Indirect Tension Research Articles

Correlating damage and cracking with air (gas) permeability in concrete using the Brazilian tension test

• Using acoustic emission and digital image correlation in the indirect Brazilian tension test, damage and cracking can be correlated to gas permeability in concrete. • A microcrack size of 40 µm can distinguish between pre-cracking and post-peak behavior of concrete. • Gas permeability of concrete increases to almost half an order of magnitude in the pre-peak region. • Gas permeability of concrete increases to about six orders of magnitude during the progression of cracking in the post-peak region. This article investigates the relationship between stress, damage, crack propagation, and air (gas) permeability evolution in concrete using the Brazilian tension test. This investigation is important for situations where hazardous gases are in contact with concrete as it quantifies the effect that damage of concrete has on gas permeability. Cylindrical concrete disc specimen of diameter 101.6 mm and thickness 50.8 mm were used for this study. Acoustic emission sensors are used to observe damage occurrence and propagation in the concrete, while a digital image correlation set-up is used to precisely measure the crack opening displacement. A vacuum flow system is attached to the rear side of the concrete under loading to measure apparent air permeability through the concrete specimen before and after cracking. The collected data is synchronized and analyzed to correlate damage and crack propagation and air permeability evolution in concrete under tension stresses. It was found that the air (gas) permeability increased by over six orders of magnitude as the concrete cracking occurs and changes in air (gas) permeability directly correlate with changes in concrete damage and fracture.

Laboratory performance of dense graded asphalt mixtures prepared using highly polymer modified binders containing corn oil as softening agent

• High Polymer Modified Asphalt (HPMA) with corn oil can resist short term aging. • Crack Propagation slows with HPMA and corn oil combination compared to Control. • Life Cycle Analysis shows the cost-effectiveness of the optimized combination of HPMA and Corn Oil. This study evaluated the impact of aging on High Polymer Modified Asphalt (HPMA) mixtures containing a softening agent (SA). The aging susceptibility was evaluated in terms of rutting, cracking, and durability. Four asphalt mixtures were prepared, one with PG 52–34 binder as control, and three others using modified PG 52–34 with varying dosages of Styrene Butadiene Styrene (SBS) and corn oil (SA). The tests performed to evaluate the impact of aging (short, long, extended long term) were the Dynamic Complex Modulus, Hamburg Wheel Tracking, Flow Number, Indirect Tension and semi-Circular Bend tests. Based on these testing results, SBS and SA increased the durability and rutting resistance of asphalt mixtures. Modified asphalt mixtures also showed better cracking resistance than the control mix (i.e. lowering of crack propagation). However, with aging, fatigue cracking performance diminished while remaining comparable to the control mix. A balanced dosage of SBS (7.5%) and SA (7%) led to the best improvement in durability, rutting, and short-term cracking performance.

Durability improvement of poroelastic road surface with treated rubber: Molecular dynamics simulation and experimental observations

Poroelastic road surface (PERS) is usually composed of rubber particles, aggregates, and polyurethane. However, the poor bonding strength between rubber granules and polyurethane affects PERS’ durability. This study aimed to improve the durability of PERS with treated rubber using molecular simulation and experimental tests. The cohesive energy density (CED), interaction energy (IE) and shear bonding capacities between two kinds of rubber granules and one-component polyurethane were simulated using molecular dynamics (MD). The hydrophilicity test and Fourier transform infrared (FTIR) spectroscopy test were utilized to demonstrate the formation of oxygen-containing groups on rubber surfaces. The indirect tension (IDT) test and Cantabro test were employed to evaluate the durability of PERS mixtures with treated rubber. The MD simulation results showed that the oxygen-containing groups, including the hydroxyl group (-OH) and the carbonyl group (CO), could improve surface polarity of natural rubber (NR) and styrene-butadiene rubber (SBR) and thereby enhance rubber-polyurethane bonding performance. In particular, hydroxyl groups improved the bonding energy of NR-polyurethane by 59% while the carbonyl groups enhanced the bonding performance of SBR-polyurethane by 20%. The hydrophilicity of the treated rubber granules was effectively improved since new carbonyl groups were introduced on rubber surface. The treatment of rubber with NaOH solution improved the durability of PERS specimens by 8.4% in terms of tensile strength ratio (TSR) and 64.7% in terms of Cantabro abrasion loss. These findings prove the feasibility of designing durable PERS with good functional performance.

Tensile Properties and Tensile Failure Criteria of Layered Rocks

Rocks are less resistant to tension than to compression or shear. Tension cracks commonly initiate compression or shear failure. The mechanical behavior of layered rocks under compression has been studied extensively, whereas the tensile behavior still remains uncertain. In this paper, we study the effect of layer orientation on the strength and failure patterns of layered rocks under direct and indirect tension through experimental and numerical testing (RFPA2D: numerical software of Rock Failure Process Analysis). The results suggest that the dip angle of the bedding planes significantly affects the tensile strength, failure patterns, and progressive deformation of layered rocks. The failure modes of the layered specimens indicate that the tensile strength obtained by the Brazilian disc test is not as accurate as that obtained by the direct tension test. Therefore, the modified Single Plane of Weakness (MSPW) failure criterion is proposed to predict the tensile strength of the layered rocks based on the failure modes of direct tension. The analytical predictions of the MSPW failure criterion agrees closely with the experimental and numerical results. In rock engineering, the MSPW failure criterion can conveniently predict the tensile strength and reflect the failure modes of layered rocks (such as shale, slate, and layered sandstone) with satisfactory accuracy.

An experimental study on the strain-rate-dependent compressive and tensile response of an alumina ceramic

This research article studied the strain-rate-dependent mechanical response of a CeramTec Alotec 98% alumina ceramic under uniaxial compression and indirect tension loadings. Mechanical testing was carried out using a load frame for quasi-static strain rates and a split-Hopkinson Pressure Bar (SHPB) for dynamic strain rates combined with the digital image correlation (DIC) technique and ultra-high-speed photography to investigate strain-rate-dependent failure behavior. Furthermore, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and X-ray microscopy was applied to determine the microstructural and failure features before and after experiments (e.g., elemental composition, grain size, voids, and impurities). Experimental results showed that the strength in compression was >10 × higher than those in tension. In addition, a strain-rate-sensitivity of strength on compression (linear fit slope of 0.68) was greater than in tension (0.39), and this was believed to be associated with crack growth and interaction, manifested as differences in measured crack speeds between the compression (2.5 ± 1.3 km/s) and tension (5.9 ± 2.1 km/s) cases. Post-mortem analysis of fracture surfaces revealed that intergranular fracture was more likely to appear in quasi-static loading and transgranular fracture in dynamic loading in alumina, with compression generating more micro-cracks as expected. Overall, this paper provides new comparative strain-rate-dependent strength and crack speed measurements of compression and tension, which serve as important inputs for future computational/numerical model development and validation.

Evaluation of fatigue characteristics of asphalt mixtures using Cracking Tolerance index (CTIndex)

Evaluation of the cracking potential of asphalt mix during the design phase can considerably limit the fatigue cracking and increase the service life of the flexible pavement. Thus, attention needs to be paid to employing a simple yet reliable performance test indicator. Indirect Tension Asphalt Cracking Test (IDEAL-CT) is one such emerging test method and is widely used in research across the world. The present study examines the potential of using the cracking tolerance index (CTIndex) as an appropriate parameter to explain the fatigue resistance of mixtures with both unmodified and modified binders. This test can be conducted using a Marshall testing machine or multispeed tester, routinely used for asphalt mixture design in India and many other countries. To evaluate the effectiveness of this parameter, fatigue resistance indicators for different binders, i.e., recovery at 3.2 kPa stress level (R3.2) from multiple stress creep and recovery (MSCR) test, fatigue life (TNf3.5) from the time sweep (TS) test at 3.5% strain, fatigue life at 2.5% (LNf2.5), and 5% (LNf5) strain from linear amplitude sweep (LAS) test, as well as for different mixtures, i.e., fatigue life from Indirect tensile fatigue test (ITFT) at 150 microstrain were considered. Two unmodified (viscosity grade 30, viscosity grade 40) and three modified (polymer, crumb rubber, sasobit) binders were evaluated for their fatigue parameters which were further correlated with CTIndex. The CTIndex exhibited good to excellent correlations (R2 ∼ 0.85 to 0.92) with the fatigue lives of the binders and the mixtures. To examine the effect of rheology and chemistry of the binder on the CTIndex, correlations of complex shear viscosity using Dynamic Shear Rheometer (DSR) at 60 °C and asphaltenes content from Thin-layer chromatography with flame ionization detector (TLC-FID) with CTIndex were explored. Viscosity, asphaltenes content, and elastic recovery of the binders depicted good correlations (R2 ∼ 0.88) with CTIndex, indicating higher cracking tolerance of stiffer yet elastic binders. Further, the sensitivity of CTIndex to binder type, binder content, aggregate gradation, and test temperature was examined. Overall, the values of the CTIndex displayed less variability (coefficient of variation < 10%) in this study.The observed sensitivity of CTIndex to asphalt mix parameters and the correlations of the CTIndex with fatigue resistance indicating parameters suggested that the CTIndex is an effective parameter for evaluating the fatigue characteristics of asphalt mixes.

Practical Considerations For The Application Of A Survival Probability Model For Rockfall

Rockfall fragmentation is a common and very complex phenomenon that is still inadequately understood and rarely modelled. When falling rock blocks break upon impact, their shape and size change and the kinetic energy is distributed amongst fragments. To efficiently design mitigation measures, it is necessary to adequately account for fragmentation when modelling rockfall trajectories. To do so, a better understanding of the fragmentation process, its occurrence and its likely outcomes is needed. The authors have recently proposed a novel model which can predict the survival probability (SP) of brittle spheres upon impact from the statistical distribution of material parameters, obtained by standard quasi- static tests (Brazilian tests and unconfined compression tests). The model predicts two Weibull parameters (shape parameter -m- and scale parameter – critical kinetic energy) that are used to define the SP. The model is based on theoretically-derived (from Hertzian contact theory) conversion factors used to transform the critical work required to fail disc samples in quasi-static indirect tension into the critical kinetic energy to cause failure of spheres at impact in vertical drop tests. The objective of this paper is to provide some practical insights into this model in relation of the analysis of the Brazilian test results and the number of Brazilian tests required to achieve an acceptable prediction. A first analysis highlights the importance of distribution of forces required to break the specimens in Brazilian tests and a common statistical based outlier removal methodology was applied to reduce the experimental error associated with the operator. After eliminating the outlier data, the quality of prediction is improved and, in particular, the influence of the specimen diameter used in Brazilian compressions to derive the model input parameter is significantly reduced. This latter point implies that the size effect is adequately captured. The second analysis reveals the highest variability for batches with low number of tests and a progressive reduction as the number of sampled test increases. Based on these results, it is suggested to use at least 30 Brazilian tests and remove outliers using the simple statistical approach presented in the paper.

Preparation and Characterization of High Modulus Agent Modified Asphalt and Its High Modulus Mixture

Improving the high-temperature stability and water damage resistance of asphalt pavements has always been a priority. This study proposed a composite high modulus modifier with rock asphalt and nanopolymer as main materials (HRMA) to prepare the high modulus asphalt mixture for their excellent rutting resistance. Moreover, its modification effect and modification mechanism were studied. The effect of HRMA content on the rheological performance of asphalt was investigated using Brookfield rotational viscosity, dynamic shear rheometers (DSR), and bending beam rheometers (BBR). Their modification mechanisms were revealed by Fourier Transformation Infrared Spectroscopy (FTIR). Besides, the properties of the mixtures were studied in various laboratory tests and compared with the 90# asphalt mixture and SBS asphalt mixture. Some of these included the rutting test, the bending test, the Marshall immersion test, and the freeze-thaw indirect tension test. The results indicated that with the increase of HRMA content, the deformation resistance of the asphalt mixture under high-temperature conditions was significantly improved, and the temperature sensitivity was changed. However, the crack resistance of its asphalt mixtures under low temperature was reduced due to the lower ductility of HRMA-modified asphalt. The recommended HRMA content was 21.8% of the asphalt, combining performance and construction cost.

Investigation of dolomite’ rock brittle fracture using fully calibrated Karagozian Case Concrete model

This paper presents a procedure to compute the parameters of the Karagozian and Case Concrete (KCC) constitutive model for brittle materials based on dolomite rock. First, the fracture energy and fracture toughness of the dolomite rock were determined from two experimental tests: the semicircular bending test (SCBT) and Brazilian indirect tension test (BT). Next, the novel optimization-based strategy was developed for efficiently calibrating the brittle damage parameters, and a broad parametric study was performed based on dolomite rock. Finally, the optimal parameters were validated through three experimental tests: SCBT, BT and a drop-weight fragmentation test. The results were compared with those obtained using three different sets of parameters for dolomite rock that is the KCC model with automatically generated parameters, parameters that provides an instable softening behavior, and the KCC model with parameters calibrated by the authors in a previous study. A qualitative and quantitative comparison of the results confirmed that the approach presented here improves the efficiency of fracture reproduction.

Unified characterizing fatigue performance of high modulus asphalt concretes under diverse stress state

As a new material, high modulus asphalt concrete (HMAC) with good durability is widely used in the pavement engineering. One of the most critical performance indexes of HMAC is the fatigue cracking. However, in the experiment of evaluating the fatigue properties, different anti-fatigue effects are obtained only by adding different modifiers. In addition, using only one loading mode to determine the fatigue properties of HMAC neglects the fact that there is a difference among the fatigue test results in various loading modes, which artificially leads to the non-uniqueness and unscientific design of high modulus asphalt pavements for the fatigue resistance. Therefore, four internationally accepted mainstream strength tests at different loading rates, including direct tension, indirect tension, unconfined compression and four-point bending tests, were carried out to enhance the veracity of structural resistance design of high modulus asphalt pavements. It is revealed that the fitted curve for the variation of strength with loading rate is a power function with velocity dependence, and the models for direct tension, indirect tension, unconfined compression, and four-point bending strengths established as a function of loading rate are SD = 3.218v0.1425, ST = 3.833v0.1768, SC = 14.391v0.1130 and SF = 7.839v0.1489 respectively. Besides, it is shown that the conventional S-N fatigue equation does not take into account the velocity dependence of the strength of HMAC in the stress ratios determined by the tests, and the velocity-dependent stress ratios defined in this paper are determined by the strength model and therefore take into account the viscoelasticity of HMAC. In addition, it is found that extending the fatigue curve backwards, when the fatigue life of HMAC is also close to 1, the velocity-dependent stress ratio is 1. Meanwhile, the fatigue model Nf = tv-5.318 was developed by unifying the characterization of HMAC and considering the effect of loading rate in various loading modes. It eliminated the difference of fatigue test results caused by the specimen sizes and loading modes, and effectively improved the completeness of structural design of high modulus asphalt pavements, which provided a theoretical basis for designing the high modulus asphalt pavements.

Improving the mechanical performance of poroelastic road surface with low polyurethane content through surface activation

The poroelastic road surface (PERS) mixture with low polyurethane content (PERS-LPC) can reduce the construction cost of PERS pavement, which exhibits promising noise reduction capacity, whereas its mechanical performance needs to be further enhanced for real practice. This study aims to investigate the effectiveness of surface activations of crumb rubber and aggregate to improve the mechanical performance of PERS-LPC. Molecular dynamics (MD) simulations and indoor experiments have been conducted, including the indirect tension (IDT) test implemented on the dry-cured and freeze–thaw PERS-LPC specimens and Cantabro test performed on water-bathed specimens. The results showed that, the oxygen-containing groups, introduced by UV irradiation and KMnO4 soaking, enhanced surface polarity of crumb rubber and rubber-polyurethane bonding strength. The surface activity of basalt aggregate was increased by the inclusion of Portland cement but not by hydrated lime. The IDT strength of the dry-cured PERS-LPC mixture was improved by 10.3–17.5% with activated rubbers and by 35.6% with activated aggregates. The tension strength ratio (TSR) of the freeze–thaw mixture was increased only by 2% with activated rubber but up to 20.8% by the inclusion of 0.5 wt% cement. The Cantabro abrasion loss (CAL) of PERS-LPC specimens was reduced significantly from 20.1% to 11.6% with the soaked rubber and dropped dramatically to 7.9% after inclusion of 0.5 wt% cement. It was recommended to activate crumb rubber with UV irradiation for 24 h and mineral aggregate with 0.5 wt% cement in PERS-LPC mixture in terms of performance enhancement and operation convenience. The findings of this research were expected to support the mix design of an inexpensive and durable PERS-LPC mixture for noise reduction.

High-Performance Fiber Reinforced Concretes in Virginia

High-performance fiber reinforced concretes (HPFRCs) provide high workability, high compressive and tensile strengths, high ductility, and high durability. They exhibit strain and deflection hardening. The Virginia Department of Transportation (VDOT), U.S., has been experimenting with various types of HPFRC, including high early strength versions, to control cracking in transverse and longitudinal connections, shear keys, blockouts that connect adjacent members, overlays, and inverts of corrugated metal pipe culverts. This paper presents laboratory and field work using three classes of HPFRC for different VDOT applications. They have high ductility and very low permeability. In addition, Class I has normal compressive strength, Class II has high compressive strength, and Class III has high early compressive strength. Laboratory work consisted of preparing and testing of in-house or prepackaged HPFRC with varying ingredients and proportions using compression, indirect tension, flexure, and pull-out tests. Synthetic and steel fibers were added in different amounts. Mixtures were prepared in the mortar or pan mixers that produce good fiber dispersion. Laboratory and field testing indicated that all three classes of HPFRC had high ductility; strengths varied according to the class. Engineered cementitious composite in Class I had normal strength, ultra-high-performance concrete in Class II had the highest strength, and concretes in Class III had high early strength, enabling minimal traffic interruption. HPFRC selected from an appropriate class can be used successfully to enable early opening to traffic, provide a short splice length, achieve satisfactory adjacent member connections, and restrict crack width for a longer service life.

Influence of bitumen emulsion on the curing behaviour of standardised cold bitumen emulsion mortars

This research was part of the RILEM TC 280-CBE interlaboratory testing aiming to characterise the role of mortars as mesoscale model systems and establish a link between the properties of bitumen emulsions and the performance of cold bitumen emulsion-based mixtures for structural layers. The objective of this specific work was to investigate the curing behaviour of such mortars with the reference volumetric composition prepared with different types of emulsions and sands. This approach enabled the preparation of specimens that could be successfully demoulded immediately after compaction and tested by indirect tension. The curing was characterised by comparing the evolution of water content and indirect tensile strength. The results showed that the estimated long-term indirect tensile strength at 5 °C of the mortars was in the range from 1.14 to 1.52 MPa. They also highlighted the importance of intrinsic properties of cationic emulsions and of their compatibility with sand particles.

The Influence of Loading Rate on Direct and Indirect Tensile Strengths: Laboratory and Numerical Methods

To investigate different responses of direct and indirect tensile strengths to loading rate, direct and indirect tension tests were performed on sandstone, rust stone, and granite specimens. Typical load curves indicate that a peak tensile stress frequently appears before the second peak stress, used to calculate the tensile strength in indirect tension tests. As expected, increase in the loading rate increases the tensile strength. In addition, the calculated tensile strengths of the indirect tension tests are frequently higher. Interestingly, the increase ratio of the tensile strength with the increase in the loading rate in indirect tension tests is higher. To verify the above results, crack propagation and stress evolution in direct and indirect tension tests were dynamically monitored using PFC 3D. For direct tension tests, specimens fail at the peak tension point, corresponding to the tensile strength. However, for indirect tension tests, minor cracks, composing of continuous microcracks, form before the peak stress and accompany with the decreased slope of the compression curve. At the peak point, tensile stresses significantly concentrate at the crack tips and further cause large-scale crack propagation. In addition, the initiation stress instead of the peak tensile stress is closer to the tensile strength, obtained from the direct tests for the same loading rate.

Influence of Aramid-Polyolefin Fibers on the Properties of Bituminous Mixtures

The use of additives in bituminous mixtures such as fibers has been the subject of various studies. Different fibres including cellulose fibres, steel fibres, basalt fibres, glass fibres and aramid fibres can be used to improve the properties of bituminous mixtures. Depending on the type of fibres used, different characteristics can be changed. The paper contains results of comparative tests of bituminous mixtures with aramid-polyolefin fibres. Asphalt concrete used for wearing course with maximum aggregate size of 11 mm was evaluated in the study. Reference mix with an average penetration grade of 50/70 was chosen as a base for modifications. Due to difficulty in preparing mixtures with fibers in a laboratory mixer, test specimens were obtained from a stationary plant. The fibers and aggregate mix was prepared before adding the asphalt. The fibers were added at a rate of 0.5 kg per 1000 kg of finished bituminous mixture. This allowed to obtain an even distribution of fibers in the mixture resulting in a homogeneity necessary for planned tests. This allowed to omit the scale effect, that could occur due to differences between laboratory and stationary mixing. Stiffness modulus tests were performed using the IT-CY (Indirect Tension to Cylindrical Specimens) method for a wide temperature range of 0-30°C. The specimen resistance to permanent deformation was evaluated. Obtained results has shown a clear increase in the resistance to permanent deformation of mixtures with aramid- polyolefin fibers, which is especially important for mixtures used for wearing course. The results has also shown a significant increase in the stiffness modulus regardless of temperature range. Results of conducted experiments has shown that it is possible to reduce the thickness of bituminous overlay in case of reinforcement of the existing pavement structure. The analysis of results has shown that the application of aramid-polyolefin fibres in bituminous mixtures can improve the functional features of the pavement and be beneficial to the investors.

Evaluation and Development of Performance-Engineered Specifications for Monotonic Loading Cracking Performance Assessment Tests and Indicators

Abstract This study investigated the validity of various monotonic cracking performance assessment testing standards and indicators to describe the expected cracking performance in the field. A total number of 17 field test sections with known field cracking performance were selected and evaluated. Field cores were extracted from these sections, and a comprehensive laboratory testing program was carried out. The authors conducted four monotonic testing standards and calculated 11 performance indicators. The study findings showed that there was no direct correlation between the laboratory testing results of monotonic tests and indicators and the observed field cracking performance. The variable air void content and thickness of the extracted field cores are believed to influence the laboratory testing results of monotonic tests and indicators. Therefore, this study proposed an alternative approach to develop performance specifications (thresholds) for monotonic tests and indicators. The thresholds were developed indirectly using a correlation between cyclic testing and both monotonic tests and the observed field cracking performance. The results demonstrated the effectiveness and success of the proposed approach in developing performance thresholds. Pass/fail cracking performance assessment thresholds were proposed for various monotonic indicators to distinguish between asphalt mixes with good, fair, and poor cracking resistance. Besides, the study recommends the Weibull cracking resistance index, determined from the indirect tension test, as a simple performance indicator to assess mixes resistance to cracking.

Influence of microstructure on the failure of ultra-high molecular weight polyethylene composite beams impacted by blunt projectiles

Increasing the fibre tensile strength is well-known to improve the ballistic performance of ultra-high molecular weight polyethylene (UHMWPE) fibre composite beams. Here we investigate modifying ply microstructure as an alternate way to enhance ballistic performance. Specifically, we numerically investigate the mechanisms via which failure is initiated in [0o/90o]nlaminates comprising UHMWPE tape plies and compare with the commonly used UHMWPE fibre composites. Each ply of the beam is discretely modelled using a pressure-dependent crystal plasticity framework with the deformation mechanisms of the tape and fibre-based microstructures modelled by recognising differences in the available slip system in these two material systems. The numerical calculations are used to construct failure mechanism maps for a range of impact velocities, ply shear strengths and ply tensile strengths. Three dominant failure mechanisms emerged from the study: (i) failure of plies immediately under the projectile via an indirect tension mechanism in which compressive stress imposed normal to the plies by the projectile induces tensile in-plane ply stress due to the anisotropic expansion of the alternating 0o/90o plies; (ii) failure due to tensile straining at the rear of the impacted beam resulting from a combination of beam bending and stretching and (iii) a shear plugging like failure mode due to tensile straining at the edge of the impact site. Tensile stress generation by indirect tension is significantly reduced in the tape-based microstructures due to the unavailability of the slip systems that result in lateral plastic expansion. In fact, our calculations suggest that over the entire range of parameters modelled here the tape-based microstructures outperform the fibre-based microstructures. This suggests an alternate route to enhancing the ballistic performance compared to the traditional methods that rely mainly on increasing fibre strength.

Mechanical analysis of a vegetable fiber versus a polymeric fiber added in cement mixtures

Some mechanical characteristics of concrete and mortar reinforced with banana fibers (Musa Paradisiaca) were studied, compared with specimens added with polypropylene fibers, which were dosed at 0.5% and 1.5% in relation to the weight of the cement and in lengths of 2 cm and 4 cm. For the characterization of the fibers, water absorption tests were carried out, as well as micrographs in the scanning electron microscope, the fine and coarse aggregates were characterized by a granulometric analysis and density and absorption tests. To evaluate the performance of the concrete, compression tests, indirect stress and average residual stress were carried out, while for mortar only compression and bending tests were carried out. The results show that the banana fiber in low percentages and long lengths increases the resistance to the indirect tension of the concrete and to the bending in the mortar, surpassing in some cases the batches with polypropylene fibers.

Evaluation of Fatigue Potential for Crumb Rubber Modified Bitumen in Stone Mastic Asphalt Mixes

SMA is a gap graded mix composed of a high concentration of coarse aggregate that is held together in a thick asphalt film by a matrix of mineral filler and stabilizers. Since natural aggregates have become expensive, hence Reclaimed Asphalt Pavement (RAP) can be reused in pavement construction to reduce the environmental hazardous due to disposal problems. Since the RAP contains used aggregates, it is highly prone to fatigue, thermal and reflective cracking effect. Rheological and chemical properties of aged bitumen in RAP can be enhanced by use of untreated waste oils such as waste engine oil as rejuvenators. This research presents a study on fatigue performance of SMA mix with Reclaimed Asphalt Pavement (RAP) materials with and without rejuvenators and results were compared with conventional SMA mix. The materials used were first characterized by common laboratory tests. Then the three SMA mixes are tested using several laboratory test procedures: Marshall Stability, indirect tensile strength, moisture susceptibility, and indirect tension fatigue test. The optimum proportions of the of the mixes with highest stability are selected from the Marshall stability test. The indirect tensile strength test results show that the SMA mix replaced with RAP without rejuvenators showed higher tensile strength ratio and resistance to moisture damage when compared to conventional mix and optimum RAP replacement mix with rejuvenators. The fatigue test was conducted for the three optimum mixes at different temperature and stresses. The fatigue test results showed that at lower temperature and stresses, the RAP replaced SMA without rejuvenator offered better fatigue resistance than those with rejuvenator and conventional SMA mix. At higher temperatures, the RAP replaced SMA mix with rejuvenator offered similar fatigue lifecycle as conventional mix. However, at high stresses, conventional SMA mix offered better fatigue lifecycle. Increase in failure stresses resulted in decrease of number of fatigue cycles and increased in initial tensile strain of the mix. Thus, with the use of RAP substantial decrease in cost can be achieved without compromising the fatigue characteristic of the SMA mix.

The effect of impact angle and bond strength on fragmentation in laminated materials

An experimental study was undertaken to explore the effects of weak laminations on the fragmentation of impacting rocks. In this work, the fragmentation behavior of manufactured disc specimens of laminated travertine marble is described according to variations in the lamination bond strength, the orientation of laminations at impact, and the impact energy. An experimental apparatus and procedure were developed so that the discs, 96mm in diameter and 25mm thick, could be impacted neatly on their circumferential edge, at a selected lamination impact angle, and subject to filming with a high speed camera. The results of the study generally indicated that weaker bonds cause fragmentation from lower drop heights, as expected. However, the results also indicate that the critical height for breakage is relatively lower and insensitive to the impact angle when the laminations are between 45 and 90 degrees relative to the impacting surface, but the critical height for breakage increases significantly (by a factor of between 2 and 4) as the orientation of the laminations becomes parallel to the impact surface. The presence of laminations and their orientation to the impact surface, directly influenced the failure mechanism of specimens upon impact. At low lamination impact angles, failure was by parting along laminations in direct tension (reflected compression). At intermediate impact angles (approximately 45 degrees), the fragmentation of the specimens was more explosive and fractures were a combination of steps across stronger sheets, and splits along weaker bonded laminations. For high impact angles, fragmentation occurred in indirect tension, along weak laminations.