Enhancing waste asphalt durability through cold recycling and additive integration

While substantial research has focused on incorporation of Reclaimed Asphalt Pavement (RAP) in hot-mixed asphalt mixtures, there is a knowledge gap related to performance of stabilized base courses. This study evaluated the laboratory performance of stabilized base courses with 100% RAP and total stabilizing agent amount of 3% (by weight of RAP). Three stabilizing agents (Portland cement, foamed bitumen, and bitumen emulsion) are evaluated individually and in combination (1.5% Portland cement with 1.5% foamed bitumen, and 1.5% Portland cement with 1.5% bitumen emulsion) to determine the optimal stabilization method using laboratory performance tests and pavement design analysis. Performance evaluation was conducted using the resilient modulus (Mr) test to determine the structural contribution and semi-circular bend (SCB) test for cracking resistance. Pavement designs were done using measured Mr values to compare pavement structures with equivalent structural capacity. Semi-circular bend (SCB) test indicates intermediate temperature cracking resistance of materials using various performance indices (fracture energy, fracture strength, flexibility index and rate-dependent cracking index). The use of Portland cement results in considerably higher stiffness and consequently a thinner pavement structure, but with a significant increase in cracking susceptibility. Mixtures stabilized with foamed bitumen tend to be stiffer than those stabilized with bitumen emulsion but have comparable cracking properties.

Assessment of modified lignin cationic emulsifier for bitumen emulsions used in road paving

This research focuses on a mineral–cement mixture containing bitumen emulsion, designed for cold recycling procedures, the formulation of which includes 80% (m/m) of waste material. Deep cold recycling technology from the MCE mixture guarantees the implementation of a sustainable development policy in the field of road construction. The utilised waste materials include 50% (m/m) reclaimed asphalt pavement (RAP) from damaged asphalt layers and 30% (m/m) recycled aggregate (RA) sourced from the substructure. In order to assess the possibility of using a significant amount of waste materials in the composition of the mineral–cement–emulsion (MCE) mixture, it is necessary to optimise the MCE mix. Optimisation was carried out with respect to the quantity and type of binding agents, such as Portland cement (CEM), bitumen emulsion (EMU), and redispersible polymer powder (RPP). The examination of the impact of the binding agents on the physico-mechanical characteristics of the MCE blend was performed using a Box–Behnken trivalent fractional design. This method has not been used before to optimise MCE mixture composition. This is a novelty in predicting MCE mixture properties. Examinations of the physical properties, mechanical properties, resistance to the effects of climatic factors, and stiffness modulus were conducted on Marshall samples prepared in laboratory settings. Mathematical models determining the variability of the attributes under analysis in correlation with the quantity of the binding agents were determined for the properties under investigation. The MCE mixture composition was optimised through the acquired mathematical models describing the physico-mechanical characteristics, resistance to climatic factors, and rigidity modulus. The optimisation was carried out through the generalised utility function UIII. The optimisation resulted in indicating the proportional percentages of the binders, enabling the assurance of the required properties of the cold recycled mix while utilising the maximum quantity of waste materials.

Cold in-place recycling with bitumen emulsion is a good environmental option for road conservation. The technique produces lower CO2 emissions because the product is manufactured and spread in the same location as the previous infrastructure, and its mixing with bitumen emulsion occurs at room temperature. Adding materials with cementitious characteristics gives the final mixture greater resistance and durability, and incorporating an industrial by-product such as ladle furnace slag (of which cementitious characteristics have been corroborated by various authors) enables the creation of sustainable, resistant pavement. This paper describes the incorporation of ladle furnace slag in reclaimed asphalt pavements (RAP) to execute in-place asphalt pavement recycling with bitumen emulsion. Various test groups of samples with increasing percentages of emulsion were created to study both the density of the mixtures obtained, and their dry and post-immersion compressive strength. To determine these characteristics, the physical and chemical properties of the ladle furnace slag and the reclaimed asphalt pavements were analyzed, as well as compatibility with the bitumen emulsion. The aforementioned tests define an optimal combination of RAP (90%), ladle furnace slag (10%), water (2.6%), and emulsion (3.3%), which demonstrated maximum values for compressive strength of the dry and post-immersion bituminous mixture. These tests therefore demonstrate the suitability of ladle furnace slag for cold in-place recycling with bitumen emulsion.

One of the key goals in the EU White Paper is to reduce carbon emissions in transport by 60% by 2050. Consequently, during the past years an effect on the environment became a decisive factor in selecting materials and technologies for road construction and rehabilitation. Cold recycling is a reasonable solution in asphalt pavement rehabilitation because it is economical and old asphalt pavements can be reused. This technology differs from others by mixing temperature. Besides, cold recycling does not require additional heating. These benefits result in wide application of cold recycling around the world. In Lithuania, cold recycling has been used for more than 15 years. Both technologies, i.e. cold in-plant recycling and cold in-place recycling, were used. In both technologies reclaimed asphalt pavement (RAP) is bound with bituminous binders (foamed bitumen or bitumen emulsion), hydraulic binders (cement) or a combination of bituminous and hydraulic binders depending on the base course specifications. This paper focuses on the Lithuanian experience in cold recycling of asphalt pavements using different types of cold recycling and binders.

Power generation from biomass is one of the most promising energy sources available today. However, this industry has a series of wastes derived from its activity, mainly biomass fly ash and biomass bottom ash. Biomass bottom ash is a waste that has no current use and, in most cases, is deposited in landfills. In turn, road construction is one of the activities that produces the most pollution, as it requires huge amounts of raw materials. Therefore, this research proposes the use of biomass bottom ashes, in an unaltered form, for the formation of cold in-place recycling with bitumen emulsion. This type of mixture, which is highly sustainable owing to the use of a high percentage of waste, was made with reclaimed asphalt pavement, biomass bottom ash, water, and bitumen emulsion. To this end, the grading curve of the materials was analyzed, different bituminous mixtures were made with varying percentages of emulsion and water, and the mechanical properties of the mixtures were analyzed. At the same time, the same type of mix was made with reclaimed asphalt pavement and commercial limestone aggregate, in order to compare the results. The tests showed a better mechanical behavior of the bituminous mixes made with biomass bottom ash, maintaining physical properties similar to those of conventional mixes. In short, it was confirmed that the production of this type of mix with biomass bottom ash was feasible, creating sustainable materials that reuse currently unused waste and avoid landfill disposal.

Crumb Rubber in cold recycled bituminous mixes: Comparison between Traditional Crumb Rubber and Cryogenic Crumb Rubber

This research developed a mechanistic-based framework for recycling rubble materials into high-value-added engineered road structural materials for use in urban road rehabilitation. Scientific-based engineering methods were integrated with advanced materials processing, road construction, and nondestructive asset management techniques to explicitly quantify the benefits of recycled material systems using reclaimed asphalt pavement (RAP) and portland cement concrete (PCC) rubble generated within the city of Saskatoon, Saskatchewan, Canada. The ability to process RAP and PCC rubble to meet or exceed conventional granular aggregate specifications with minimal waste was demonstrated. It was found that RAP and PCC aggregates can exceed the mechanistic material constitutive properties of conventional city of Saskatoon granular base aggregates by at least 30%. The mechanistic material property value of unstabilized RAP and PCC was demonstrated in addition to the benefits of various cold stabilization systems using cement and emulsion. Recycled RAP was used as a black base layer and PCC was used as a subbase course or a drainage and stress-dissipation layer, or both, in rehabilitated road structures of nine “Green Street” test sections constructed in Saskatoon. These test sections met or exceeded target structural designs and were validated by using nondestructive heavy-weight deflectometer testing. The use of recycled RAP and PCC rubble materials for urban road rehabilitation had economic, social, environmental, and energy benefits for the city of Saskatoon. Recycled rubble materials were found to provide a technically viable and cost-effective solution for rehabilitating urban low-volume roads relative to conventional granular aggregates.

In order to investigate the influences of emulsifier types on properties of cement bitumen emulsion mortars (CBEM), anionic and cationic emulsifiers were used to prepare CBEM in this work. Influences of anionic and cationic bitumen emulsions on workability, mechanical properties, and viscoelastic property of CBEM were studied. The workability of CBEM was evaluated by fluidity and extensibility tests. The mechanical properties were assessed by compressive strength and flexural strength tests. XRD was used to analyze the phase before and after bitumen emulsion was added. The viscoelastic property was studied by a dynamic mechanical analyzer (DMA). The results show that CBEM prepared by cationic bitumen emulsion (CBE) has better workability. The mechanical properties of CBEM are negatively affected by bitumen emulsion. The impact on the compressive strength of CBEM prepared by CBE is higher. Bitumen emulsion can significantly improve the viscoelastic property of CBEM. With the increase of bitumen emulsion dosage, the loss factor of CBEM increases. The viscoelastic property at low frequency is better than that at high frequency. In contrast to CBEM prepared by CBE, CBEM prepared with anionic bitumen emulsion (ABE) possesses better viscoelastic property.

The use of reclaimed asphalt pavement (RAP) aggregates in concrete

Cement bitumen emulsion asphalt (CBEA) is obtained by mixing bitumen emulsion, cement, aggregates and filler at ambient temperature. CBEA is thought to be a promising substitute for hot mix asphalt because of its low environmental impact and cost-effectiveness. Disadvantages of this material are the long time required to reach its full strength and the inadequate understanding of the hardening mechanisms. This study aims at accelerating the development of mechanical properties of CBEA by using rapid-hardening cements while at the same time gaining a deeper understanding of the role of cement in CBEA. With this purpose, cold mix asphalt mixtures with cationic and anionic emulsions and different types of cement (ordinary Portland, calcium sulfoaluminate and calcium aluminate cement) were studied by means of isothermal calorimetry, measurements of water evaporation and Marshall tests. The results indicate that both anionic and cationic bitumen emulsions may affect the initial hydration rates of the cements used but have no significant influence on their degree of hydration after a few days. The addition of calcium sulfoaluminate and calcium aluminate cement to CBEA leads to mechanical properties after 1-day curing similar to those obtained with Portland cement after 1-week curing. Cement hydration dominates the strength gain, especially for rapid-hardening cements, and the type of cement influences both the amount of bound water and the rate of water evaporation from the CBEA.

In recent years, global climate change and energy shortages have become serious issues of common concern internationally. The majority of roads and highways are paved using hot mix asphalt (HMA) technology. The manufacture of hot mix asphalt is a key source of energy consumption, greenhouse gas emissions and air pollution. As such, efforts have been made to develop sustainable techniques to reduce energy consumption by lowering manufacturing temperatures, which in turn, will reduce CO2 emissions and subsequent negative impacts on the environment. Cold bitumen emulsion mixtures (CBEMs) are an excellent alternative to traditional HMA, from both an economic and environmental point of views. However, there are certain issues related to the mechanical properties of CBEMs that make them inferior to HMA, limiting their use to low traffic roads, reinstatement works and footways. Accordingly, the development of a CBEM with high early strength and minimal curing time is of increasing interest to researchers in the asphalt industry. The aim of this research work was to develop a new, high performance and environmentally friendly, surface course, cold bitumen emulsion mixture for heavily trafficked roads. This aim has been achieved by i) addressing the longstanding problems associated with conventional bitumen emulsions, namely large and non-uniform distribution of bitumen droplets within the emulsion, and ii) reducing the long curing time of CBEMs by replacing conventional limestone filler (LF) with a new secondary cementitious filler made primarily from waste materials. Ultrasound technology was used to reduce the size of the bitumen droplets through the cavitation phenomenon. A cationic bitumen emulsion (C50B4) was treated using ultrasound apparatus, over different periods of time. The results revealed an 85% reduction in mean droplet size (D50), under 7 minutes sonication treatment compared to the untreated sample. Reductions in D90 and D10 were 90% and 86%, respectively, in comparison to the untreated sample. The particle size distribution (PSD) curve shows more uniformly distributed droplets closer to the mean values, in comparison to the untreated emulsion. The viscosity of the 7minute sonicated bitumen emulsion decreased by 28%, compared to the untreated emulsion. CBEM-LF, made with 7-minute sonicated bitumen emulsion, showed an enhancement in indirect tensile stiffness modulus (ITSM) at 3 days curing by approximately 70%, compared with the same mixture containing conventional bitumen emulsion. To eliminate the long curing time required by CBEMs, a new cementitious filler was developed from waste materials and used as a substitute to conventional LF. The new alkali ternary blended filler, ATBF2, comprises ordinary Portland cement (OPC), a high volume of waste sewage sludge fly ash (SSFA) and calcium carbide residue (CCR). A waste calcium hydroxide solution was used as a replacement for the aggregate pre-wetting water in the CBEM. CCR played a vital role activating the SSFA by breaking the glassy phases of the non-amorphous silica in the SSFA, while the waste calcium hydroxide solution increased the hydraulic reactivity of the cementitious components. Scanning electron microscopy (SEM) and x-ray diffraction (XRD) were used to investigate the development of hydration products in the new CBEM. Concentrations of heavy metals in the samples incorporating ATBF2, were observed to be less than the regulatory levels determined for hazardous materials. The mechanical properties of the novel CBEM incorporating both the sonicated bitumen emulsion and ATBF2 filler, were investigated in terms of ITSM at different curing times, rutting resistance, fatigue resistance, water damage resistance and age hardening. The said mixture offers a substantial improvement in stiffness modulus, compared to HMA and CBEM containing conventional emulsion and LF. The ITSM for the newly developed CBEM at 3 days of age, increased by approximately 19 times that of the conventional cold mixture, and almost 2.5 times that of traditional 100/150 HMA. The new mixture also displayed considerably higher resistance to permanent deformation in comparison to the reference cold and hot asphalt mixtures, demonstrating its potential for use in heavily trafficked roads. Resistance to fatigue was significantly enhanced by the use of both ATBF2 and the modified emulsion in the CBEM, compared to conventional cold and hot mixtures. This mixture is more durable because of improvements in resistance to water damage and enhanced long term ageing performance. This improvement has been achieved by the presence of smaller bitumen droplets that provide more bitumen surface area and even coating of aggregate particles. This helps form a cohesive mixture working in parallel with the hydration products which resulted from the hydration process of the cementitious filler in the presence of water within the bitumen-water solution.

Rehabilitation and repair of flexible pavements produce huge amounts of reclaimed asphalt pavement (RAP) material. Using RAP in the formulation of portland cement concrete (PCC) is a technique that is part of a sustainable development approach since it reduces on the consumption of new aggregates and reuses a material that is considered as waste. This paper describes the semi-adiabatic calorimetry test performed on a concrete mix incorporating RAP material as aggregate. Results showed that the cement hydration process is not affected by the presence of asphalt coated on the surface of RAP material. Classical tests (compressive strength, flexural and indirect-tensile strengths, elastic modulus, and free-shrinkage) were also performed on PCC mixes incorporating different percentages of RAP. It was found that as the percentage of RAP increases, the PCC mechanical properties decrease. This is mainly attributed to the presence of voids in the transition zone between the asphalt-coated aggregates and the hydrated cement paste as confirmed by scanning-electron microscope images. Unrestrained shrinkage testing showed statistically insignificant change in shrinkage strain with RAP content. The strength and shrinkage results lead to conclude that as much as 40% of RAP could be incorporated into the formulation of PCC and achieve properties that are acceptable for the construction of rigid pavements.

Characterization of fatigue performance of cold mix recycled asphalt mixtures through uniaxial tension–compression testing

This study explores the use of reclaimed asphalt pavement (RAP) as a sustainable and cost-effective substitute for coarse natural aggregates in concrete. Concrete mixtures were prepared with RAP replacement levels of 0%, 15%, 30%, 50%, and 80% by weight, aiming for a minimum compressive strength of 240 ksc in 15x15x15 cm cube specimens after 28 days of curing. Key engineering properties including compressive strength, flexural strength, and modulus of elasticity were evaluated. The results show that increasing the RAP content leads to greater deviation from optimal aggregate gradation and a gradual decrease in both compressive and flexural strengths. Nevertheless, mixtures containing up to 30% RAP met the target compressive strength (exceeding 240 ksc) and achieved flexural strengths over 24.6 ksc 11% above the design specification. At a 50% RAP replacement, compressive strength remained above 180 ksc and flexural strength still exceeded 24.6 ksc. The modulus of elasticity decreased with higher RAP content, ranging from 5,000 to 25,000 MPa (53,986 to 254,930 ksc). Economically, using 30% RAP reduced the production cost by 6.89%, while a 50% RAP substitution resulted in a 12.03% cost reduction compared to conventional concrete. These findings highlight RAP’s potential as a viable alternative in concrete for applications with moderate strength requirements. GRAPHICAL ABSTRACT HIGHLIGHTS A 30% RAP replacement in concrete achieved a compressive strength exceeding 240 ksc and a flexural strength greater than 24.6 ksc, which is 11% above the design specification. With a 50% RAP replacement, the concrete maintained a compressive strength above 180 ksc and a flexural strength exceeding 24.6 ksc, although the modulus of elasticity decreased with higher RAP content. Economically, a 30% RAP replacement reduced production costs by 6.89%, while a 50% replacement resulted in a 12.03% cost reduction compared to conventional concrete.