Development of Superpave Direct Tension Test Device

1997 ◽  
Vol 1586 (1) ◽  
pp. 32-39 ◽  
Author(s):  
Raj Dongré ◽  
John D’Angelo ◽  
Steve McMahon
Keyword(s):  
Asphalt Binder ◽  
Tension Test ◽  
Asphalt Binders ◽  
Temperature Control System ◽  
Materials Testing ◽  
Direct Tension ◽  
Direct Tension Test ◽  
New Device ◽  
Failure Properties ◽  
User Friendly

The redesign and evaluation of the Superpave direct tension test (DTT) are described. The prototype of the DTT device was developed during the Strategic Highway Research Program (SHRP). The DTT device, an integral part of the new Superpave asphalt binder specification, was developed to test asphalt binders and determine their failure properties, such as the stress and strain at failure. The strain at failure is used in the Superpave asphalt binder specification to determine the lowest temperature at which the asphalt can be used to avoid low-temperature thermal cracking. When the SHRP program was completed, an affordable specification version of the prototype SHRP-DTT device was introduced for field implementation. Unfortunately, this version was plagued with mechanical problems, producing excessive variability and inconsistency in data. The device also was less user-friendly than other test devices that were being implemented for the asphalt binder specification. These problems led to implementation delays and difficulties. The problems were addressed by FHWA in cooperation with Instron Corporation of Canton, Massachusetts (a manufacturer of materials testing equipment). On the basis of recommendations made by FHWA, Instron developed a new, easy-to-use specification-type DTT device. This device is compact (approximately one-tenth the size of the original) and uses a fluid-based temperature control system similar to that used in the bending beam rheometer. The new device also employs feedback elongation (strain) rate control. However, unlike the previous device, the new DTT uses an extensometer between the loading pins instead of a laser to measure elongation (strain). The evaluation and resulting recommendations by FHWA, which led to the development of the new specification-type devices are discussed. The repeatability and testing protocols also are discussed.

Low-Temperature Fracture Testing of Asphalt Binders: Regular and Modified Systems

2000 ◽  
Vol 1728 (1) ◽  
pp. 36-42 ◽  
Author(s):  
Todd R. Hoare ◽  
Simon A. M. Hesp
Keyword(s):  
Low Temperature ◽  
Performance Indicator ◽  
Tension Test ◽  
Asphalt Binders ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Fracture Testing ◽  
Reliable Performance ◽  
Temperature Fracture ◽  
Notched Strength

The results of low-temperature fracture testing of a large number of both regular and modified asphalt binders are discussed. Two Strategic Highway Research Program (SHRP) binders (Materials Reference Library Codes AAG-2 and AAN) were evaluated with 5 percent by weight of a variety of commonly used polymer modifiers. Specimens of three different sizes were tested in a three-point bend configuration, both with and without a notch. The original SHRP effort was aware of the need for a rigorous fracture mechanics-type binder test, but because of a lack of time and resources, only the bending beam rheometer and the direct tension test were ultimately developed. Some of the differences between failure strain and fracture toughness measurements are discussed, as well as how these differences may relate to pavement performance. The results of this study demonstrate that there is a large range of notch sensitivities and fracture energies for different polymer-modified binders, suggesting that the ductile-to-brittle transition (as measured with the direct tension test) may not be a totally reliable performance indicator. Fracture energy may be a better choice, since it combines the notched strength with a stiffness to yield a true material property that is independent of sample size and configuration.

Polymer Modification of Paving Asphalt Binders

1994 ◽  
Vol 67 (3) ◽  
pp. 447-480 ◽  
Author(s):  
L. H. Lewandowski
Keyword(s):  
Low Temperature ◽  
Permanent Deformation ◽  
Tension Test ◽  
Asphalt Binders ◽  
Polymer Modification ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Modified Asphalt ◽  
Asphalt Rubber ◽  
Polymer Modified Asphalt

Abstract • Polymer modification of asphalt binders has become a more accepted method for addressing pavement distresses. The heavier vehicle loads, higher traffic volumes and increased tire pressures have forced user agencies to explore polymer modification for asphalt pavement applications. • The compatibility between the asphalt and polymer depends on many factors. The most significant of these, based on microscopy, are the asphalt crude source, polymer microstructure and the thermal/mechanical history of the polymer-modified asphalt binder. • Classical methods and methods derived specifically for measuring the effect of polymers in the asphalt have poor correlation to mixture performance. The tests also seem to be specific to the different polymers tested. The test conditions make it difficult to extract basic information about the binder's mechanical properties. • Considerable work has been done on the rheology of asphalt and polymer-modified asphalt binders over a wide range of temperatures and rates of loading. Time-temperature superposition has been used to describe the effect of rate of loading on the complex shear modulus (G*) of both polymer modified and unmodified asphalt binders. The addition of polymers has been found to dramatically change the properties at high temperatures or low rates of loading. This has been correlated with varying degrees of success to permanent deformation in the asphalt mixture. • The bending beam rheometer and the direct tension test are ideally suited for measuring the low temperature properties of polymer-modified asphalt binders. Good correlation was found with bending beam results and the fracture temperature of the mixture using the TSRST method. Failure strains, measured for polymer-modified asphalt binders with the direct tension test, were up to ten times greater than that observed for unmodified binders. Polymer-modifiers generally decreased the fracture temperature of the mixture by 6–10°C. • Polymer modifiers for asphalt binders which contain a large percentage of butadiene (50% or greater), exhibit improved low temperature properties. This was observed as a decreased Tg for a polybutadiene modified asphalt measured using dynamic mechanical analysis. Also direct tension results for SB (50% butadiene) -modified asphalt binders showed a marked increase in low temperature failure strains. • The performance-based specifications (SHRP) show good correlation with mixture performance. The best correlations were observed between the binder's Theological properties and the load-associated fatigue and low-temperature thermal cracking resistance. For permanent deformation, it was observed that the aggregate plays a significant role in the resulting rutting. Further testing and field studies are required to validate these laboratory measurements. • Asphalt-rubber mixtures have been shown to have useful properties with respect to distresses observed in asphalt concrete pavements. Most notably a large increase in viscosity and improved low-temperature cracking resistance have been measured. Only a limited body of test results exists and further testing is required to fully understand the contribution of asphalt-rubber to the mixture's performance.

scholarly journals An Innovative Test Method for Tensile Strength of Concrete by Applying the Strut-and-Tie Methodology

Materials ◽  
2020 ◽  
Vol 13 (12) ◽  
pp. 2776 ◽  
Author(s):  
Wen-Cheng Liao ◽  
Po-Shao Chen ◽  
Chung-Wen Hung ◽  
Suyash Kishor Wagh
Keyword(s):  
Tensile Strength ◽  
Test Methods ◽  
Standard Test ◽  
Strength Test ◽  
Tension Test ◽  
Test Method ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Strut And Tie ◽  
Tensile Strength Test

Tensile strength is one of the important mechanical properties of concrete, but it is difficult to measure accurately due to the brittle nature of concrete in tension. The three widely used test methods for measuring the tensile strength of concrete each have their shortcomings: the direct tension test equipment is not easy to set up, particularly for alignment, and there are no standard test specifications; the tensile strengths obtained from the test method of splitting tensile strength (American Society for Testing and Materials, ASTM C496) and that of flexural strength of concrete (ASTM C78) are significantly different from the actual tensile strength owing to mechanisms of methodologies and test setup. The objective of this research is to develop a new concrete tensile strength test method that is easy to conduct and the result is close to the direct tension strength. By applying the strut-and-tie concept and modifying the experimental design of the ASTM C78, a new concrete tensile strength test method is proposed. The test results show that the concrete tensile strength obtained by this proposed method is close to the value obtained from the direct tension test for concrete with compressive strengths from 25 to 55 MPa. It shows that this innovative test method, which is precise and easy to conduct, can be an effective alternative for tensile strength of concrete.

Statistical Distribution of Failure Stress Values from Superpave® Direct Tension Test

2002 ◽  
Vol 1810 (1) ◽  
pp. 72-77
Author(s):  
Raj Dongré ◽  
Charles Antle
Keyword(s):  
Weibull Distribution ◽  
Standard Test ◽  
Tension Test ◽  
Failure Stress ◽  
Test Method ◽  
Direct Tension ◽  
Data Set ◽  
Direct Tension Test ◽  
Data Points ◽  
Made In

A statistically robust method was developed using the Weibull distribution to identify and eliminate outliers from the failure stress determinations. The method is applicable to any failure stress data set that follows the Weibull distribution; however, in this application, it was developed for the AASHTO standard test method for conducting the direct tension test (DTT). A large number of stress-at-failure measurements with the DTT were made in the course of instructing users of this device. These data, all for the same asphalt, provided the means for studying the nature of the distribution of the breaking strength of these asphalt specimens. The training database contains more than 900 data points. The current AASHTO practice of eliminating the lowest two stress values was found to be reasonable. However, it is an arbitrary method that may lead to problems in the future. On the basis of the results of this study, the procedure is recommended for use and implementation in the next AASHTO version of the DTT standard.

An Unconfined Direct Tension Test for Compacted Clays

1974 ◽  
Vol 2 (3) ◽  
pp. 163 ◽  
Author(s):  
SF Etris ◽  
YR Fiorini ◽  
KC Lieb ◽  
IC Moore ◽  
AL Batik ◽  
...  
Keyword(s):  
Tension Test ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Compacted Clays

Establishing Linear Viscoelastic Conditions for Asphalt Binders

2000 ◽  
Vol 1728 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Mihai O. Marasteanu ◽  
David A. Anderson
Keyword(s):  
Single Point ◽  
Superposition Principle ◽  
Asphalt Binder ◽  
Testing Procedure ◽  
Constitutive Relationship ◽  
Asphalt Binders ◽  
Direct Tension ◽  
Linear Viscoelastic Material ◽  
Frequency Domains ◽  
Linear Viscoelastic

The linear viscoelastic regime is defined in terms of the constitutive relationship between the stress and the strain. The set of equations that define the fundamental linear viscoelastic material properties in the time and frequency domains and their relationship to one another is based on the validity of the linearity principle. A material must obey two simultaneous conditions to be linear viscoelastic: the homogeneity (also called proportionality) condition and the superposition principle. On the basis of these considerations a testing procedure was developed to check linear viscoelastic conditions for tests performed on asphalt binders with the dynamic shear rheometer (DSR), the bending beam rheometer (BBR), and direct tension (DT). The testing procedure for the DSR requires performing strain sweeps and multiwave single-point tests. For the BBR, tests performed using different constant loads are required. In addition, the recovery part of the specification test is recorded. For the DT, tests performed at different strain rates and relaxation tests performed at different strain levels are required. When applied to asphalt binder data, the testing procedure found no departure from viscoelastic conditions for the DSR and BBR test data. However, the DT procedure indicated a departure from linear viscoelastic conditions.

scholarly journals A New Direct Tension Test Method for Soils and Soft Rocks

2020 ◽  
Vol 43 (6) ◽  
pp. 20190308
Author(s):  
Yanrong Li ◽  
Fanfan Guan ◽  
He Su ◽  
Adnan Aydin ◽  
Mary Antonette Beroya-Eitner ◽  
...  
Keyword(s):  
Tension Test ◽  
Test Method ◽  
Direct Tension ◽  
Direct Tension Test ◽  
Soft Rocks
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