Predicting Dynamic Properties of Asphalt Mastic Considering Asphalt-Filler Interaction Based on 2S2P1D Model.

The relationship between the various phases of asphalt materials, from asphalt binder to mastic and mixture, has received great attention over the years, with efforts being made to establish linkages among these phases. Many methods for predicting the rheology properties of asphalt mastics from those of asphalt and filler volume fractions exist. However, most prediction methods are based on an empirical formula and on the micromechanical model. Very few research studies focus on the constitutive model. In addition, relatively little research has explored the influence of asphalt-filler interaction on mastic's rheology properties, which is believed to be an important factor. In this study, the 2S2P1D (two springs, two parabolic elements, and one dashpot) model was applied to link the behavior of asphalt binder, filler volume fraction, asphalt-filler interaction and asphalt mastic. First, the interaction between asphalt and filler was evaluated, and the interaction parameter C of the Palierne model was used as an assessment indicator to calculate the effective filler volume fraction of asphalt mastic. Then, the relation between the 2S2P1D model parameters of asphalt mastic and those of asphalt binder and the effective filler volume fraction was analyzed. Finally, a simple relationship associating the 2S2P1D model parameters h, log(τ0) of mastic and that of asphalt binder and the effective filler volume fraction was developed. The proposed expression was validated, and the result showed that it was an efficient model for the shear complex modulus prediction of virgin asphalt mastic.

Laboratory Investigation of Aging Resistance for Rubberized Bitumen Modified by Using Microwave Activation Crumb Rubber and Different Modifiers.

Different modification methods, such as adding modifiers and pretreating crumb rubber, have been developed to achieve decent engineering properties and reduce the viscosity of rubberized bitumen. This study evaluated the influence of the modification methods on the aging resistance for rubberized bitumen. Two types of crumb rubber-a 40-mesh crumb rubber and a microwave-pretreated crumb rubber-and two kinds of modifiers-Sasobit and Trans-polyoctenamer-were selected to prepare rubberized bitumen. The samples were subjected to a Thin-Film Oven Test for the simulation of the short-term aging condition, while a Pressure-Aging-Vessel test was used to simulate the long-term aging condition. The indexes of rubberized bitumen, including softening point, elastic recovery ratio, maximum load, ductility, fracture energy, phase angle, and dynamic modulus, were tested before and after aging. The result showed that trans-polyoctenamer displayed the best resistance to short-term aging, while Sasobit significantly improved the fracture energy of rubberized bitumen after short-term aging. Microwave pretreated partially destroyed the internal structure of crumb rubber, leading to a decrease of short-term aging resistance for rubberized bitumen. Compared with short-term aging, the changing trends of various indexes were basically same, except the discrepancy of properties indexes was reduced after long-term aging.

A Study on Physical and Rheological Properties of Rubberized Bitumen Modified by Different Methods.

Crumb rubber (CR) manufactured from waste tires used in bitumen could improve bitumen performance and reduce environmental pollution. In this work, three different modification methods, pretreatment of the CR particles (microwave activation), warm mix additive (Sasobit), and trans-polyoctenamer (TOR) were used to improve the compatibility of CR with bitumen. Moreover, two other specimens, Sasobit and microwave activated and TOR and microwave activation were fabricated, and their performance was investigated. The softening point, elastic recovery, force ductility, rotational viscosity, temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) tests were measured to evaluate the physical and rheological properties of rubberized bitumen. The results showed that TOR improved the physical properties of rubberized bitumen significantly but had a negative effect on the viscosity. Sasobit decreased the viscosity of rubberized bitumen considerably and improved the physical properties of rubberized bitumen moderately. Microwave treatment on CR had a negative effect on the high temperature performance and elastic recoverability of rubberized bitumen, however, attributing to the degradation and devulcanization effect of microwave on CR, the viscosity of rubberized bitumen was improved. From the results of composite modification, the influence of TOR on the performance of rubberized bitumen was more obvious than that of the microwave activation treatment. Moreover, the influence of Sasobit on its performance was less than that of the microwave activation treatment.

Preparation and Properties of Rubber Blends for High-Damping-Isolation Bearings.

To improve the energy dissipation capacity of rubber isolation bearings, it is important to find a new rubber material with good applicability and high damping properties. Two types of blends were prepared using nitrile rubber (NBR), brominated butyl rubber (BIIR) and ethylene-vinyl acetate copolymer (EVA): NBR/BIIR and NBR/BIIR/EVA. The vulcanization, mechanical and damping properties of the blends were analyzed. The results show that both blends exhibit excellent vulcanization plateaus and mechanical properties. For NBR/BIIR, as the BIIR content increases, the complementary effects of NBR and BIIR afforded by blending are enhanced. Two damping peaks appeared in the tanδ-T curve and shifted toward lower and higher temperatures, respectively, which clearly widened the effective damping temperature range. However, the damping value in the valley of the tanδ-T curve was as low as 0.39. For NBR/BIIR/EVA, the addition of EVA greatly increased damping in the valley of the tanδ-T curve to approximately 0.54. EVA was observed to be the optimal polymer for improving the compatibility of the NBR/BIIR blend. Moreover, hot air thermal aging tests showed that both blends demonstrated good stability.

The Performance of Super Absorbent Polymer (SAP) Water-Retaining Asphalt Mixture.

Lowering the temperature of the road surface is one efficient way to alleviate the urban heat island effect. Therefore water-retaining asphalt mixture was produced by adding super absorbent polymer (SAP) containing cement mortar to the porous asphalt mixture. In this study, the water absorption capacity, mechanical strength and fluidity of the cured water-retaining mortar were investigated to determine the optimum SAP dosage in water-retaining mortar. Furthermore, the microstructure of the hardened water-retaining mortar was studied using scanning electron microscopy (SEM) to determine the morphology and distribution of SAP in the final product, which may help to understand the influence of SAP on water retention performance and decipher its underlying mechanism. Compared to the raw porous asphalt mixture, the water-retaining asphalt mixture showed good moisture susceptibility (retained stability (RS) ≥ 88.2%, tensile strength ratio (TSR) ≥ 81.8%), good rutting resistance (9336-10,552 times/mm) and low temperature crack resistance (3383-3621 MPa), as well as significant cooling effects (10-12 °C). The results illustrate that the prepared SAP water-retaining asphalt mixture has good potential in reducing dust and enhancing road performance.

Effect of Rejuvenator Containing Dodecyl Benzene Sulfonic Acid (DBSA) on Physical Properties, Chemical Components, Colloidal Structure and Micro-Morphology of Aged Bitumen.

DBSA was used as a solubilizer together with conventional rejuvenator (CR) to produce a solubilized rejuvenator (SR), two kinds of aged bitumen involving TFOT aged bitumen and PAV aged bitumen were obtained by thin film oven test (TFOT) and pressurized aging vessel (PAV), respectively. Effects of CR and SR on the physical properties, chemical components, colloidal structure and micro-morphology of TFOT aged bitumen and PAV aged bitumen were investigated. Testing results of physical properties and chemical components indicated that CR and SR can replenish aged bitumen with necessary aromatics, TFOT aged bitumen that chemical component variation deteriorates its physical properties. With regard to PAV aged bitumen, of which the performance attenuation lies in chemical components variation and colloidal structure transformation, even if the content of CR reached up to 10 wt %, the regenerated bitumen cannot meet the regeneration requirement yet due to its definite influence on colloidal structure transformation, comparatively, sulfonic group in SR can react with the superficial atoms of asphaltenes to reform a solvation layer to facilitate the colloidal structure transformation of PAV aged bitumen, performance and beelike structure of regenerated PAV aged with bitumen with 10 wt % SR were approximated to that of virgin bitumen.

Feasibility Evaluation of Preparing Asphalt Mixture with Low-Grade Aggregate, Rubber Asphalt and Desulphurization Gypsum Residues.

Road construction consumes great amounts of high-grade natural resources. Using low-grade natural rocks or some solid wastes as substitute materials is a hot topic. Considering this, the feasibility of using low-grade granite aggregate, solid waste-based filler (desulphurization gypsum residues, DGR) and binder (waste tire rubber modified asphalt, RMA) simultaneously in asphalt mixtures has been fully investigated in this research. The commonly used base asphalt and limestone powder (LP) filler were control groups. Material characteristics of raw materials mainly including micro-morphology, functional group, mineral phase, chemical composition and thermal stability were first evaluated in order to recognize them. Four asphalt mixtures (two asphalt binder and two filler) were then designed by standard Superpave method. Finally, a detailed investigation into the pavement performance of asphalt mixtures was carried out. The moisture damage resistance and low-temperature crack resistance were detected by the changing rules of stability, strength and fracture energy, and the high-temperature stability and fatigue performance were determined by wheel tracking test and indirect tensile (IDT) fatigue test, respectively. Results suggested that RMA and DGR both showed positive effects on the low-temperature crack resistance and fatigue property of the granite asphalt mixture. DGR also strengthened moisture stability. The contribution of RMA on high-temperature deformation resistance of the granite asphalt mixture was compelling. It can offset the insufficiency in high-temperature stability made by DGR. A conclusion can be made that asphalt mixture prepared with granite, DGR and RMA possesses satisfactory pavement performances.

Diffusibility Enhancement of Rejuvenator by Epoxidized Soybean Oil and Its Influence on the Performance of Recycled Hot Mix Asphalt Mixtures.

Epoxidized soybean oil (ESO) was employed as a novel penetrant cooperating with a conventional rejuvenator (CR) for the recycling of reclaimed asphalt pavement (RAP). The influence of ESO on the diffusibility and the regenerating effects of CR on RAP were investigated. The diffusibility testing result shows that the diffusibility of CR is enhanced by the addition of ESO because the epoxy group in ESO can facilitate asphaltene dispersion due to its high polarity, which simultaneously reduces the viscosity and improves the fluidity of aged bitumen so as to allow diffusion of the rejuvenator into the aged bitumen. Road performance testing of a recycled hot mix asphalt mixture (RHMA) indicates that the fatigue and cracking resistance properties as well as the water stability of RHMA containing CR can be improved by the addition of ESO due to the diffusibility enhancement of CR, which boosts the regenerating effect of CR on aged bitumen in RAP. The fatigue and cracking resistance properties as well as the water stability of the recycled hot mix asphalt mixture containing CR with 7 wt % ESO approximate those of the hot mix asphalt mixture composed of the same virgin aggregates and bitumen. Taking into account the rutting resistance decline versus the addition of ESO, the content of ESO should not exceed 7 wt % of the conventional rejuvenator.