Critical Tip Opening Displacement Research Articles

Fundamental cracking performance of asphalt-filler mastics with hydrated lime

This study evaluates the impact of hydrated lime (HL) on the cracking performance at intermediate temperature of asphalt-filler mastics, specifically as a partial replacement for limestone filler (LF). HL, is an active filler known for its multiple benefits in asphalt applications. The Double Edge Notched Tension (DENT) test was used to assess fracture properties, including specific total work of fracture, plastic work of failure, essential work of fracture, and average critical tip opening displacement. The results revealed several key findings: a notable loss of ductility and toughness with increasing HL dosages, a stiffening effect evidenced by increased peak loads and reduced failure deformation, and a decrease in the specific total work of fracture, indicating a loss of fracture energy. However, an enhancement in fracture resistance to plastic deformation is observed with HL addition, although identifying trends at high dosages remains challenging due to complex interactions between HL and LF. Furthermore, using low volumetric concentrations of HL minimizes the adverse impact on fracture performance while leveraging its other beneficial active filler properties. These findings suggest that while HL can improve certain fracture properties, optimal dosages are crucial to avoid adverse effects. Overall, this paper provides an updated and comprehensive study of the fracture of mastics at intermediate temperatures, which adds up to the understanding of asphalt-filler interactions, which can potentially lead to further investigations, such as how the partial replacement of LF with HL affects asphalt mixtures’ performance-related characteristics, particularly the fatigue cracking resistance.

Experimental investigations on fracture parameters of random and aligned steel fiber reinforced cementitious composites

Experimental research was carried out to evaluate the comparative fracture performance of random steel fiber-reinforced composite (SFRC) and aligned steel fiber-reinforced composite (ASFRC). The desired direction of steel fiber in the fresh cementitious mortar was achieved by the electromagnetic field. Three-point bending tests were conducted on geometrically similar notched beam specimens. Various dimensions and steel fiber contents by volume Vf were considered to study fracture performance and investigate the size effect. The fracture parameters were analyzed by nonlinear fracture models, namely the size effect model (SEM), work of fracture method (WFM), and double-K fracture criterion (DKFC). Initial fracture energy, critical fracture toughness KIC, length of fracture process zone, and critical tip opening displacement from SEM, total fracture energy, and characteristic length from WFM was studied for SFRC and ASFRC. The initial cracking load was detected with strain gages to evaluate initial fracture toughness KICini. Unstable fracture toughness KICun from DKFC with special emphasis on size effect was obtained. The results show that the rise of specimen depth has no considerable effect on the KICun while the size effect of KICini is not significant. As the increment of Vf, both the KICini and KICun show a linear ascending trend and both of them are greater for ASFRC than those of SFRC specimens. It is found that there exists a strong correlation between the fracture toughness measured by DKFC and SEM (KIC from SEM≅KICun from DKFC). Generally, the fracture performance of ASFRC relative to that of random SFRC is improved by more than 80%.

Fracture performance of concrete incorporating different levels of recycled coarse aggregate

AbstractThis study investigated the fracture performance of concrete containing different levels of recycled coarse aggregate (RA; i.e., 0, 30, 70, and 100%) with equivalent compressive strength using three‐point bend tests. In total, 32 beams with different notch depths (i.e., 40, 50, and 60 mm) were fabricated to test the load–deflection (P–δ) curves and load‐cracking mouth opening displacement (P‐CMOD) curves. The effects of RA substitutions on fracture parameters were analyzed and the size effect on fracture energy was also discussed. The results demonstrated that with the incremental of RA, the static elastic modulus continuously decreased, while the splitting tensile strength, fracture energy, fracture toughness, and effective crack length remained mostly unchanged. In contrast, the critical cracking opening displacement (CMODC) and critical tip opening displacement increased first and then deceased with the increase of RA substitution, the maximums appeared at 70%. The characteristic length of recycled aggregate concrete (RAC) was entirely less than that of natural aggregate concrete, indicating that RAC presented greater brittleness. Furthermore, increasing cross‐sectional area of ligament gradually increased the fracture energy.

Estimation of Cement Composites Fracture Parameters Using Deformation Criterion.

A simple deformation criterion based on Dugdale’s cohesive zone model is presented. The criterion can be used for both the experimental determination of the critical stress intensity factor, KIc, and the critical tip opening displacement, CTODc. It can also be applied for the evaluation of the load capacity of structural elements. The criterion is presented in explicit and compact form, which allows straightforward calculations to be performed for the estimation of KIc and CTODc values from the experimental data obtained from samples with a U-shaped notch, rounded with an arbitrary radius. Thanks to the simple form of the approximate relationship between the maximal load level and the dimensionless notch tip opening displacement, the reverse procedure was obtained, i.e., the estimation of the value of the maximal force loading the structural element as a function of the known critical stress intensity factor.

Influence of Basalt, Hydrated Lime, and Fly-Ash Fillers on Aging Behavior of Asphalt Mastic Using Essential and Plastic Work of Fracture

Abstract The present study was undertaken to investigate the influence of Basalt (B), Hydrated Lime (HL), and Fly-Ash (FA) fillers on aging behavior based on the fracture properties of asphalt mastic. The asphalt mastic samples were prepared in the laboratory using an AC-30 asphalt binder with various combinations of B-HL and B-FA fillers by maintaining a constant filler-binder ratio of 0.8:1 (by mass ratio and 22.5 % by volume). The HL and FA contents were selected as 0 %, 5 %, 10 %, 15 %, and 20 % by the weight of the asphalt binder, and the content of B filler was adjusted accordingly. Correspondingly, three types of asphalt mastic samples, namely, unaged, short-term aged, and long-term aged were prepared in the present study to understand the effects of oxidative aging. Fracture properties of asphalt mastic samples were evaluated at an intermediate temperature using a Double Edge Notched Tension test. The analysis of fracture behavior includes the load-displacement curve pattern, Total Work of Fracture (TWF), Essential Work of Fracture (EWF), Plastic Work of Fracture (PWF), and Critical Tip Opening Displacement (CTOD) values. The results showed that nature, surface texture, mineralogy, and interaction ability of HL and FA fillers strongly influence the aging and fracture resistance of the asphalt mastic. The load-displacement curve pattern, TWF, and PWF values signify a clear indication of an increase in ductile behavior with the incorporation of HL or FA fillers. Similarly, the EWF and CTOD values showed that the inclusion of HL or FA fillers in the asphalt mastic enhanced the aging and fracture resistance behavior. The inclusion of the HL filler has a predominant impact in comparison to the FA filler in the enhancement of both the aging and fracture resistance of asphalt mastic.

Evaluation of intermediate temperature cracking performance of warm mix additive modified asphalt binders

In the present study, intermediate temperature cracking performance of different types of asphalt binders containing warm mix asphalt (WMA) additives was evaluated using three test methods namely, Superpave fatigue parameter, linear amplitude sweep (LAS) and double edge notch test (DENT). The Superpave fatigue, LAS, and DENT tests are based on dissipated energy, viscoelastic continuum damage (VECD) and work of fracture approaches, respectively, and thus each of the tests may result into different performance ranking of asphalt binders. The outcome of the Superpave fatigue, LAS and DENT tests are G∗sinδ, number of cycles to fatigue failure (Nf), and critical tip opening displacement (CTOD) based on which cracking potential of asphalt binder can be assessed. An asphalt binder having a low Superpave parameter, high Nf and high CTOD values are expected to have better intermediate temperatures cracking performance. The present study selected three control binders namely virgin (AC), styrene-butadienestyrene (SBS) and crumb rubber modified (CRM) binders were modified using three WMA additives namely Fischer-tropsch (FT) wax based, chemical surfactant (CS) based and water based (WB). Control binders were modified with 2%, 6% and 2% (by weight of asphalt binder) of FT, WB and CS, respectively, using a mixer. The results showed that, based on G∗sinδ and CTOD parameters, CS modification reduced stiffness (reduced G∗sinδ) and improved ductile performance (increased CTOD) of control binders. However, WB and FT modification increased stiffness and degraded the ductile performance of control binders, except for SBS with 6%WB binder which showed higher CTOD than control SBS binder. On the other hand, considering performance based on Nf parameter, WMA additive modification improved fatigue life of control binders, except for SBS with 2%CS binder which showed lower Nf as compared to control SBS binder. Control binders with and without WMA additives were ranked based on G∗sinδ, Nf and CTOD parameters. AC and CRM binder with and without WMA additives followed similar performance ranking based on G∗sinδ and CTOD parameters. It is difficult to conclude over the best suitability of intermediate temperature performance parameter as mentioned tests involve different loading conditions and analysis approaches. Hence, further investigation on asphalt mixes is necessary to identify the best suited intermediate temperature performance parameter of asphalt binders, and its possible correlation with mix performance.

Fracture Properties of Concrete Reinforced with Steel Fibers

Background: Concrete is a material strong in compression but exhibits low tensile strength, low strain capacity in tension and low cracking & fracture resistance due to presence of defects like voids, cracks, air pockets. Hence to improve fracture resistance of concrete, different types of discrete short fibers are added in concrete at the time of casting. Objectives: To evaluate the various fracture properties such as fracture energy, toughness (KIC) and Critical Tip Opening Displacements (CTODC ) of normal strength concrete reinforced with Steel Fiber (SF) (0, 0.25, 0.5, 0.75 & 1% by volume of concrete). Methods: Authors have studied the effect of addition of steel fibers on various fracture properties of concrete. Normal strength concrete was cast by using water to cement ratio as 0.38 and a total of five mixtures were prepared by using steel fibers (0.25, 0.5, 0.75 & 1% by volume of concrete) into those concretes. Notched beam specimen was used to conduct three-point bending test to study fracture properties such as fracture energy, fracture toughness (KIC) and CTODC of different concrete mixes. Findings: Test results showed an improvement in tensile strength and fracture properties of steel fiber reinforced concrete mixes when compared with control mix. Fracture energy was enhanced by 243 % & 208 % with addition of 0.75% and 1% steel fibers. Fracture toughness was also enhanced by 95% & 94 % with addition of 0.75% and 1% steel fibers. However inclusion of steel fibers resulted in reduction in the workability of concrete mixture with increasing fiber contents. Novelty/Improvements: For the novel material containing steel fibers, fracture properties of concrete are enhanced to a great extent and thus brittle and sudden failure of concrete can be avoided and material undergoes a more ductile failure which in turn improves the performance of structure in terms of durability and serviceability. Keywords: Critical Tip Opening Displacement, Fracture Energy, Fracture Toughness, Steel Fibers

Evaluation of the fracture performance of different rubberised bitumens based on the essential work of fracture

The fracture performance of rubberised bitumen in addition to one pre-treated with a Warm Mix Additive (Sasobit®) was investigated using different test methods measuring different damage mechanisms. Two Recycled Tyre Rubber (RTR) modifiers together with two base binders were blended in the laboratory to produce various combinations of Recycled Tyre Rubber Modified Bitumens (RTR-MBs). The first RTR is a standard recycled polymer derived from discarded truck and passenger car tyres by ambient grinding. The second RTR consists of 100% recycled truck tyres derived by cryogenic grinding and pre-treated with special oil and WMA to allow further decrease of asphalt mixture production temperatures. A fracture mechanics testing approach was used for evaluating the binder fatigue resistance; consisting of the double-edge-notched tension (DENT) test. The critical tip opening displacement (CTOD) obtained from the DENT test was used for fracture characterization of the binders within the ductile failure region. The study applied the partitioning concept of the total energy of bituminous binders to have a more reliable parameter that could be independent of the stress state of the ligament. The results show that generally the addition of RTR improves the fracture properties of binders indicating better fatigue performance. Pre-treatment with Sasobit® makes the materials more brittle and hence more susceptible to fracture.

Investigation of rutting, fracture and thermal cracking behavior of asphalt mastic containing basalt and hydrated lime fillers

The present study was undertaken to evaluate rutting, fracture and thermal cracking resistance behavior of asphalt mastic containing inert and active fillers. A control neat binder (AC-30) along with basalt (B) as an inert filler and hydrated lime (HL) as active filler were selected in this study. The asphalt mastics were prepared for different percentages of HL (5, 10, 15 and 20%) filler, in such a way that Filler to Binder (F/B) ratio becomes 0.8. A total of five combinations of asphalt mastic were prepared such as: AC-30+80% B+0% HL, AC-30+75% B+5%HL, AC-30+70% B+10%HL, AC-30+65% B+15%HL, and AC-30+60% B+20%HL. The rutting, fracture and thermal cracking resistance of asphalt mastics was evaluated using Superpave rutting factor parameter, Double Edge Notched Tension (DENT) and Bending Beam Rheometer (BBR), respectively. Influence of HL on the performance of neat asphalt mastic was observed to be predominant in high-temperature range as obtained from the G∗/Sinδ value. The aging resistivity of asphalt mastic increased with the inclusion of HL, indicating a better rutting performance of asphalt mastic. The intermediate-temperature performance of asphalt mastic with HL was found to be higher compared to neat asphalt mastic from Critical Tip Opening Displacement (CTOD) results, implying better resistance to fracture. The addition of HL increased the low-temperature performance of asphalt mastic obtained from S(t) and m(t) values with S(t) and E(t) master curve, indicating enhanced resistance to thermal cracking. The combined effect of B and HL filler on the G∗/Sinδ, CTOD, S(t), m(t) and E(t) parameters are presented in this study. In addition, ranking of asphalt mastics based on various parameters (i.e. CTOD and m(t)) is discussed in this paper.

Sheets of branched poly(lactic acid) obtained by one-step reactive extrusion–calendering process: physical aging and fracture behavior

The architectural modifications of a linear poly(D,L-Lactide) acid (PD,L-LA) commercial grade were induced by a one-step reactive extrusion–calendering process using a styrene-glycidyl acrylate copolymer as reactive agent. The melt degradation was counteracted by chain extension and branching reactions, leading to a stabilization of the melt properties and an increase in the molecular weight. For such modified samples [poly(lactic acid) (PLA)-reactive extrusion (REX)], the rate of physical aging at 30 °C was investigated during 1 week in order to simulate industrial storage conditions. Fracture behavior of “de-aged” and “controlled aged” (1 week) samples was investigated using the essential work of fracture (EWF) methodology and the critical tip opening displacement at the crack propagation onset, respectively. These analyses were complemented by digital image correlation analysis and inspection of the fractured surfaces by scanning electronic microscopy. As a result of the architectural modifications, the entanglement network density was increased. Those accounted for a slight decrease in the physical aging rate. Under uniaxial loading, aged reactive extrusion (REX) samples exhibited multiple crazing, leading to a slight increase in strain at break. Nevertheless, as a result of a similar dynamic environment of the entangled polymer coils, de-aged REX samples disclosed similar mechanical properties as compared to their neat counterparts. Regarding de-aged samples, the EWF analysis revealed no changes in the work required for the onset of crack propagation. However, the energy consumed up to the onset of crack propagation of aged PLA-REX samples decreased due to an apparently decreased network extensibility, promoting a premature craze–crack transition.