Recycling waste oil from a power plant to asphalt

Bitumen deterioration is one of the main challenges of using recycled asphalt pavement (RAP) in hot mix asphalt (HMA); thus, the proportion of RAP in the HMA is restricted. The latest research published in Mmaterials evaluates the rheological characteristics of RAP bonding as well as the effectiveness of HMA with a high concentration of RAP while using residual engine oil (WEO).

Study: Investigation of Waste Power Plant Oil as a Rejuvenating Agent for Recovered Asphalt Binders and Mixtures. Image Credit: DifferR/Shutterstock.com

Industrial relevance of bitumen

Bitumen is one of the most commonly used binder ingredients for asphalt pavements. The paving industry consumes approximately 95% of all bitumen generated worldwide each year. Dwindling amounts of commonly accessible good quality resources, escalating waste disposal issues and soaring bitumen costs have contributed to the increased use of recycled asphalt pavement (RAP) in project development. infrastructure.

Flowchart of the experimental program.

Flowchart of the experimental program. Image credit: El-labbad EM et al., Materials

Pavement Recycling for Recycled Pavement Asphalt

Pavement regeneration includes the use of old or damaged materials in the creation of new pavements. When the proportion of asphalt used in the hot mix asphalt (HMA) approaches 25% or more, the mix design process takes into account the percentage of bitumen in the mix.

Moisture degradation, stress and thermal degradation are practically expected to occur in reused high RAP mixes as the bitumen stiffens. Therefore, the characterization of the binder and the RAP aggregates is a critical step in the design process.

RAP Binder Aging – A Critical Issue

The main difficulty that has limited the use of RAP material to small percentages is the aging of the RAP binder. The aging of the bitumen leads to excessive crumbling of the pavements. As a result, the expenses for the reconstruction and maintenance of bituminous pavements increase.

The term “asphalt aging” most likely leads to variations in the rheological properties of the RAP binder caused by chemical and thermal fluctuations. The aging of the RAP binder has a significant impact on its rheological characteristics, impacting the overall efficiency of the asphalt pavement.

Brookfield viscosity of virgin bitumen, recovered and rejuvenated by WEO content.  (A) RCRD recovered aged binder;  (B) Recovered aged binder RNCCD.

Brookfield viscosity of virgin bitumen, recovered and rejuvenated by WEO content. (A) recovered aged binder RCRD; (B) RNCCD aged binder recovered. Image credit: El-labbad EM et al., Materials

Importance of the rejuvenation process

The most common method of restoring the characteristics of the RAP binder to a state similar to virgin bitumen is rejuvenation. Additives, renewing (recycling) compounds and softening substrates are commercially available and can be used on RAP pavements. Recycling chemicals is an effective approach to reducing stiffness while increasing the percentage of RAP in the mix.

The effectiveness of the recycling agent is mainly determined by the initial source. The main difference between softening and rejuvenating substances is that rejuvenating agents can preserve the chemical composition of aging bitumen.

Waste oils as a source of asphalt rejuvenation

Making asphalt reclaimers from waste oil has gained popularity in recent years. Filtration, separation and mixing are all common operations in the manufacture of regenerators. The rejuvenation system works by restoring the colloidal architecture of bitumen and improving molecular mobility. Bio-oils can renew the binder of aging.

They can be used to soften aged bitumen and reduce stiffness in binders and high-RAP mixes, according to recent research results. Moreover, according to a recent study, the inclusion of bio-binder increased the quality of the asphalt binder at high temperatures while decreasing it at low temperatures.

Waste engine oil (WEO) from power plant machinery is one of the municipal waste resources that can be used to renew the RAP binder. It is a technologically modified heavy-duty oil blend that, unlike automotive engine oils, retains the correct oil viscosity under severe working conditions.

Stream number results.

Stream number results. Image credit: El-labbad EM et al., Materials

search results

For the RCRD adhesive, the WEO was mixed with the RAP binder in proportions of 0.5, 2.0 and 3.0% of the total bitumen mass. The inclusion of WEO lowered the sweet point temperature of the reclaimed bitumen. The proportions of WEO achieved for the recovered aged binders RCRD and RNCCD were 0.5% and 3%, respectively.

The high viscosity of the old bitumen was the greatest. Viscosity values ​​were comparable to virgin bitumen when 0.5% and 3% WEO were added to recoverable bitumen for RCRD and RNCCD recovered binders, respectively.

It was found that the increase in WEO corresponded to a reduction in all morphological indices, implying a reduction in aging. The introduction of 3% WEO reduced the structural indices to those of the virgin binder. This decrease in sulfoxides and carbonyls indicates a chemical modification of the bituminous binder. Additionally, as the tensile stress ratio improved, the resilience to moisture damage also increased.

In summary, the addition of WEO to the recycled mix weakened the RAP binder, lowering the cyclic modulus of the reclaimed mixes and making them more resistant to fatigue failure.

Further reading

El-labbad EM, Heneash U, El-Badawy SM. (2022). Investigation of waste power plant oil as a rejuvenating agent for reclaimed asphalt binders and mixes. Materials. 15(14). 4811. Available at: https://www.mdpi.com/1996-1944/15/14/4811

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