Successful Use of Reclaimed Asphalt Pavement in Asphalt Mixtures

Over 99 percent of reclaimed asphalt pavement (RAP) is put back to use, with most of it in asphalt pavements. Using RAP in asphalt mixtures can provide initial cost savings by replacing a portion of the aggregate and virgin asphalt binder in the asphalt mixture. It is important to consider the engineering performance of mixture containing RAP, as well as sustainable benefits and recognize that long RAP transportation distances can offset the environmental benefits. This keeps the RAP from being discarded in landfills. Improvements in mixture design and materials processing and handling have increased the amount of RAP that can be used in asphalt mixtures. The performance history of RAP mixtures over the past 50 years, when properly engineered, produced, and constructed, can provide comparable levels of service as asphalt mixtures with no reclaimed materials, referred to as virgin asphalt mixtures. The participating State DOTs indicated that optimizing RAP for good pavement performance can be accomplished through: 1) regular review of DOT specifications and mixture design procedures; 2) monitoring pavement performance; 3) working with asphalt producers, and 4) performing research as a basis for changes. However, in some cases, the durability of asphalt mixtures containing RAP has been poor. Additionally, State DOT rationale for using RAP can be for very different reasons with different goals. Virtual field visits of State DOTs regularly using RAP in asphalt mixtures revealed that DOTs with detailed policy and specifications on RAP use had obtained good control and pavement performance. A wide range of techniques and criteria used by State DOTs specifying and designing mixtures and pavements incorporating RAP were identified and summarized. All of the participating State DOTs indicated the desire to use mixture performance tests. Some wanted to use them for mixture designs in a BMD approach, for test strips (startup evaluations) and production or acceptance. Common themes with this were the need to get adequate virgin asphalt binder in mixtures, the need for appropriately setting performance test criteria and recognition of the benefit of long-term aging cracking test specimens. Another common theme was recognition that the resources required to implement BMD or use of performance tests on a regular basis are significant and may not be available in the short-term

Moisture sensitivity examination of asphalt mixtures using thermodynamic, direct adhesion peel and compacted mixture mechanical tests

Moisture damage in asphalt mixtures is a complicated mode of pavement distress that results in the loss of stiffness and structural strength of the asphalt pavement layers. This paper evaluated the moisture sensitivity of different aggregate–bitumen combinations through three different approaches: surface energy, peel adhesion and the Saturation Ageing Tensile Stiffness (SATS) tests. In addition, the results obtained from these three tests were compared so as to characterise the relationship between the thermodynamic and the mechanical tests. The surface energy tests showed that the work of adhesion in dry conditions was bitumen type dependent, which is in agreement with the peel test. After moisture damage, all of these three tests found that the moisture sensitivity of aggregate–bitumen combinations were mainly aggregate type dependent. Based on the peel test, the moisture absorption and mineralogical compositions of aggregate were considered as two important factors to moisture sensitivity. This phenomenon suggests that in a susceptible asphalt mixture, the effect of aggregate may be more influential than the effect of bitumen. The SATS test and the peel test showed similar moisture sensitivity results demonstrating the good correlation between these two mechanical tests. However, the surface energy tests and the mechanical tests cannot correlate in terms of moisture sensitivity evaluation

Experimental evaluation of cohesive and adhesive bond strength and fracture energy of bitumen-aggregate systems

Degradation of asphalt pavements is an inevitable phenomenon due to the combined effects of high traffic loads and harsh environmental conditions. Deterioration can be in the form of cohesive failure of the bitumen and/or bitumen-filler mastic or by adhesive failure between bitumen and aggregate. This paper presents an experimental investigation to characterise the cohesive and adhesive strength and fracture energy of bitumen-aggregate samples. The pneumatic adhesion tensile testing instrument test and the peel test were used to quantify the tensile fracture strength and fracture energy of different bitumen-aggregate combinations, with a view to analyse the influence of several parameters on the strength of the bitumen film or bitumen-aggregate interface. From the experimental results, harder (40/60 pen) bitumen tends to show much higher tensile strength and fracture energy than softer (70/100 pen) bitumen. Tensile strength is shown to be sensitive to testing temperature with the failure regime changing from cohesive to mixed cohesive/adhesive failure with decreasing temperature. In addition, the results show that aggregate properties do not influence the bonding strength if cohesive failure occurs, but with adhesive failure, granite aggregate tends to produce a higher bonding strength than limestone aggregate in the dry condition. In terms of the peel test, the fracture energy experienced an increasing trend with increasing film thickness. However, the normalised toughness decreased when film thickness increased from 0.2 to 0.9 mm

Moisture damage assessment using surface energy, bitumen stripping and the SATS moisture conditioning procedure

Durability is one of the most important properties of an asphalt mixture. A key factor affecting the durability of asphalt pavements is moisture damage. Moisture damage generally results in the loss of strength of the mixture due to two main mechanisms; the loss of adhesion between bitumen and aggregate and the loss of cohesion within the mixture. Conventional test methods for evaluating moisture damage include tests conducted on loose bitumen-coated aggregates and those conducted on compacted asphalt mixtures. The former test methods are simpler and less expensive to conduct but are qualitative/subjective in nature and do not consider cohesive failure while the latter, though more quantitative, are based on bulky mechanical test set-ups and therefore require expensive equipment. Both test methods are, however, empirical in nature thus requiring extensive experience to interpret/use their results. The rolling bottle test (RBT) (EN 12697-11) for loose aggregate mixtures and the saturation ageing tensile stiffness (SATS) test (EN 12697-45) for compacted asphalt mixtures are two such methods, which experience suggests, could clearly discriminate between ‘good’ and ‘poor’ performing mixtures in the laboratory. A more fundamental approach based on surface energy (SE) measurements offers promise to better understand moisture damage. This article looks at results from the rolling bottle and the SATS tests in an attempt to better understand the underlying processes and mechanisms of moisture damage with the help of SE measurements on the constituent bitumen and aggregates. For this work, a set of bitumens and typical acidic and basic aggregate types (granite and limestone) were selected. Combinations of these materials were assessed using both the rolling bottle and SATS tests. The SE properties of the binders were measured using a dynamic contact angle Analyser and those of the aggregates using a dynamic vapour sorption device. From these SE measurements it was possible to predict the relative performance of both the simple RBT and the more complicated SATS test. Mineralogical composition of the aggregates determined using a mineral liberation analyser was used to explain the differences in performance of the mixtures considered

Tech Brief: Resource Responsible Use of Reclaimed Asphalt Pavement in Asphalt Mixtures

This Technical Brief summarizes techniques employed by State DOTs in the use of high doses of reclaimed asphalt pavement (RAP) in asphalt mixtures and communicates the benefits observed.U.S. Department of Transportatio

WRSC-TR-20-01

The use of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) in asphalt mixtures can provide initial cost savings through the replacement of a portion of the aggregate and virgin asphalt binder in a mixture for use in highways and trails. This keeps the reclaimed material from being discarded in landfills. Improvements in mixture design and materials processing and handling have increased the amount of RAP and RAS that can be used in asphalt mixtures today. The performance history of RAP mixtures over the past 40 years and RAS over the past 20 years, when properly engineered, produced, and constructed, can provide comparable levels of service as asphalt mixtures with no reclaimed materials, referred to as virgin asphalt mixtures. However, in some cases durability of asphalt mixtures containing RAS has been poor. Additionally, agency rationale for using RAS can be for very different reasons with different goals. Field visits of six agencies regularly using RAS in asphalt mixtures took place in the Summer of 2019. This effort showed that agencies with detailed policy and specifications on RAS use had the best control and performance. Field performance reviews of in-service pavements up to 9 years old containing RAS or RAP and RAS revealed that with appropriate policy, mixture design and control of quality, good performance can be obtained. This was typically obtained through the following comprehensive steps: 1) regular and diligent review of specifications and mixture design procedures, 2) monitoring pavement performance, 3) working with industry and 4) performing research as a basis for changes

Tech Brief: Asphalt Pavement Recycling Technologies

This Technical Brief summarizes techniques successfully used by State DOTs and Federal Lands Highway Divisions to implement use of cold asphalt and hot in-place asphalt recycling technologies.U.S. Department of Transportatio

DAPT series - Resource Responsible Use of High RAP (up to 50%) Asphalt Mixtures

FHWA COOPERATIVE AGREEMENT No. 693JJ31850010 “Development and Deployment of Innovative Asphalt Pavement Technologies