Semi-circular Bending Fracture Test Research Articles

Feasibility Analysis of Current Pavement Condition Monitoring Technologies: 3D Pavement Profiler and Infographic Pavement Management Program Using the Semi-Circular Bending Fracture Test

Feasibility Analysis of Current Pavement Condition Monitoring Technologies: 3D Pavement Profiler and Infographic Pavement Management Program Using the Semi-Circular Bending Fracture Test

Evaluation of the impact of long-term aging on fracture properties of warm mix asphalt (WMA) with high RAP contents

This study aimed to investigate the effects of long-term aging on the fracture characteristics of Warm Mix Asphalt (WMA) containing Reclaimed Asphalt Pavement (RAP). To this end, various RAP contents (0, 50, 75, and 100%) and one WMA additive (Zycotherm) were used. The Semi-Circular Bending (SCB) fracture test was conducted at intermediate temperature and fracture parameters, including the fracture force, fracture toughness, strain energy, J-integral, stiffness, and flexibility index were measured to identify the impact of aging and RAP addition on different fracture properties of WMA mixtures. To remedy the problem concerning the amorphous trend of fracture properties over the service time and intersecting the curves of fracture parameters versus service time, the area beneath the fracture parameter was employed as a reliable index for comparing different mixes. Then, summations of the area of all fracture parameters versus service time for various mixtures with different RAP content were identified as the overall fracture resistance of each mixture. Finally, an analysis of variance (ANOVA) was determined to statistically assess the results of the SCB fracture test. This study highlights the importance of considering long-term aging effects on WMA mixtures containing RAP and the potential benefits of using high RAP content in flexible pavements. Overall, this research can help agencies make a more precise decision regarding the consequences of high RAP content on the long-term performance of asphalt pavements.

Performance characterization of asphalt mixtures under different aging levels: A fracture-based method

This paper proposes a straightforward approach to characterize the fracture properties and fatigue life of asphalt mixtures over the service time. Since the serviceability of flexible pavements varies as they age, assessing the performance of asphalt mixes under aged conditions is essential. To investigate the sensitivity of fracture-related parameters to aging, accelerated laboratory aging, which is conditioning asphalt concrete samples in a force draft oven for different aging times (0, 3, 5, 7, and 9 days), was used. The Semi-Circular Bending (SCB) test at 25 °C was carried out on neat and activated carbon-modified samples to examine the fracture responses of asphalt mixes. First, force–displacement curves at failure were plotted. Then, fracture-related parameters (e.g., peak load, fracture toughness, strain energy, and J-integral) and damage levels corresponding to each fracture criteria were measured versus aging levels. In addition, the fatigue life ratio was determined to measure the influence of aging on the long-term performance of asphalt mixtures. To incorporate the effect of aging on the overall cracking resistance of asphalt mixtures, different fracture-related parameters versus service time were studied. Experimental findings suggest that the area under the fracture property versus service time can provide a reliable index for evaluating the long-term performance of asphalt mixtures. In addition, statistical analysis was performed to assess the impact of aging on fracture-related parameters obtained from the SCB fracture test. The proposed method was able to simultaneously factor in the fracture resistance and the rate of damage development during flexible pavement service life.

Laboratory Investigation on the Rutting and Fracture Resistance of Hot-Mix Asphalt Containing Nanographene Oxide

The use of nanomaterials has brought about a huge revolution in the development of various industries. Moreover, in the pavement industry, researchers have been applying nanomaterials for many years due to their unique properties to enhance the features of asphalt mixtures and increase their resistance to various failures. In this study, nanographene oxide (GO) has been used in the amount of 0.2, 0.5, and 0.8 percent of consumed bitumen to improve the low-temperature cracking resistance and the high-temperature rutting resistance of hot-mix asphalt (HMA). For this purpose, to examine the impact of this material on the HMA, the semicircular bending (SCB) fracture test and Hamburg wheel tracking (HWT) test were applied. In addition, conventional bitumen tests were performed to investigate the impact of nanoGO on virgin bitumen in this study. The outcomes of conventional bitumen experiments displayed that the addition of nanoGO to pure bitumen augments viscosity, specific gravity, and softening point and reduces the penetration and ductility of pure bitumen. Furthermore, outcomes of the SCB fracture test indicated that nanoGO enhances the stress intensity factor (SIF) of the asphalt mixture and improves the low-temperature cracking resistance of asphalt specimens. Moreover, the addition of nanoGO to the asphalt mixture increased rutting resistance and decreased rutting depth. In addition, the results of the ANCOVA statistical analysis demonstrated the significant effect of this nanomaterial on the improvement of the low-temperature cracking resistance and the rutting resistance of HMA.

Novel Model to Predict Critical Strain Energy Release Rate in Semi-Circular Bend Test as Fracture Parameter for Asphalt Mixtures Using an Artificial Neural Network Approach

Growing use of recycled asphalt materials in asphalt pavement means the current volumetric-based Superpave mixture design may not address durability concerns arising from replacement of a proportion of virgin binder with recycled ones. To address this limitation, performance-based testing is introduced to supplement conventional volumetric mixture design in assessing cracking performance of asphalt mixtures. Louisiana Department of Transportation and Development’s Specifications for Roads and Bridges specify a criterion for the critical strain energy release rate, Jc, obtained from semi-circular bend (SCB) test as a complement of current practice to evaluate cracking resistance of asphalt mixtures. Quality control/assurance practices, however, require SCB samples to be long-term aged for five days at 85°C, which is a time-consuming process. Therefore, it is beneficial to be able to estimate SCB Jc for long-term aged asphalt mixtures based on SCB Jc measured from plant-produced asphalt mixtures. Asphalt mixture aging is complex, and various variables are involved in the aging process, including volumetric properties of asphalt mixture and chemical/rheological characteristics of asphalt binder. With the capability of artificial neural network (ANN) to address complex relationships between input and output variables, this study aims to predict the fracture parameter, SCB Jc, of asphalt mixtures using ANN. A total of 34 asphalt mixtures were selected for this study. SCB fracture test and asphalt binder tests for chemical and rheological characterization were conducted. Stepwise regression analysis was used to determine the significant parameters in the correlation with SCB Jc. With determined significant parameters, ANN using the gradient descent backpropagation approach was then applied to develop and validate the predictive model. It was shown that the developed ANN model was able to predict the fracture parameter, SCB Jc, of asphalt mixtures more accurately than linear and non-linear regression models.

The effects of nano zinc oxide (ZnO) and nano reduced graphene oxide (RGO) on moisture susceptibility property of stone mastic asphalt (SMA)

Moisture damage is one of the most common and main distresses in asphalt pavements. Using Nanomaterials due to their unique and outstanding properties in the asphalt pavement industry has received much attention in recent years. This paper investigated the effects of Nano Zinc Oxide (ZnO) and Nano Reduced Graphene Oxide (RGO) on moisture susceptibility resistance of Stone Mastic Asphalt (SMA) mixtures. SMA mixtures are a type of hot mix asphalt (HMA) containing two main parts of coarse aggregates and bitumen-filled mortar (bitumen, stabilizing additives, and filler aggregates). There is a wide range of test methods for evaluating the moisture resistance of asphalt mixtures; this study used the immersion Marshall test, indirect tensile strength test, boiling water test, static creep test, pull-off adhesion, and Semi-circular bending (SCB) fracture test for this aim. The pure bitumen was modified with three content of Nano ZnO and Nano RGO (0.2 %, 0.4 %, and 0.6 % by weight of asphalt binder). The experimental results obtained in this research indicated that the addition of Nano RGO in pure binder increases the softening point and viscosity and decreases the penetration and ductility properties of pure bitumen. Also, the addition of Nano ZnO in bitumen can increase the ductility, softening point, and viscosity, and decrease the penetration properties of pure bitumen. The mechanical test results showed that an increase in the percentage of Nano ZnO and RGO lead to a rise in Marshall Stability, indirect tensile strength, accumulated strain, pull-off adhesion strength, and fracture energy and improve the bitumen coating on aggregates in SMA mixtures. According to calculated moisture susceptibility indices of the mentioned tests above, the Nano ZnO and Nano RGO can significantly improve the resistance of stone mastic asphalt mixtures against moisture susceptibility. Examination of the test results showed that the ITS, pull-off, and Semi-circular bending (SCB) fracture test can give a good estimation of the moisture susceptibility of asphalt mixture. In addition, the results of the ANOVA test depicted that in ITS, Pull-off, and SCB fracture tests, Nano ZnO has a more significant effect on improving moisture susceptibility than Nano RGO.

Characterization of the fatigue behavior of asphalt mixture under full support using a Wheel-tracking Device

Most existing fatigue testing methods in the laboratory are designed to evaluate the cracking resistance of asphalt mixture only, regardless what types of structural support it is used in the field. However, literature has confirmed that fatigue cracking is a structural related distress, and the cracking potential of asphalt layer is strongly affected by its underneath structural supporting conditions. On the other hand, the Hamburg Wheel-tracking Device (HWTD) has gained popularity for characterizing the rut-resistance and moisture susceptibility of asphalt mixtures under moving loads among state Department of Transportation (DOT) and agencies, and it has the capability to be modified to specify supporting conditions. Therefore, in this study, we propose to make some modifications to the existing HWTD and to study its capability of being also utilized as a cracking device for its potential advantages in equipment availability and simulating field loading and structural conditions. The developed HWTD fatigue test was used to simulate the conditions experienced by an asphalt mixture layer paved on the flexible base and applied with a vertical moving load. Three mixtures were specially designed to have known fatigue behavior difference for evaluating the reliability of this newly developed method, and to be compared with the standard American Association of State Highway and Transportation officials (AASHTO) semi-circular bending (SCB) method (AASHTO TP 124-18). A variety of strain and pressure gauges were used to record the load responses for fatigue behavior analysis. Both the phenomenological fatigue life analysis approach and the dissipated energy based ratio of dissipated energy change (RDEC) approach were used for data analysis. It was found that the HWTD fatigue test was essentially a type of laboratory scale accelerated loading test which can simulate the fatigue cracking phenomenon under the proposed testing setup. The RDEC approach with different failure criteria were suitable and effective in analyzing the testing data and can quantify the fatigue behavior of specific mixture within reasonable time frame. The results were consistent with the standard SCB fracture test results. In conclusion, the HWTD fatigue test has the potential to be a rational and convenient method for characterizing the fatigue behavior of hot mix asphalt (HMA) materials with the consideration of supporting conditions.

Characterisation of rheological properties of sulfur-extended asphalt with/without crumb rubber

ABSTRACT This study is to characterise rheological properties of sulfur-extended asphalts with/without crumb rubber at high, intermediate, and low temperatures using standard asphalt binder tests. Four dosages of sulfur (i.e. 0%, 15%, 30% and 45%) by weight of neat asphalt binder were used. The results indicated that a low level of sulfur addition, such as 15%, softened original asphalt binder. When the sulfur dosage was larger than 15%, the extra sulfur would act as fillers to stiffen asphalt binder. The addition of crumb rubber significantly increased high temperature performance grade. For sulfur-extended asphalts with/without crumb rubber, an increase in the sulfur dosage resulted in an increase of low temperature performance grade. Sulfur-extended asphalt with 15% sulfur exhibited the largest non-recovery creep compliance (Jnr) value, while the 30% and 45% exhibited the lowest values since more extra sulfur acts as fillers to stiffen asphalt binder. The addition of sulfur significantly decreased viscosity. The semi-circular bending fracture test results indicated that the mixture with the addition of 15% sulfur was softer and behaved in a more ductile manner than the others, which is consistent with the asphalt binder test results of high temperature performance grade and non-recovery creep compliance.

Semicircular bending fracture test to evaluate fracture properties and ductility of cement mortar reinforced by scrap tire recycled steel fiber

The existing test methods using single-edge notched-beam (SEN(B)) specimens to characterize the fracture properties of cementitious materials have some drawbacks. A novel approach using a single fracture test to assessing multiple cementitious materials properties with semi-circular bending (SCB) specimens is presented in this study. In comparison with the conventionally used SEN(B) specimens, the fabrication of the SCB geometry is less material- and labor- intensive. The geometry is also more suitable for field applications due to the ease of extracting cylindrical specimens. In this study, the utility of the SCB fracture method has been demonstrated by testing cement mortars reinforced by recycled steel fiber (RSF) from scrap tire. Based on the SCB fracture test, adding 2% RSF into the cement mortar increased the critical stress intensity factor (KIcs) and the critical crack tip opening displacement (CTODc) by up to 45% and 90%, respectively, and the fracture energy parameters (Gf and GF) by up to 128% and 475%. The ductility indexes were defined based on stress intensity factors rather than tensile strengths, and the results reveal the extremely high ductility of the RSF reinforced cement mortar. It is also found that early age cement mortar specimens are less brittle than mature specimens. Additionally, the theoretical tensile strength was determined. By comparing the theoretical tensile strength with the splitting tensile strength, the level of size effect was evaluated, which again verified that the cement mortar reinforced by 2% RSF is more ductile compared to the plain cement mortar.

Performance Characterization of Hot Mix Asphalt with High RAP Content and Basalt Fiber.

Incorporating reclaimed asphalt pavement (RAP) into asphalt mixtures achieves astonishingly environmental and economic benefits. However, there is hesitation to use higher RAP content due to the concern regarding the deterioration in pavement performance, especially the cracking resistance. Basalt fiber has been considered an effective additive to reinforce the performance of asphalt mixtures and, subsequently, the reinforcement effect is also expected for high-RAP content mixtures. Therefore, this study investigated the effect of basalt fiber on the pavement performance of asphalt mixtures with 0%, 30%, 40%, and 50% RAP contents against high-temperature performance, moisture susceptibility, low-temperature and intermediate-temperature cracking resistance, based on the wheel-tracking test, the uniaxial penetration test, the freeze-thaw splitting test, the low-temperature bending beam test, the semicircular bend fracture test and the indirect tensile asphalt cracking test, respectively. In addition, a performance-space diagram was developed to determine the mixture performance shift caused by basalt fiber. The results showed that adding basalt fiber compensated for the detrimental effect caused by RAP, leading to significant enhancement in moisture susceptibility and low- and intermediate-temperature cracking resistance of mixtures with high RAP content, along with the enhancement in high-temperature performance, indicating that basalt fiber can contribute to the use of high RAP content.

Fracture Properties and Restrained Shrinkage Cracking Resistance of Cement Mortar Reinforced by Recycled Steel Fiber from Scrap Tires

Thanks to better processing technology, quality recycled steel fiber (RSF) is routinely extracted from scrap tires, offering opportunities to reinforce cementitious materials in a more economical and sustainable manner. In this study, a detailed experimental program on cement mortar reinforced by up to 2 vol. % RSF was carried out. The work involved conventional tests to characterize cement mortar mechanical properties including compressive strength, elastic modulus, and splitting tensile strength. It also featured an innovative semi-circular bending (SCB) fracture test to characterize fracture-related properties, and a customized ring test to study the cracking resistance under restrained drying shrinkage of the studied mortars. The combined use of the fracture and ring tests is believed to lead to a better assessment of concrete structure behaviors in the field. Based on the test results, the addition of up to 2% RSF shows noticeable improvement on the splitting tensile strength, but it has marginal effects on the cement mortar compressive strength and elastic modulus. The improved fracture properties of the cement mortar reinforced by 2% RSF from the SCB fracture test demonstrate that the RSF-reinforced mortar not only has a better resistance to the initiation of major cracks but also exhibits an enhanced post-cracking performance. Based on the ring test results, the longer cracking time and higher residual strain level of the 2% RSF mortar samples clearly reveal that the RSF could effectively delay and bridge cracks.

Characterization of two-parameter fracture properties of portland cement concrete containing reclaimed asphalt pavement aggregates by semicircular bending specimens

Although few available test results showed that portland cement concrete containing reclaimed asphalt pavement (RAP-PCC) can have equivalent (or even improved) fracture properties and ductility compared to plain PCC, the limitations of the existing experimental methods to test the two-parameter fracture properties (TPFP) of concrete (critical stress intensity factor, KIcs, and critical crack tip opening displacement, CTODc) have hindered an effective characterization of RAP-PCC's fracture properties and ductility. To provide an easy but effective approach, this paper developed an innovative fracture test using the semicircular bending (SCB) geometry to characterize the TPFP of the studied RAP-PCC mixtures. Based on the results, it is confirmed that addition of RAP improves PCC's CTODc and Gf, despite of a reduction in mechanical strengths. The material length, Q, of the RAP-PCC mixture is statistically higher than that of the plain PCC, suggesting that RAP-PCC is a more ductile material. Besides, the theoretical tensile strength, tensile MOE, and bilinear softening curve of the RAP-PCC can be easily obtained using the developed SCB fracture test.

Fracture prediction of rocks under mode I and mode II loading using the generalized maximum tangential strain criterion

The effects of specimen geometry on mode I and mode II fracture toughness (i.e., KIc and KIIc), and the ratio of KIIc to KIc for a given rock material were derived on the basis of a generalized maximum tangential strain (GMTSN) fracture criterion, in which the effects of T-stress and radial stress on rock fracturing can be taken into consideration. To verify these theoretical predictions, laboratory tests using semi-circular bend (SCB) and center-cracked circular disc (CCCD) specimens were conducted. Experimental results indicate that the GMTSN criterion is capable of estimating the geometry dependence of KIc and KIIc, the ratio of KIIc to KIc and the fracture initiation angle of rocks. Moreover, the GMTSN criterion can provide better estimates for the experimental results than some other frequently-used fracture criteria. In addition, our study reveals that the SCB fracture test using asymmetric bottom supports can be identified as a suitable testing method to estimate the upper bound of mode II fracture resistance.

Correlation of low temperature fracture and strength properties between SCB and IDT tests using a simple 2D FEM approach

In this paper, the low temperature strength of asphalt mixture is investigated based on indirect tensile (IDT) and semi-circular bending (SCB) tests and on two-dimensional numerical simulation. The values of maximum stress at crack tip in SCB simulation are obtained using commercial finite element software and cohesive zone modelling. Then, a correlation between the numerically determined maximum SCB stress and the strength value experimentally measured on IDT specimens is derived. It is found that the newly proposed relationship can be used to predict the asphalt mixtures strength of IDT un-notched specimens-based SCB fracture tests and contribute to better understanding of the low temperature strength properties of asphalt pavements.

R-curves characterisation analysis for asphalt concrete

Fracture tests, especially at lower testing temperatures, have become quite popular in quantifying low-temperature cracking. However, current fracture testing analysis methods often use a single number, such as fracture energy or fracture toughness, to quantify cracking resistance. These tests do not capture both the initiation and propagation of the crack. The Resistance Curve, or R-curve, is widely applied in many fields, such as metal, polymer and composites. The R-curve considers cracking resistance as a function of crack extension, which includes initiation and propagation. In this research, three asphalt concrete mixtures, including hot mix, hot mix with reclaimed asphalt pavement (RAP) and warm mix with RAP were tested at two temperatures, three levels of ageing and two levels of moisture condition by the Semi-Circular Bend fracture test. R-curves were constructed using the data from the fracture test, and digital images were utilised to capture the crack extension. In addition to capturing the traditional fracture energy, two new parameters were explored using the R-curves: the cohesive energy and the propagation parameter energy rate. It was found that cohesive energy was always in a narrow range (approximately 500–1000 J/m2) compared to the fracture energy range (approximately 500–1700 J/m2) over all combinations of ageing and moisture conditions, which indicates that the crack initiation may not be as sensitive to temperature, ageing and moisture as fracture energy. The results of energy rate indicated that moisture and short-term ageing impact the crack propagation by reducing the resistance of crack growth. These results proved that R-curves are a potentially useful tool to quantify the cracking resistance of asphalt concrete in both crack initiation and propagation.

Mixed-mode fracture characterization of fine aggregate mixtures using semicircular bend fracture test and extended finite element modeling

This paper presents integrated experimental-computational efforts to characterize the mixed-mode fracture of a fine aggregate matrix mixture which is the primary phase of cracks around stiffer coarse aggregates when typical asphalt concrete mixtures are subjected to intermediate service temperatures. Experimentally, semicircular bend fracture tests were conducted by varying the geometric-loading configurations with different initial notch inclination angles and supporting spans to achieve different fracture modes (opening mode-I, in-plane shear mode-II, and mixed). The semicircular bend fracture test results were then integrated with the extended finite element model which is also incorporated with mode-dependent cohesive zone fracture to properly identify the mode-dependent fracture properties. The test and model simulation results indicated that the cohesive zone fracture toughness of in-plane shear mode-II is quite different (approximately three times greater) from opening mode-I fracture toughness. The critical fracture energy was related to the mixed-mode ratio, which presented a power relationship between the total fracture toughness and involvement of in-plane shear mode-II fracture in the total. Findings and observations from this study, although they are limited at this stage, imply that the mixed-mode fracture characteristics are significant and need to be considered in the structural design of asphalt pavements with which multi-axial cracking is usually associated.

Avaliação da resistência ao trincamento de misturas asfálticas compostas por agregados miúdos com diferentes tamanhos máximos nominais

The fatigue cracking could be related to a small-scale phenomenon (microcracks). Authors have used the fine portion of the hot mix asphalt (HMA), known as fine aggregate matrix (FAM), to estimate the HMA behavior. This study aims to evaluate the influence of the nominal maximum size (NMS) of the fine aggregates in the HMA cracking resistance. As from the HMA design, three corresponding FAMs with different aggregates’ NMS were designed. As higher is the NMS of FAM, the lower is the binder content. The FAMs were subjected to the semicircular bending fracture test in order to measure the dissipated energy during the crack propagation at two temperatures: 15 and 25°C. The results at 15°C indicated that as the NMS decreases, the HMA resistance to cracking increases. At 25°C, it is believed that other damage mechanisms occur simultaneously, making difficult the mixtures ranking based on the NMS

Rate- and Temperature-Dependent Fracture Characteristics of Asphaltic Paving Mixtures

Abstract Cracking in asphaltic pavement layers causes primary failure of the roadway structure, and the fracture resistance and characteristics of asphalt mixtures significantly influence the service life of asphaltic roadways. A better understanding of the fracture process is considered a necessary step to the proper development of design-analysis procedures for asphaltic mixtures and pavement structures. However, such effort involves many challenges because of the complex nature of asphaltic materials. In this study, experiments were conducted using uniaxial compressive specimens to characterize the linear viscoelastic properties and semi-circular bending (SCB) specimens to characterize fracture behavior of a typical dense-graded asphalt paving mixture subjected to various loading rates and at different temperatures. The SCB fracture test was also incorporated with a digital image correlation (DIC) system and finite-element model simulations including material viscoelasticity and cohesive-zone fracture to effectively capture local fracture processes and resulting fracture properties. The test results and model simulations clearly demonstrate that: (1) the rate- and temperature-dependent fracture characteristics need to be identified at the local fracture process zone, and (2) the rate- and temperature-dependent fracture properties are necessary in the structural design of asphaltic pavements with which a wide range of strain rates and service temperatures is usually associated.

Mode I Fracture Characterization of Bituminous Paving Mixtures at Intermediate Service Temperatures

This study presents an integrated approach combining experimental tests and numerical modeling to characterize mode I fracture behavior of bituminous paving mixtures subjected to a wide range of loading rates at intermediate temperature conditions. A simple experimental protocol is developed using the semi-circular bending (SCB) test geometry. The local fracture behavior at the initial notch tip of the SCB specimens is monitored using high-speed cameras with a digital image correlation (DIC) system. The DIC results of the SCB fracture tests are then simulated using a finite element method that is incorporated with material viscoelasticity and cohesive zone fracture. Fracture properties are obtained locally at the notch tip by identifying two cohesive zone fracture parameters (cohesive strength and fracture energy) that result in a good agreement between test results and numerical simulations. The results clearly present significant rate-dependent fracture characteristics of bituminous paving mixtures at intermediate service temperatures. This study further demonstrates that fracture properties of viscoelastic materials need to be characterized at the local fracture process zone when they present ductile fracture behavior.

Factors Study in Low-Temperature Fracture Resistance of Asphalt Concrete

An investigation of various factors that can affect the fracture resistance of asphalt mixtures at low temperatures was conducted. The fracture resistance of 28 asphalt mixtures—which represent a combination of factors including binder type, binder modifier, aggregate type, asphalt content, and air voids—was evaluated by performing semi-circular bending fracture tests at three low temperatures. Two parameters, fracture energy and fracture toughness, were calculated from the experimental data. The statistical analysis indicated that fracture resistance is strongly dependent on temperature and significantly affected by the type of aggregate and air void content. The results of the analysis also confirmed the significance of binder grade and modifier type with relation to cracking resistance of asphalt mixtures. Asphalt content was also found to be significant for fracture energy but not a significant factor affecting fracture toughness.