volumetric properties and balanced performance. This paper presents an experimental evaluation of the RAP content and source on the mechanical performance of AC mixes as measured by overlay tester, Hamburg wheel tracking device, and indirect tension tests. Several Superpave mixes with 12.5 mm nominal maximum aggregate size and recycled binder replacement ratios ranging from 0 to over 50 were designed and evaluated in this study. A performance interaction diagram was used to interpret collectively the cracking susceptibility, rutting potential, and tensile strength of the AC mixes. Asphalt concrete mixes with high RAP content can be balanced with proper individual mix design and their performance assessed through mechanical characterization. Furthermore, AC mixes with RAP from different sources yielded different cracking and rutting potentials. The performance tests and analysis methodology from this study could potentially be incorporated into the balanced mix design process to provide well-performing mixes containing optimal amounts for recycled materials.