Recycled Mixes Research Articles

The Influence of the Binder in RAP on Recycled Asphalt Properties

ABSTRACT A virgin mix and a recycled mix (containing 50% RAP) were manufactured so as to have identical aggregate grading and binder content. The viscosity of the binder in the recycled mix was also identical to that in the recycled mix, assuming complete intermixing of the hardened RAP binder with the added fresh binder. The mechanical properties of the two mixes were compared and it was found that the recycled mix had a lower modulus, a higher wheel tracking rate and a lower fatigue life than the virgin mix. This indicated that the two binders in the recycled mix had not been completely mixed and reasons for this are proposed. RAP often contains aggregate/binder or filler/binder agglomerations which it is difficult for the fresh bitumen or rejuvenating agent to penetrate. Some of the fresh bitumen in the recycled asphalt then forms a “shell” round the aged binder-coated aggregate particles or the binder aggregate agglomerations which came from the RAP. There are thus regions of low viscosity (fresh binder) in the recycled mix and this influences its mechanical properties.

Effect of Recycle and Axial Mixing on Microbial Selection in Activated Sludge

A mathematical model was developed to simulate the effect of axial mixing and recycle on competition between filamentous and floc-forming microbial populations based on the Monod equation and the plug flow with recycle flow model, and a matched artificial recycle ratio was defined to include the effects of both axial mixing and recycle flow on the residence time distribution. The model predicted that low recycle ratios (R 10) eventually eliminated the competitive advantage of the floc-formers over the filaments. The feed concentration was also an important factor in microbial selection with a predominantly filamentous biomass predicted when R> 0.1 and Si< 100 mg/L as COD. An operating diagram prepared based on the model output showed that a high recycle ratio and/or low feed concentration favored filamentous domination, while floc-formers dominated at a low recycle ratio and/or high feed concentration. Strategies to control or...

Adapting Superpave Technology to Design of Hot Recycled Mixes

Abstract Mix design procedures for recycled asphalt pavements require the selection of virgin asphalt or recycling agent and recycled hot mix asphalt (HMA) mix design. This research project was undertaken (a) to develop a procedure for selecting the performance grade (PG) of virgin asphalt binder based on the Superpave PG grading system and (b) to design hot recycled mix using Superpave technology. Blending charts were constructed and used to select the PG grade of virgin asphalt binder for mixes with 0, 20, 30, and 40 percent of recycled asphalt pavement material (RAP). Superpave volumetric mix design were conducted on mixes with 0, 20, 30, and 40 percent RAP. Evaluation of the volumetric properties of these mixes has indicated that the Superpave volumetric mix design procedures can be adapted to design recycled HMA mixtures with minimal modification.

A comparison of the predicted performance of virgin and recycled mixes

The Marshall design method is the most commonly used method for the design of virgin and recycled mixes. However, the Marshall design procedure does not provide the field performance of the mix in terms of fatigue, rutting, thermal cracking, and moisture damage. The Asphalt Aggregate Mixture Analysis System (AAMAS) and the program called SUPERPAVE, developed in Strategic Highway Research Program, are two performance-based mix design methods that can address most forms of pavement distress. Although the AAMAS program was developed using virgin mixes, the AAMAS design criterion for this study was applied to recycled mixes. Specifically, the predicted performance of recycled mixes was compared with that of virgin mixes. In general, all of the mixes evaluated satisfied the AAMAS criteria. However, the results indicated that the fatigue resistance decreased as the recycling percentage increased. The recycled mixes had higher resistance to moisture damage when compared with virgin mixes.

Recyclability of Moisture Damaged Flexible Pavements

Stripping has damaged some of South Carolina's asphaltic concrete pavements. It is not known whether the material properties of stripped asphalt pavement will allow its use for recycling. A field and laboratory study was initiated to investigate the feasibility of reusing moisture‐damaged asphaltic concrete; to determine the effects of antistrip additives on recycled mixtures; and to evaluate the recycled mix design procedures that use cored reclaimed asphalt pavement (RAP) instead of milled RAP. A total of 144 laboratory Marshall specimens were made and tested. In addition, field cores were obtained and tested before and after recycling. The dry and wet modulus resilience (MR) and indirect tensile strength (ITS), visual strip rating (VSR), and air voids (AV) of all specimens were obtained. Marshall specimens containing moisture‐damaged asphaltic concrete mixtures produced significantly higher strength values than those using only virgin material. Antistrip agents were found to be effective in increasing ...

Microbial recolonization and suppression of Rhizoctonia solani in a bedding-plant potting mix amended with recycled mix before aerated-steam treatment

Some South Australian bedding-plant nurseries add recycled potting mix to fresh potting mix before aerated-steam treatment in an attempt to decrease fungal root diseases. To test the hypothesis that this addition of recycled potting mix affects microbial colonization and, consequently, the disease-suppressiveness of mixes treated with aerated steam, recycled potting mix was added to or withheld from fresh potting mix. The mixes were then treated with aerated steam at 60°C for 35 min or not treated. Their recolonization by actinomycetes, heat-resistant organisms, pseudomonads, and fungi was followed for 25 days. The addition of recycled potting mix frequently increased the numbers of actinomycetes and heat-resistant microbes recovered from the mixes, whether treated with steam or not, but decreased the numbers of aerobic bacteria. Fungal populations were rarely influenced by the addition of recycled potting mix. Pseudomonad populations dropped to undetectable levels after the aerated-steam treatment and failed to reach levels comparable to those in treatments without steam during the next 25 days. Organisms from each group were tested for in vitro antagonism to Rhizoctonia solani Kuhn (AG-8). The proportion of inhibitory organisms varied with the microbial group, the mix treatment, and the time since mix treatment. Where aerated-steam treatment was applied, the addition of recycled potting mix rarely affected the development of Rhizoctonia disease symptoms on seedlings of Celosia argentea. The potential for improving the suppressiveness of aerated-steam-treated nursery mixes via microbial inoculation is discussed.

Behaviour of recycled asphalt pavements at low temperatures

This paper summarizes the results of a study conducted to evaluate the behaviour of recycled asphalt pavements with respect to low-temperature cracking. For this purpose, a recycled mix consisting of 45.2% reclaimed materials and 54.8% virgin materials as well as a virgin control mix were used in the research program. In the design of both mixes, their initial properties were kept as close as possible to each other to allow for a proper comparison between recycled and virgin asphalt pavements. Using mix properties that were determined experimentally in the laboratory, thermal stresses resulted from drop in temperature and the expected cracking temperatures were determined for both mixes. An experimental analysis based on laboratory tests that consider the pavement properties only as well as a more complete theoretical analysis based on a finite element computer program known as FETAB were included in this study. The program incorporates subgrade parameters, as well as pavement properties and thickness. Using these variables as inputs to the program, the expected performance of recycled and virgin asphalt pavements of various thicknesses and resting on different types of subgrade, with respect to low-temperature cracking, was studied. The results of the study indicated that recycled asphalt pavements would perform better than virgin asphalt pavements of similar initial properties. Key words: asphalt, finite element, low-temperature cracking, reclaimed, recycled, thermal stresses.

An internal recycle mixer for solvent extraction. Mass transfer characterization with liquid surfactant membranes

A novel internal recycle mixing device, in which the solvent-to-feed ratio may be enhanced without the introduction of an external recycle stream, is proposed. The device was tested on, and found to be effective for, the extraction of ammonia from water using a liquid surfactant membrane (LM) system. A detailed model of the mass transfer processes occurring within the system is presented and used to develop an equation suitable for th sizing of LM contactors. This equation accounts for the effect of the internal reagent on the overall mass transfer rate. The experimental data are in favorable agreement with the model predictions.