Tirupan Mandal

Protocol for testing flexural strength, flexural modulus, and fatigue failure of cementitiously stabilized materials using third-point flexural beam tests

In this study, a testing protocol was developed to measure the flexural strength, flexural modulus, and fatigue failure of cementitiously stabilized materials (CSMs) for both lightly and heavily stabilized soils. Four soils (sand, gravel, silt, and clay) and four binders (cement, lime, class C fly ash, and class F fly ash) were used in this study. Beam specimens (100 mm high by 100 mm wide by 400 mm long) were prepared and tested using third-point flexural beam tests. A fatigue distress model was developed, and the data from this study was validated using other existing stress-based fatigue models. Results indicated that the testing protocol could be used to determine the flexural strength, flexural modulus, and fatigue behavior of the cementitiously stabilized layers (CSL). A stress-based fatigue performance model was a good fit for the whole range of CSMs, which is needed to predict the fatigue performance of CSL in the field and to determine the fatigue life of the CSLs.

Sensitivity of the Illinois Flexibility Index Test to Mixture Design Factors

The semicircular bend test was recently modified to develop the Illinois flexibility index test (I-FIT). The I-FIT test quantifies the cracking resistance of asphalt mixtures by using the flexibility index (FI), which includes the fracture energy and postpeak behavior of a mixture. This paper presents results from testing asphalt mixtures in Wisconsin. A statistical analysis approach was chosen for this study, in which the I-FIT procedure was used to differentiate between mixtures on the basis of changes in mixture composition and aging treatments. Mixtures included in this study varied in terms of the percentage of reclaimed asphalt pavement, design traffic levels, binder grades, modification levels, and aging conditions. In addition, a laboratory experiment to evaluate the effects of variability in mixture production, including asphalt content and filler content, on the I-FIT testing results was performed to provide a basis for evaluating the tolerance limits of the current production and for setting reasonable specification criteria. The statistical analysis indicated that the FI could discriminate between types of asphalt mixtures and aging conditions. The FI parameter was found to be a better parameter for capturing some of the critical changes in mixture variables and aging than the fracture energy and other parameters from the I-FIT procedure. It was also clear that the FI parameter was sensitive to the variation in production binder and filler contents within the tolerances of the current construction specifications of the Wisconsin Department of Transportation.

Effect of cross-linking agents on the rheological properties of polymer-modified bitumen

The use of polymer-modified bitumen (PMB) has increased significantly for more than two decades. Cross-linking agents are used in PMB as an additive, mainly for improving the durability of this material as the cross-linking agent chemically reacts with the PMB by forming a covalent or ionic bond. This study tries to investigate the effect of cross-linking agents on the rheological properties of PMBs. Two types of elastomers – linear and radial – and seven types of cross-linking agents were used. A functional polyethylene (FPE) was added to all the binders. The rheological properties (creep and recovery) were studied using the dynamic shear rheometer. The viscosity and storage stability for each of the modified binder were also studied. Among all the cross-linking agents used in this study, sulphur was found to be the most effective. Two more cross-linking agents were found to have similar results as that of sulphur.

Study on flexural strength, modulus, and fatigue cracking of cementitiously stabilised materials

Flexural and resilient properties (flexural strength, flexural modulus, fatigue cracking, and resilient modulus) of common cementitiously stabilised materials (CSMs) in pavement systems are presented in this paper. These properties are critical parameters for pavement analysis to determine stress/strain and thus, pavement performance prediction. Four materials (sand, gravel, silt, and clay) and four binders (cement, lime, class C fly ash, and a combination of lime and class F fly ash) were studied. Beam and cylindrical specimens were prepared to study the flexural and resilient properties, respectively. The effect of compaction, binder content, and curing time was evaluated. Modulus growth tests were conducted at 28, 56, 90, 120, 150, and 180 d. A power relationship (R2 = 0.92) between flexural strength and unconfined compressive strength (UCS) for the CSMs was observed. The flexural strength test adopted here was found to be applicable for the whole range of CSMs – both heavily and lightly stabilised soils. The results indicate that determination of flexural modulus is strongest at a stress level of 30%. The number of cycles to achieve a 50% reduction from initial modulus could be considered to define fatigue failure if the specimen does not fail within 8 h.

Challenges in using the Disc-Shaped Compact Tension (DCT) test to determine role of asphalt mix design variables in cracking resistance at low temperatures

ABSTRACT There have been many fracture tests – the Thermal Stress Restrained Specimen Test, the Single-Edge Notched Beam test, the Semi-Circular bend test, the Indirect Tensile Test and the Disc-Shaped Compact Tension (DCT) test – developed to understand thermal cracking in asphalt pavement. Among these tests, the DCT test is the most recent test method developed that has gained significant interest. This paper includes a laboratory study to measure the effect of different mixture design parameters on the DCT test results. The parameters include per cent binder replacement from recycled asphalt pavement, binder modification, low-temperature binder grade, oxidative ageing and mix design traffic level. To investigate the significance on the factors controlled, ANOVA and multi-linear regression analyses are used to show that only a few factors can be considered significant in terms of their effects on DCT parameters, and the significance of those factors could not explain the range in DCT response variables. Some of the trends in change in the DCT test responses with mixture ageing and some other factors are also found to be illogical. This paper does not offer solutions, but highlights some of the challenges experienced when applying the DCT test to performance specifications.