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DOE OSTI2022

Weather aging effects on modified asphalt with rubber-polyethylene composites

Weather aging may cause more severe degradation on asphalt than thermal-oxidative aging due to the synergistic effect among oxygen, heat, ultraviolet (UV) radiation, and moisture. This study aimed to investigate weather aging effects and anti-aging mechanisms on asphalt modified with rubber-polyethylene (PE) composites. The modified binder blends and asphalt mixtures were subjected to outdoor weather aging. Dynamic shear rheometer (DSR), Fourier transform infrared spectroscopy (FTIR), Gel permeation chromatography (GPC), and optical microscopy tests were adopted to characterize the rheological properties, aging resistance, polymer degradation, and anti-aging mechanisms of modified binder blends, respectively. Mixture performance tests including Asphalt Pavement Analyzer (APA) and Ideal-CT tests were used to evaluate rutting and cracking resistance of asphalt mixtures. Results showed that weather aging can cause more severe aging to asphalt binders than pressure aging vessel (PAV) due to the severe degradation of PE particles. Rubber-PE composites alloyed with an extruder proved to stabilize PE particles in asphalt and significantly improve the aging resistance of modified binder blends. Furthermore, the enhanced aging resistance is attributed to the dispersion of PE particles and carbon black released by soluble rubbers.

Aging resistance↗

DOE OSTI2023

Reactive Extrusion of Waste Plastics with Compatibilizer and Lightly Pyrolyzed Crumb Rubber for Asphalt Modification

Modifying asphalt is a potentially high-value application for reusing waste plastics because of the high-volume usage of asphalt in highway construction. However, simply blending hot plastics and asphalt encounters difficulties related to the poor solubility of polymers, which limits the formation of a swollen network with asphalt molecules. The polymer phases also tend to coalesce and separate from asphalt during high-temperature storage in static conditions. The present study developed an innovative process to stabilize waste plastics in asphalt and improve binder storage stability by using lightly pyrolyzed crumb rubber together with a chemical compatibilizer. Both polymers were extruded to produce a thermoplastic elastomer (TPE) for asphalt modification. The mechanical performance and chemical reactions of TPEs were characterized via tension test and Fourier transform infrared spectroscopy. The storage stability and rheological properties of modified binder blends were evaluated through laboratory asphalt stability test and dynamic shear rheometer test. Polymer phases and network structures were characterized through optical microscopy. It was found that the pyrolyzed and reactive extrusion process improved the rubber solubility and polymer interaction, and therefore the storage stability of modified binder blends. The co-existence of rigid plastic and soft rubbery regimes in an entangled network provided a promising pathway to improve the mechanical performance of asphalt binders in both high- and low-temperature domains.

Ma, Yuetan↗

DOE OSTI2025

Compatibilization Strategy and Mechanism for Co-stabilizing Commingled Plastics and Pyrolyzed Rubber in Asphalt

Hot mix asphalt mixture is considered the ideal approach to reuse waste plastics in high-value applications because of its very high amount of usage in highway construction. However, the differences in polarity and density between polymers and asphalt lead to polymer coalescence and therefore the poor storage stability of modified asphalt. These challenges are exalted when recycling commingled plastics. This study introduced an innovative compatibilization strategy and mechanism for co-stabilizing commingled plastics and pyrolyzed rubber in asphalt. Commingled plastics were first grafted with maleic anhydride for surface activation, followed by reactive kneading with pyrolyzed rubber and crosslinking agent to form an integrated thermoplastic elastomer (ITPE) for asphalt modification. The mechanical, thermal, and interfacial behaviors of the ITPE were evaluated through tensile testing, thermogravimetric analysis, and scanning electron microscopy. The storage stability and rheological properties of the modified binder blends were evaluated through the cigar tube test and dynamic shear rheometer testing. Results demonstrated a successful formation of imide bonds in the ITPE, which can improve the strength, ductility, and thermal stability of rubber–plastic composites. Appropriate utilization of crosslinking agents can improve both rutting and fatigue resistance of ITPE-modified asphalt with good storage stability because of the co-existence of rigid plastic and soft rubbery regimes and the formation of a crosslink network. Furthermore, excessive content of crosslinker led to severe phase separation and reduced storage stability of modified binder blends. Extra crosslinker tended to float in asphalt because of its low density and caused an excessive formation of the crosslink network in the top section of the asphalt.

asphalt binder modifiers↗

DOE OSTI2021

Recycled polyethylene and crumb rubber composites modified asphalt with improved aging resistance and thermal stability

Crumb rubbers (CR) and recycled Polyethylene (PE) are commonly used as modifiers to improve the asphalt properties. However, the addition of these modifiers individually may result in phase separation of PE and inadequate degradation of CR, which may not simultaneously satisfy the rheological and aging resistance of the binder blends. In this study, a type of CR/PE composites manufactured through melt extrusion procedures was adopted for the improvement of the modified binder blends. The modified binder blends after short-term (RTFO) and long-term (PAV) aging were collected for dynamic shear rheometer and bending beam rheometer tests. FTIR tests were also used to quantify the aging resistance, while differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were applied to evaluate the thermal behaviors of the binder blends. Optical microscopy tests were used to explore the modification mechanism and visualize the microstructures of original and PAV aged binder blends. Test results showed that CR/PE composites could significantly improve the aging resistance of the binder blends. The dispersed PE particles still interacted with each other and meanwhile worked with the diffused rubbery phase, which could form a similar TPEs network. The oxidation and high-temperature aging of such binder blends would strengthen the network that resisted the aging severity of the binder blends. Furthermore, it was also revealed that CR/PE modified asphalt could sustain more heat before a rapid degradation and the well-dispersed PE particles could interact with the diffused CR particles to form a network to resist aging.

02 PETROLEUM↗

DOE OSTI2021

Towards ternary binders involving limestone additions — A review

The review summarises literature to examine the transition from portland limestone cement system to composite ternary binder systems involving limestone. Interest in limestone addition as an ideal component in multicomponent binder systems has surged as evident from the large volume of literature published in the recent past. A ternary blended system, with co-substitution of limestone, has the potential to complement the reaction of the supplementary cementitious materials (SCMs). The direct addition of limestone powder helps to attain higher substitution levels of portland cement clinker, improve early age properties, and supplement SCM's reactivity. However, the dilution of hydrates could hamper the long-term benefits. In this review, the interaction of fine limestone is classified and elaborated under two broad umbrellas: physical and chemical interactions. The physical interactions can manifest in three ways, namely, filler action, shearing action and improved packing, which alters reaction rate and extent at early ages. The chemical interactions also modify the reaction kinetics and phase assemblage due to nucleation of C-S-H on calcite surfaces, preservation of the ettringite phase and formation of carboaluminates. Two different forms of carboaluminate hydrates — hemicarboaluminate and mono-carboaluminate can be present in the hydrate matrix depending on the balance between carbonate ions and aluminates in the pore solution. Several factors such as replacement level, particle size, choice of SCM, its reactivity and reactive aluminates content, sulphate levels, curing temperature, and duration of curing can control the carboaluminate formation, reaction degree of SCMs and chemical interaction from limestone additions. A combination of physical and chemical effects makes fine limestone a potential material for co-substitution with aluminosilicate based SCMs, mainly fly ash, slag, and calcined clay. In this review, the factors affecting limestone-SCM composites are summarised based on a detailed literature survey. The effects of SCM-limestone cement composites on hydration kinetics, reaction chemistry, the reactivity of SCMs, the stability of hydrated phases, and contribution to the physical structure development and macroscopic properties by evaluating hydration and mechanical properties are discussed. The importance of AFm (Al{sub 2}O{sub 3}–Fe{sub 2}O{sub 3}-mono) phases in various deterioration mechanisms in concrete and their influence on performance characteristics in different exposure environment is critically appraised.

36 MATERIALS SCIENCE↗

DOE OSTI2021

Shrinkage-induced deformations and creep of structural concrete: 1-year measurements and numerical prediction

Highlights: • Extensive experimental study on drying shrinkage, creep and microcracking of concrete • All specimens prepared from a single batch of ordinary-strength structural concrete • 1st year of measurements of (not only) non-uniformly drying beams with span up to 3-m • The database is downloadable from free-to-use research data repository • Modified MPS model for concrete creep used in blind prediction of all experiments The material models for creep and shrinkage operating on the material point level in FEM are usually intended for challenging complex applications and structures, where the average cross-sectional approach does not suffice. The identification of the growing number of material parameters induced by increasing model capabilities relies on very specific and narrow-oriented yet interconnected experiments which are scarce. The presented comprehensive experiments aim to provide a clearer image of the complicated interaction among the basic phenomena: drying, shrinkage, creep, and microcracking. The cornerstone of this ongoing research is a unique set of 30 partially-sealed unreinforced concrete beams with span 1.75–3.0 m subjected to drying. To minimize material variation, all specimens in this study were cast from a single batch of ordinary strength structural concrete with slag-blended binder. The resulting experimental database will be suitable both for validation and development of the constitutive models.

36 MATERIALS SCIENCE↗