Hot Mix Asphalt Plants Research Articles

Reinforcement corrosion in self-compacting concrete made with waste filler of bituminous mixtures

This study aims to investigate the properties of self-compacting concrete (SCC) manufactured with a recovered filler (RF) that comes from hot-mix asphalt plants. This material is a waste that sometimes implies an environmental problem and its use in the manufacturing of concrete could be solved it and would be a new sustainable way of casting concrete. The use of this material did not compromise the self-compacting character of the concrete. Durability properties are barely studied when a new product is incorporated to a construction material. This work estimates the service life related to reinforcement corrosion of a SCC elaborated with the waste from hot-mix asphalt plants. Mechanical properties were studied, especially those related to its behaviour against rebar corrosion, and according to the results, this SCC might allow structure durability similar to those elaborated with conventional raw materials. In other words, acceptable service life will be achieve based on carbonation as well as chloride penetration. Furthermore, good behaviour against shulphates has been demonstrated.

Emissions from Hot Mix Asphalt Plants and their Impact on Ambient Air Quality

Emissions from Hot Mix Asphalt Plants and their Impact on Ambient Air Quality

Ternary Blends for Self-Compacting Mortars Production Composed by Electric Arc Furnace Dust and Other Industrial by-Products.

This study is framed within the circular economy model through the valorisation of industrial by-products. This research shows the results of producing self-compacting mortars (SCMs) with electric arc furnace dust (EAFD) and other industrial by-products such as fly ash, conforming (FA) or not conforming (NcFA), from coal-fired power plants, or recovery filler (RF) from hot-mix asphalt plants. Three batches of SCMs, each with one industrial-by product (FA, NcFA, or RF), and three levels of EAFD ratio incorporation (0%, 10%, 20%), were tested. An extra batch with a greater amount of FA was manufactured. When the incorporation ratio of EAFD rose, the mechanical strength decreased, due to the presence of a calcium zinc hydroxide dihydrate phase; nevertheless, this decrease diminished over time. All SCM mixes, except the 40C 40FA 20 EAFD mix, were above 20 MPa at 28 days. All mixes named 70C and 40C reached 40 and 30 MPa, respectively, at 90 days. Mixes with EAFD showed less capillarity and no difference in water absorption by immersion with respect to mixes without EAFD after 91 days. The SCMs designed proved to be stable in terms of leaching of the heavy metals contained in EAFD, where all the hardened SCMs were classified as inert.

The impact of silo storage on the fatigue and cracking resistance of asphalt mixes

During production, hot mix asphalt plants can store mixes in silos for a few hours before they get transported to the job site. Additional aging and possible blending between RAP and virgin binders take place inside the silo which affect mix properties. This study addresses the impact of silo storage on mix fatigue and cracking performance. The flexural beam test has been widely established as a representative fatigue test, however due to its complexity, it is difficult to implement as a quality control test. The semi-circular bending test (SCB) and the indirect tensile asphalt cracking test (IDEAL-CT) are simple and quick tests that are currently being used by some state agencies to assess the cracking resistance of asphalt mixes. The ability of SCB and IDEAL-CT to predict fatigue-related cracking as compared to flexural beam testing is also investigated in this study. Four plant-produced mixes were collected before and after silo storage, and tested using flexural beam, SCB, and IDEAL-CT. It was noted that the SCB and IDEAL-CT are highly influenced by the mix stiffness, and the cracking resistance was reduced considerably with silo storage. This finding has important implications when using either of these tests for construction quality control and assurance. It was concluded that the flexibility index (FI) from the SCB and the cracking tensile index (CTindex) from the IDEAL-CT did not provide a direct measure of the fatigue performance as compared to the flexural beam test.

Durability and Mechanical Properties of Self-Compacting Concrete Incorporating Recovered Filler from Hot Mix Asphalt Plants and Recycled Fine Aggregate

In this research, a sustainable approach is followed to develop efficient mixtures incorporating recycled fine aggregate (RFA) remained from structure demolition as well as limestone filler (LF) from production of hot mix asphalt (HMA). The LF is a byproduct of the drying process in HMA production plant which is not entirely consumed in the production of the HMA and must be hauled and disposed in landfills. The maximum particle size of the LF is approximately 40 µm. Self-Compacting Concrete (SCC) mixtures were designed replacing 5% and 10% of the cement with LF. Incorporation of 50%, and 100% RFA with the fines in the mixtures were considered with and without addition of the LF. Due to the formwork and prefabrication restrictions, the paste volume and the high range water reducer content were tuned in such a way that the slump flow of the mixtures remained between 660 mm to 700 mm without segregation. Durability and mechanical performance of the mixtures were evaluated by resistance against freeze-thaw scaling exposed to deicing agents and compressive strength. It was observed that the SCC mixtures containing 10% LF outperformed those without the use of LF while 5% SCC mixtures did not exhibit tangible superiority. Incorporation of RFA as the fine fraction degraded the durability of all the mixtures. While replacing all the fine fraction with RFA significantly impaired durability and compressive strength, 50% RF mixtures could be designed containing 10% LF that remained in the allowable limits.

Assessment of heavy metal pollution in soils and health risk consequences of human exposure within the vicinity of hot mix asphalt plants in Rivers State, Nigeria.

This study evaluated the level of heavy metal pollution in soils within the vicinity of hot mix asphalt (HMA) plants and the health risk consequences of human exposure to the heavy metals. Soil samples collected from two asphalt plants during dry and rainy seasons were analyzed for Cr, Co, Cu, Ni, Mn, Cd, Pb, and Zn with atomic absorption spectrophotometer (AAS). Health risk indices were assessed as chronic daily intake (CDI), hazard quotient (HQ), hazard index (HI), and carcinogenic risk (CR) while the degree of pollution was assessed with geo-accumulation index (Igeo) and contamination factor (CF). The pollution assessment revealed that the soil samples were moderately to highly polluted with Cd. In both seasons, Zn and Mn, respectively, had the highest CDI values for ingestion, inhalation, and dermal route for both asphalt plants while Cd has the least CDI values for all the routes in both plants. The HQ and HI values for all the metals were less than 1.00E + 00 indicating no non-carcinogenic risk from exposure to any of the metals. Furthermore, the dermal route was found to be the least likely model for health risks associated with human exposure to soil heavy metals within the vicinity of the plants. The CR values for the metals were also within threshold value indicating non-significant cancer risk from exposure to the metals. Though no significant health risks were observed in the study, clean and efficient production of hot mix asphalt should be encouraged to minimize health risks and environmental pollution during production and usage.

Air Pollution Control for a Hot Mix Asphalt Plant

The report explores how to reduce pollution by improving the emission control system in Hot Mix Asphalt (HMA) plants. The majority of emissions come from the combustion of fuel and particulate matter (PM) diffusion. The key finding is that combining a wet scrubber system and baghouse system will reduce the major pollutants significantly. Thousands of HMA plants across the country are in operation every day in rural, suburban, and urban areas, affecting all neighbors in their local communities. How an asphalt plant impacts the neighborhood and the environment mainly depends on their sustainable operation. Asphalt plant emissions are very low and getting lower due to innovative control systems and manufacturing technology. The objective of this report is to exppore the emission control system of a Hot Mix Asphalt plant. The main point is how to improve the scrubber system and baghouse filter for controlling criteria pollutants in the Hot Mix Asphalt plant during production to reduce the emissions.

Towards resource-efficient management of asphalt waste in Lombardy region (Italy): Identification of effective strategies based on the LCA methodology

This study presents a comparison of alternative strategies for managing asphalt waste currently implemented in Lombardy Region (Italy). The waste under study is the one arising from deconstruction and milling of old pavements not containing tar, and, hereafter, it is referred as reclaimed asphalt pavement (RAP). The life cycle assessment (LCA) methodology was applied to the regional system to evaluate its current performance, to identify critical aspects and to suggest actions for improving it. As first step, the amount of RAP generated and recycled within the region was computed by elaborating raw waste data annually collected by the regional agency for the environmental protection. Roughly 1 million tonne of RAP was managed in Lombardy in 2014; most of it was recovered/recycled and only 1% was directly landfilled. Data revealed that RAP was mainly recovered as unbound aggregate for road bases and sub-bases or fillings (52.5%) whereas RAP addition into new asphalt mixtures was less widespread (39.4%). In this case, RAP was mostly recycled in stationary hot mix asphalt (HMAs) and cold mix asphalt (CMAs) plants. Hence, the present LCA focused on these two types of techniques. Primary data on both processes were directly collected from some investigated facilities to set out the current scenario. Sensitivity analyses were then performed to find out the key parameters and their influence on the LCA outcome. Results indicate that recycling RAP in hot/cold mixes is significantly more beneficial than its recovery as unbound material. Moreover, hot recycling provides better environmental performance than cold processes performed at stationary plants, despite the lower RAP addition (20% in HMAs vs 80% in CMAs); this is mainly due to the use of stabilizing agents in the production of CMAs and to the lower field performance of CMAs compared to virgin HMAs. Based on these results, a best-case scenario has been developed to quantify the benefits arising from the suggested actions.

Overview of Catalytic Methanation in Hot Mixing Asphalt Plants Towards Greenhouse Gas Emissions

Road works mainly involve the use of asphalt for pavement construction. Among Hot-Mix asphalt (HMA) production processes, HMA plants are the most commonly used for asphalt production in world. HMA is shown as an industrial activity in which energy consumption can reach 60% of the total energy consumed by the construction and the maintenance of a road during 30 years of service life. Rate of production, bitumen temperature, burner flow rate and type of fuel consumption are the parameters which directly link to energy consumption and greenhouse gas (GHG) emission during HMA plant operation. Carbon dioxide (CO2) in GHG has increased the temperature of the earth. Introduction of catalytic methanation as a new method in the HMA production was introduced as an effective way to convert CO2 released from HMA plants to methane (CH4). The optimum parameters were found through the experimental result which showed that Ru/Cr/Mn (5:10:85)/Al2O3 calcined at 700°C with 10 g of catalyst dosage gave 100% of CO2 conversion, determined using FTIR, and yielded about 80% of CH4 at reaction temperature of 300°C. Field Emission Scanning Electron Microscope (FESEM) show the presence of dispersed particles with undefined shape covering the catalyst surface. EDX analysis revealed that the mass ratio of Mn was high compared to the other elements. Thus, this study has proven that the catalytic methanation technology as the new effective method in HMA production plants can convert CO2 in GHG emission to methane (CH4). In conclusion, it is highly advisable to adapt these alternatives as the green roads and highways industry.

Durability of self-compacting concrete made with recovery filler from hot-mix asphalt plants

In construction, there is a need to respond to environmental challenges and implement the Circular Economy as a strategy for the sustainable growth of the sector.To eliminate the lack of confidence in the application of the waste from this sector, it is necessary to carry out research in order to achieve an effective and integral management, as well as the reuse and recycling of these materials.In this work, a detailed study of Self-Compacting Concrete (SCC) was carried out, using as filler a waste from the drying process of the aggregate used in the manufacture of hot-mix asphalt. The results showed that it is possible to obtain a high-performance SCC in terms of durability by replacing a commercial siliceous filler (SF) with this dolomitic residual powder (RF), with high performance against the attack of aggressive agents (chloride, sulphate and carbonate ions) and shrinkage.In this study the analysis of the physical parameters of the materials (density, open porosity and pore size distribution as obtained from mercury intrusion porosimetry) and water absorption (by immersion and capillarity) was fundamental. The joint analysis of all the studied parameters allowed obtaining exhaustive results about the durability of the mixes and its interrelation with the properties of the constituents.

Analytical assessment of asphalt odor patterns in hot mix asphalt production

During the various stages of asphalt paving mixtures production and placement, as a result of binder heating, a complex mixtures of hydrocarbons and volatile organic compounds (VOCs) is released into the atmosphere. As far as hot mix asphalt plants is concerned, several standards and directives were drawn up for limiting the emissions of certain specific substances, without setting any specific limit on the odorous perspective. But, odor is increasingly considered an atmospheric pollutant that can have a significant negative impact on both quality of life and economic activity. The odorous flows of HMA emitted in plants or during the paving operations and hot-in-place recycling processes in the worksites can severely limit the usability of the territory. Advances in sensor technology have made possible the development of artificial olfactory systems (AOS), which are devices designed to mimic the human olfactory system capable of characterizing osmogene mixtures. However, their potentialities have not been explored until now at any stages of asphalt and asphalt mixtures production chain. Thus, the main purpose of this study was an analytical-sensory characterization, mainly based on AOS approach, of asphalt emissions generated during the various stages of road pavement construction. The analytical and sensory analyses have firstly demonstrated the effective application of these instruments in the pavement engineering sector: an odor fingerprint of asphalt emissions, specific for each type of binder and temperature class, was determined. Thanks to the photoionization, a technique which allow the detection of organic compounds in gaseous mixtures, a pseudo-hyperbolic relationship between the release of airborne substances in asphalt emissions and the heating temperature was identified; whereas the AOS demonstrated that this increase of VOCs corresponded contextually to a change in their odorous patterns. Moreover, the existence of variations in the odor fingerprints of different asphalt binders heated at the same temperature was assessed. Through a specific statistical approach for the treatment and post-processing of data and the following elaboration of a geometric based procedure for the determination of the numerical inter-class separation, a quantitative value to the purely qualitative response of the AOS was assigned.

Occurrence and sources of aliphatic hydrocarbons in soils within the vicinity of hot mix asphalt plants in Obigbo and Igwuruta Areas of Rivers State, Nigeria

This study investigated the occurrence and sources of aliphatic hydrocarbons (AHCs) in soils within the vicinity of hot mix asphalt (HMA) plants. Soil samples were collected from two HMA plants and analysed with gas chromatography - flame ionisation detector (GC-FID). Sample collection was from both surface (0-15 cm) and subsurface (15-30 cm) soils at an increasing distance of 10 m from the HMA plants while the control samples at both depths were collected at 1 km away from the plants. The AHCs concentration (nC9-nC38) in soils from both HMA Plants ranged from 8.16 - 433.04 mg/kg and 5.91-177.83 mg/kg for surface and subsurface soils respectively while the concentration in the control samples ranged from 5.97 - 23.95 mg/kg and 2.52 - 13.31 for surface and subsurface soil respectively. The sources of the AHCs were determined using isoprenoid ratios, carbon preference index (CPI) and maximum carbon chain (Cmax). The isoprenoid ratios and CPI values of the samples closer ( 20 m from the HMA plants showed mixture of both anthropogenic and biogenic sources. Keywords : Asphalt Plants; Soil; Aliphatic hydrocarbons; Pristane; Phytane.

Mechanical behaviour of self-compacting concrete made with recovery filler from hot-mix asphalt plants

The aim of this paper is to assess the feasibility of the use of a fine grain waste generated in hot-mix asphalt plants (HMA), namely recovery filler (RF), as filler materials in self-compacting concrete (SCC) production. A comparative study of two types of SCC was performed. The first concrete type was made incorporating recovery filler (SCC-RF) of a dolomitic nature and the second was made with commercial siliceous filler (SCC-SF), the latter used as reference. Good results of self-compatibility were obtained using RF. The thermogravimetric study showed that in SCC-SF the higher loss weight occurs in the dehydration zone (0–400°C) and in SCC-RF it occurs in the decarbonation area (550–735°C). The aging mechanism of both concrete types (SCC-SF and SCC-RF) was different. In the SCC-SF mixes, portlandite undergoes carbonation processes and pozzolanic reactions and in the SCC-RF mixes it only undergoes carbonation processes. The experimental results (splitting tensile strength, flexural strength and static modulus of elasticity) show the validity of using EHE-08, initially proposed for NVC (Normally Vibrated Concrete), in SCC. The ultrasonic pulse velocity values for SCC-SF was greater than for SCC-RF, which can be attributed to compacity and compressive strength. The shrinkage behaviour was better in SCC-RF than SCC-SF, mainly due to the greater particle size of recovery filler (RF), although the SCC-RF mixes showed lower density and mechanical strength than SCC-SF. In short, the SCC manufactured with recovery filler from plants manufacturing hot-mix asphalt (HMA) – SCC-RF – is expected to have better features than SCC-SF in relation to shrinkage and early appearance of cracks.

Effect of Silo Storage Time on the Characteristics of Virgin and Reclaimed Asphalt Pavement Mixtures

Many hot-mix asphalt plants store material in heated silos before it is ready to be transported to construction sites. The time that material is stored in the silo is not controlled and varies widely, depending on several factors. As the material is exposed to elevated temperatures, short-term aging of the binder may occur. Another important consideration is the interaction between reclaimed asphalt pavement (RAP) and virgin binders, as blending or diffusion could occur between the binders. In this study, a virgin and 25% RAP mixture were sampled at incremental silo storage times up to 10 h. Characterization testing included performance grading, rheological indexes, Glover–Rowe parameter evaluation, rolling thin film oven aging on the binders, complex modulus, a simplified viscoelastic continuum damage model (S-VECD) for fatigue, and thermal stress restrained specimen testing of the mixtures. Simulations that used layered viscoelastic critical distresses pavement analysis to predict fatigue behavior from the S-VECD model were used to show the potential effects of silo storage time on pavement life. Results from all tests indicated that mixtures aged with an increase in silo storage time. RAP materials experienced a greater effect; this effect may be a function of the air void content or indication of blending–diffusion in the silo. Rolling thin film oven aging showed that current laboratory conditioning methods do not necessarily simulate asphalt plant production. Production parameters, such as silo storage time, have a significant impact on mixture performance.

Design and performance of a warm high-modulus asphalt concrete

Undoubtedly, the road system around the world, if effective, is one of the keys to economic growth. However, the asphalt production in particular provokes a giant environmental impact. Among the several ways that have been researched to minimize these negative consequences, warm mix asphalt concrete has emerged, giving a response to the need to reduce energy costs and emissions of greenhouse gases (GHG) caused by hot mix asphalt plants. This is particularly important in the case of high-modulus asphalt concrete (HMAC), because these mixtures are produced from hard bitumens that need high temperatures to achieve the required viscosity and ensure the proper coating of the aggregates, the workability and compactability of the mixture. Higher heating temperatures results in higher energy consumption and increased environmental impacts. This issue is very important in hot mix asphalt (HMA) in general, as discussed in several studies, but it is even more important in the case of HMAC. On the other hand, reducing the manufacturing temperature, while keeping the quality of the final mixture, presents a greater challenge. A study was conducted to verify if the performance of a high-modulus asphalt concrete, produced at temperatures lower than the conventional ones, would be compromised by the introduction of a chemical additive, compared to a standard mix.

Multivariate data analysis applied in Hot-Mix asphalt plants

A multivariate data analysis was used with environmental data obtained from Hot-Mix asphalt (HMA) plants. The main objectives of the study were to describe and interpret the real “phenomena” that exist on HMA plants; also, to search for the best mixing conditions, i.e. production with less energy consumption and less emissions. Another important objective was to identify means to allow HMA plants to be designed and operated in better ways. Along the study, an approach of the manufacturing process is presented, allowing for an overall comprehension of the plant's operation.There is not only one parameter to be controlled and checked when HMA are being produced. In this context, a multivariate data analysis was carried out, and the main control parameters considered for prediction and regression analysis were Hot-Mix asphalt formula, fuel type, burner flow rate, fuel consumption, negative pressure of the drum, air temperature, moisture of aggregates, asphalt temperature and rate of production.“Global warming emissions”, “organic emissions”, and “energy consumption” were chosen as models of regression. Globally, plants powered by natural gas emit half the amount of CO2, nine times less NOx and eighteen times less CO than plants with fuel oil. Considering NOx and CO2 emissions, small plants are preferable over big plants. For organic emissions, if the asphalt temperature increases, TOC emissions are increased; however, if the rate of production increases, TOC emissions are decreased. Previously supposed as an important parameter, moisture of aggregates had no great importance in the statistical analysis. Likewise, the formula of HMA produced also had no great importance, despite many types of formulas studied.The main conclusions in regards to the means with which Hot-Mix asphalt plants can be designed and operated in better ways were: the manufacturing of hyper-mobile and small HMA plants as opposed to stationary large plants, and the use of burners with natural gas instead of fuel oil in all cases. The production of HMA plants, aiming at a cleaner production, means to operate asphalt plants always considering timespan in the long term. This encompasses undertaking daily, weekly and yearly analyses. Therefore, it is necessary to produce with low rate of production and low bitumen temperature, and to maintain a regular production in order to avoid peaks of production and unnecessary starts and stops. It is also interesting to increase the culture of heated stocks.Finally, this study shows that would be an advantage to use multivariate data analysis and then to estimate with very good accuracy emissions and energy consumption in HMA plants using current parameters of control.

CHARACTERISATION OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) IN ROAD PAVING ASPHALT

This study characterised the polycyclic aromatic hydrocarbons (PAHs) in five road paving asphalt samples randomly collected from two hot mix asphalt (HMA) plants in Port Harcourt, Nigeria. The ∑16PAHs of the samples ranged from 103.79 mg/kg - 190.93 mg/kg. Naphthalene, Acenaphthylene, fluorene and benzo(g,h,i )perylene were not detected in any of the samples. The characteristic isomer ratios of the asphalt samples were also calculated to serve as a reference for road runoffs and leachates studies.

Built Environment: New Default for Asphalt?

Built Environment: New Default for Asphalt?

Assessing Potential for Warm-Mix Asphalt Technology Adoption

Warm-mix asphalt (WMA) describes a range of technologies that seek to lower emissions and reduce energy consumption by lowering the temperature at which asphalt mixtures are produced and placed. Despite these benefits, reduced mixture viscosity may be the most likely reason for widespread adoption of WMA technologies. Hot-mix asphalt (HMA) producers are unlikely to adopt WMA technologies solely to lower emissions, because current environmental regulations and the relatively clean nature of HMA plants make lower emissions unnecessary and unprofitable except in select air pollution areas. Producers are also unlikely to adopt WMA technologies solely to reduce energy consumption, because energy savings are less than the associated costs except in the most expensive energy markets. Reduced viscosity makes the best business case for widespread WMA technology adoption, because this benefit offers cost and risk reduction: it can (a) alleviate compaction problems associated with cool weather, (b) reduce compaction equipment needs at the job site, and (c) lower the risk of poor compaction when working with stiff mixtures. This conclusion is supported by basic economic calculations, a survey of the Icelandic pavement industry showing strong support for WMA technology use to improve cool weather paving, and two projects in Maryland showing the potential for WMA technology use to lower the risk of poor compaction of high reclaimed asphalt-pavement mixtures.

Comparison of laboratory-generated and field-obtained HMA VOCs with odour potential

Previous research developed a gas chromatography (GC) methodology for simulating and evaluating hot mix asphalt (HMA) volatile organic compounds (VOCs). The objectives of this research were to determine if (1) the VOCs produced and measured in the laboratory method represented the relative ranking of VOCs measured during the production of HMA, and (2) the odour reducer had a quantifiable influence on the VOCs during HMA production. Three HMA plants were run using asphalt binders with and without a commonly used commercial additive used for reducing odour complaints from neighbouring communities. Air samples were obtained over 4 h of continuous operation of each plant for each asphalt binder (i.e. one with and one without odour reducer). Two locations at each plant were concurrently sampled: at the drag slat (i.e. where the HMA moves from the drum to the storage and/or loading area, and from the head space in the storage tank. Good correlations were found between the laboratory and field measurements; the laboratory GC method provides a good relative ranking of concentrations for the VOC compounds monitored in this study. The odour reducer used in this study significantly reduced VOCs at both sampling locations.