Indirect Tensile Strength Values Research Articles

Laboratory Evaluation of Foamed Warm Mix Asphalt

A laboratory study was designed and executed to evaluate the performance of Warm Mix Asphalt prepared using foamed asphalt binders (WMA-FA) and compare it to traditional Hot Mix Asphalt (HMA). Two aggregates (crushed limestone and natural gravel) and two asphalt binders (neat PG 64-22 and polymer modified PG 70-22M) were used in this study. The Indirect Tensile Strength (ITS), Dynamic Modulus (E*), Modified Lottman (AASHTO T 283), and Asphalt Pavement Analyzer (APA) tests were utilized to evaluate the laboratory performance of the considered mixtures. The test results showed lower ITS values for the WMA-FA mixtures than for the HMA mixtures. No significant difference in dynamic modulus was found between the WMA-FA and HMA mixtures. The WMA-FA mixtures were slightly more susceptible to moisture-induced damage than the HMA mixtures. However, both mixtures met the Ohio Department of Transportation (ODOT) minimum Tensile Strength Ratio (TSR) requirement of 0.7 for medium traffic. The WMA-FA mixtures were more prone to rutting than the HMA mixtures. However, the results suggested that using an appropriate type of aggregate and asphalt binder can address any adverse effects from using the foaming technology.

Moisture and Rutting Resistances of Foamed Asphalt Mixtures Containing Recycled Coal Ash or Shingles With Moist Aggregates

Abstract The objective of this study was to evaluate the laboratory moisture and rutting susceptibility of foamed warm mix asphalt (WMA) mixtures containing moist aggregates and recycled materials such as manufactured roofing shingles and coal ash material. The test properties of these mixtures included the indirect tensile strength (ITS), tensile strength ratio, flow value, and rut depth of dry and wet specimens. The experimental design included two percentages of coal ash (10 % and 5 % by weight of the aggregate), two shingle contents (5 % and 3 % by weight of the aggregate), foaming WMA and control mixtures, and two aggregate sources (containing approximately 0.5 % moisture). A total of 24 mix designs were used in this study. The test results indicate that the aggregate source significantly affected the moisture and rutting resistance, regardless of the foaming technology and/or recycled material type. In addition, the dry and wet rut depth values of mixtures containing moist aggregate generally satisfied the demand of pavement performance without requiring additional treatment. Moreover, all mixtures have high dry and wet ITS values as using recycled shingle and coal ash materials along with hydrated lime or liquid anti-stripping additive. Furthermore, the utilization of recycled coal ash and roofing shingles significantly improved the moisture and rutting resistance of WMA mixtures.

Investigation of Moisture Susceptibility of Warm-Mix Asphalt Mixes through Laboratory Mechanical Testing

Moisture can lead to serious damage and failures in hot-mix asphalt concrete pavements. This is an even greater concern for warm-mix asphalt because the much lower production temperatures may not completely dry the aggregates. In this Maine Department of Transportation study, the use of fracture energy parameters was evaluated to determine the influence of incomplete drying of mixes on their mechanical properties. Fracture energy–based parameters [energy ratio (ER); ratio of energy ratio (RER)] were determined from the following testing of mixes with fully and partially dried aggregates, some of which were subjected to moisture conditioning: resilient modulus, creep compliance, and indirect tensile strength (ITS) at 5°C. The results indicate that (a) resilient modulus, creep compliance, and ITS were all affected by the presence of moisture in mixes; (b) the trend and the degree of influence of moisture for different mechanical parameters were different; (c) the moisture conditioning process caused larger decreases in modulus and ITS values than did incomplete drying of aggregates; however, the same moisture conditioning process caused much larger decreases in modulus and ITS in mixes prepared with incompletely dried aggregates than did the counterparts prepared with fully dried aggregates; and (d) fracture energy–based parameters (ER and RER) appeared to be more-distinctive moisture effect and damage indicators than are the other parameters.

Moisture Susceptibility of Polymerized Stone Matrix Asphalt Mixtures using Warm Mix Asphalt Technologies using Moist Aggregates

Abstract The present study is focused on evaluating the moisture susceptibility of polymerized stone matrix asphalt (SMA) mixtures using moist aggregates and three different warm mix asphalt (WMA) additives. Indirect tensile strength (ITS), tensile strength ratio (TSR), deformation, and toughness were performed to determine the moisture sensitivity of these mixtures. The experimental design included two aggregate moisture contents (0% and ∼0.5% by weight of dry mass of the aggregate), three sources of aggregates (A, B, and C) and three WMA additives (Asphamin, Sasobit, and Evotherm) along with control mixture, and four different types of binders (i.e., PG 64-22 + 10% crumb rubber (−40 mesh CR), PG 64-22 + 15% CR, PG 64-22 + 20% CR, and PG 76-22 with fibers) were used in this study. In total, 384 samples were utilized for the ITS testing in this study. Test results indicated that even though by using 2% hydrated lime as an anti-stripping agent, 32% of the mixtures failed to meet the TSR requirement of 85% as per SCDOT specifications. Mixtures with PG 76-22 + fibers showed improved wet ITS values compared to rubberized SMA mixtures as using moist aggregates. No significant differences in the wet deformation values were observed for mixtures using WMA additives using moist aggregates. Mixtures with 15% CR content showed improved resistance to the percent toughness loss under a warm water bath treatment. Test results indicated that recycled rubberized asphalt binder can be effectively used to improve resistance to moisture-induced damage of SMA mixtures as using WMA technology.

Evaluating in-service asphalt concrete damage using surface waves

Two in-service asphalt concrete highway sections exhibiting surface distresses indicative of moisture damage were evaluated using multichannel analysis of surface waves. The computed viscoelastic moduli were shifted to a typical 25 Hz design value using a dynamic modulus-based master curve using drilled core specimens. Models of the built-up asphalt concrete layers were constructed using frequency-shifted shear wave velocity dispersion curves. Dynamic modulus and indirect tensile strength values from drilled core specimens did not correlate well with observed surface distresses or internal damage levels. However, the modelled frequency-shifted moduli derived from surface wave testing appeared to correlate well with variations in material layering, modulus and damage observed over the depth of the asphalt concrete. Evaluating the built-up asphalt concrete layer in pavement structures enables a more rigorous evaluation of the internal stresses and strains for failure and service life prediction than can be achieved using an average modulus approach.

Effects of recycling agents on aged asphalt binders and reclaimed asphalt concrete

This paper aims to study the effect of adding different ratios (from 10 to 40%) of three recycling agents (RAs), including RA-25, RA-75 and RA-250, to the reclaimed asphalt binder (RAB) with a viscosity of 42800 poises and also to the reclaimed asphalt concrete (RAC) according to the Marshall mix design method. The study includes a variety of tests designed to determine the difference between the three RAs in terms of penetration, viscosity, softening point, ductility, toughness of the asphalt binder, as well as indirect tensile strength, and stability value of Marshall specimens. The results show that adding the RA increased the cohesiveness of RAB and thus improved the applicability of RAB. Of the three RAs in this study, RA-25 offered the best performance when added to asphalt binder. This study proposes a recycling model to predict the changes in RAB viscosity when adding RAs. The results of this model show a close fit with experimental data from laboratory tests. This model allows highway engineers to estimate the amount of RA added to aged binder. Marshall tests show that the RA-75 specimen had higher indirect tensile strength and stability value than the RA-25 and RA-250 specimens. Based on overall performance and cost comparisons among the three RAs, this study regards RA-75 as the RA of choice.

Rheological properties and moisture susceptibility of WMA mixture containing moist agregate

The objective of this study was to investigate and evaluate the rheological and moisture susceptibility of the WMA mixtures containing moist aggregates. The experimental design included the utilizations of two aggregate sources, two moisture, two anti-stripping additives, and three WMA additives and control. Several properties of the binders and mixtures were obtained including: viscosity, dynamic shear rheometer, beam bending rheometer of WMA binders, indirect tensile strength (ITS), tensile strength ratio (TSR), and flow values. The experimental results indicate that the WMA additives can result in a slight decrease in viscosity and an increase in failure temperature. In addition, the moisture susceptibility results illustrated that the mixtures containing moist aggregates generally have similar ITS values to other mixtures regardless of HMA or WMA types. Moreover, there were no significant differences in the wet ITS values of WMA mixture amongst four types of mixtures under identical conditions (same moisture and lime contents) except for the mixtures containing liquid anti-stripping additive and Asphamin additive.

An Example of Realistic Modelling of Rock Dynamics Problems: FEM/DEM Simulation of Dynamic Brazilian Test on Barre Granite

The scope of this study is to numerically simulate the behaviour of Brazilian disc specimens as observed in laboratory during dynamic, high-strain rate, indirect tensile tests using an innovative combined finite-discrete element method (FEM/DEM) research code. Laboratory experiments using a split Hopkinson pressure bar (SHPB) apparatus were conducted by the authors and the measured indirect tensile strength values were used to verify the FEM/DEM models. In the models the applied boundary conditions, related to the loading rate of the specimen, were matched with the experimental observations. The results of the numerical simulations, including tensile strength and failure time, are in agreement with the laboratory findings. The main failure mechanisms, i.e. tensile splitting along loading axis and shear failure close to loading platens are captured by the numerical model. A linear relationship between tensile strength and loading rate is found for the range of dynamic strain rates tested and simulated. The simulation results are in good agreement with laboratory observations and demonstrate the potential for using FEM/DEM to realistically model dynamic response of rocks.

Effects of liquid antistrip additives on rheology and moisture susceptibility of water bearing warm mixtures

Warm mix asphalt (WMA) has been gaining increasing popularity in recent years around the world. Rising energy prices, global warming, and more stringent environmental regulations have resulted in an interest in WMA technologies as a mean to decrease the energy consumption and emissions. However, the water absorption and release process caused by water bearing WMA additive (Asphamin) makes the charge re-distribution complex and thus may result in the moisture induced damage of asphalt mixtures. Especially, the liquid antistrip additives (ASAs) blended with the binder and then mixed with aggregate and Asphamin make the issue more complicated. The objective of this study was to investigate and evaluate the rheological properties and moisture susceptibility of the binder and mixture containing ASAs and Asphamin additive. The experimental design for this study included rheological property tests of binders and moisture susceptibility of mixtures. The materials included one binder (PG 64-16), two liquid ASAs and hydrated lime, one water bearing additive, and three aggregate sources. The performed testing included viscosity, performance grade, creep and creep recovery, amplitude sweep, frequency sweep, boiling test, and indirect tensile strength (ITS). The results indicated that the addition of Asphamin can slightly increase the viscosity, failure temperature and G */sin δ values. The mixture containing Asphamin has a lower ITS value than others. Statistical analysis illustrates that there is not significant difference in ITS value between any mixtures containing Asphamin additive and control mixtures. However, significant differences can be found between mixtures containing Asphamin and without any Asphamin additive.

Forensic Investigations to Evaluate Sulfate-Induced Heave Attack on a Tunnel Shotcrete Liner

This paper presents the results of a comprehensive research study to determine the potential causes for an inordinate distress developed on a shotcrete liner material of a tunnel located near Dallas, TX. This tunnel was originally founded on a limestone material. Distress locations were identified where possible delamination of shotcrete layer and moisture leaks were either suspected or noticed. As a part of the research, rock cores and white powderlike substance behind the liner were collected around the distressed locations, and these cores and powder material were subjected to chemical, mineralogical, and engineering tests to understand the potential causes of this distress. Mineralogical tests, in particular, X-ray powder diffraction analysis on a powder material and gel-like substances collected on the liner, showed the presence of anhydrite, gypsum, and ettringite traces. High amounts of sulfate measurements in chemical and energy dispersive X-ray spectroscopy studies also showed that both gypsum and ettringite formations were possible in and around the limestone material. Upon hydration, mineral expansion of ettringite and anhydrite led to heaving and subsequent cracking of the adjacent shotcrete layer. Engineering characterization tests including unconfined compression strength (UCS), indirect tensile strength (ITS), and triaxial tests on rock cores embedded with a powder type sulfate material revealed that low strength cores were obtained near high distress zones and high strength cores were collected at low distress zones. The UCS values ranged from 6.2 (high distress) to 13.8 MPa (low distress) whereas the ITS values of the cores varied from 0.5 to 1.1 MPa for the same distress locations. This indicates the potential loss of strength of these rock materials from the presence of gypsum material in them. Possible methods to mitigate this heaving problem behind the liner are also discussed.

Laboratory investigation of moisture damage in rubberised asphalt mixtures containing reclaimed asphalt pavement

In many parts of the world, highway officials are utilising crumb rubber and reclaimed asphalt pavement (RAP) in order to save money, protect the environment, and improve the life of asphalt pavement. However, due to the use of these materials, the effects of moisture damage should be investigated for rubberised asphalt concrete (RAC) mixtures containing RAP. The objective of this research involved investigating the moisture susceptibility of RAC containing RAP. The testing conducted included the determination of binder viscosity, toughness and indirect tensile strength (ITS) analysis. Several mixtures containing different crumb rubber types, two different RAP sources and various percentages of rubber and RAP were evaluated. The results indicated that, in general, the additional of RAP was beneficial in improving the ITS values and reducing the moisture susceptibility of the mixture although the addition of crumb rubber had a slightly negative effect.

Laboratory investigation of utilizing high percentage of RAP in rubberized asphalt mixture

The utilization of crumb rubber and reclaimed asphalt pavement (RAP) has proven to be economical, environmentally sound and effective in increasing the performance properties of the asphalt mixtures. The objective of this research was to investigate the laboratory engineering behavior characteristics of the rubberized asphalt binders and mixtures made with PG 64-22 and a softer binder (PG 52-28) containing a high percentage of RAP (30%). Some of the testing used for this research included viscosity, dynamic shear rheometer (DSR), bending beam rheometer (BBR), indirect tensile strength (ITS), resilient modulus, and fatigue life evaluations. The experimental design included the use of two aggregate and RAP sources, two virgin binder grades (PG 64-22 and PG 52-28), two types of crumb rubber (ambient and cryogenic), and four rubber contents (0%, 5%, 10%, and 15%). The results indicated that: (1) the crumb rubber improved the aging resistance of the aged binder and prolonged the fatigue life of the mixtures containing 0% RAP, in addition, results indicated a decrease of ITS and resilient modulus values was found as the rubber content increased, regardless of rubber type; (2) the utilization of softer binder decreased the influence of aged binder and decreased the resilient modulus values of the mixtures. In most cases, regardless of rubber types, the rubberized mixtures containing 30% RAP made with PG 52-28 binder did not show a significant increase in fatigue life with those made with PG 64-22 binder.

Laboratory Investigation of Moisture Damage in Warm-Mix Asphalt Containing Moist Aggregate

In recent years, rising energy prices, global warming, and more stringent environmental regulations have generated interest in warm-mix asphalt (WMA) technologies as a means to decrease energy consumption and emissions associated with conventional hot-mix asphalt. In this study, a laboratory investigation was conducted of moisture damage in WMA mixtures containing moist aggregates. Indirect tensile strength (ITS), tensile strength ratio, deformation, and toughness tests were performed to determine the mixtures’ moisture susceptibilities. The experimental design included two percentages of moisture content (0% and ∼0.5% by weight of the dry mass of the aggregate), two WMA additives (Asphamin and Sasobit), and three aggregate sources. In this study 15 mix designs were performed, and 180 specimens were tested. Test results indicated that, as expected, dry ITS values were affected by aggregate moisture and hydrated lime contents, whereas a WMA additive did not significantly alter the dry ITS and toughness values. Statistical analysis showed no significant differences in the wet ITS values of WMA mixture of three types of mixtures (control, Asphamin, and Sasobit) under identical conditions (same moisture and lime contents). Statistical analysis also showed that wet ITS values, generally, were statistically different for mixtures made with various aggregate sources. The deformation resistance values of mixtures containing moisture were lower than those of mixtures made with dry aggregate. However, the results indicated that the addition of hydrated lime increased the deformation resistance of all mixtures.

Estimating Indirect Tensile Strength of Mixtures Containing Anti-Stripping Agents Using an Artificial Neural Network Approach

The objective of this study was to develop a series of artificial neural network (ANN) models to predict the indirect tensile strength (ITS) and tensile strength ratio (TSR) of various mixtures considering five input variables such as asphalt binder source, aggregate source, anti-striping agents (ASA), conditioning duration, and asphalt binder content. The results indicate that ANN-based models are effective in predicting the ITS and TSR values of mixtures regardless of the test conditions and can easily be implemented in a spreadsheet, thus making it easy to apply. In addition, the developed ANN models can be used to predict (or estimate) the ITS values of the mixtures used in other research projects. Furthermore, the results also show that the asphalt binder source, aggregate source, and asphalt binder content are the most important factors in the developed ANN models while the conditioning duration is relatively unimportant (i.e., it has less effect on the ITS values in comparison with other variables). In addition, the sensitivity analysis of input variables indicated that the changes of ITS values are significant as the changes of the most important independent variables.

Resilient Modulus Behavior of Rubberized Asphalt Concrete Mixtures Containing Reclaimed Asphalt Pavement

ABSTRACT The resilient modulus is the modulus to be used with the elastic theory during any analysis of a flexible pavement. It is well known that most paving materials (e.g., asphalt pavements) are not elastic but experience some permanent deformation after each load application. With respect to the complexity of the Rubberized Asphalt Concrete (RAC) containing Reclaimed Asphalt Pavement (RAP), the Indirect Tensile Strength (ITS) and resilient modulus evaluation of modified mixtures are important to understand. The aging of binder containing crumb rubber obviously alters the visco-elastic and plastic characteristics of the modified mixtures. The deformation of the mixture under repeated loading, nearly completely recoverable, should also be considered. The experimental design included the use of two aggregate sources, one rubber type (ambient), four rubber contents (0%, 5%, 10%, and 15%), one crumb rubber size (-40 mesh [-0.425 mm]), and four RAP contents (0%, 15%, 25%, and 30%). The findings indicated that an increase in the rubber content in the modified mixture leads to a decrease in ITS and resilient modulus values regardless of rubber content, and this increase also improves the aging resistance and increases the viscous characteristics of the modified binder. However, as RAP content increased, not only the viscosity and G*sinδ values of the modified binder increased, the ITS and resilient modulus values of the modified mixtures also increased.

Influences of crumb rubber size and type on reclaimed asphalt pavement (RAP) mixtures

Over the years, recycling has become one of the most attractive pavement rehabilitation alternatives, and different recycling methods are now available to address specific pavement distresses and structural needs. The objective of this study was to investigate and evaluate the engineering properties of crumb rubber size and type influences on reclaimed asphalt pavement (RAP) mixtures. The experimental design for this study included the use of three rubber sizes and two rubber types (ambient or cryogenic) in the mixture containing 25% RAP mixtures. In this study, the results of the experiments indicated that the addition of crumb rubber was helpful in increasing the voids in mineral aggregate (VMA) in Superpave mix design and improving rutting resistance of mixture regardless of rubber size and type. On the other hand, indirect tensile strength (ITS) values show no significant difference for mixtures made with three type rubber sizes. However, the increase of rubber size, regardless of rubber type, reduced the resilient modulus values but extended the fatigue life of the modified mixtures.

Laboratory Evaluation of SBS Modified Bituminous Paving Mix

This paper presents the laboratory investigations carried out to determine the various engineering properties such as physical properties of asphalt cement and (polymer modified asphalt binder) PMAB with (styrene-butadiene-styrene triblock copolymer) SBS, Marshall properties using modified Marshall method, static indirect tensile strength at different temperatures, tensile strength ratio, and resilient modulus ratio for asphalt concrete (AC) and polymer modified asphalt concrete mixes (PMAC) with SBS. The temperature susceptibility of PMAB-SBS is lower than asphalt cement. Marshall stability and flow values of PMAC mix are higher when compared to AC mix at optimum binder content. The static indirect tensile strength values for PMAC mixes were higher when compared to AC mixes at different temperatures. Moisture susceptibility of PMAC mixes is low when compared to AC mixes.

Resilient Modulus Behavior of Rubberized Asphalt Concrete Mixtures Containing Reclaimed Asphalt Pavement

ABSTRACT The resilient modulus is the modulus to be used with the elastic theory during any analysis of a flexible pavement. It is well known that most paving materials (e.g., asphalt pavements) are not elastic but experience some permanent deformation after each load application. With respect to the complexity of the Rubberized Asphalt Concrete (RAC) containing Reclaimed Asphalt Pavement (RAP), the Indirect Tensile Strength (ITS) and resilient modulus evaluation of modified mixtures are important to understand. The aging of binder containing crumb rubber obviously alters the visco-elastic and plastic characteristics of the modified mixtures. The deformation of the mixture under repeated loading, nearly completely recoverable, should also be considered. The experimental design included the use of two aggregate sources, one rubber type (ambient), four rubber contents (0%, 5%, 10%, and 15%), one crumb rubber size (-40 mesh [-0.425 mm]), and four RAP contents (0%, 15%, 25%, and 30%). The findings indicated that an increase in the rubber content in the modified mixture leads to a decrease in ITS and resilient modulus values regardless of rubber content, and this increase also improves the aging resistance and increases the viscous characteristics of the modified binder. However, as RAP content increased, not only the viscosity and G*sinδ values of the modified binder increased, the ITS and resilient modulus values of the modified mixtures also increased.

Reuse of crumb rubber and plastic on hot-mixed asphalt concrete : Cetin, A. et al. Petroleum and coal, 2001, 43, (3–4), 183–187

In this study, the effects of crumbed rubber and plastics on asphalt concrete pavements were investigated. For this purposes, one type of limestone aggregate and one penetration-grade asphalt cement (75-100) were selected according to Turkish Highway Specifications. Crumbed rubber sieved (#4 - #20, #20 - #200 and #4- #200) was obtained by copping from scrap automobile tires. Plastic sieved between #4 and #10 were used. Crumbed rubber and plastic were chosen 5%, 10% and 20% by total weight of asphalt cement. The Marshall stability and flow test, the indirect tensile test and the moisture susceptibility test were performed on rubber and plastic mixed asphalt concrete specimens. It was found that while the addition of rubber decreased the Marshall stability, addition of plastic increased it. Marshall stability values were significantly decreased after adding 10% rubber. Indirect tensile strength values of mixtures decreased as the amount of rubber increased. Tensile strength values of plastic mixed asphalt cement were increased with increasing amount of plastic. Asphalt cement with 20% plastic increased tensile strength value by 69%. Addition of 20% rubber between #4 and #200 sieve decreased indirect tensile strength value by 7%. However the largest decrement of 36% occurred by mixing rubber between #20 and #200 sieve. For the covering abstract see ITRD E107185.

Laboratory design and investigation of the properties of continuously graded Asphaltic concrete containing recycled plastics aggregate replacement (Plastiphalt)

This paper discusses the laboratory design of continuously graded Asphaltic concrete (AC) mixtures containing recycled plastics aggregate replacement (Plastiphalt). Recycled waste plastics, predominantly composed of low density polyethylene (LDPE) in pellet form, were used in dense graded bituminous mixes to replace (by volume) a portion of the mineral aggregates of an equal size, i.e., 5.00-2.36 mm. The results obtained in this investigation indicate that at the same air-void content, the compacted Plastiphalt mix has lower bulk density than that of the conventional control mix. A 30% aggregate replacement by volume with the LDPE, results in a reduction in bulk compacted mix density of 16%. This reduction in density is advantageous in terms of haulage costs. LDPE partial aggregate replacement also results in a 250% times increase in the Marshall stability (strength) value and an improved Marshall quotient value (resistance to deformation). The value of creep stiffness of the Plastiphalt mix after 1 h loading of 60°C is found to be slightly lower than the control mix; however, the Plastiphalt gives 14% recovery after 1 h unloading time compared to 0.6% for the control mix. The indirect tensile stiffness modulus (ITSM) values of the Plastiphalt compacted mix were found to be lower than that of the control mix, whereas the static indirect tensile strength (ITS) values were found to be much higher. In this study, the future recyclability of the Plastiphalt was also investigated. The mechanical properties of the recycled mix were found to be equal to that of the original Plastiphalt and better than the control mixes.