Loose Asphalt Research Articles

Investigation and optimization of short-term aging test conditions for asphalt binders

The existing short-term aging test methods have disadvantages such as not being suitable for high viscosity modified asphalt, different aging degrees between them and poor testing convenience. Therefore, this paper investigated and optimized the aging test conditions of asphalt. The macroscopic rheology and microchemistry of aged asphalt prepared by different aging conditions were comprehensively evaluated. Finally, the most suitable aging test conditions for asphalt was determined by referring to the aging degree of loose asphalt mixture. The experiment results showed that after aging, the rutting factor, carbonyl index, asphaltene content, and creep stiffness of asphalt would increase. The aging degree of existing asphalt aging methods (TFOT and RTFOT) and the corresponding loose asphalt mixture was quite different, and the difference percentage could reach 86.6%. Based on the TFOT test, the asphalt aging conditions were optimized. The aging temperature was 163 ℃. For 70# and SBS modified asphalt, the recommended asphalt film thickness and aging time were 1.59 mm–85 min and 0.80 mm–85 min, respectively. The aging degree of high viscosity modified asphalt under the condition of 0.80 mm–85 min was close to the aging degree of loose asphalt mixture at 135 ℃, and the aging degree of 0.80 mm–100 min was close to the aging degree of loose asphalt mixture at 165 ℃. The proposed aging test conditions can not only accurately simulate the short-term aging behavior of asphalt, but also shorten aging time and save resources.

Multi-recyclability of asphalt mixtures modified with recycled plastic: Towards a circular economy

Although asphalt pavements modified with recycled plastic have demonstrated enhanced performance, their recyclability remains under-explored, which is crucial under the scope of a circular economy. To address this, the present study investigates the multi-recyclability of asphalt mixtures, both with and without a recycled plastic modifier, at a recycling rate of 50 % over two cycles using an open-loop and a closed-loop model. The research utilised an innovative recycled plastic modifier made from hard waste plastics, incorporated into the mixture via the dry method. To ensure control over consistency and variables while also considering the novelty of the recycled plastic modifier, the reclaimed asphalt pavements (RAPs) were prepared using a loose asphalt mixture ageing protocol. Additionally, a rejuvenator made of vegetal derivatives was used as the recycling agent, considering the high recycling rate over each cycle. The comprehensive evaluation of volumetric and mechanical performance revealed that asphalt mixtures containing the recycled plastic modifier performed comparably to unmodified mixtures over two recycling cycles. Furthermore, all the recycled mixtures exhibited superior performance in resistance to rutting, moisture susceptibility, and fatigue compared to the conventional asphalt mixture. Overall, it can be inferred that the asphalt mixture modified with recycled plastic is capable of being recycled over multiple life cycles without compromising its mechanical and performance characteristics.

Valorisation of Pulp and Paper Industry Wastes—Incorporation in Bituminous Mixtures for Road Construction

Some wastes from the paper pulp production process are still sent to a controlled waste landfill. These materials can constitute alternative resources for constructing road pavements. The study aimed to characterize and explore the sustainable application of two inorganic wastes resulting from the paper pulp process, the dregs (green liquor wastes) and the grits (slaker wastes), in the production of bituminous mixtures by the analysis of samples prepared with 5 and 10% of dregs and 5 and 10% of grits on the baseline reference bituminous mixture AC 14 surf 35/50. Some relevant mechanical properties of the blends were assessed based on Marshall compression, sensitivity to water and wheel-tracking tests. Additionally, water poured on the loose asphalt and compacted slabs’ surface was analysed to determine the portion of harmful chemical compounds leached from the asphalt material. The results show that using dregs presented some technical limitations related to mechanical performance and that the incorporation of grits has an acceptable mechanical behaviour. Moreover, the study shows that the measured leachate resulting from water flow in a reference asphalt mixture and the blends with grits are insignificant. It can be concluded that using grits in asphalt mixtures is a promising technique regarding mechanical behaviour and environmental impacts that need further studies.

Evaluating the Ageing Sensitivity of the Asphalt Binder via Distinct Ageing Methods

Asphalt binder is a crucial component of asphalt pavements that undergoes ageing over time, which can result in the reduced performance and deterioration of pavements. Consequently, artificial ageing methods play a significant role in providing valuable insights into the ageing behaviour and long-term performance of asphalt binders. However, a consensus on the most effective method for simulating ageing behaviour remains elusive, leading to disparities in the outcomes across different research studies. To address this issue, the study utilises two thermo-oxidative ageing approaches, one focusing on the binder itself and another on the loose asphalt mixture. The study investigates the effect of these ageing methods on the behaviour of asphalt binder using physical, rheological, and chemical characterisation. For the binder ageing method, a rolling thin film oven (RTFO) and a pressure ageing vessel (PAV) were utilised, whereas the loose asphalt mixture ageing was performed in an oven at 95 °C for various durations. The results indicated that the ageing trend differed between the two oxidative ageing approaches as the ageing duration increased. However, by employing an ageing sensitivity index, comparable rheological properties were observed between the binders aged using the PAV for 20 h and the loose asphalt mixture for 5 days. The Fourier Transform Infrared (FTIR) spectroscopy analysis revealed that the ageing methods influenced the functional groups associated with ageing in distinct ways, even though they exhibited similar rheological behaviour. Overall, this study provides a comprehensive understanding of different thermo-oxidative ageing approaches, their correlation, and their relevance to the studied field-aged binders.

Digital image colour analysis to evaluate the moisture sensitivity of hot-mix asphalt mixes

Moisture in hot-mix asphalt (HMA) can cause serious damage such as cracks and ruts if left untreated. This is due to the separation of binder and aggregates caused by moisture-induced stripping. Existing approaches for assessing moisture damage in asphalt are time consuming, destructive and expensive to implement. In contrast, digital image analysis provides a simple, inexpensive and non-destructive method for identifying moisture-sensitive mixes. Colour, as an essential characteristic of an image, effectively conveys information about its content. This study seeks to explore the potential of analysing digital image colour in the L*a*b* colour space to assess the moisture sensitivity of HMA after moisture-induced stress tester conditioning. Laboratory-compacted specimens of loose asphalt mixtures from the field were studied by image processing followed by statistical tests of significance. It is found that two parameters – namely, the ‘average colour value for the L* channel’ and the ‘standard deviation value for the b* channel’ – can be used to distinguish between moisture-sensitive and non-sensitive mixes. The findings of this study suggest that future research may find colour to be a helpful criterion for characterising asphalt materials using digital image processing.

Investigation of 6PPD-Quinone in Rubberized Asphalt Concrete Mixtures.

N-(1,3-dimethylbutyl)-N'-phenyl-p-phenylenediamine (6PPD)-quinone (6PPD-Q), a transformation byproduct of 6PPD used in tires as an antiozonant and antioxidant, was recently discovered as the chemical primarily responsible for the acute lethal toxicity of urban storm runoff to coho salmon. The asphalt concrete (AC) surface layer is the primary medium to contact 6PPD-Q immediately upon its release from tires, and the addition of recycled tire rubber (RTR) to the asphalt binder and mixture is a widely accepted practice in asphalt production. Therefore, it is urgent to understand the fate of 6PPD-Q at the asphalt concrete surface layer-water interface. This study analyzed the sorption and desorption of 6PPD-Q by compacted and crushed loose (loose particles, ∼5 mm) rubberized asphalt mixtures and their mobilization from compacted asphalt mixtures during simulated rainfall events. It should be noted that the crushed loose asphalt mixtures demonstrated the physicochemical properties of the asphalt materials, while the compacted asphalt mixtures represent in-service AC layers. Sorption of 6PPD-Q by crushed loose and compacted asphalt mixtures reached equilibrium within 12 days, with a sorption coefficient of 151.57-257.51 L/kg for compacted asphalt mixtures. Within 12 days, desorption of 6PPD-Q from crushed loose and compacted rubberized asphalt mixtures (20 g particles/L) to the double deionized (DDI) water and synthetic stormwater was 0.01-0.09 and 0.025-0.05 μg/L, respectively. Through the rainfall simulation experiments, 0.0015-0.0049 μg/L 6PPD-Q was detected in the runoff water, much lower than the lethal concentration (LC50) of 6PPD-Q of 0.095 μg/L and 308.67 μg/L for coho salmon and zebrafish larvae. Our results indicate that, while the release of 6PPD-Q from compacted rubberized asphalt mixtures is minor, the mixtures can serve as sorbents for tire-derived 6PPD-Q and retain this emerging contaminant.

MODEL VALUE OF RESIDUAL STRENGTH OF CONCRETE ASPHALT PAVEMENT CONSEQUENCES OF SOAKING OF RAINWATER AND SEAWATER BY CONTINUOUS AND PERIODIC METHODS

High rain intensity and limited draninase capacity result in high waterlogging on the road surface for a long time. After dry inundation, the pavement surface undergoes a bond between the aggregate and loose asphalt. This loose condition, when crossed by vehicles, causes cracks and holes so that the road is damaged. In addition, large-scale waterlogging can cause groundwater located below the soil surface to become saturated. The research method is an experimental laboratory with the help of descriptive statistics in analyzing data to find out an overview of the characteristics of concrete asphalt mixture materials. Penelitian aims to: Knowing the relationship between variations in soaking duration to the durability performance of asphalt concrete mixtures, Evaluating differences in residual strength index values due to length soaking by using seawater and rainwater with continuous and periodic mrtode, and Determining the relationship model between the Residual Strength Bonding of the asphalt mixture to time of soaking seawater and rainwater. The residual strength bond value (IKS) is greatly influenced by the soaking time, where the longer the concrete asphalt issoaked, the significantly lower the IKS value. As for the Modelh the difference between the Residual Strength Index against the bath time is a polynomial model.

Investigating the Multi-Recyclability of Recycled Plastic-Modified Asphalt Mixtures

Although the benefits of asphalt recycling have been scientifically proven and several best practices are being implemented, further research is required in specific and specialized areas. One of these circumstances is the recycling of Reclaimed Asphalt Pavements (RAPs) that contain asphalt modifiers such as elastomers and/or plastomers. Following the principles of the circular economy and considering the sustainability implications of asphalt mixtures, this paper deals with the multi-recyclability of asphalt mixtures containing 50% RAP with and without a recycled plastic asphalt modifier and rejuvenating agent. The recycled plastic asphalt modifier was made of hard recycled plastics and was introduced to the mixture via a dry method. The research focuses on the characterization of binders via conventional, rheological, and chemical analysis. To control the consistency and variables of the mixtures, the RAP was produced artificially in the laboratory following an ageing protocol for loose asphalt mixtures. According to the obtained results, at all three cycles of binder recycling, comparable properties for (i) the extracted binders from the recycled plastic-modified asphalt mixture, (ii) the extracted binders from the control un-modified mixture, and (iii) the reference bitumen 50/70 were obtained. This was even noticed when a nearly similar quantity of the rejuvenator was needed during the rejuvenator optimization process. Overall, it can be deduced that from the binder-scale point of view, the mixture containing the introduced recycled plastic additive could be recycled for multiple life cycles without any degradation of its mechanical and physical properties.

Road performance and thermal-insulation effect in construction of asphalt mixture containing phase-change thermal-insulation agent

Highway construction strategies impact the early damage of asphalt pavement and its sustainability. The pavement quality is directly influenced by the temperature of the asphalt mixture during paving and rolling, but delaying the cooling of the mixture at this stage has rarely been investigated. An asphalt mixture modified with a phase-change thermal-insulation agent (PCTIA) was prepared potentially improve the temperature of the asphalt mixture during construction. The high-temperature, low-temperature, and water-stability performance of asphalt mixtures with different PCTIA contents were analysed. The temperature regulation test was carried out, and the temperature field model of the asphalt pavement paving process was established. Based on the laboratory test and FEM models, the influence of different construction environmental conditions on the thermal-insulation performance of PCTIA and its thermal-insulation mechanism were analysed by using the distribution of temperature, average temperature, and equivalent temperature. The thermal-insulation effect of PCTIA was quantified by latent heat accumulated temperature value (LHATV). Results show that PCTIA improves the high and low-temperature performance of asphalt mixture, and has little effect on water stability. The best overall road performance is achieved at 2.5% PCTIA content. PCTIA can significantly reduce the cooling rate of asphalt mixture, and the distribution of temperature difference and time difference is obviously different in different positions of loose asphalt mixture layer and different external environments. Latent heat accumulated temperature value (LHATV) can characterize the phase-change insulation effect of PCTIA well. The wind speed increases and air temperature-bottom temperature decreases reduced LHATV indicating that too rapid cooling of asphalt mixture would weaken the thermal-insulation performance of PCTIA. Both average temperature and equivalent temperature can reflect the thermal-insulation effect of PCTIA, where the average temperature can be used to analyse the specific phase-change process of PCTIA in asphalt mixture and then analyse the insulation mechanism of PCTIA. Combining average temperature and equivalent temperature, PCTIA had the most application value in low temperature and low wind speed environments. This study aims to explore the effective method of delaying the cooling of high-temperature asphalt mixture from the perspective of phase-change energy storage and explain its mechanism.

Evaluation of effects of short and long-term thermo-oxidative aging on chemo-rheological and mechanical properties of asphalt concretes

The effects of short and long-term thermo-oxidative aging on stripping resistance, rut depth, stiffness modulus, fracture and fatigue resistances of asphalt concretes have been assessed. A modified RILEM thermo-oxidative aging procedure on loose asphalt mixtures has been used to evaluate the gradual evolution of these properties with the aging duration. Two short-term aging durations (4 and 8 hours at 135C) and three long-term thermo-oxidative aging durations (3, 6 and 9 days at 85C) and a reference mixture (0 day aging) have been considered to this end. The impact of long-term thermo-oxidative aging on the chemo-rheological properties of recovered asphalt binders have been investigated. At the binder scale, the results show an increase in the Fraass temperature, the softening point, the shear modulus , the aging index (AI= + ) and a decrease in the penetration grade with the aging duration. Some correlations between the viscoelastic transition parameters (, and ) of the recovered asphalt binders and the aging index have been established. At the mixture scale, the results show that the stiffness modulus () increases with the aging duration, while the index of fracture resistance (IFR), the stripping resistance (), the rut depth (P) and the fatigue deformation () decrease with the aging duration. Finally, some correlations between the aging index and the rheological and the mechanical properties of binders and concretes (, , P, IFR, ) have been proposed.

Moisture Damage Characterization of Rubber-Modified Asphalt Mixture Containing Waste Steel Slag under Multiple Freeze–Thaw Cycles

Recycling waste materials has become popular in the pavement industry because of its potential for significant environmental benefits, conservation of natural resources, and sustainability. This study investigated the feasibility of simultaneously recycling waste steel slag and tire rubber in bituminous pavements and analyze the moisture susceptibility of asphalt mixtures made of these solid wastes. The physical and chemical characteristics of the aggregates and the adhesive behavior of the aggregate–bitumen system were explored to determine their impact on moisture sensitivity. Accordingly, two different methods, freeze–thaw splitting test and fracture energy tests, were employed to assess the moisture stability of mixes in a multiple freeze–thaw environment. The microstructure of the interface between the aggregate and bitumen was investigated, and the long-term moisture damage process of the mixes was clarified and verified. The results indicate that the natural hyperalkalinity and porous structure of the steel slag have a favorable effect on the adhesion performance. Cohesive failure was found to be the primary mode of failure of loose asphalt mixtures in a multiple freeze–thaw environment. We tentatively propose that the adhesion energy loss is a secondary failure mode of the loose asphalt mixtures. The addition of 100% steel slag and asphalt rubber had the greatest impact on improving the long-term moisture resistance of the asphalt mixtures. The present work is beneficial for the practical application of waste tire rubber and steel slag in highway engineering.

Chemo-rheological equivalence of bitumen between different lab ageing procedures: from binder to mixture

In an attempt to mimic the in-situ ageing of asphalt pavements, the exploration of appropriate laboratory ageing simulations has led to multiple standards on binder level. On asphalt mixture level, however, less consensus exists regarding ageing simulation protocols. This study aims to compare the chemo-rheological performance of bitumen between lab ageing protocols for binders, compacted and loose asphalt mixtures. A bituminous binder was used in bitumen ageing protocols, while it was also used to produce an AC10 mixture that was conditioned as a loose mixture and for compacted cylinders and slabs. Oven ageing of the mixtures was conducted for up to 9 days at 85 °C. The binder testing results, derived from empirical, rheological and chemical tests, indicate that 20 h of PAV ageing yields approximately similar results as 1–2 days of loose mixture oven ageing. Furthermore, in compacted samples, only the outer edge was influenced significantly by oxidative ageing.

Comprehensive evaluation of the oxidative gas based aging method for loose asphalt mixtures

• Use of Vocus PTR-TOF spectrometer to investigate accelerated aging mechanisms of binders. • Formation of oxygenated species significantly higher under oxidative gas-based environment as compared to air. • Upscaling of an oxidative gas based aging method for the large-scale evaluation of loose mixtures. • Mixture and binder results indicate the clear effectiveness of the developed approach. The simulation of field aging using laboratory techniques is an essential prerequisite in the design of high-quality asphalt mixtures. Previous studies in this area have indicated the potential to use an accelerated method for aging loose mixtures using highly oxidative gases, namely ozone and other reactive oxygen species (ROS). Based on that, the present work was concerned with the investigation of the accelerated aging mechanisms in effect and upscaling of the experimental setup to accommodate larger quantity of mixes. Firstly, the chemical transformations and real time oxidation products formed under an ozone rich environment were compared to an air-based environment for three binders using a Vocus proton transfer reaction (PTR-TOF) time-of-flight mass spectrometer. It was observed that the formation of oxygenated species was significantly higher under an ozone rich environment, indicating higher levels of oxidation. The high-resolution level characterization of the oxidation series of several different molecules provided definitive evidence to support the previous hypothesis of using ozone and ROS to fast-track the oxidation of asphalt mixtures. Following this, an experimental method was developed to age up to nine kilograms (kg) of loose mixtures obtained from a mixing plant using ozone and ROS, in a duration of 22 h. After aging, different properties of the mixtures were compared to analogous mixtures aged as per a benchmark method of loose mixture aging at 95 °C for 5 days in a laboratory oven. The various results obtained from the IDEAL-CT tests, rheological and chemical property analyses of extracted binders clearly illustrated the effectiveness of the oxidative gas based aging method for the accelerated aging of loose mixtures, providing comparable levels of aging as traditional methods. Overall, the work conducted in this study provides comprehensive results regarding critical aspects of the developed method and alludes to the opportunity for wide scale applicability.

Evaluation of the adhesion property and moisture stability of rubber modified asphalt mixture incorporating waste steel slag

The present study was conducted to recycle waste tire rubber and steel slag (SS) in asphalt pavement and investigates the moisture stability of asphalt mixtures incorporating these solid wastes. To this end, two types of aggregates (SS and diabase), three kinds of SS content and multiple freeze–thaw cycles were considered and three kinds of adhesion assessment methods: pull-out test and surface free energy (SFE) method, and freeze–thaw splitting test were performed. Three corresponding adhesion evaluation indicators like adhesion strength, SFE characteristics, and tensile strength ratio were obtained and six energy parameters were introduced to characterize moisture susceptibility of asphalt mixture. To explore the relations between the SFE parameters and the adhesion evaluation indicators, a grey correlation analysis method was adopted. Asphalt mixtures with high consumption of SS obtained a better moisture resistance because SS has a superior adhesion strength and higher SFE components than diabase aggregate. Stripping energy increase was found to be the main failure mode of the asphalt rubber-SS aggregate system. SFE method provides a comprehensive and accurate evaluation of adhesion property of loose asphalt rubber–SS aggregate system and moisture stability of compacted asphalt mixtures.

Accelerated aging of loose asphalt mixtures using ozone and other reactive oxygen species

Efficient and practical techniques to simulate aging of asphalt mixtures is a focus area for practitioners around the world. In this study, a laboratory procedure was developed for accelerated aging of loose asphalt specimens using highly oxidative gas consisting of two types of reactive oxygen species (ROS) i.e., ozone (O3) and nitrogen oxides (NOx). The procedure involved the aging of loose mixtures in an enclosed ROS rich environment for a period of 1 day at 95 °C. The chemical and rheological properties of the extracted binders from 5 different mixtures aged using this method were then compared to analogous binders aged using a benchmark of loose mixture aging at 95 °C for 5 days in a laboratory oven. Different metrics for oxidation and aging were comprehensively evaluated including extent of oxidative groups by Fourier transform infrared spectroscopy (FTIR), high and low temperature rheological properties using dynamic shear rheometer (DSR), and polarity based chemical fractionation into saturates, aromatics, resin and asphaltene (SARA) fractions. Favorable chemo-mechanical correlations were obtained from the results which confirmed that the mixtures aged using the ROS aging method showed similar or higher levels of aging just after 24 hrs when compared to the conventional 5-day aging method. Overall, the procedure developed serves as a proof of concept and provides encouraging results for further work towards the development and standardization of such an approach.

Modeling of Asphalt Aging Based on Short-Term Aging Temperature and Time of Normal Asphalt Mixture for Quantifying Binder Aging

The binder in hot-mix asphalt (HMA) is aged (oxidized) in a short-time period during haul-and-queue in the field. Since the oxidative aging of asphalt is a complex chemical process, it is difficult to define the asphalt aging as a function of limited variables. When comparing the same types of asphalt mixes, however, the mix temperature (T) and time (t) kept at the T will be the primary source of variation affecting aging levels of the binder in the mix. Since the binder aging level is not easy to estimate without measuring a physical property, this study concentrated on developing an aging quantity (AQ) model for estimating aging levels of the binder in the mix based on T and t. The loose asphalt mixes were artificially short-term aged at various Ts for different t; 130, 160, and 180 °C for 1, 2, 4, and 8 h. The absolute viscosity (AV) values, which represent aging levels of the recovered binder after each short-term aging (SA) of normal dense-graded mix, were used for regression with AQ values computed by the AQ model. The best-fit AQ model was selected by trial-and-error regression iterations between measured AV and computed AQ. The AQ was then used to estimate AV (EAV) of the aged asphalts in various normal asphalt mixes. It was found that the AQ was useful for estimating AV of the binder in the SA-treated mix, and the EAV by AQ showed an excellent correlation with the measured AV with R2 > 0.99. Therefore, it was possible to conclude that the AQ could be used to predict aging level of various short-term-aged normal asphalt mixes if the materials sources were limited.

Moisture damage analysis based on adhesive failure in asphalt mixtures

ABSTRACT This study explored a unique digital image analysis technique to quantify the adhesive failure (AF) in asphalt mixtures subjected to indirect tensile testing and different levels of aging and moisture conditions. Using the tensile strength ratio (TSR) in conjunction with AF, this study grouped asphalt mixture’s moisture resistance into three zones as high (TSR > 80%), moderate (70% < TSR < 80%), and low (TSR < 70%). Asphalt mixtures with AF less than 10% were grouped as highly resistant to moisture damage. Likewise, the asphalt mixtures with AF between 10%–15% were grouped as moderate and AF more than 15% was classified as asphalt mixtures with a low resistance to moisture intrusion. The association of fracture energy (FE) with proposed zones of moisture susceptibility was evaluated. The asphalt mixtures with FE higher than 5200 J/m2 was found to be highly resistant to moisture damage (AF<10%). Whereas asphalt mixtures with FE lower than 3300 J/m2 were less resistant (AF>15%) to moisture damage. Further, the percent loss in the coating on loose asphalt mixtures subjected to boiling water test agreed with the proposed AF limits. The findings showed that AF would help screen the moisture damage susceptible asphalt mixture stringently when used in conjunction with TSR and FE.

Refinement of Climate-, Depth-, and Time-Based Laboratory Aging Procedure for Asphalt Mixtures

This paper refines the oxidation kinetics-based approach originally proposed in the NCHRP 09-54 project to determine the laboratory aging durations at 95°C that best reflect the effects of time, climate, and depth on loose asphalt mixtures. Aging durations that match the field aging at various pavement depths were determined in this study for asphalt mixtures, including warm-mix asphalt (WMA), polymer-modified asphalt (PMA), and reclaimed asphalt pavement (RAP). Here, the laboratory aging durations were used to calibrate a climatic aging index to prescribe the laboratory aging duration, given hourly pavement temperature history obtained from Enhanced Integrated Climatic Model analysis of the Modern Era Retrospective-Analysis for Research and Applications, Version 2 weather data. The recalibrated procedure determines the required laboratory aging durations with reasonable accuracy for virgin hot-mix asphalt (HMA) and WMA mixtures. From the recalibrated results, no variations were found with regard to the laboratory aging durations for WMA materials compared with HMA materials, but there were differences between the RAP and non-RAP mixtures. In some instances, the short-term aged RAP mixtures that were prepared according to AASHTO R 30 exceeded the aging level of 4-year-old field cores, suggesting that refinement of this standard short-term aging procedure may be necessary. Approximately half of the PMA sections evaluated exhibited outlier behavior that could have been caused by the unrealistically harsh thermal history of the field projects from which the cores were acquired.

Effect of contact slip behaviour of particle on compaction characteristics of the asphalt mixture

ABSTRACT To evaluate the contact slip behaviour of particle on compaction characteristics of the asphalt mixture, the relation between contact slip behaviour and compaction characteristic was analyzed. The specimen was molded by Superpave Gyratory Compactor, and the densification curve average slopes and densification energy index were adopted to evaluate the compaction characteristics of asphalt mixture. Based on the self-developed mineral contact tester and interface contact slip tester, the maximum slip force and the maximum slip shear stress were proposed to respectively evaluate the contact slip behaviours of the loose asphalt mixture and the formed asphalt mixture. The results show that the contact slip behaviour is well correlated with compaction characteristics. The maximum slip force of loose asphalt and the maximum slip shear stress can effectively evaluate the compaction characteristics of different compaction stages. The more the coarse aggregates, the stronger the contact effect among the particles, and the more difficult the asphalt mixture is to be compacted. AC-13 asphalt mixture has better workability than SMA-13 asphalt mixture and OGFC-13 asphalt mixture. The larger the nominal maximum aggregate size, the more energy the asphalt mixture needs to attach the target degree of compaction, and the better the anti-slipping deformation ability.

Doses and radiation risks estimation of adding steel slag to asphalt for road construction in Qatar

Roughly annual production of slag in Qatar is 350ktp/a. For the purpose of exposure evaluation about 2 million tons slag considered. For radioactivity estimation of produced slag, samples taken from steel slag pile randomly, the slag samples prepared for measurements by low background Gamma ray spectroscopy system equipped with high-purity germanium (HPGe). The presence of isotopes 40 K, 232Th (228Ra), 226Ra and 238U were determined and effective dose for public and workers have been estimated according to exposure scenario. The presence of natural isotopes seem to be in normal concentration and comparable with the published data. The main concentration of Th-232 and Ra-226 are 135.176 and 273.176 Bq/Kg respectively. For the purpose of compression,the radioactivity in normal gabbro have been analyzed. The results of gabbro analyses for 40 K, 232Th (228Ra), 226Ra are 25, 0.7 and 10 Bq/kg respectively. Radiation risk estimation were done for two sets of asphalt samples including the loose asphalt and asphalt cores from the Qatar Steel trials with different ratio (20%,40, and 50%) of slag ,the same ratios used for making concrete block samples. Radioactivity’s, radiation exposure and hazard index were measured and calculated for each case. The calculated absorbed dose value for the 20% slag asphalt is 26.13 μSv/y, and 78.12 μSv/y for the 40% slag asphalt, For extreme conditions at full occupancy factor (indoor with direct contact with human), the dose values are 134.68 and 396.6 μSv/y for the 20% and 40% slag asphalt, respectively. Two case studies were considered for the dose estimation to the public when steel slag aggregate used to replace 40% of total aggregate weight in asphalt applications. In the case studies, the Uranium (U-238) decay chain was considered in the analysis which takes into account all radionuclides in the chain including Radium (Ra-226), Radon (Rn-222) and Lead (Pb-210). The first case study was made for a car park constructed of asphalt pavement. Steel slag aggregate was used to fully replace the coarse aggregate, i.e. replacing 40% of the total normal gabbro, The dose to an adult from external exposure from the ground is 0.08 μSv/y. The second case study considered a children’s playing area made with 40% slag asphalt pavement. Similar to the car park, The doses to 10-year old children from playing on the 40% slag asphalt. The total dose from external irradiation from the play area is 2 μSv/y. It is recommended that loose steel slag aggregate may not use internally in direct contact with humans. However, it could be used in external construction applications below the ground surface. Asphalt made with up to 40% steel slag aggregate could be safely used in road applications in cities. However, concrete made with up to 50% slag aggregate could be safely used in construction applications.