Conventional Hot Mix Asphalt Research Articles

Life Cycle Cost Analysis Comparison of Hot Mix Asphalt and Reclaimed Asphalt Pavement: A Case Study

In the construction and maintenance of asphalt pavement, reclaimed asphalt pavement (RAP) is being widely used as a cheaper alternative to the conventional hot mix asphalt (HMA). HMA incorporated with a high RAP content (e.g., 40%), which is the most commonly used, may have prominent adverse effects on life cycle, performance properties, and related costs. Thus, before utilizing RAP, it is essential to investigate whether it is still economical to use under the local climate by taking into consideration the life cycle performance. Therefore, for this paper, a case study was conducted using 20% RAP, assessed in terms of materials related to cost analysis. The results of the analysis showed that, from the total life cycle costing measurement, a total of 14% cost reduction was reported using RAP as compared to conventional materials. Moreover, the two materials (conventional HMA and RAP) are manufactured in different types of manufacturing plants. Thus, in analyzing the cost difference between the two chosen manufacturing plants for virgin materials and RAP, a total of 57% cost reduction was observed for a RAP manufacturing plant. Besides this, no cost difference was observed in the rest of the phases, such as manpower, materials transportation, and construction activities, as the same procedures and types of machinery are used. Furthermore, assessing the carbon dioxide impact and cost, the transportation and machinery emissions were considered, while the plant’s operation emission was omitted due to the unavailability of the data.

Mechanical performance and global warming potential of unaged warm cup lump modified asphalt

The use of natural rubber modified bitumen to improve pavement performance exist over a century. However, few documented research explore its mechanical performance in warm mix asphalt (WMA). This paper examined the rutting, moisture damage, tensile properties and carbon emission of cup lump rubber modified asphalt (CMA) in hot mix asphalt (HMA) and WMA. Aggregate coating and compactability tests were employed to select the production temperature of the WMA. The result shows that the warm cup lump modified asphalt (WCMA) has excellent rutting resistance of less than 2 mm rut depth at 8000 load repetitions representing 21% improvement compared with the conventional HMA. The tensile property was improved by 62% due to cup lump rubber (CLR) modification. Moisture damage evaluation shows that the WCMA retained more than 95% bitumen coating and has a tensile strength ratio (TSR) value of 99%, thus fulfilling the AASHTO T283 minimum requirement of 80%. The asphalt mixtures resistance to severe condition of stripping and rutting happening simultaneously revealed that the mixes are more sensitive to rutting than the stripping component of the APA-moisture damage test. The emission test result shows that producing WCMA at 40 °C lower than CMA reduced 5 kg of CO2 equivalent, amounting to 23% reduction in global warming potential. The multi-attribute analysis combined the mechanical performance results and environmental impact to rank WCMA as the optimum mixture for future road construction.

Sustainable Development with Microsurfacing: A Review

Abstract In recent times, sustainable development has been the primary focus of research and development in the pavement industry. In this respect, microsurfacing was viewed as sustainable pavement preservation and has emerged as a cost-effective pavement maintenance alternative for enhancing performance, increasing service life, and ensuring safety with minimal environmental impact. In this review, the impact of microsurfacing application on the economic, social, and environmental components were explored from the published literature. Studies show that with microsurfacing application, there was a 31 % savings in cost as compared with conventional hot-mix asphalt. Furthermore, a brief economic analysis was carried out, which confirmed microsurfacing as one of the most cost-effective preventative treatment with minimum equivalent uniform annual cost. However, the economic benefits of microsurfacing were dependent upon distress type and intensity, pavement age, climatic conditions, and traffic volume. In addition, the social benefits included enhanced skid resistance, reduced hydroplaning, better riding quality, and pleasing aesthetic appearance. Moreover, the main environmental benefits of microsurfacing, as reported by various researchers, included low energy consumption, reduced greenhouse gas emission, conservation of natural resources, and reduction in tire-pavement noise. Review also reported the strength, weakness, opportunities, and threats of microsurfacing application. Even with certain weakness and probable challenges, application of microsurfacing showed enormous potential for further improvement. Incorporation of recycled or waste materials, compaction prior to opening for traffic, and project-related specifications are some areas for further research. However, certain challenges, like insufficient fund allocation, implementation or performance issues, and production variability, had to be mitigated for smooth and rapid development. Thus, with encouraging results and a promising future, microsurfacing had excelled in both technological and sustainability aspects.

Economic and Environmental Cost Analysis of Cold In-Place Recycling

The purpose of this study is to evaluate and quantify the construction costs, energy costs, and environmental benefits of using cold in-place recycling (CIR) as a pavement rehabilitation technique. For this study, the costs of using CIR mixes prepared using either asphalt emulsion (CIR-E) or foamed asphalt (CIR-F) were compared with conventional 5.1-cm (2-in.) hot-mix asphalt (HMA) mill and overlays. Three different costs were considered for the production of each pavement rehabilitation technique: (1) construction, (2) energy, and (3) environmental costs. To facilitate the cost comparisons, an equivalent pavement structural analysis was conducted between each pavement rehabilitation technique using a standard design method. The results of the study showed that initial construction costs of using CIR are less than the conventional HMA mill and overlay. The energy and environmental costs were also found to be much lower for CIR mixtures compared with the HMA mill and overlay, with energy savings of up to 63%. Overall, when considering all costs, the use of CIR has lower costs compared with traditional HMA overlays. Cost savings of approximately $34,000–$39,000 were observed when using CIR with HMA overlays, with a total cost savings between 41% and 47% over traditional HMA mill and overlays. This study gives an overall procedure for assessing the economic and environmental costs of different pavement rehabilitation techniques and provides further evidence of the cost benefits associated with CIR to practitioners.

Estimation of Reclaimed Asphalt Pavement (RAP) characteristics using simple indicative tests

The design of hot recycled asphalt mixes with high RAP content, say more than 25%, as per existing guidelines is complex compared to the conventional Hot Mix Asphalt (HMA) design. This is due to the fact that the mix design requires the properties of bitumen in the RAP material and hence, it involves using solvents to recover the bitumen and testing of the recovered bitumen using sophisticated equipment. Considering the issues associated with bitumen recovery procedure that were reported in the literature and the practicalities involved in testing the recovered bitumen, the present study aims to identify indices that can reasonably estimate the RAP characteristics without the need to recover the bitumen. For this purpose, two tests namely, the Fragmentation test and Cohesion test that were proposed by the RIlEM Technical Committee 237-SIB committee for RAP classification for cold mix design were evaluated. These two tests can be conducted using conventional apparatus used for quality control tests that are available at most of the field laboratories. Fragmentation test was carried out on six different RAP sources and at three different conditioning temperatures (5°C, 20°C, and 40°C). Cohesion test was carried out on RAP from five different sources at five conditioning temperatures (70°C, 100°C, 140°C, 170°C, and 190°C). The test results suggest that the index derived from fragmentation test (S frag) correlated well with the physical properties of recovered bitumen such as penetration, softening point, and complex shear viscosity. Further, the index was able to estimate the difference in % of fines in black and white curves. The sensitivity of the air voids and Indirect Tensile Strength (ITS) of the Marshall specimen (S air voids and S ITS) obtained from the cohesion test correlated well with bitumen content and bitumen type respectively.

Improving fracture and moisture resistance of cold mix asphalt (CMA) using crumb rubber and cement

Due to environmental and economic advantages, cold mix asphalt (CMA) can be considered as a good alternative to conventional hot mix asphalt (HMA). Nevertheless, it has inferior performance compared to HMA, so that the application of CMA is not recommended in the surface layer of pavements subjected to high traffic volume and/or regions with very cold or hot climate. Considering the high potential of distress occurring in the CMAs, this research is aimed at investigating the effect of crumb rubber (CR) on fracture and moisture damage resistance of the CMAs. Different CR percentages were applied through two different modification methods and, then by means of Semi-Circular Bending (SCB) test, the fracture energy and flexibility index (FI) of modified CMAs were obtained and compared with the unmodified HMA and CMA. The moisture sensitivity of the modified CMAs was also evaluated using modified AASHTO T 283. Moreover, the effects of the addition of cement along with CR were investigated. The results show that simultaneous use of 14% CR and 2% cement in the CMA can considerably improve the fracture and moisture damage resistance so that it has comparable performance to the conventional HMAs.

Warm asphalt rubber: A sustainable way for waste tire rubber recycling

Recycling end-of-life tire rubber as asphalt modifier is known as a sustainable paving technology with merits including enhanced pavement durability, waste tire consumption and noise reduction. However, the criticisms on the high construction emissions of asphalt rubber (AR) have limited its application. Warm mix asphalt (WMA) effectively reduces the mixing and compaction temperatures of conventional hot mix asphalt mixtures. The combination of AR and WMA, called warm asphalt rubber (WAR), is a promising paving material which achieves pavement sustainability from principles to practices. Many studies have demonstrated that WMA technologies work effectively with AR pavement in different ways, alleviating the concerns of potential higher emissions of AR by decreasing mixing and paving temperatures. A comprehensive literature review about WAR brings a better understanding of this promising paving technology. The findings of 165 publications were summarized in this review. It summarized the recent developments of WAR in various aspects, including rheological properties, mix design, mixture mechanical performance, field application, construction emission, and asphalt-rubber-WMA additive interaction. It is expected that this review is able to provide extensive information to explore further research development and application of WAR.

Influence of recycled concrete aggregates from different sources in hot mix asphalt design

The waste generated by the construction industry generally has an undesired negative impact on both human and animal life as well as the environment. Among these wastes, recycled concrete aggregate (RCA), due to its good residual physical, mechanical, mineralogical, and chemical properties, has attracted promising potential for re-use and incorporation in the construction of new infrastructural elements. These infrastructure applications include construction of sidewalks, curb and gutters, subbase/base layers, and/or as a partial replacement of natural aggregates (NA) in the production of hot mix asphalt (HMA) mixtures. In this laboratory study, experimental research work was conducted to evaluate the influence of RCA on the mechanical properties and performance of RCA modified HMA mixtures against a control HMA mixture without any RCA. RCAs were obtained from two different concrete sources, namely: (a) one from the demolition of a building (RCAB), and (b) another one from the rehabilitation of a Portland cement concrete pavement (RCAP). Both NA and RCA were characterized taking into account physical and mechanical properties. HMA mixtures were produced using the Marshall mix-design method by replacing 0.0% (control), 15%, 30%, and 45%, respectively, of the coarse NA fraction with RCA. Thereafter, laboratory testing (i.e., Scanning Electron Microscopy [SEM], resilient modulus, indirect tensile strength, etc.) including material property characterization and performance evaluation were conducted on HMA samples. Overall, the laboratory test results showed that the RCA modified mixtures exhibited a similar behavior to conventional HMA mixtures, but with greater environmental benefits and potential cost savings through the recycling and reuse of waste concrete aggregates. However, it was observed that the laboratory performance of RCA modified mixtures is strongly dependent on the RCA source and dosage, with RCAP exhibiting superior performance over RCAB. HMA mixtures produced with RCA provided higher optimum asphalt-binder content (OAC) than that of mixes with NA.

Artificial Intelligence-Based Model for the Prediction of Dynamic Modulus of Stone Mastic Asphalt

Stone Mastic Asphalt (SMA) is a tough, stable, rut-resistant mixture that takes advantage of the stone-to-stone contact to provide strength and durability for the material. Besides, the warm mix asphalt (WMA) technology allows reducing emissions and energy consumption by reducing the production temperature by 30–50 °C, compared to conventional hot mix asphalt technology (HMA). The dynamic modulus |E*| has been acknowledged as a vital material property in the mechanistic-empirical design and analysis and further reflects the strains and displacements of such layered pavement structures. The objective of this study is twofold, aiming at favoring the potential use of SMA with WMA technique. To this aim, first, laboratory tests were conducted to compare the performance of SMA and HMA through the dynamic modulus. Second, an advanced hybrid artificial intelligence technique to accurately predict the dynamic modulus of asphalt mixtures was developed. This hybrid model (ANN-TLBO) was based on an Artificial Neural Network (ANN) algorithm and Teaching Learning Based Optimization (TLBO) technique. A database containing the as-obtained experimental tests (96 data) was used for the development and assessment of the ANN-TLBO model. The experimental results showed that SMA mixtures exhibited higher values of the dynamic modulus |E*| than HMA, and the WMA technology increased the dynamic modulus values compared with the hot technology. Furthermore, the proposed hybrid algorithm could successfully predict the dynamic modulus with remarkable values of R2 of 0.989 and 0.985 for the training and testing datasets, respectively. Lastly, the effects of temperature and frequency on the dynamic modulus were evaluated and discussed.

Laboratory evaluation of foamed asphalt mixtures with 100% RAP and rejuvenator

ABSTRACT This study, conducted in Georgia, analyzes the impact of rejuvenators on foamed asphalt mixtures containing 100% reclaimed asphalt pavement (RAP) and assesses the feasibility of using the mixture as a structural layer in a pavement system. Three laboratory tests, the Marshall stability (MS), indirect tensile strength (ITS), and semi-circular bending (SCB), were conducted for the structural evaluation. Results indicate that the MS and ITS of the mixtures without rejuvenator are sufficiently high for use as a subsurface structural layer. However, dosing the mixture with ≥6% rejuvenator significantly decreases the MS and ITS. SCB tests for fracture resistance at an intermediate temperature indicate that mixtures without rejuvenators are more brittle than conventional hot mix asphalt (HMA). The flexibility index indicates that the mixtures with ≥6% rejuvenator have higher crack resistance than HMA and no-rejuvenator 100% RAP foamed asphalt mixtures. In conclusion, addition of rejuvenators significantly affects the structural integrity of 100% RAP foamed asphalt mixtures by increasing the cracking resistance but considerably decreasing the stability and indirect strength. Therefore, for practical purposes, the use of a rejuvenator in foamed asphalt mixtures is not recommended.

The Role of Additives in Warm Mix Asphalt Technology: An Insight into Their Mechanisms of Improving an Emerging Technology.

The asphalt industry’s incentive to reduce greenhouse gas emissions has increased since the 1990s due to growing concerns on environmental issues such as global warming and carbon footprint. This has stimulated the introduction of Warm Mix Asphalt (WMA) and its technologies which serve the purpose of reducing greenhouse gas emissions by reducing the mixing and compaction temperatures of asphalt mix. WMA gained popularity due to the environmental benefit it offers without compromising the properties, performance and quality of the asphalt mix. WMA is produced at significantly lower temperatures (slightly above 100 °C) and thus results in less energy consumption, fewer emissions, reduced ageing, lower mixing and compaction temperatures, cool weather paving and better workability of the mix. The latter of these benefits is attributed to the incorporation of additives into WMA. These additives can also confer even better performance of WMA in comparison to conventional Hot Mix Asphalt (HMA) methods. Even though there are recommended dosages of several WMA additives, there is no general standardized mixture design procedure and this makes it challenging to characterize the mechanism(s) of action of these additives in the warm mix. The effects of the addition of additives into WMA are known to a reasonable extent but not so much is known about the underlying interactions and phenomena which bring about the mechanism(s) by which these additives confer beneficial features into the warm mix. Additives in a certain way are being used to bridge the gap and minimize or even nullify the effect of the mixing temperature deficit involved in WMA processes while improving the general properties of the mix. This review presents WMA technologies such as wax, chemical additives and foaming processes and the mechanisms by which they function to confer desired characteristics and improve the durability of the mix. Hybrid techniques are also briefly mentioned in this paper in addition to a detailed description of the specific modes of action of popular WMA technologies such as Sasobit, Evotherm and Advera. This paper highlights the environmental and technical advantages of WMA over the conventional HMA methods and also comprehensively analyzes the mechanism(s) of action of additives in conferring desirable characteristics on WMA, which ultimately improves its durability.

Laboratory Investigation of the Performance Evaluation of Fiber-Modified Asphalt Mixes in Cold Regions

Thermal cracking of pavement is caused by contraction of the asphalt layer at low temperatures, when tensile stresses build up to a critical point at which a crack is formed. The cracks formed then propagate under traffic loading conditions. Freeze-thaw cycles accelerate crack propagation and deterioration of the asphalt layer, and can also lead to the formation of more severe distresses such as potholes. Fibers have attracted increasing attention in the asphalt industry for use as asphalt concrete modifiers. The addition of fibers to hot mix asphalt (HMA) results in a composite material that has a higher tensile strength, along with the ability to absorb greater energy during the fracture process. The fibers within the material also act as a barrier preventing the formation and propagation of cracks in the asphalt mix. This research evaluates the effectiveness of adding polymer fibers to HMA to increase both its resistance to cracking at intermediate and low temperatures, and its rutting resistance and moisture susceptibility at high temperatures. For this purpose, three different types of polymer fibers: aramids, polyethylene terephthalate (PET), and polyacrylonitrile (PAN), were added to conventional HMA mixes. The resulting samples were compacted, and their mechanical properties were compared with conventional HMA in the laboratory. At the end of the paper, a material cost comparison is provided as a reliable source of information when selecting materials to fulfill minimum industry specifications.

Promoting the Circular Economy of Concrete Through Innovation in Asphalt Pavements

The circular economy is seeking to maximize the use of resources and reduceing the consumption of raw materials as well as waste generation. In a circular economy, the producer takes responsibility, directly or indirectly, for the waste generated by the production process and for their products at the end of their life cycle. This concept is being integrated in most countries to achieve an environmental and economic balance. This paper presents a work in which this concept is used, where the waste generated in a concrete research project (waste aggregates) were drawn on asphalt mixtures. This project consisted of using the fine aggregates as a total or partial replacement of raw aggregates to manufacture asphalt mixtures. These fine aggregates are generated in the production process of high-quality recycled concrete aggregates. In this research, an IV-A 12 semi-dense gradation size and a CA-24 asphalt binder were used, where four different percentages of natural aggregate replacement were evaluated (0%, 25%, 75% and 100%). These asphalt mixtures were evaluated in their compliance of Chilean standards, as well as their performance in different properties such as cracking and water sensitivity. The results obtained show that the mixtures with total replacement of raw aggregates can be used, since they fulfill the Chilean standards. However, taking into account the water sensitivity results, the percentage of suitable replacement would be 50% for the same binder content. According to the cracking results, it is noted that increasing the replacement content of the aggregates in the mixture increases the fracture resistance compared to the conventional hot mix asphalt.

Warm Mix Asphalt Surfacing Performance for Different Aggregate Gradations with Cecabase RT Additive

Hot mix asphalt (HMA) surface course normally consists of wearing and binder layers, with different aggregate gradations. Hot mix asphalt (HMA) mixtures are traditionally produced at relatively high temperatures of between 150°C to 180°C. Warm Mix Asphalt (WMA) offers a sustainable solution to the problem by lowering the production temperature and energy requirements. However, to be accepted as an alternative to HMA, the performance of WMA must be comparable or better than HMA. The objective of this research is to investigate the performance of WMA wearing and binder course in terms of stiffness and moisture resistance, using Cecabase RT as warm mix asphalt additive. Different concentrations of Cecabase RT were added to determine the optimum percentage Cecabase RT. Marshall method was used to produce all samples investigated and analysis as carried out on the samples. Stiffness and moisture resistance tests were carried out to measure the performance of the mixes. The stiffness modulus values obtained for WMA mixes are higher than HMA mixes, indicating better stiffness. In addition, all the mixes investigated achieved the required minimum TSR value of 80%. It can be concluded that warm mix asphalt using Cecabase RT is comparable in terms of stiffness and moisture resistance to conventional HMA and could be a sustainable alternative to the conventional HMA mix as it can be produced at lower temperatures.

Performance evaluation of warm mix asphalt using natural rubber modified bitumen and cashew nut shell liquid

Warm Mix Asphalt (WMA) is an innovative technology that aims at decreasing the mixing and compaction temperature of asphalt mixtures as compared to the conventional Hot Mix Asphalt (HMA) thereby reducing harmful emissions and fuel consumption. The rubberized asphalt mixtures are found to have better physical and strength properties, but they are compacted at a higher temperature than that of conventional mixes. In this study Cashew Nut Shell Liquid (CNSL), an organic additive, was added from 0.5% to 3 % by weight of the binder at an increment of 0.5 % to modify the bitumen. The optimum content of CNSL to reduce the viscosity was found to be 2% and the viscosity reduction was 44.4 % at 140°C The modified NRMB (Natural Rubber Modified Bitumen) was used to prepare Dense Bituminous Macadam (DBM) and a comparison of volumetric, stability and rutting characteristics of both Natural Rubber modified Hot Mix Asphalt (RHMA) and Natural Rubber modified Warm Mix Asphalt with CNSL additive (RWMA) was made. Storage stability results indicated that there was no phase separation between rubberized bitumen and additive at high temperature and will act as uniform blend at high temperatures. Dynamic Shear Rheometer test results showed that the addition of CNSL to rubberized bitumen increased the values of G*/sinδ and could improve the resistance of asphalt binder against rutting. Stability value of RWMA was 11.5 % higher than that of RHMA and rutting depth was 10.1 % less than that of RHMA. The fatigue strength results obtained from Repeated Load Testing showed that the number of cycles to failure at 20% stress level was 9.04 % more for RWMA than RHMA. All volumetric properties of both RHMA and RWMA were within the limits specified by Ministry of Road Transport and highways (MoRTH) 2013. The statistical analysis authenticates the experimental findings. ANOVA analysis for Marshall Quotient revealed that RWMA had improved compaction characteristics than RHMA and the result for rutting and fatigue strength showed that the additive CSNL and temperature had significant effect on rutting resistance and fatigue life.

Warm Mix Asphalt—A German Case Study

In Germany, warm mix asphalt (WMA) is not commonly used although this technology was initially introduced to the practice between the 60s and the 80s. The current guidelines are devoted to the reduction of the mixing temperature for mastic asphalt (MA) (Gussasphalt). Due to this requirement, a number of products consisting of plain or polymer modified binder premixed with additives such as wax are available on the market. However, a well-established set of regulations addressing the production process and performance parameters is not available as in the case of conventional hot mix asphalt (HMA). For this reason, a case study which aimed to address the effects of viscosity changing additives (waxes) on asphalt mixture properties was conceived. In this large experimental study, three different additives (waxes) were used. First, the impact of waxes on asphalt binder properties and the corresponding rheological response were evaluated. Then, performance tests, such as rutting resistance tests, fatigue tests, and low temperature behavior tests, were conducted on asphalt mixtures AC 11 B S and AC 16 D S prepared with plain and polymer modified binders. No significant reduction in compaction temperature was observed when waxes were incorporated in the mix design. All additives were capable of improving rutting resistance, while poorer low temperature performance was exhibited. Based on the experimental campaign, the use of waxes could be recommended only to facilitate mixing.

Warm mix asphalt (WMA) for rapid construction in airfield pavement

Warm-mix asphalt (WMA) is commonly mixed and compacted 15°C to 30°C below that of conventional hot mix asphalt (HMA). The lower production temperature of WMA is expected to give an advantage of a lower cooling time of newly laid asphalt overlay before it can be opened to traffic during the nighttime airfield pavement construction. The reduced cooling time of WMA would allow shorter airport closure time window and/or extend the time for the contractor for paving, and thus shorten the overall construction period due to more volume done each night. This is a beneficial practical advantage to hectic airports where the typical off-peak period is as short as 6–8 h. In this research, two different WMA technologies, Sasobit® and Rediset® (organic and chemical) were investigated through laboratory tests to see if there were notable differences in WMA rutting performance that could have considerable practical effects on the permissible temperature at the opening to traffic as compared to the HMA. Furthermore, a validated finite element (FE) solution for one-dimensional transient heat-transfer model is used to simulate the effect of the use of warm mix on shortening the cooling time and the overall project time. The laboratory test shows that the WMA with Sasobit has a significantly better rutting performance at the elevated temperature, enabling the WMA to be opened to traffic at a higher temperature, compared to HMA. The cooling analysis showed that, in comparison to HMA, the use of WMA could shorten the closure time of airport during the night time construction by 8–67 min (5–73% reductions), depending on the asphalt overlay thickness, specified traffic opening temperature and WMA production temperature. The use of WMA could also reduce the overall construction period by 2–16 nights for a single lift overlay, for the cases studied – which would represent a shortening of the overlay period by 4–24%.

Long-Term Field Performance of Flexible Pavements Using Warm Mix Asphalt Technologies

An increased awareness of sustainability in the pavement industry has encouraged the use of warm mix asphalt (WMA) technologies. Compared to conventional hot mix asphalt (HMA) that requires a high production temperature, WMA has several benefits, such as saving fuel and energy, reducing greenhouse gas emissions, and improving the work environment. However, systematic analysis of long-term field performance for pavements containing WMA mixtures has been scarce. Therefore, the objectives of this paper are to evaluate the field performance of flexible pavements using WMA technologies (referred as WMA pavements in this paper) and compare the general trend of the longer-term performance between WMA and HMA pavements across the United States. Specifically, 28 WMA pavement projects along with their companion HMA pavements were evaluated for an extended performance period in terms of transverse cracking, longitudinal cracking, rutting, and moisture damage. A companion HMA pavement refers to the an pavement that shares similar pavement structure, climate, traffic conditions and mixture design with the WMA pavement; the main differences are the usage of WMA technologies in the surface layer and the reduced production temperature for WMA mixtures. The selected projects include five projects constructed during the course of the study, and 23 in-service projects covering different service ages, traffic volumes, pavement structures, WMA technologies, and four climatic zones across the United States. It was found that pavements containing various WMA technologies exhibited comparable long-term field performance as compared to that of the companion HMA pavement in terms of transverse cracking, wheel path longitudinal cracking, and rutting. No moisture-related distress was found in the field for either HMA or WMA pavements. Overall, cracking and rutting performance show a clear pattern of climate influence. Cracking distress appears to be more of a concern within wet climatic zones while less typical in dry climatic zones, which suggests that moisture should be considered in evaluating the cracking potential of asphalt mixtures. Results presented herein were part of NCHRP Project 9-49A on the Performance of WMA Technologies: Stage II—Long-Term Field Performance.

Comparative life cycle assessment of warm mix asphalt with recycled concrete aggregates: A Colombian case study

Abstract This paper presents the results of a comparative life cycle assessment undertaken to compare the potential environmental impacts associated with the use of Recycled Concrete Aggregate (RCA) as a partial replacement of natural aggregates in the production of Warm Mix Asphalt (WMA), with those of a conventional Hot Mix Asphalt (HMA). Laboratory testing results were used as inputs in a pavement design software with the purpose of designing several pavement structures with different percentages of RCA and according to the typical Colombian pavement design conditions. Primary data was collected from several companies in the northern region of Colombia. The SimaPro 8.4.0 software was used for modeling the processes analyzed in the case study and all the life cycle inputs and outputs related to the functional unit were characterized during the life cycle impact assessment (LCIA) phase into potential impacts according to the impact assessment methodology TRACI v.2.1. The LCIA results of the case study showed that the use of WMA with RCA as a replacement of coarse natural aggregates leads to a deterioration of the environmental profile of the pavement structures.

Resilient Modulus Performance of Warm Mix Asphaltic Concrete using Cecabase RT Additive

Warm mix asphalt is an energy efficient mix that can be produced at lower temperature than the conventional hot mix asphalt, while maintaining the properties and performance required for the conventional hot mix asphalt. This paper presents a study in mix design of dense graded asphaltic concrete using a warm mix additive known as Cecabase RT. Type AC14 gradation for granite aggregates and bitumen of penetration type 60/70 were used for this study based on the Public Works Department of Malaysia’s Standard Specification for Road Works. The mixing temperature for the control sample AC14 mix without the additive was set at 160°C while for the mix using the Cecabase RT additive, the mixing temperature was set at 135°C. Marshall test procedure were then used to prepare the samples and volumetric properties were then evaluated to determine the optimum bitumen content. The optimum Cecabase RT additive content was then determined using samples prepared at the optimum bitumen content. The resilient modulus test was then carried out on the samples based on the repeated load indirect tensile test at temperatures of 25°C and 40°C at three different pulse repetition periods. From the analysis of the results, it was found that optimum bitumen content was at 4.9% while the optimum Cecabase RT additive content for the AC14 mix is 0.3%. The resilient modulus values obtained for the mix using Cecabase RT warm mix additive is higher than the control samples at both test temperatures and at all the pulse repetition period tested. It can be concluded that the use of Cecabase RT additive have the advantages of reducing the mixing temperature, thus producing a more energy efficient mix while improving the stiffness of the mix in terms of resilient modulus values, thus increasing a pavement load carrying capacity.