Search

In this study, the mutual effect of polyphosphoric acid (PPA) and ethylene bis(stearamide) (EBS) modification was examined on the high and low service temperatures and viscosity of a performance grade (PG) 58-22 asphalt binder as a conventional neat bitumen widely used for paving applications. Three different dosages of PPA, including 0.5%, 1.0%, and 1.5% were used to modify the neat asphalt binder, and 3% of EBS as a selected percentage was added to PPA-modified samples. The dynamic shear rheometer was used to evaluate the high-temperature properties of the neat and modified bitumens based on standard Superpave protocol parameter (G*/sinδ) and multiple stress creep and recovery test. The low service temperatures of the samples were determined using the bending beam rheometer test. Also, the high-temperature ranges viscosities of the samples were evaluated using a series of rotational viscometer tests. The results have shown that increasing the PPA dosage up to 1.5% enhances the high service temperature of the neat asphalt binder 20.4°C and 14.7°C based on Superpave protocol and multiple stress creep and recovery test, respectively. However, it deteriorates the low-temperature performance of modified binders from −24.3°C to −16.9°C. The EBS can significantly compensate for the negative effect of PPA modification on the low-temperature behavior of modified bitumens. The optimum combination was 1% PPA+3% EBS as it provides a similar low-temperature grade to the neat asphalt binder having a significant two grades enhancement of high service temperature. Modifying a PPA-modified asphalt binder with EBS can reduce its viscosity at high temperatures, leading to saving energy of mixing and compaction. [ABSTRACT FROM AUTHOR]

This paper examines effects of a new biobased modifier, 'biobinder,' on low-temperature properties of asphalt binder and compares the results with those of conventional modifiers: crumb rubber, Gilsonite, styrene-butadiene-styrene (SBS), and polyphosphoric acid (PPA). Low-temperature characteristics of modified and nonmodified asphalts were studied using experimental and modeling approaches. A three-point bending beam rheometer was used to measure the stress-strain response of each specimen. A theoretical approach was used to determine stiffness and stress release rate; in addition, the Burgers model was implemented to predict the stored and dissipated energy ratio and quantity of derivation of creep compliance in each of modified and nonmodified asphalt specimens. Effects of various modifications were compared based on both the calculated stored and dissipated energy ratio and quantity of derivation of creep compliance. The proposed biobinder is produced from the thermochemical conversion of biomass (including animal waste, switch grass, and woody biomass). Biobinder is then blended with virgin binder to produce biomodified binder (BMB). This paper argues that the improved low-temperature rheological properties in biomodified binder is reflected in the enhancement in energy dissipation ratio and quantity of derivation of creep compliance. [ABSTRACT FROM AUTHOR]

• SBS and PPA with three different dosages are used to fabricate modified asphalt mastic. • Fractional viscoelastic model (FDM-4) is used to describe mechanical behavior of modified asphalt mastic. • The RSM is used to relate parameters of asphalt mastic models to parameters of asphalt binder models. • Additive's dosage, temperature, and filler volume filling rate are model inputs. The main aim of this study is to develop prediction equations of asphalt mastic fractional model parameters based on the fractional model parameters of asphalt binder, taking into consideration many parameters including, styrene–butadienestyrene (SBS) and polyphosphoric acid (PPA) modification, modifier's dosage, volume filling rate of siliceous filler, and test temperature. Experimental tests were conducted on original, SBS- and PPA-modified asphalt binders and asphalt mastics fabricated with these binders by using a dynamic shear rheometer device to achieve this aim. The asphalt mastic samples were fabricated considering a couple of volume filling rates of siliceous filler: 18 and 35%. Then, a fractional viscoelastic and the generalized Maxwell model were implemented and compared to describe the viscoelastic behavior of binder and mastic samples. The results showed that the fractional viscoelastic model could accurately predict the viscoelastic behavior of the original and modified asphalt mastic using fewer parameters compared to the well-known generalized Maxwell model so that the fitting accuracy of all samples is more than 0.99. In addition, the response surface methodology (RSM) was used to develop the prediction equation between the parameters of modified asphalt binders and the correspondent asphalt mastic fractional model. R2 values of SBS and PPA prediction models for fractional model coefficients are between 0.89 and 0.96. The predictive models presented a high accuracy so that mastic parameters with asphalt binder parameters, additive's percentage, temperature, and volume filling rate can be achieved. [ABSTRACT FROM AUTHOR]

Abstract: In this research, the effects of four modifiers including crumb rubber, gilsonite, styrene–butadiene–styrene (SBS) and polyphosphoric acid (PPA) on the mechanical and rheological properties of asphalt binder at low service temperature are investigated. The main objective of this paper is to rank modifiers due to their effect on low service performance characteristics of asphalt binder for all type and extent of observed modified asphalt binders. For this purpose, the bending beam rheometer (BBR) test is performed on different extent of modifiers at five temperatures: −6°C, −12°C, −18°C, −24°C and −30°C. Asphalt binder is categorized as a viscoelastic material. Among several linear viscoelastic models, the Burgers model is selected for describing the mechanical behavior of modified asphalt binders. Four Burgers parameters are calculated by means of the principle of multiple non-linear regression and then these parameters are used for comparing the performance of asphalt binders by these three approaches: SuperPAVE Performance Grading (PG) protocol, dissipated energy ratio and derivation of creep compliance. Utilizing these three approaches, modified asphalt binders are ranked based on higher quantity of low temperature, dissipated energy ratio and derivation of creep compliance for all type and extent of modifiers alongside. Results show that each approach produces a particular grading which is not same as another one. In spite of variation of rankings, among the all evaluated modified asphalt binders, crumb rubber modified asphalt binder totally shows superior performance on low service temperature in all three methods. [Copyright &y& Elsevier]

• A new fracture resistantce indicator was developed accounting for the crack growth rate. • Increasing the polyphosphoric acid dosage increases fracture resistance at low temperatures. • Asphalt fracture resistance was the highest when 1 wt.% polyphosphoric acid was added. This paper examines the effect of polyphosphoric acid (PPA) on asphalt's fracture properties. While PPA has been commonly used in the asphalt industry to increase the elasticity and stiffness of asphalt binder, its effects on fracture properties are not thoroughly understood. Fracture as relates to thermal cracking is often associated with asphalt binder rather than a stone skeleton. However, because PPA not only interacts with molecules of asphalt binder but also strongly interacts with stone aggregates due to its highly polar molecules, we hypothesize that the presence of PPA in asphalt will change both bulk and interface properties in asphalt composites, which consequently alter asphalt fracture properties. To test this hypothesis, various PPA dosages (0.5–1.5% wt.) were introduced to the original asphalt binder, and thermo-mechanical and fracture properties of asphalt binder and asphalt mixture were examined. The study results showed that introducing up to 1% PPA enhances the asphalt resistance to fracture; however, excessive PPA weakens the asphalt against cracking. Considering that polar molecules of bitumen supersede others to adsorb to stone aggregate surfaces, the observed weakening effect could be attributed to PPA's preferential adsorption to stone aggregate surfaces compared to those of asphalt binder. The study outcomes provide insights pertaining to PPA's role and its interplay with other components in asphalt pavements. [ABSTRACT FROM AUTHOR]

This study exploits silica and polyphosphoric acid (PPA) synergistic effects to produce air-blown bitumen with desired stiffness and reduced carbon footprint. This in turn enhances the durability of the resulting air-blown bitumen while reducing gaseous emissions associated with its production. Here, we hypothesize that PPA-grafted silica made by adsorption of polyphosphoric acid to pristine silica nanoparticles promotes intermolecular interactions in vacuum bottom (VB), facilitating the production of air-blown bitumen. To test this hypothesis, laboratory experiments and modeling were used to determine the underlying molecular interactions determining PPA-grafted silica's role in facilitating the production of air-blown bitumen. Our molecular modeling showed PPA promotes the interaction between VB molecules by up to 10.28%; this combined with the increased polarity of VB molecules during the air-blowing process, leads to a significant increase in intermolecular interactions accelerating VB's stiffening. The latter was evidenced in our experiments showing that the required air-blowing time to reach desired stiffness measured by penetration and softening point was reduced up to 25% (time to reach required stiffness was reduced from 120 min to 90 min when silica-grafted polyphosphoric acid was used). Reduction of manufacturing time reduces VB's exposure to heat which leads to the formation of secondary organic aerosols. This promotes the economic and environmental sustainability aspects of the air-blowing process and contributes to resource conservation. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Three types of additives were used at three different dosages: crumb rubber, SBS, and PPA to modify bitumen. • Genetic programming based closed-form equations are developed for G* and δ of modified bitumens. • G* and δ of original bitumen, test temperature and frequency were considered as model inputs. • The performance of models were successfully verified using statistical indices and external data validation. The objective of this research was to develop prediction models for complex shear modulus (G*) and phase angle (δ) of bitumens modified with crumb rubber, styrene-butadiene styrene, and polyphosphoric acid at low and moderate temperatures. The experiments consisted of three different dosages of each modifier added to the original bitumen followed by measurement of G* and δ of the original and modified bitumen using the dynamic shear rheometer (DSR) test in frequency sweep mode (21 loading frequencies from 0.1 to 100 Hz) at seven test temperatures: −22, −16, −10, 0, 10, 16 and 22 °C. Having the experimental database, a robust genetic programming (GP) method was used to develop an individual prediction model for each modifier based on temperature, loading frequency, the G* and δ of the original bitumen, and the dosage of the modifier. Results showed that GP successfully developed accurate and meaningful expressions for calculating G* and δ of the modified bitumen as two main constitutive components of the viscoelastic behavior of bituminous composites. Then, a parametric study and sensitivity analysis were performed on the developed models to better understand the effect of variables on the trend of the models. The modifier dosage is the most effective input variable of the model and the amount of G* and δ of the original bitumen accurately reflect the effect of temperature and loading frequency on viscoelastic behavior of the modified bitumen, as they behave linearly at the considered test temperatures. [ABSTRACT FROM AUTHOR]